Old page wikitext, before the edit (old_wikitext) | '{{short description|Atomic bomb dropped on Hiroshima}}
{{about|the type of atomic bomb that was dropped on Hiroshima}}
{{good article}}
{{Infobox weapon
| name = Little Boy
| image = [[File:Little boy.jpg|center|300px]]
| caption = A post-war Little Boy model
| origin = United States
| type = [[Nuclear weapon]]
<!-- Type selection -->
| is_explosive = yes
<!-- Production history -->
| designer = [[Project Y|Los Alamos Laboratory]]
| design_date =
| manufacturer = {{ulist | [[Naval Gun Factory]],<br/>Washington, D.C. | Naval Ordnance Plant,<br/>Center Line, Michigan | Expert Tool and Die Company,<br/>Detroit, Michigan}}
| unit_cost =
| production_date = 1945–1947
| number = 1 wartime + 5 postwar
<!-- General specifications -->
| weight = {{convert|9700|lb}}
| length = {{convert|10|ft|m}}
| diameter = {{convert|28|in|cm}}
<!-- Explosive specifications -->
| filling = [[Highly enriched uranium]]
| filling_weight = 64 kg
| detonation =
| yield = {{convert|15|ktonTNT}}
}}
'''Little Boy''' was the name of the type of [[atomic bomb]] used in the [[Atomic bombings of Hiroshima and Nagasaki|bombing of the Japanese city of Hiroshima]] on 6 August 1945 during [[World War II]], making it the first nuclear weapon used in warfare. The bomb was dropped by the [[Boeing B-29 Superfortress]] ''[[Enola Gay]]'' piloted by [[Colonel (United States)|Colonel]] [[Paul W. Tibbets Jr.]], commander of the [[509th Composite Group]], and Captain [[Robert A. Lewis]]. It exploded with an energy of approximately {{convert|15|ktonTNT|lk=on}} and caused widespread death and destruction throughout the city. The Hiroshima bombing was the second nuclear explosion in history, after the [[Trinity nuclear test]].
Little Boy was developed by [[Lieutenant commander (United States)|Lieutenant Commander]] [[Francis Birch (geophysicist)|Francis Birch]]'s group at the [[Manhattan Project]]'s [[Los Alamos Laboratory]] during World War II, a reworking of their abandoned [[Thin Man (nuclear bomb)|Thin Man]] nuclear bomb. Like Thin Man, it was a [[gun-type fission weapon]]. It derived its explosive power from the [[nuclear fission]] of [[uranium-235]], whereas Thin Man was based on fission of [[plutonium-239]]. Fission was accomplished by shooting a hollow cylinder (the "bullet") onto a solid cylinder of the same material (the "target") by means of a charge of [[nitrocellulose]] propellant powder. Little Boy contained {{convert|64|kg}} of [[highly enriched uranium]], although less than a kilogram underwent nuclear fission. Its components were fabricated at three different plants so that no one would have a copy of the complete design. Unlike the implosion design, which required sophisticated coordination of shaped explosive charges, the gun-type design was considered almost certain to work so it was never tested before its first use at Hiroshima.
After the war, a number of components for further Little Boy bombs were built. By 1950, only five complete weapons had been created, and these were retired by November 1950.
==Naming==
[[File:The_Thin_Man_1934_Poster.jpg|right|thumb|[[Robert Serber]] claims that the original gun-type design, Thin Man, was named after the series of [[Film noir|noir films]] based on the work of [[Dashiell Hammett]] that were popular in the 1930s and 1940s. "Little Boy" was itself derived from the earlier design codenames of "Thin Man" and "Fat Man".]]
There are two primary accounts of how the first atomic bombs got their names.
Los Alamos and [[Project Alberta]] physicist [[Robert Serber]] claimed, many decades after the fact, to have named the first two [[atomic bomb]] designs during [[World War II]] based on their shapes: [[Thin Man (nuclear bomb)|Thin Man]] and [[Fat Man]]. The "Thin Man" was a long, thin device and its name came from the [[Dashiell Hammett]] detective novel and [[The Thin Man (film)|series of movies]] about ''[[The Thin Man]]''. The "Fat Man" was round and fat so it was named after Kasper Gutman, a rotund character in Hammett's 1930 novel [[The Maltese Falcon (novel)|''The Maltese Falcon'']], played by [[Sydney Greenstreet]] in the 1941 [[The Maltese Falcon (1941 film)|film version]]. Little Boy was named by others as an allusion to Thin Man since it was based on its design.{{sfn|Serber|Crease|1998|p=104}}
In September 1945, another Project Alberta physicist, [[Norman F. Ramsey]], claimed in his brief "History of Project A," that the early bomb ballistic test shapes designs were referred to as "Thin Man" and "Fat Man" by (unspecified) "Air Force representatives" for "security reasons," so that their communications over telephones sounded "as if they were modifying a plane to carry [[Franklin Delano Roosevelt|Roosevelt]] (the Thin Man) and [[Winston Churchill|Churchill]] (the Fat Man)," as opposed to modifying the [[B-29]]s to carry the two atomic bomb shapes as part of Project [[Silverplate]] in the fall of 1943.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=419}}<ref>{{cite book |last=Ramsey |first=N. F. |author-link=Norman F. Ramsey |contribution=History of Project A |editor-last=Coster-Mullen |editor-first=John |title=Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man |location=United States |publisher=J. Coster-Mullen |year=2012 |oclc=298514167 }}</ref>
Another explanation of the names, from a classified [[United States Air Force]] history of Project Silverplate from the 1950s, implies a possible reconciliation of the two versions above: that the terms "Thin Man" and "Fat Man" were first developed by someone at or from Los Alamos (i.e., Serber), but were consciously adopted by the officers in Silverplate when they were adopting their own codenames for their own project (including "Silverplate"). As Silverplate involved modifying B-29s for a secret purpose, deliberately using codenames that would align with modifying vehicles for Roosevelt and Churchill would serve their needs well.<ref>{{cite book|last=Bowen|first=Lee|title=A History of the Air Force Atomic Energy Program, 1943-1953, Volume I (Project Silverplate, 1943-1946)|publisher=United States Air Force Historical Division|date=1959|page=96}}</ref>
==Development==
{{main|Manhattan Project}}
===Early gun-type design work===
{{main|Thin Man (nuclear bomb)}}
[[File:Los Alamos Primer assembly methods.png|thumb|upright|Different fission bomb assembly methods explored during the July 1942 conference. The gun-type design was the first described; third from the top is an early concept of implosion, while the last shows an autocatalytic concept in which the process of the reaction would increase its own efficiency.|alt=A series of doodles]]
Because of its perceived simplicity, the [[gun-type fission weapon|gun-type nuclear weapon design]] was the first approach pursued by the scientists working on bomb design during the Manhattan Project. In 1942, it was not yet known which of the two [[fissile material]]s pathways being simultaneously pursued — [[uranium-235]] or [[plutonium-239]] — would be successful, or if there were significant differences between the two fuels that would impact the design work. Coordination with British scientists in May 1942 convinced the American scientists, led by [[J. Robert Oppenheimer]], that the atomic bomb would not be difficult to design, and that the difficulty would lie only in the production of fuel. Early calculations in the summer of 1942 by theoretical physicists working on the project reinforced the idea that an ordinary artillery gun barrel would be able to impart sufficient velocity to the fissile material projectile.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=42-44}}
Several different weapon designs, including autocatalytic assembly, a nascent version of implosion, and alternative gun designs (e.g., using high explosives as a propellent, or creating a "double-gun" with two projectiles) were pursued in the early years of the project, while the facilities to manufacture fissile material were being constructed. The belief that the gun design would be an easy engineering task once fuel was available led to a sense of optimism at Los Alamos, although Oppenheimer established a small research group to study implosion as a fallback in early 1943.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=67, 75}} A full ordnance program for gun-design development was established by March 1943, with expertise provided by [[E.L. Rose]], an experienced gun-designer and engineer. Work was begun to study the properties of barrels, internal and external ballistics, and tampers of gun weapons. Oppenheimer himself led aspects of the effort, telling Rose that "at the present time [May 1945] our estimates are so ill founded that I think it better for me to take responsibility for putting them forward." He would soon delegate the work to Naval Captain [[William Sterling Parsons]], who, along with [[Edwin McMillan|Ed McMillan]], [[Charles Critchfield]], and [[Joseph Hirschfelder]] would be responsible for rendering the theory into practice.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=82-84}}
[[File:Thin Man plutonium gun bomb casings.jpg|right|thumb|"Thin Man" plutonium gun test casings at [[Wendover Air Force Base|Wendover Army Air Field]], as part of [[Project Alberta]] in the [[Manhattan Project]], illustrating their relative length and size.]]
Concern that impurities in reactor-bred plutonium would make predetonation more likely meant that much of the gun-design work was focused on the plutonium gun. To achieve high projectile velocities, the plutonium gun was {{convert|17|ft}} long with a narrow diameter — suggesting its code-name as the [[Thin Man (nuclear bomb)|Thin Man]] — which created considerable difficulty in its ballistics dropping from aircraft and fitting it into
the bomb bay of a [[B-29]].{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=87, 114}}
In the spring of 1944, [[Emilio G. Segrè]] and his P-5 Group at Los Alamos received the first samples of plutonium produced from a nuclear reactor, the [[X-10 Graphite Reactor]] at Oak Ridge. Analyzing it, they discovered that the presence of the isotope [[plutonium-240]] raised the rate of [[spontaneous fission]] of the plutonium to an unacceptable amount. Previous analyses of plutonium had been made from samples created by [[cyclotron]]s, and did not have as much of the contaminating isotope. If reactor-bred plutonium were to be used in a gun-type design, they concluded, [[fizzle (nuclear test)|it would predetonate]], causing the weapon to destroy itself before achieving the conditions for a large-scale explosion.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=228}}
[[File: Atombombe Little Boy.jpg|thumb|As part of [[Project Alberta]], Commander [[Francis Birch (geophysicist)|A. Francis Birch]] (left) assembles the bomb while physicist [[Norman Ramsey]] watches. This is one of the rare photos where the inside of the bomb can be seen.]]
=== From Thin Man to Little Boy ===
As a consequence of the discovery of the Pu-240 contamination problem, in July 1944 almost all research at Los Alamos was redirected to the implosion-type plutonium weapon, and the laboratory itself was entirely reorganized around the implosion problem. Work on the gun-type weapon continued under Person's Ordnance (O) Division, for use exclusively with highly-enriched uranium as a fuel. All the design, development, and technical work at Los Alamos was consolidated under [[Lieutenant Commander (United States)|Lieutenant Commander]] [[Francis Birch (geophysicist)|Francis Birch]]'s group.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=245–249}} In contrast to the plutonium [[implosion-type nuclear weapon]] and the plutonium gun-type fission weapon, the uranium gun-type weapon was much simpler to design. As a high-velocity gun was no longer required, the overall length of the gun barrel could be dramatically decreased, and this allowed the weapon to fit into a B-29 bomb bay without difficulty. Though not an optimal use of fissile material compared to the implosion design, it was seen as a nearly guaranteed weapon. Because of its smaller size compared to the Thin Man, it was given the code-name "Little Boy," while the plutonium implosion bomb was given the name "Fat Man."{{sfn|Rhodes|1986|p=541}} It was also sometimes referred to as the "Mark I" nuclear bomb design, with "Mark II" referring to the abandoned Thin Man, and "Mark III" to the "Fat Man."<ref>While "Mark III" has always referred to "Fat Man" designs, there is inconsistency in the historical record as to the weapons referred to as "Mark I" and "Mark II", with some documents referring to the "Mark II" as an low-efficiency, lensless implosion concept that was pursued as a fallback concept. The "Mark" nomenclature did not become standardized until the postwar period.</ref>
The design specifications were completed in February 1945, and contracts were let to build the components. Three different plants were used so that no one would have a copy of the complete design. The gun and breech were made by the [[Naval Gun Factory]] in Washington, D.C.; the target case and some other components by the Naval Ordnance Plant in [[Center Line, Michigan]]; and the tail fairing and mounting brackets by the Expert Tool and Die Company in [[Detroit, Michigan]].{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=257}} The bomb, except for the uranium payload, was ready at the beginning of May 1945.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=262}} Manhattan District Engineer [[Kenneth Nichols]] expected on 1 May 1945 to have enriched uranium "for one weapon before August 1 and a second one sometime in December", assuming the second weapon would be a gun type; designing an implosion bomb for enriched uranium was considered, and this would increase the production rate.{{sfn|Nichols|1987|pp=166,175–176}} The enriched uranium projectile was completed on 15 June, and the target on 24 July.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=265}} The target and bomb pre-assemblies (partly assembled bombs without the fissile components) left [[Hunters Point Naval Shipyard]], California, on 16 July aboard the [[heavy cruiser]] {{USS|Indianapolis|CA-35|6}}, arriving on 26 July.{{sfn|Coster-Mullen|2012|p=30}} The target inserts followed by air on 30 July.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=265}}
Although all of its components had been individually tested,{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=265}} no full test of a gun-type nuclear weapon occurred before the Little Boy was dropped over [[Hiroshima]]. The only [[nuclear testing|test explosion]] of a nuclear weapon concept had been of an implosion-type device employing plutonium as its fissile material, and took place on 16 July 1945 at the [[Trinity nuclear test]]. There were several reasons for not testing a Little Boy type of device. Primarily, there was the issue of fissile material. Oak Ridge was designed to produce around 30 kilograms of enriched uranium per month, and the Little Boy design used over 60 kilograms per bomb. So testing the weapon would incur a considerable delay in use of the weapon. (By comparison, the Hanford plant was designed to produced around 20 kilograms of plutonium per month, and each Fat Man bomb used only around 6 kilograms of material.){{sfn|Hansen|1995|pp=111–112}} Because of the simplicity of the gun-type design, laboratory testing could establish that its parts worked correctly on their own — for example, dummy projectiles could be shot down the gun barrel to make sure they were "seated" correctly onto a dummy target. By comparison, with the implosion design it was much more difficult to establish absence of a full-scale test whether the necessary simultaneity of compression had been achieved. While there was at least one prominent scientist ([[Ernest O. Lawrence]]) who advocated for a full-scale test, by the spring of 1945 Little Boy was regarded as nearly a sure-thing, and was expected to have a higher-yield than the first-generation implosion bombs.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=293}}
Though Little Boy incorporated various safety mechanisms, an accidental detonation of a fully-assembled weapon was very possible. For example, should the bomber carrying the device crash then the hollow "bullet" could be driven into the "target" cylinder, possibly detonating the bomb from gravity alone (though tests suggested this was unlikely), but easily creating a critical mass that would release dangerous amounts of radiation.{{sfn|Hansen|1995|p=113}} And crash of the B-29 and subsequent fire could trigger the explosives, causing the weapon to detonate.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=333}} If immersed in water, the uranium components were subject to a [[neutron moderator]] effect, which would not cause an explosion but would release [[radioactive contamination]]. For this reason, pilots were advised to crash on land rather than at sea.{{sfn|Hansen|1995|p=113}} Ultimately, Parsons opted to keep the explosives out of the Little Boy bomb until after the B-29 had taken off, to avoid the risk of a crash that could destroy or damage the military base the weapon was being launched from.
==Design==
[[File:Gun-type fission weapon en-labels thin lines.svg|thumb|The "gun" assembly method. When the hollow [[uranium]] projectile was driven onto the target cylinder, a nuclear explosion resulted.]]
[[File:Little boy casing open.png|thumb|Two Little Boy type bomb assemblies on Tinian, with casings open. For unit L-1, in the foreground, boxes containing hardware for the clock timers, radar fuzing units, and batteries are visible and arranged around the central gun tube. Pull-out wires are visible on top. L-1 was test-dropped without nuclear fuel on July 23, 1945, to gain experience in assembling, handling, and using the weapons prior to the actual strike (which used unit L-11).]]
The Little Boy was {{convert|120|in|cm}} in length, {{convert|28|in|cm}} in diameter and weighed approximately {{convert|9700|lb}}.{{sfn|Gosling|1999|page=51}} The design used the gun method to explosively force a hollow sub-[[critical mass (nuclear)|critical mass]] of [[enriched uranium]] and a solid target cylinder together into a super-critical mass, initiating a [[nuclear chain reaction]].{{sfn|Coster-Mullen|2012|p=18}} This was accomplished by shooting one piece of the uranium onto the other by means of four cylindrical silk bags of [[cordite]] powder. This was a widely used smokeless propellant consisting of a mixture of 65 percent [[nitrocellulose]], 30 percent [[nitroglycerine]], 3 percent [[petroleum jelly]], and 2 percent [[centralite|carbamite]] that was extruded into tubular granules. This gave it a high surface area and a rapid burning area, and could attain pressures of up to {{convert|40000|psi}}. Cordite for the wartime Little Boy was sourced from Canada; propellant for post-war Little Boys was obtained from the [[Picatinny Arsenal]].{{sfn|Coster-Mullen|2012|p=27}} The bomb contained {{convert|64|kg}} of enriched uranium. Most was enriched to 89% but some was only 50% uranium-235, for an average enrichment of 80%.{{sfn|Coster-Mullen|2012|p=18}} Less than a kilogram of uranium underwent [[nuclear fission]], and of this mass only {{convert|0.7|g}} was transformed into several forms of energy, mostly [[kinetic energy]], but also heat and radiation.{{sfn|Glasstone|Dolan|1977|page=12}}
===Assembly details===
Inside the weapon, the uranium-235 material was divided into two parts, following the gun principle: the "projectile" and the "target". The projectile was a hollow cylinder with 60% of the total mass ({{convert|38.5|kg|disp=sqbr}}). It consisted of a stack of nine uranium rings, each {{convert|6.25|in}} in diameter with a {{convert|4|in|adj=on}} bore in the center, and a total length of {{convert|7|in}}, pressed together into the front end of a thin-walled projectile {{convert|16.25|in}} long. Filling in the remainder of the space behind these rings in the projectile was a [[tungsten carbide]] disc with a steel back. At ignition, the projectile slug was pushed {{convert|42|in}} along the {{convert|72|in|mm|adj=mid|-long}}, {{convert|6.5|in|mm|adj=mid|-wide}} smooth-bore gun barrel. The slug "insert" was a 4-inch cylinder, 7 inches in length with a {{convert|1|in|adj=on}} axial hole. The slug comprised 40% of the total fissile mass ({{convert|25.6|kg|disp=or}}). The insert was a stack of six washer-like uranium discs somewhat thicker than the projectile rings that were slid over a 1-inch rod. This rod then extended forward through the tungsten carbide tamper plug, impact-absorbing anvil, and nose plug backstop, eventually protruding out of the front of the bomb casing. This entire target assembly was secured at both ends with locknuts.<ref name=nukearchive>{{cite web |title=Nuclear Weapons Frequently Asked Questions, Section 8.0: The First Nuclear Weapons |first=Carey |last=Sublette |url=http://nuclearweaponarchive.org/Nwfaq/Nfaq8.html |access-date=29 August 2013}}</ref>{{sfn|Coster-Mullen|2012|pp=18–19, 27}}
When the hollow-front projectile reached the target and slid over the target insert, the assembled super-critical mass of uranium would be completely surrounded by a tamper and neutron reflector of tungsten carbide and steel, both materials having a combined mass of {{convert|2300|kg}}.{{sfn|Bernstein|2007|p=133}} [[Neutron initiator]]s inside the assembly were activated by the impact of the projectile into the target.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=263–265}}
[[File:Little Boy Internal Components.png|center]]
===Counter-intuitive design===
For the first fifty years after 1945, every published description and drawing of the Little Boy mechanism assumed that a small, solid projectile was fired into the center of a larger, stationary target.{{sfn|Samuels|2008}} However, critical mass considerations dictated that in Little Boy the more extensive, hollow piece would be the projectile. The assembled fissile core had more than two [[critical mass]]es of uranium-235. This required one of the two pieces to have more than one critical mass, with the larger piece avoiding criticality prior to assembly by means of shape and minimal contact with the neutron-reflecting tungsten carbide tamper.
A hole in the center of the larger piece dispersed the mass and increased the surface area, allowing more fission neutrons to escape, thus preventing a premature chain reaction.{{sfn|Coster-Mullen|2012|pp=23–24}} But, for this larger, hollow piece to have minimal contact with the tamper, it must be the projectile, since only the projectile's back end was in contact with the tamper prior to detonation. The rest of the tungsten carbide surrounded the sub-critical mass target cylinder (called the "insert" by the designers) with air space between it and the insert. This arrangement packs the maximum amount of fissile material into a gun-assembly design.{{sfn|Coster-Mullen|2012|pp=23–24}}
===Fuze system===
[[File:Little Boy arming plugs in October 2009.JPG|thumb|Arming plugs for a Little Boy type atomic bomb on display at the [[National Air and Space Museum]]'s [[Steven F. Udvar-Hazy Center]]]]
The [[fuze|fuzing]] system was designed to trigger at the most destructive altitude, which calculations suggested was {{convert|1900|ft|m|order=flip|sp=us}}. It employed a three-stage interlock system:{{sfn|Hansen|1995a|pp=2–5}}
* A timer ensured that the bomb would not explode until at least fifteen seconds after release, one-quarter of the predicted fall time, to ensure the safety of the aircraft. The timer was activated when the electrical [[arming plug|pull-out plugs]] connecting it to the airplane pulled loose as the bomb fell, switching it to its internal 24-volt battery and starting the timer. At the end of the 15 seconds, the bomb would be {{convert|3600|ft}} from the aircraft, and the radar altimeters were powered up and responsibility was passed to the [[barometric]] stage.{{sfn|Hansen|1995a|pp=2–5}}
* The purpose of the barometric stage was to delay activating the radar altimeter firing command circuit until near detonation altitude. A thin metallic membrane enclosing a vacuum chamber (a similar design is still used today in old-fashioned wall barometers) gradually deformed as ambient air pressure increased during descent. The barometric fuze was not considered accurate enough to detonate the bomb at the precise ignition height, because air pressure varies with local conditions. When the bomb reached the design height for this stage (reportedly {{convert|2000|m|disp=semicolon|sp=us}}), the membrane closed a circuit, activating the radar altimeters. The barometric stage was added because of a worry that external radar signals might detonate the bomb too early.{{sfn|Hansen|1995a|pp=2–5}}
* Two or more [[redundancy (engineering)|redundant]] [[radar altimeter]]s were used to reliably detect final altitude. When the altimeters sensed the correct height, the firing switch closed, igniting the three BuOrd Mk15, Mod 1 Navy gun primers in the breech plug, which set off the charge consisting of four silk powder bags each containing {{convert|2|lb|g}} of WM slotted-tube [[cordite]]. This launched the uranium projectile towards the opposite end of the gun barrel at an eventual [[muzzle velocity]] of {{convert|300|m/s|sp=us}}. Approximately 10 milliseconds later the chain reaction occurred, lasting less than 1 microsecond. The radar altimeters used were modified U.S. Army Air Corps [[Monica (radar)|APS-13]] [[tail warning radar]]s, nicknamed "Archie", normally used to warn a fighter pilot of another plane approaching from behind.{{sfn|Hansen|1995a|pp=2–5}}
==Rehearsals==
[[File:Atombombe Little Boy 2.jpg|thumb|Little Boy in the bomb pit on [[Tinian]] island, before being loaded into ''Enola Gay''{{'}}s bomb bay. A section of the bomb bay door is visible on the top right.]]
The Little Boy pre-assemblies were designated L-1, L-2, L-3, L-4, L-5, L-6, L-7, and L-11. Of these, L-1, L-2, L-5, and L-6 were expended in test drops. The first drop test was conducted with L-1 on 23 July 1945. It was dropped over the sea near Tinian in order to test the radar altimeter by the B-29 later known as ''[[Big Stink (aircraft)|Big Stink]]'', piloted by [[Colonel (United States)|Colonel]] [[Paul W. Tibbets]], the commander of the [[509th Composite Group]]. Two more drop tests over the sea were made on 24 and 25 July, using the L-2 and L-5 units in order to test all components. Tibbets was the pilot for both missions, but this time the bomber used was the one subsequently known as ''[[Jabit III|Jabit]]''. L-6 was used as a dress rehearsal on 29 July. The B-29 ''[[Next Objective]]'', piloted by [[Major (rank)|Major]] [[Charles W. Sweeney]], flew to [[Iwo Jima]], where emergency procedures for loading the bomb onto a standby aircraft were practiced. This rehearsal was repeated on 31 July, but this time L-6 was reloaded onto a different B-29, ''[[Enola Gay]]'', piloted by Tibbets, and the bomb was test dropped near Tinian. L-11 was the assembly used for the Hiroshima bomb, and was fully assembled with its nuclear fuel by 31 July.{{sfn|Campbell|2005|pp=46, 80}}{{sfn|Coster-Mullen|2012|pp=100–101}}
==Bombing of Hiroshima==
{{main|Atomic bombings of Hiroshima and Nagasaki#Bombing of Hiroshima}}
[[File:Enola Gay (plane).jpg|thumb|upright=1.6|right|''Enola Gay'' after Hiroshima mission, entering [[hardstand]]. It is in its 6th Bombardment Group livery, with [[USAAF unit identification aircraft markings|victor number]] 82 visible on fuselage just forward of the tail fin.]]
Parsons, the ''Enola Gay''{{'}}s weaponeer, was concerned about the possibility of an accidental detonation if the plane crashed on takeoff, so he decided not to load the four cordite powder bags into the gun breech until the aircraft was in flight. After takeoff, Parsons and his assistant, [[Second Lieutenant]] [[Morris R. Jeppson]], made their way into the bomb bay along the narrow catwalk on the port side. Jeppson held a flashlight while Parsons disconnected the primer wires, removed the breech plug, inserted the powder bags, replaced the breech plug, and reconnected the wires. Before climbing to altitude on approach to the target, Jeppson switched the three safety plugs between the electrical connectors of the internal battery and the firing mechanism from green to red. The bomb was then fully armed. Jeppson monitored the bomb's circuits.{{sfn|Coster-Mullen|2012|pp=34–35}}
[[File: Atomic cloud over Hiroshima - NARA 542192 - Edit.jpg|thumb|upright=1.2|left|The [[mushroom cloud]] over [[Hiroshima]] after the detonation of Little Boy on 6 August 1945. A separation between the upper mushroom head and the stem is visible. This photograph and its vaguely [[question mark]] appearance was used as the inspiration for the [[:File:Manhattan_District.svg|insignia of the Manhattan Engineer District]], and was widely reprinted globally within days of the attack.]]
The bomb was dropped at approximately 08:15 (JST) on 6 August 1945. After falling for 44.4 seconds, the time and barometric triggers started the firing mechanism. The detonation happened at an altitude of {{convert|1968|+/-|50|ft}}. It was less powerful than the [[Fat Man]], which was dropped on [[Nagasaki]], but the damage and the number of victims at Hiroshima were much higher, as Hiroshima was on flat terrain, while the [[hypocenter]] of Nagasaki lay in a small valley. According to figures published in 1945, 66,000 people were killed as a direct result of the Hiroshima blast, and 69,000 were injured to varying degrees.<ref>{{cite web|author=The Manhattan Engineer District|date=29 June 1946|title=The Atomic Bombings of Hiroshima and Nagasaki|url=https://www.gutenberg.org/cache/epub/685/pg685.html|access-date=|via=[[Project Gutenberg]] |page=3}}</ref> Later estimates put the deaths as high as 140,000 people.<ref>{{cite web|last=Wellerstein|first=Alex|authorlink=Alex Wellerstein|date=4 August 2020|title=Counting the Dead at Hiroshima and Nagasaki|url=https://thebulletin.org/2020/08/counting-the-dead-at-hiroshima-and-nagasaki/|work=[[Bulletin of the Atomic Scientists]]}}</ref> The [[United States Strategic Bombing Survey]] estimated that out of 24,158 [[Imperial Japanese Army]] soldiers in Hiroshima at the time of the bombing, 6,789 were killed or missing as a result of the bombing.{{sfn|Craven|Cate|1983|p=723}}
The exact measurement of the explosive yield of the bomb was problematic since the weapon had never been tested. [[President of the United States|President]] [[Harry S. Truman]] officially announced that the yield was {{convert|20|ktonTNT}}. This was based on Parsons's visual assessment that the blast was greater than what he had seen at the [[Trinity nuclear test]]. Since that had been estimated at {{convert|18|ktonTNT}}, speech writers rounded up to 20 kilotons. Further discussion was then suppressed, for fear of lessening the impact of the bomb on the Japanese. Data had been collected by [[Luis Walter Alvarez|Luis Alvarez]], [[Harold Agnew]], and [[Lawrence H. Johnston]] on the instrument plane, ''[[The Great Artiste]]'', but this was not used to calculate the yield at the time.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=393}} More rigorous estimates of the bomb yield and conventional bomb equivalent were made when more data was acquired following the end of the war. A 1985 study estimated the bomb's yield was around {{convert|15|ktonTNT}}.{{sfn|Malik|1985|p=1}} {{See|Little boy#Conventional weapon equivalent}}
==Physical effects==
[[File: General Effects of Atomic Bomb on Hiroshima and Nagasaki.ogv|thumb|left|''The General Effects of the Atomic Bombs on Hiroshima and Nagasaki'', a U.S. Air Force film]]
After being selected in April 1945, Hiroshima was spared conventional bombing to serve as a pristine target, where the effects of a nuclear bomb on an undamaged city could be observed.{{sfn|Groves|1962|page=267, "To enable us to assess accurately the effects of the [nuclear] bomb, the targets should not have been previously damaged by air raids." Four cities were chosen, including Hiroshima and Kyoto. War Secretary Stimson vetoed Kyoto, and Nagasaki was substituted. p. 275, "When our target cities were first selected, an order was sent to the Army Air Force in Guam not to bomb them without special authority from the War Department."}} While damage could be studied later, the energy yield of the untested Little Boy design could be determined only at the moment of detonation, using instruments dropped by parachute from a plane flying in formation with the one that dropped the bomb. Radio-transmitted data from these instruments indicated a yield of about 15 kilotons.{{sfn|Malik|1985|page=1}}
Comparing this yield to the observed damage produced a rule of thumb called the {{convert|5|psi|lk=on}} lethal area rule. Approximately all the people inside the area where the shock wave carried such an overpressure or greater would be killed.{{sfn|Glasstone|1962|page=629}} At Hiroshima, that area was {{convert|2.2|mi|km|order=flip|sp=us}} in diameter.{{sfn|Glasstone|Dolan|1977|page=Nuclear Bomb Effects Computer}}
The damage came from three main effects: blast, fire, and radiation.{{sfn|Glasstone|Dolan|1977|page=1}}
===Blast===
The blast from a nuclear bomb is the result of [[X-ray]]-heated air (the fireball) sending a shock wave or pressure wave in all directions, initially at a velocity greater than the speed of sound,{{sfn|Diacon|1984|page=18}} analogous to thunder generated by lightning. Knowledge about urban blast destruction is based largely on studies of Little Boy at Hiroshima. Nagasaki buildings suffered similar damage at similar distances, but the Nagasaki bomb detonated {{convert|2.0|mi|km|order=flip|sp=us}} from the city center over hilly terrain that was partially bare of buildings.{{sfn|Glasstone|Dolan|1977|pages=300, 301}}
[[File:House 1953 Nevada Nuclear Test 5 psi.jpg|thumb|Frame house in 1953 nuclear test, 5 [[Pound per square inch|psi]] overpressure]]
In Hiroshima, almost everything within {{convert|1.0|mi|km|order=flip|sp=us}} of the point directly under the explosion was completely destroyed, except for about 50 heavily reinforced, earthquake-resistant concrete buildings, only the shells of which remained standing. Most were completely gutted, with their windows, doors, sashes, and frames ripped out.{{sfn|The Atomic Bombings of Hiroshima and Nagasaki, 1946|page=14}} The perimeter of severe blast damage approximately followed the {{convert|5|psi}} contour at {{convert|1.1|mi|km|order=flip|sp=us}}.
Later test explosions of nuclear weapons with houses and other test structures nearby confirmed the 5 psi overpressure threshold. Ordinary urban buildings experiencing it were crushed, toppled, or gutted by the force of air pressure. The picture at right shows the effects of a nuclear bomb-generated 5 psi pressure wave on a test structure in Nevada in 1953.{{sfn|Glasstone|Dolan|1977|page=179}}
A major effect of this kind of structural damage was that it created fuel for fires that were started simultaneously throughout the severe destruction region.
===Fire===
The first effect of the explosion was blinding light, accompanied by radiant heat from the fireball. The Hiroshima fireball was {{convert|1200|ft|m|order=flip|sp=us}} in diameter, with a surface temperature of {{convert|6000|C}}, about the same temperature as at the surface of the sun.{{sfn|Nuclear Weapon Thermal Effects|1998}} Near ground zero, everything flammable burst into flame. One famous, anonymous Hiroshima victim, sitting on stone steps {{convert|260|m}} from the hypocenter, left only a shadow, having absorbed the fireball heat that permanently bleached the surrounding stone.{{sfn|Human Shadow Etched in Stone}} Simultaneous fires were started throughout the blast-damaged area by fireball heat and by overturned stoves and furnaces, electrical shorts, etc. Twenty minutes after the detonation, these fires had merged into a [[firestorm]], pulling in surface air from all directions to feed an inferno which consumed everything flammable.{{sfn|Glasstone|Dolan|1977|pages=300–304}}
[[File: Hiroshima Damage Map.png|thumb|Hiroshima blast and fire damage, U.S. Strategic Bombing Survey map]]
The Hiroshima firestorm was roughly {{convert|2.0|mi|km|order=flip|sp=us}} in diameter, corresponding closely to the severe blast-damage zone. (See the USSBS{{sfn |D'Olier|1946|pp=22–25}} map, right.) Blast-damaged buildings provided fuel for the fire. Structural lumber and furniture were splintered and scattered about. Debris-choked roads obstructed firefighters. Broken gas pipes fueled the fire, and broken water pipes rendered hydrants useless.{{sfn|Glasstone|Dolan|1977|pages=300–304}} At Nagasaki, the fires failed to merge into a single firestorm, and the fire-damaged area was only one-quarter as great as at Hiroshima, due in part to a southwest wind that pushed the fires away from the city.{{sfn|Glasstone|Dolan|1977|page=304}}
As the map shows, the Hiroshima firestorm jumped natural firebreaks (river channels), as well as prepared firebreaks. The spread of fire stopped only when it reached the edge of the blast-damaged area, encountering less available fuel.{{sfn|The Atomic Bombings of Hiroshima and Nagasaki, 1946|pages=21–23}} The Manhattan Project report on Hiroshima estimated that 60% of immediate deaths were caused by fire, but with the caveat that "many persons near the center of explosion suffered fatal injuries from more than one of the bomb effects."{{sfn|The Atomic Bombings of Hiroshima and Nagasaki, 1946|page=21}}
===Radiation===
[[Nuclear fallout|Local fallout]] is dust and ash from a bomb crater, contaminated with radioactive fission products. It falls to earth downwind of the crater and can produce, with radiation alone, a lethal area much larger than that from blast and fire. With an [[air burst]], the fission products rise into the [[stratosphere]], where they dissipate and become part of the global environment. Because Little Boy was an air burst {{convert|1900|ft|m|order=flip|sp=us}} above the ground, there was no bomb crater and no local radioactive fallout.{{sfn|Glasstone|Dolan|1977|page=409 "An air burst, by definition, is one taking place at such a height above the earth that no appreciable quantities of surface material are taken up into the fireball. ... the deposition of early fallout from an air burst will generally not be significant. An air burst, however, may produce some induced radioactive contamination in the general vicinity of ground zero as a result of neutron capture by elements in the soil." p. 36, "at Hiroshima ... injuries due to fallout were completely absent."}}
However, a burst of intense [[neutron radiation|neutron]] and [[gamma radiation]] came directly from the fission of the uranium. Its lethal radius was approximately {{convert|0.8|mi|km|order=flip|sp=us}},{{sfn|Glasstone|Dolan|1977|pages=Chapter VIII and the 'Nuclear Bomb Effects Computer'}}<ref>{{cite web |url=https://nuclearsecrecy.com/nukemap/?&kt=15&lat=34.39468&lng=132.45462&hob_opt=2&hob_psi=5&hob_ft=1968&psi=20,5,1&zm=13 |title=NUKEMAP |last=Wellerstein |first=Alex |website=nuclearsecrecy.com |publisher=[[Alex Wellerstein]] |access-date=2021-07-28}}</ref> covering about half of the firestorm area. An estimated 30% of immediate fatalities were people who received lethal doses of this direct radiation, but died in the firestorm before their radiation injuries would have become apparent. Over 6,000 people survived the blast and fire, but died of radiation injuries.{{sfn|The Atomic Bombings of Hiroshima and Nagasaki, 1946|page=21}} Among injured survivors, 30% had radiation injuries{{sfn|Glasstone|Dolan|1977|pages=545, 546}} from which they recovered, but with a lifelong increase in [[Radiation-induced cancer|cancer]] risk.{{sfn|Richardson RR 2009}}<ref>{{cite news |url=http://www.radionetherlandsarchives.org/50th-anniversary-of-the-a-bomb-attacks-the-ongoing-research-into-the-effects-of-radiation/ |title=The ongoing research into the effects of radiation |newspaper=Radio Netherlands Archives |date=31 July 2005 |access-date=16 December 2018}}</ref> To date, no radiation-related evidence of heritable diseases has been observed among the survivors' children.{{sfn|Genetic Effects}}{{sfn|Izumi BJC 2003}}{{sfn|Izumi IJC 2003}}
After the surrender of Japan was finalized, Manhattan Project scientists began to immediately survey the city of Hiroshima to better understand the damage, and to communicate with Japanese physicians about radiation effects in particular. The collaboration became the [[Atomic Bomb Casualty Commission]] in 1946, a joint U.S.–Japanese project to track radiation injuries among survivors. In 1975 its work was superseded by the [[Radiation Effects Research Foundation]].<ref>{{cite journal |last=Putnam |first=F. W. |title=The Atomic Bomb Casualty Commission in retrospect|journal=Proceedings of the National Academy of Sciences of the United States of America |date=12 May 1998 |volume=95 |issue=10 |pages=5426–5431 |doi=10.1073/pnas.95.10.5426|pmid=9576898 |pmc=33857 |bibcode=1998PNAS...95.5426P |doi-access=free }}</ref>
In 1962, scientists at Los Alamos created a mockup of Little Boy known as "Project Ichiban" in order to answer some of the unanswered questions about the exact [[dosimetry|radiation output]] of the bomb, which would be useful for setting benchmarks for interpreting the relationship between radiation exposure and later health outcomes. But it failed to clear up all the issues. In 1982, Los Alamos created a replica Little Boy from the original drawings and specifications. This was then tested with enriched uranium but in a safe configuration that would not cause a nuclear explosion. A hydraulic lift was used to move the projectile, and experiments were run to assess neutron emission.{{sfn|Coster-Mullen|2012|pp=86–87}}
===Conventional weapon equivalent===
{{see also|Operation Meetinghouse}}
After hostilities ended, a survey team from the Manhattan Project that included [[William Penney]], Robert Serber, and [[George T. Reynolds]] was sent to Hiroshima to evaluate the effects of the blast. From evaluating the effects on objects and structures, Penney concluded that the yield was 12 ± 1 kilotons.{{sfn|Malik|1985|pp=18–20}} Later calculations based on charring pointed to a yield of 13 to 14 kilotons.{{sfn|Malik|1985|p=21}} In 1953, [[Frederick Reines]] calculated the yield as {{convert|15|ktonTNT}}.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=393}} Based on the Project Ichiban data, and the pressure-wave data from ''The Great Artiste'', the yield was estimated in the 1960s at 16.6 ± 0.3 kilotons.{{sfn|Malik|1985|p=16}} A review conducted by a scientist at Los Alamos in 1985 concluded, on the basis of existing blast, thermal, and radiological data, and then-current models of weapons effects, that the best estimate of the yield was {{convert|15|ktonTNT}} with an uncertainty of 20% (±3 kt). By comparison, the best value for the Nagasaki bomb was evaluated as {{convert|21|ktonTNT}} with an uncertainty of 10% (±2 kt), the difference in uncertainty owing to having better data on the latter. {{sfn|Malik|1985|p=1}}
Although Little Boy exploded with the energy equivalent of around 15 kilotons of TNT, in 1946 the [[Strategic Bombing Survey]] estimated that the same blast and fire effect could have been caused by 2.1 kilotons of [[conventional bomb]]s: "220 B-29s carrying 1.2 kilotons of [[incendiary bombs]], 400 tons of [[high-explosive]] bombs, and 500 tons of [[anti-personnel weapon|anti-personnel]] [[fragmentation bombs]]."{{sfn|D'Olier|1946|p=24}} Since the target was spread across a two-dimensional plane, the vertical component of a single spherical nuclear explosion was largely wasted. A [[cluster bomb]] pattern of smaller explosions would have been a more energy-efficient match to the target.{{sfn|D'Olier|1946|p=24}}
==Post-war==
[[File: Spare Little Boy atomic bomb casing at the Imperial War Museum in London in November 2015.jpg|thumb|One of five casings built for the Little Boy bomb used on Hiroshima on display at the [[Imperial War Museum]] in London during 2015]]
[[File:Cumuative Shipments of U-235 from Y-12 to Los Alamos 1944-1946.png|thumb|Graph of cumulative shipments of U-235 from the Y-12 electromagnetic enrichment plant at Oak Ridge to Los Alamos, 1944-1946]]
When the war ended, it was not expected that the inefficient Little Boy design would ever again be required, and many plans and diagrams were destroyed. However, by mid-1946 the Hanford Site reactors were suffering badly from the [[Wigner effect]]. Faced with the prospect of no more plutonium for new cores and no more [[polonium]] for the initiators for the cores that had already been produced, the Director of the Manhattan Project, [[Major general (United States)|Major General]] [[Leslie R. Groves]], ordered that some Little Boys be prepared as an interim measure until a solution could be found. No Little Boy assemblies were available, and no comprehensive set of diagrams of the Little Boy could be found, although there were drawings of the various components, and stocks of spare parts.{{sfn|Coster-Mullen|2012|p=85}}{{sfn|Abrahamson|Carew|2002|pp=41–42}}
At [[Sandia Base]], three Army officers, [[Captain (United States O-3)|Captains]] Albert Bethel, Richard Meyer, and Bobbie Griffin attempted to re-create the Little Boy. They were supervised by Harlow W. Russ, an expert on Little Boy who served with [[Project Alberta]] on Tinian, and was now leader of the Z-11 Group of the Los Alamos Laboratory's Z Division at Sandia. Gradually, they managed to locate the correct drawings and parts, and figured out how they went together. Eventually, they built six Little Boy assemblies. Although the casings, barrels, and components were tested, no enriched uranium was supplied for the bombs. By early 1947, the problem caused by the Wigner effect was on its way to solution, and the three officers were reassigned.{{sfn|Coster-Mullen|2012|p=85}}{{sfn|Abrahamson|Carew|2002|pp=41–42}}
The Navy [[Bureau of Ordnance]] began in 1947 to produce 25 "revised" Little Boy mechanical assemblies for use by the nuclear-capable [[Lockheed P2V Neptune]] [[aircraft carrier]] aircraft (which could be launched from, but not land, on the [[Midway-class aircraft carrier|''Midway''-class aircraft carriers]]). Components were produced by the Naval Ordnance Plants in [[Pocatello, Idaho]], and [[Louisville, Kentucky]]. Enough fissionable material was available by 1948 to build ten projectiles and targets, although there were only enough initiators for six. However, no actual fissionable components were produced by the end of 1948, and only two outer casings were available. {{sfn|Hansen|1995|pp=116–118}} By the end of 1950, only five complete Little Boy assemblies had been built. All were retired by November 1950.{{sfn|Hansen|1995|p=115}}
The [[Smithsonian Institution]] displayed a Little Boy (complete, except for enriched uranium), until 1986. The [[United States Department of Energy|Department of Energy]] took the weapon from the museum to remove its inner components, so the bomb could not be stolen and detonated with fissile material. The government returned the emptied casing to the Smithsonian in 1993. Three other disarmed bombs are on display in the United States; another is at the [[Imperial War Museum]] in London.{{sfn|Samuels|2008}}
{{Clear}}
==Notes==
{{reflist}}
==References==
{{refbegin|30em}}
* {{cite book |last1=Abrahamson |first1=James L. |last2=Carew |first2=Paul H. |title=Vanguard of American Atomic Deterrence |publisher=Praeger |location=Westport, Connecticut |year=2002 |isbn=0-275-97819-2 |oclc=49859889 }}
* {{cite web |title=The Atomic Bombings of Hiroshima and Nagasaki |publisher=The Manhattan Engineer District |date=29 Jun 1946 |url=http://www.cddc.vt.edu/host/atomic/hiroshim/hiro_med.pdf |ref={{Harvid|The Atomic Bombings of Hiroshima and Nagasaki, 1946}} |access-date=2013-11-06 |url-status=dead |archive-url=https://web.archive.org/web/20120406172413/http://www.cddc.vt.edu/host/atomic/hiroshim/hiro_med.pdf |archive-date=6 April 2012 |df=dmy-all }} This report can also be found [http://www.atomicarchive.com/Docs/MED/index.shtml here] and [http://avalon.law.yale.edu/subject_menus/mpmenu.asp here].
* {{cite book |last=Bernstein |first=Jeremy |authorlink=Jeremy Bernstein |title=Nuclear Weapons: What You Need to Know |year=2007 |publisher=Cambridge University Press |isbn=978-0-521-88408-2 |url-access=registration |url=https://archive.org/details/nuclearweaponswh0000bern }}
* {{cite book |last=Campbell |first=Richard H. |year=2005 |title=The Silverplate Bombers: A History and Registry of the Enola Gay and Other B-29s Configured to Carry Atomic Bombs |location=Jefferson, North Carolina |publisher=McFarland & Company |isbn=0-7864-2139-8 |oclc=58554961 }}
* {{cite book |last=Coster-Mullen |first=John |title=Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man |location=Waukesha, Wisconsin |publisher=J. Coster-Mullen |year=2012 |oclc=298514167 }}
* {{cite book |editor-first1=W. F. |editor-last1=Craven |editor-first2=J. L. |editor-last2=Cate |series=The Army Air Forces in World War II |volume=5 |title=The Pacific: Matterhorn to Nagasaki, June 1944 to August 1945 |date=1983 |publisher=Office of Air Force History |location=Washington, D.C. |url=https://www.ibiblio.org/hyperwar/AAF/V/AAF-V-23.html |access-date=28 March 2023 |oclc=9828710 }}
* {{cite book |last=Diacon |first=Diane |year=1984 |title=Residential Housing and Nuclear Attack |location=London |publisher=Croom Helm |url=https://books.google.com/books?id=nqYOAAAAQAAJ |isbn=978-0-7099-0868-5 }}
* {{cite book |editor-last=D'Olier |editor-first=Franklin |editor-link=Franklin D'Olier |year=1946 |title=United States Strategic Bombing Survey, Summary Report (Pacific War) |location=Washington |publisher=United States Government Printing Office |url=http://www.anesi.com/ussbs01.htm |access-date=6 November 2013 }} This report can also be found [http://marshall.csu.edu.au/Marshalls/html/WWII/USSBS_Summary.html here].
* {{cite web |title=Genetic Effects: Question #7 |publisher=Radiation Effects Research Foundation |url=http://rerf.or.jp/general/qa_e/qa7.html |ref={{Harvid|Genetic Effects}} |access-date=2013-11-06 }}
* {{cite book |last=Glasstone |first=Samuel |authorlink=Samuel Glasstone|title=The Effects of Nuclear Weapons, Revised Edition |location=United States |publisher=United States Department of Defense and United States Atomic Energy Commission |year=1962 |isbn=978-1258793555 }}
* {{cite book |last1=Glasstone |first1=Samuel |authorlink=Samuel Glasstone |last2=Dolan |first2=Philip J. |authorlink2=Philip J. Dolan |title=The Effects of Nuclear Weapons, Third Edition |location=United States |publisher=United States Department of Defense and United States Department of Energy |url=http://www.fourmilab.ch/etexts/www/effects/ |year=1977 |isbn=978-1603220163 }}
* {{cite book|last=Gosling|first=F. G.|title=The Manhattan Project: Making the Atomic Bomb|year=1999|publisher=Diane Publishing|isbn=978-0-7881-7880-1|url=https://archive.org/details/bub_gb_SKaSCzKs8ZsC<!--full view-->}}
* {{cite book |last=Groves |first=Leslie R. |authorlink=Leslie Groves |year=1962 |title=Now it Can Be Told: the Story of the Manhattan Project |location=New York |publisher=Da Capo Press (1975 reprint)|isbn=0-306-70738-1 }}
* {{cite book |last=Hansen |first=Chuck |authorlink=Chuck Hansen |series=Swords of Armageddon: US Nuclear Weapons Development since 1945 |title=Volume V: US Nuclear Weapons Histories |location=Sunnyvale, California |publisher=Chuckelea Publications |year=1995 |isbn=978-0-9791915-0-3|oclc=231585284 }}
* {{cite book |last=Hansen |first=Chuck |series=Swords of Armageddon: US Nuclear Weapons Development since 1945 |title=Volume VII: The Development of US Nuclear Weapons |location=Sunnyvale, California |publisher=Chuckelea Publications |year=1995a |isbn=978-0-9791915-7-2|oclc=231585284 }}
* {{cite book |last1=Hoddeson |first1=Lillian |authorlink=Lillian Hoddeson |first2=Paul W. |last2=Henriksen |first3=Roger A. |last3=Meade |first4=Catherine L. |last4=Westfall |authorlink4=Catherine Westfall |title=Critical Assembly: A Technical History of Los Alamos During the Oppenheimer Years, 1943–1945 |location=New York |publisher=Cambridge University Press |year=1993 |isbn=0-521-44132-3 |oclc=26764320 |url-access=registration |url=https://archive.org/details/criticalassembly0000unse }}
* {{cite web |title=Human Shadow Etched in Stone |work=Photographic Display |publisher=[[Hiroshima Peace Memorial Museum]] |url=http://www.pcf.city.hiroshima.jp/virtual/cgi-bin/museum.cgi?no=1001&l=e |ref={{harvid|Human Shadow Etched in Stone}} |access-date=6 November 2013 |archive-date=20 July 2021 |archive-url=https://web.archive.org/web/20210720110334/http://www.pcf.city.hiroshima.jp/virtual/cgi-bin/museum.cgi?no=1001&l=e |url-status=dead }}
* {{cite journal |vauthors=Izumi S, Koyama K, Soda M, Suyama A |title=Cancer incidence in children and young adults did not increase relative to parental exposure to atomic bombs |journal=British Journal of Cancer |volume=89 |issue=9 |pages=1709–1713 |date=November 2003 |pmid=14583774 |pmc=2394417 |ref={{Harvid|Izumi BJC 2003}} |doi=10.1038/sj.bjc.6601322}}
* {{cite journal |vauthors=Izumi S, Suyama A, Koyama K |title=Radiation-related mortality among offspring of atomic bomb survivors: a half-century of follow-up |journal=International Journal of Cancer |volume=107 |issue=2 |pages=292–297 |date=November 2003 |pmid=12949810 |ref={{Harvid|Izumi IJC 2003}} |doi=10.1002/ijc.11400|s2cid=23902907 |doi-access=free }}
* {{cite book |last=Jones |first=Vincent |title=Manhattan: The Army and the Atomic Bomb |publisher=United States Army Center of Military History |location=Washington, D.C. |year=1985 |url=http://www.history.army.mil/html/books/011/11-10/CMH_Pub_11-10.pdf |access-date=25 August 2013 |oclc=10913875 |archive-date=7 October 2014 |archive-url=https://web.archive.org/web/20141007074359/http://www.history.army.mil/html/books/011/11-10/CMH_Pub_11-10.pdf |url-status=dead }}
* {{cite web |last=Malik |first=John S. |title=The yields of the Hiroshima and Nagasaki nuclear explosions |publisher=Los Alamos National Laboratory report number LA-8819 |year=1985 |url=http://library.lanl.gov/cgi-bin/getfile?00313791.pdf |access-date=6 November 2013 }}
* {{cite book |last= Nichols |first= Kenneth |authorlink=Kenneth Nichols |title= The Road to Trinity: A Personal Account of How America's Nuclear Policies Were Made |year= 1987 |publisher= William Morrow |location= New York |isbn= 068806910X |oclc=15223648 }}
* {{cite web |title=Nuclear Weapon Thermal Effects |work=Special Weapons Primer, Weapons of Mass Destruction |publisher=[[Federation of American Scientists]] |year=1998 |url=https://fas.org/nuke/intro/nuke/thermal.htm |ref={{Harvid|Nuclear Weapon Thermal Effects|1998}} |access-date=2013-11-05 |url-status=dead |archive-url=https://web.archive.org/web/20130422224749/http://www.fas.org/nuke/intro/nuke/thermal.htm |archive-date=22 April 2013 |df=dmy-all }}
* {{cite book |last=Rhodes |first=Richard |authorlink=Richard Rhodes |year=1986 |title=The Making of the Atomic Bomb |url=https://archive.org/details/makingofatomicbo00rhod |url-access=registration |location=New York |publisher=Simon & Schuster |isbn=0-684-81378-5 |oclc=13793436 }}
* {{cite book |last=Rhodes |first=Richard |authorlink=Richard Rhodes |title=Dark Sun: The Making of the Hydrogen Bomb |publisher=Touchstone |year=1995 |location=New York |isbn=0-684-82414-0 |url-access=registration |url=https://archive.org/details/darksun00rich }}
* {{cite journal |last=Richardson |first=David |s2cid=12463437 |title=Ionizing Radiation and Leukemia Mortality among Japanese Atomic Bomb Survivors, 1950–2000 |journal=Radiation Research |volume=172 |issue=3 |pages=368–382 |date=September 2009 |pmid=19708786 |ref={{Harvid|Richardson RR 2009}} |doi=10.1667/RR1801.1 |display-authors=etal|bibcode=2009RadR..172..368R }}
* {{cite news |newspaper=[[The New Yorker]] |first=David |last=Samuels |date=15 December 2008 |url=http://www.newyorker.com/reporting/2008/12/15/081215fa_fact_samuels |title=Atomic John: A truck driver uncovers secrets about the first nuclear bombs |access-date=30 August 2013 }}
* {{cite book |last1=Serber |first1=Robert |authorlink=Robert Serber |first2=Robert P. |last2=Crease |title=Peace & War: Reminiscences of a Life on the Frontiers of Science |location=New York |publisher=Columbia University Press |year=1998 |isbn=978-0231105460 |oclc=37631186 |url-access=registration |url=https://archive.org/details/peacewarreminisc00serb }}
{{refend}}
==External links==
{{Commons|Little Boy}}
* [http://nuclearweaponarchive.org/Nwfaq/Nfaq8.html#nfaq8.1.3 Little Boy description] at Carey Sublette's NuclearWeaponArchive.org
* [http://www.nuclearfiles.org/menu/key-issues/nuclear-weapons/history/pre-cold-war/manhattan-project/littleboy.htm Nuclear Files.org] Definition and explanation of 'Little Boy'
* [http://nuclearweaponarchive.org/Usa/Med/Lbfm.html The Nuclear Weapon Archive]
* [http://beltoforion.de/article.php?a=little_boy Simulation of "Little Boy"] an interactive simulation of "Little Boy"
* [http://www.atomicarchive.com/Movies/index.shtml Little Boy 3D Model]
* [http://www.hiroshima-remembered.com/history/index.html Hiroshima & Nagasaki Remembered] information about preparation and dropping the Little Boy bomb
* [http://www.ssrichardmontgomery.com/download/littleboy.jpg Little boy Nuclear Bomb at Imperial War museum London UK (jpg)]
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New page wikitext, after the edit (new_wikitext) | '{{short description|Atomic bomb dropped on Hiroshima}}
{{about|the type of atomic bomb that was dropped on Hiroshima}}
{{good article}}
{{Infobox weapon
| name = Little Boy
| image = [[File:Little boy.jpg|center|300px]]
| caption = A post-war Little Boy model
| origin = United States
| type = [[Nuclear weapon]]
<!-- Type selection -->
| is_explosive = yes
<!-- Production history -->
| designer = [[Project Y|Los Alamos Laboratory]]
| design_date =
| manufacturer = {{ulist | [[Naval Gun Factory]],<br/>Washington, D.C. | Naval Ordnance Plant,<br/>Center Line, Michigan | Expert Tool and Die Company,<br/>Detroit, Michigan}}
| unit_cost =
| production_date = 1945–1947
| number = 1 wartime + 5 postwar
<!-- General specifications -->
| weight = {{convert|9700|lb}}
| length = {{convert|10|ft|m}}
| diameter = {{convert|28|in|cm}}
<!-- Explosive specifications -->
| filling = [[Highly enriched uranium]]
| filling_weight = 64 kg
| detonation =
| yield = {{convert|15|ktonTNT}}
}}
'''Little Boy''' was the name of the type of [[atomic bomb]] used in the [[Atomic bombings of Hiroshima and Nagasaki|bombing of the Japanese city of Hiroshima]] on 6 August 1945 during [[World War II]], making it the first nuclear weapon used in warfare. The bomb was dropped by the [[Boeing B-29 Superfortress]] ''[[Enola Gay]]'' piloted by [[Colonel (United States)|Colonel]] [[Paul W. Tibbets Jr.]], commander of the [[509th Composite Group]], and Captain [[Robert A. Lewis]]. It exploded with an energy of approximately {{convert|15|ktonTNT|lk=on}} and caused widespread death and destruction throughout the city. The Hiroshima bombing was the second nuclear explosion in history, after the [[Trinity nuclear test]].
Little Boy was developed by [[Lieutenant commander (United States)|Lieutenant Commander]] [[Francis Birch (geophysicist)|Francis Birch]]'s group at the [[Manhattan Project]]'s [[Los Alamos Laboratory]] during World War II, a reworking of their abandoned [[Thin Man (nuclear bomb)|Thin Man]] nuclear bomb. Like Thin Man, it was a [[gun-type fission weapon]]. It derived its explosive power from the [[nuclear fission]] of [[uranium-235]], whereas Thin Man was based on fission of [[plutonium-239]]. Fission was accomplished by shooting a hollow cylinder (the "bullet") onto a solid cylinder of the same material (the "target") by means of a charge of [[nitrocellulose]] propellant powder. Little Boy contained {{convert|64|kg}} of [[highly enriched uranium]], although less than a kilogram underwent nuclear fission. Its components were fabricated at three different plants so that no one would have a copy of the complete design. Unlike the implosion design, which required sophisticated coordination of shaped explosive charges, the gun-type design was considered almost certain to work so it was never tested before its first use at Hiroshima.
After the war, a number of components for further Little Boy bombs were built. By 1950, only five complete weapons had been created, and these were retired by November 1950.
==Naming==
[[File:The_Thin_Man_1934_Poster.jpg|right|thumb|[[Robert Serber]] claims that the original gun-type design, Thin Man, was named after the series of [[Film noir|noir films]] based on the work of [[Dashiell Hammett]] that were popular in the 1930s and 1940s. "Little Boy" was itself derived from the earlier design codenames of "Thin Man" and "Fat Man".]]
There are two primary accounts of how the first atomic bombs got their names.
Los Alamos and [[Project Alberta]] physicist [[Robert Serber]] claimed, many decades after the fact, to have named the first two [[atomic bomb]] designs during [[World War II]] based on their shapes: [[Thin Man (nuclear bomb)|Thin Man]] and [[Fat Man]]. The "Thin Man" was a long, thin device and its name came from the [[Dashiell Hammett]] detective novel and [[The Thin Man (film)|series of movies]] about ''[[The Thin Man]]''. The "Fat Man" was round and fat so it was named after Kasper Gutman, a rotund character in Hammett's 1930 novel [[The Maltese Falcon (novel)|''The Maltese Falcon'']], played by [[Sydney Greenstreet]] in the 1941 [[The Maltese Falcon (1941 film)|film version]]. Little Boy was named by others as an allusion to Thin Man since it was based on its design.{{sfn|Serber|Crease|1998|p=104}}
In September 1945, another Project Alberta physicist, [[Norman F. Ramsey]], claimed in his brief "History of Project A," that the early bomb ballistic test shapes designs were referred to as "Thin Man" and "Fat Man" by (unspecified) "Air Force representatives" for "security reasons," so that their communications over telephones sounded "as if they were modifying a plane to carry [[Franklin Delano Roosevelt|Roosevelt]] (the Thin Man) and [[Winston Churchill|Churchill]] (the Fat Man)," as opposed to modifying the [[B-29]]s to carry the two atomic bomb shapes as part of Project [[Silverplate]] in the fall of 1943.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=419}}<ref>{{cite book |last=Ramsey |first=N. F. |author-link=Norman F. Ramsey |contribution=History of Project A |editor-last=Coster-Mullen |editor-first=John |title=Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man |location=United States |publisher=J. Coster-Mullen |year=2012 |oclc=298514167 }}</ref>
Another explanation of the names, from a classified [[United States Air Force]] history of Project Silverplate from the 1950s, implies a possible reconciliation of the two versions above: that the terms "Thin Man" and "Fat Man" were first developed by someone at or from Los Alamos (i.e., Serber), but were consciously adopted by the officers in Silverplate when they were adopting their own codenames for their own project (including "Silverplate"). As Silverplate involved modifying B-29s for a secret purpose, deliberately using codenames that would align with modifying vehicles for Roosevelt and Churchill would serve their needs well.<ref>{{cite book|last=Bowen|first=Lee|title=A History of the Air Force Atomic Energy Program, 1943-1953, Volume I (Project Silverplate, 1943-1946)|publisher=United States Air Force Historical Division|date=1959|page=96}}</ref>
==Development==
{{main|Manhattan Project}}
===Early gun-type design work===
{{main|Thin Man (nuclear bomb)}}
[[File:Los Alamos Primer assembly methods.png|thumb|upright|Different fission bomb assembly methods explored during the July 1942 conference. The gun-type design was the first described; third from the top is an early concept of implosion, while the last shows an autocatalytic concept in which the process of the reaction would increase its own efficiency.|alt=A series of doodles]]
Because of its perceived simplicity, the [[gun-type fission weapon|gun-type nuclear weapon design]] was the first approach pursued by the scientists working on bomb design during the Manhattan Project. In 1942, it was not yet known which of the two [[fissile material]]s pathways being simultaneously pursued — [[uranium-235]] or [[plutonium-239]] — would be successful, or if there were significant differences between the two fuels that would impact the design work. Coordination with British scientists in May 1942 convinced the American scientists, led by [[J. Robert Oppenheimer]], that the atomic bomb would not be difficult to design, and that the difficulty would lie only in the production of fuel. Early calculations in the summer of 1942 by theoretical physicists working on the project reinforced the idea that an ordinary artillery gun barrel would be able to impart sufficient velocity to the fissile material projectile.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=42-44}}
Several different weapon designs, including autocatalytic assembly, a nascent version of implosion, and alternative gun designs (e.g., using high explosives as a propellent, or creating a "double-gun" with two projectiles) were pursued in the early years of the project, while the facilities to manufacture fissile material were being constructed. The belief that the gun design would be an easy engineering task once fuel was available led to a sense of optimism at Los Alamos, although Oppenheimer established a small research group to study implosion as a fallback in early 1943.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=67, 75}} A full ordnance program for gun-design development was established by March 1943, with expertise provided by [[E.L. Rose]], an experienced gun-designer and engineer. Work was begun to study the properties of barrels, internal and external ballistics, and tampers of gun weapons. Oppenheimer himself led aspects of the effort, telling Rose that "at the present time [May 1945] our estimates are so ill founded that I think it better for me to take responsibility for putting them forward." He would soon delegate the work to Naval Captain [[William Sterling Parsons]], who, along with [[Edwin McMillan|Ed McMillan]], [[Charles Critchfield]], and [[Joseph Hirschfelder]] would be responsible for rendering the theory into practice.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=82-84}}
[[File:Thin Man plutonium gun bomb casings.jpg|right|thumb|"Thin Man" plutonium gun test casings at [[Wendover Air Force Base|Wendover Army Air Field]], as part of [[Project Alberta]] in the [[Manhattan Project]], illustrating their relative length and size.]]
Concern that impurities in reactor-bred plutonium would make predetonation more likely meant that much of the gun-design work was focused on the plutonium gun. To achieve high projectile velocities, the plutonium gun was {{convert|17|ft}} long with a narrow diameter — suggesting its code-name as the [[Thin Man (nuclear bomb)|Thin Man]] — which created considerable difficulty in its ballistics dropping from aircraft and fitting it into
the bomb bay of a [[B-29]].{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=87, 114}}
In the spring of 1944, [[Emilio G. Segrè]] and his P-5 Group at Los Alamos received the first samples of plutonium produced from a nuclear reactor, the [[X-10 Graphite Reactor]] at Oak Ridge. Analyzing it, they discovered that the presence of the isotope [[plutonium-240]] raised the rate of [[spontaneous fission]] of the plutonium to an unacceptable amount. Previous analyses of plutonium had been made from samples created by [[cyclotron]]s, and did not have as much of the contaminating isotope. If reactor-bred plutonium were to be used in a gun-type design, they concluded, [[fizzle (nuclear test)|it would predetonate]], causing the weapon to destroy itself before achieving the conditions for a large-scale explosion.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=228}}
[[File: Atombombe Little Boy.jpg|thumb|As part of [[Project Alberta]], Commander [[Francis Birch (geophysicist)|A. Francis Birch]] (left) assembles the bomb while physicist [[Norman Ramsey]] watches. This is one of the rare photos where the inside of the bomb can be seen.]]
=== From Thin Man to Little Boy ===
As a consequence of the discovery of the Pu-240 contamination problem, in July 1944 almost all research at Los Alamos was redirected to the implosion-type plutonium weapon, and the laboratory itself was entirely reorganized around the implosion problem. Work on the gun-type weapon continued under Person's Ordnance (O) Division, for use exclusively with highly-enriched uranium as a fuel. All the design, development, and technical work at Los Alamos was consolidated under [[Lieutenant Commander (United States)|Lieutenant Commander]] [[Francis Birch (geophysicist)|Francis Birch]]'s group.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=245–249}} In contrast to the plutonium [[implosion-type nuclear weapon]] and the plutonium gun-type fission weapon, the uranium gun-type weapon was much simpler to design. As a high-velocity gun was no longer required, the overall length of the gun barrel could be dramatically decreased, and this allowed the weapon to fit into a B-29 bomb bay without difficulty. Though not an optimal use of fissile material compared to the implosion design, it was seen as a nearly guaranteed weapon. Because of its smaller size compared to the Thin Man, it was given the code-name "Little Boy," while the plutonium implosion bomb was given the name "Fat Man."{{sfn|Rhodes|1986|p=541}} It was also sometimes referred to as the "Mark I" nuclear bomb design, with "Mark II" referring to the abandoned Thin Man, and "Mark III" to the "Fat Man."<ref>While "Mark III" has always referred to "Fat Man" designs, there is inconsistency in the historical record as to the weapons referred to as "Mark I" and "Mark II", with some documents referring to the "Mark II" as an low-efficiency, lensless implosion concept that was pursued as a fallback concept. The "Mark" nomenclature did not become standardized until the postwar period.</ref>
The design specifications were completed in February 1945, and contracts were let to build the components. Three different plants were used so that no one would have a copy of the complete design. The gun and breech were made by the [[Naval Gun Factory]] in Washington, D.C.; the target case and some other components by the Naval Ordnance Plant in [[Center Line, Michigan]]; and the tail fairing and mounting brackets by the Expert Tool and Die Company in [[Detroit, Michigan]].{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=257}} The bomb, except for the uranium payload, was ready at the beginning of May 1945.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=262}} Manhattan District Engineer [[Kenneth Nichols]] expected on 1 May 1945 to have enriched uranium "for one weapon before August 1 and a second one sometime in December", assuming the second weapon would be a gun type; designing an implosion bomb for enriched uranium was considered, and this would increase the production rate.{{sfn|Nichols|1987|pp=166,175–176}} The enriched uranium projectile was completed on 15 June, and the target on 24 July.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=265}} The target and bomb pre-assemblies (partly assembled bombs without the fissile components) left [[Hunters Point Naval Shipyard]], California, on 16 July aboard the [[heavy cruiser]] {{USS|Indianapolis|CA-35|6}}, arriving on 26 July.{{sfn|Coster-Mullen|2012|p=30}} The target inserts followed by air on 30 July.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=265}}
Although all of its components had been individually tested,{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=265}} no full test of a gun-type nuclear weapon occurred before the Little Boy was dropped over [[Hiroshima]]. The only [[nuclear testing|test explosion]] of a nuclear weapon concept had been of an implosion-type device employing plutonium as its fissile material, and took place on 16 July 1945 at the [[Trinity nuclear test]]. There were several reasons for not testing a Little Boy type of device. Primarily, there was the issue of fissile material. Oak Ridge was designed to produce around 30 kilograms of enriched uranium per month, and the Little Boy design used over 60 kilograms per bomb. So testing the weapon would incur a considerable delay in use of the weapon. (By comparison, the Hanford plant was designed to produced around 20 kilograms of plutonium per month, and each Fat Man bomb used only around 6 kilograms of material.){{sfn|Hansen|1995|pp=111–112}} Because of the simplicity of the gun-type design, laboratory testing could establish that its parts worked correctly on their own — for example, dummy projectiles could be shot down the gun barrel to make sure they were "seated" correctly onto a dummy target. By comparison, with the implosion design it was much more difficult to establish absence of a full-scale test whether the necessary simultaneity of compression had been achieved. While there was at least one prominent scientist ([[Ernest O. Lawrence]]) who advocated for a full-scale test, by the spring of 1945 Little Boy was regarded as nearly a sure-thing, and was expected to have a higher-yield than the first-generation implosion bombs.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=293}}
Though Little Boy incorporated various safety mechanisms, an accidental detonation of a fully-assembled weapon was very possible. For example, should the bomber carrying the device crash then the hollow "bullet" could be driven into the "target" cylinder, possibly detonating the bomb from gravity alone (though tests suggested this was unlikely), but easily creating a critical mass that would release dangerous amounts of radiation.{{sfn|Hansen|1995|p=113}} And crash of the B-29 and subsequent fire could trigger the explosives, causing the weapon to detonate.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=333}} If immersed in water, the uranium components were subject to a [[neutron moderator]] effect, which would not cause an explosion but would release [[radioactive contamination]]. For this reason, pilots were advised to crash on land rather than at sea.{{sfn|Hansen|1995|p=113}} Ultimately, Parsons opted to keep the explosives out of the Little Boy bomb until after the B-29 had taken off, to avoid the risk of a crash that could destroy or damage the military base the weapon was being launched from.
==Design==
[[File:Gun-type fission weapon en-labels thin lines.svg|thumb|The "gun" assembly method. When the hollow [[uranium]] projectile was driven onto the target cylinder, a nuclear explosion resulted.]]
[[File:Little boy casing open.png|thumb|Two Little Boy type bomb assemblies on Tinian, with casings open. For unit L-1, in the foreground, boxes containing hardware for the clock timers, radar fuzing units, and batteries are visible and arranged around the central gun tube. Pull-out wires are visible on top. L-1 was test-dropped without nuclear fuel on July 23, 1945, to gain experience in assembling, handling, and using the weapons prior to the actual strike (which used unit L-11).]]
The Little Boy was {{convert|120|in|cm}} in length, {{convert|28|in|cm}} in diameter and weighed approximately {{convert|9700|lb}}.{{sfn|Gosling|1999|page=51}} The design used the gun method to explosively force a hollow sub-[[critical mass (nuclear)|critical mass]] of [[enriched uranium]] and a solid target cylinder together into a super-critical mass, initiating a [[nuclear chain reaction]].{{sfn|Coster-Mullen|2012|p=18}} This was accomplished by shooting one piece of the uranium onto the other by means of four cylindrical silk bags of [[cordite]] powder. This was a widely used smokeless propellant consisting of a mixture of 65 percent [[nitrocellulose]], 30 percent [[nitroglycerine]], 3 percent [[petroleum jelly]], and 2 percent [[centralite|carbamite]] that was extruded into tubular granules. This gave it a high surface area and a rapid burning area, and could attain pressures of up to {{convert|40000|psi}}. Cordite for the wartime Little Boy was sourced from Canada; propellant for post-war Little Boys was obtained from the [[Picatinny Arsenal]].{{sfn|Coster-Mullen|2012|p=27}} The bomb contained {{convert|64|kg}} of enriched uranium. Most was enriched to 89% but some was only 50% uranium-235, for an average enrichment of 80%.{{sfn|Coster-Mullen|2012|p=18}} Less than a kilogram of uranium underwent [[nuclear fission]], and of this mass only {{convert|0.7|g}} was transformed into several forms of energy, mostly [[kinetic energy]], but also heat and radiation.{{sfn|Glasstone|Dolan|1977|page=12}}
===Assembly details===
Inside the weapon, the uranium-235 material was divided into two parts, following the gun principle: the "projectile" and the "target". The projectile was a hollow cylinder with 60% of the total mass ({{convert|38.5|kg|disp=sqbr}}). It consisted of a stack of nine uranium rings, each {{convert|6.25|in}} in diameter with a {{convert|4|in|adj=on}} bore in the center, and a total length of {{convert|7|in}}, pressed together into the front end of a thin-walled projectile {{convert|16.25|in}} long. Filling in the remainder of the space behind these rings in the projectile was a [[tungsten carbide]] disc with a steel back. At ignition, the projectile slug was pushed {{convert|42|in}} along the {{convert|72|in|mm|adj=mid|-long}}, {{convert|6.5|in|mm|adj=mid|-wide}} smooth-bore gun barrel. The slug "insert" was a 4-inch cylinder, 7 inches in length with a {{convert|1|in|adj=on}} axial hole. The slug comprised 40% of the total fissile mass ({{convert|25.6|kg|disp=or}}). The insert was a stack of six washer-like uranium discs somewhat thicker than the projectile rings that were slid over a 1-inch rod. This rod then extended forward through the tungsten carbide tamper plug, impact-absorbing anvil, and nose plug backstop, eventually protruding out of the front of the bomb casing. This entire target assembly was secured at both ends with locknuts.<ref name=nukearchive>{{cite web |title=Nuclear Weapons Frequently Asked Questions, Section 8.0: The First Nuclear Weapons |first=Carey |last=Sublette |url=http://nuclearweaponarchive.org/Nwfaq/Nfaq8.html |access-date=29 August 2013}}</ref>{{sfn|Coster-Mullen|2012|pp=18–19, 27}}
When the hollow-front projectile reached the target and slid over the target insert, the assembled super-critical mass of uranium would be completely surrounded by a tamper and neutron reflector of tungsten carbide and steel, both materials having a combined mass of {{convert|2300|kg}}.{{sfn|Bernstein|2007|p=133}} [[Neutron initiator]]s inside the assembly were activated by the impact of the projectile into the target.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=263–265}}
[[File:Little Boy Internal Components.png|center]]
===Counter-intuitive design===
The material was split almost in half, with at one end a group of rings of U-235 with 40% of the supercritical mass, and at the other end another group of slightly larger rings with 60% of the supercritical mass, which was fired onto onto the smaller group, with a polonium-breryllium “initiator” to make the supercritical mass explode. {{sfn|Monk |2012 |pp=409,410}}
A hole in the center of the larger piece dispersed the mass and increased the surface area, allowing more fission neutrons to escape, thus preventing a premature chain reaction.{{sfn|Coster-Mullen|2012|pp=23–24}} But, for this larger, hollow piece to have minimal contact with the tamper, it must be the projectile, since only the projectile's back end was in contact with the tamper prior to detonation. The rest of the tungsten carbide surrounded the sub-critical mass target cylinder (called the "insert" by the designers) with air space between it and the insert. This arrangement packs the maximum amount of fissile material into a gun-assembly design.{{sfn|Coster-Mullen|2012|pp=23–24}}
For the first fifty years after 1945, every published description and drawing of the Little Boy mechanism assumed that a small, solid projectile was fired into the center of a larger, stationary target.{{sfn|Samuels|2008}} However, critical mass considerations dictated thAat in Little Boy the more extensive, hollow piece would be the projectile. The assembled fissile core had more than two [[critical mass]]es of uranium-235. This required one of the two pieces to have more than one critical mass, with the larger piece avoiding criticality prior to assembly by means of shape and minimal contact with the neutron-reflecting tungsten carbide tamper. In 2004 John Coster-Mullen a truck driver amd modelmaker from Illinois who had studied every photograph and document on the Hiroshima bomb to make an accurate model corrected earlier published accounts. {{sfn|Monk |2012 |pp=409,410}}
===Fuze system===
[[File:Little Boy arming plugs in October 2009.JPG|thumb|Arming plugs for a Little Boy type atomic bomb on display at the [[National Air and Space Museum]]'s [[Steven F. Udvar-Hazy Center]]]]
The [[fuze|fuzing]] system was designed to trigger at the most destructive altitude, which calculations suggested was {{convert|1900|ft|m|order=flip|sp=us}}. It employed a three-stage interlock system:{{sfn|Hansen|1995a|pp=2–5}}
* A timer ensured that the bomb would not explode until at least fifteen seconds after release, one-quarter of the predicted fall time, to ensure the safety of the aircraft. The timer was activated when the electrical [[arming plug|pull-out plugs]] connecting it to the airplane pulled loose as the bomb fell, switching it to its internal 24-volt battery and starting the timer. At the end of the 15 seconds, the bomb would be {{convert|3600|ft}} from the aircraft, and the radar altimeters were powered up and responsibility was passed to the [[barometric]] stage.{{sfn|Hansen|1995a|pp=2–5}}
* The purpose of the barometric stage was to delay activating the radar altimeter firing command circuit until near detonation altitude. A thin metallic membrane enclosing a vacuum chamber (a similar design is still used today in old-fashioned wall barometers) gradually deformed as ambient air pressure increased during descent. The barometric fuze was not considered accurate enough to detonate the bomb at the precise ignition height, because air pressure varies with local conditions. When the bomb reached the design height for this stage (reportedly {{convert|2000|m|disp=semicolon|sp=us}}), the membrane closed a circuit, activating the radar altimeters. The barometric stage was added because of a worry that external radar signals might detonate the bomb too early.{{sfn|Hansen|1995a|pp=2–5}}
* Two or more [[redundancy (engineering)|redundant]] [[radar altimeter]]s were used to reliably detect final altitude. When the altimeters sensed the correct height, the firing switch closed, igniting the three BuOrd Mk15, Mod 1 Navy gun primers in the breech plug, which set off the charge consisting of four silk powder bags each containing {{convert|2|lb|g}} of WM slotted-tube [[cordite]]. This launched the uranium projectile towards the opposite end of the gun barrel at an eventual [[muzzle velocity]] of {{convert|300|m/s|sp=us}}. Approximately 10 milliseconds later the chain reaction occurred, lasting less than 1 microsecond. The radar altimeters used were modified U.S. Army Air Corps [[Monica (radar)|APS-13]] [[tail warning radar]]s, nicknamed "Archie", normally used to warn a fighter pilot of another plane approaching from behind.{{sfn|Hansen|1995a|pp=2–5}}
==Rehearsals==
[[File:Atombombe Little Boy 2.jpg|thumb|Little Boy in the bomb pit on [[Tinian]] island, before being loaded into ''Enola Gay''{{'}}s bomb bay. A section of the bomb bay door is visible on the top right.]]
The Little Boy pre-assemblies were designated L-1, L-2, L-3, L-4, L-5, L-6, L-7, and L-11. Of these, L-1, L-2, L-5, and L-6 were expended in test drops. The first drop test was conducted with L-1 on 23 July 1945. It was dropped over the sea near Tinian in order to test the radar altimeter by the B-29 later known as ''[[Big Stink (aircraft)|Big Stink]]'', piloted by [[Colonel (United States)|Colonel]] [[Paul W. Tibbets]], the commander of the [[509th Composite Group]]. Two more drop tests over the sea were made on 24 and 25 July, using the L-2 and L-5 units in order to test all components. Tibbets was the pilot for both missions, but this time the bomber used was the one subsequently known as ''[[Jabit III|Jabit]]''. L-6 was used as a dress rehearsal on 29 July. The B-29 ''[[Next Objective]]'', piloted by [[Major (rank)|Major]] [[Charles W. Sweeney]], flew to [[Iwo Jima]], where emergency procedures for loading the bomb onto a standby aircraft were practiced. This rehearsal was repeated on 31 July, but this time L-6 was reloaded onto a different B-29, ''[[Enola Gay]]'', piloted by Tibbets, and the bomb was test dropped near Tinian. L-11 was the assembly used for the Hiroshima bomb, and was fully assembled with its nuclear fuel by 31 July.{{sfn|Campbell|2005|pp=46, 80}}{{sfn|Coster-Mullen|2012|pp=100–101}}
==Bombing of Hiroshima==
{{main|Atomic bombings of Hiroshima and Nagasaki#Bombing of Hiroshima}}
[[File:Enola Gay (plane).jpg|thumb|upright=1.6|right|''Enola Gay'' after Hiroshima mission, entering [[hardstand]]. It is in its 6th Bombardment Group livery, with [[USAAF unit identification aircraft markings|victor number]] 82 visible on fuselage just forward of the tail fin.]]
Parsons, the ''Enola Gay''{{'}}s weaponeer, was concerned about the possibility of an accidental detonation if the plane crashed on takeoff, so he decided not to load the four cordite powder bags into the gun breech until the aircraft was in flight. After takeoff, Parsons and his assistant, [[Second Lieutenant]] [[Morris R. Jeppson]], made their way into the bomb bay along the narrow catwalk on the port side. Jeppson held a flashlight while Parsons disconnected the primer wires, removed the breech plug, inserted the powder bags, replaced the breech plug, and reconnected the wires. Before climbing to altitude on approach to the target, Jeppson switched the three safety plugs between the electrical connectors of the internal battery and the firing mechanism from green to red. The bomb was then fully armed. Jeppson monitored the bomb's circuits.{{sfn|Coster-Mullen|2012|pp=34–35}}
[[File: Atomic cloud over Hiroshima - NARA 542192 - Edit.jpg|thumb|upright=1.2|left|The [[mushroom cloud]] over [[Hiroshima]] after the detonation of Little Boy on 6 August 1945. A separation between the upper mushroom head and the stem is visible. This photograph and its vaguely [[question mark]] appearance was used as the inspiration for the [[:File:Manhattan_District.svg|insignia of the Manhattan Engineer District]], and was widely reprinted globally within days of the attack.]]
The bomb was dropped at approximately 08:15 (JST) on 6 August 1945. After falling for 44.4 seconds, the time and barometric triggers started the firing mechanism. The detonation happened at an altitude of {{convert|1968|+/-|50|ft}}. It was less powerful than the [[Fat Man]], which was dropped on [[Nagasaki]], but the damage and the number of victims at Hiroshima were much higher, as Hiroshima was on flat terrain, while the [[hypocenter]] of Nagasaki lay in a small valley. According to figures published in 1945, 66,000 people were killed as a direct result of the Hiroshima blast, and 69,000 were injured to varying degrees.<ref>{{cite web|author=The Manhattan Engineer District|date=29 June 1946|title=The Atomic Bombings of Hiroshima and Nagasaki|url=https://www.gutenberg.org/cache/epub/685/pg685.html|access-date=|via=[[Project Gutenberg]] |page=3}}</ref> Later estimates put the deaths as high as 140,000 people.<ref>{{cite web|last=Wellerstein|first=Alex|authorlink=Alex Wellerstein|date=4 August 2020|title=Counting the Dead at Hiroshima and Nagasaki|url=https://thebulletin.org/2020/08/counting-the-dead-at-hiroshima-and-nagasaki/|work=[[Bulletin of the Atomic Scientists]]}}</ref> The [[United States Strategic Bombing Survey]] estimated that out of 24,158 [[Imperial Japanese Army]] soldiers in Hiroshima at the time of the bombing, 6,789 were killed or missing as a result of the bombing.{{sfn|Craven|Cate|1983|p=723}}
The exact measurement of the explosive yield of the bomb was problematic since the weapon had never been tested. [[President of the United States|President]] [[Harry S. Truman]] officially announced that the yield was {{convert|20|ktonTNT}}. This was based on Parsons's visual assessment that the blast was greater than what he had seen at the [[Trinity nuclear test]]. Since that had been estimated at {{convert|18|ktonTNT}}, speech writers rounded up to 20 kilotons. Further discussion was then suppressed, for fear of lessening the impact of the bomb on the Japanese. Data had been collected by [[Luis Walter Alvarez|Luis Alvarez]], [[Harold Agnew]], and [[Lawrence H. Johnston]] on the instrument plane, ''[[The Great Artiste]]'', but this was not used to calculate the yield at the time.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=393}} More rigorous estimates of the bomb yield and conventional bomb equivalent were made when more data was acquired following the end of the war. A 1985 study estimated the bomb's yield was around {{convert|15|ktonTNT}}.{{sfn|Malik|1985|p=1}} {{See|Little boy#Conventional weapon equivalent}}
==Physical effects==
[[File: General Effects of Atomic Bomb on Hiroshima and Nagasaki.ogv|thumb|left|''The General Effects of the Atomic Bombs on Hiroshima and Nagasaki'', a U.S. Air Force film]]
After being selected in April 1945, Hiroshima was spared conventional bombing to serve as a pristine target, where the effects of a nuclear bomb on an undamaged city could be observed.{{sfn|Groves|1962|page=267, "To enable us to assess accurately the effects of the [nuclear] bomb, the targets should not have been previously damaged by air raids." Four cities were chosen, including Hiroshima and Kyoto. War Secretary Stimson vetoed Kyoto, and Nagasaki was substituted. p. 275, "When our target cities were first selected, an order was sent to the Army Air Force in Guam not to bomb them without special authority from the War Department."}} While damage could be studied later, the energy yield of the untested Little Boy design could be determined only at the moment of detonation, using instruments dropped by parachute from a plane flying in formation with the one that dropped the bomb. Radio-transmitted data from these instruments indicated a yield of about 15 kilotons.{{sfn|Malik|1985|page=1}}
Comparing this yield to the observed damage produced a rule of thumb called the {{convert|5|psi|lk=on}} lethal area rule. Approximately all the people inside the area where the shock wave carried such an overpressure or greater would be killed.{{sfn|Glasstone|1962|page=629}} At Hiroshima, that area was {{convert|2.2|mi|km|order=flip|sp=us}} in diameter.{{sfn|Glasstone|Dolan|1977|page=Nuclear Bomb Effects Computer}}
The damage came from three main effects: blast, fire, and radiation.{{sfn|Glasstone|Dolan|1977|page=1}}
===Blast===
The blast from a nuclear bomb is the result of [[X-ray]]-heated air (the fireball) sending a shock wave or pressure wave in all directions, initially at a velocity greater than the speed of sound,{{sfn|Diacon|1984|page=18}} analogous to thunder generated by lightning. Knowledge about urban blast destruction is based largely on studies of Little Boy at Hiroshima. Nagasaki buildings suffered similar damage at similar distances, but the Nagasaki bomb detonated {{convert|2.0|mi|km|order=flip|sp=us}} from the city center over hilly terrain that was partially bare of buildings.{{sfn|Glasstone|Dolan|1977|pages=300, 301}}
[[File:House 1953 Nevada Nuclear Test 5 psi.jpg|thumb|Frame house in 1953 nuclear test, 5 [[Pound per square inch|psi]] overpressure]]
In Hiroshima, almost everything within {{convert|1.0|mi|km|order=flip|sp=us}} of the point directly under the explosion was completely destroyed, except for about 50 heavily reinforced, earthquake-resistant concrete buildings, only the shells of which remained standing. Most were completely gutted, with their windows, doors, sashes, and frames ripped out.{{sfn|The Atomic Bombings of Hiroshima and Nagasaki, 1946|page=14}} The perimeter of severe blast damage approximately followed the {{convert|5|psi}} contour at {{convert|1.1|mi|km|order=flip|sp=us}}.
Later test explosions of nuclear weapons with houses and other test structures nearby confirmed the 5 psi overpressure threshold. Ordinary urban buildings experiencing it were crushed, toppled, or gutted by the force of air pressure. The picture at right shows the effects of a nuclear bomb-generated 5 psi pressure wave on a test structure in Nevada in 1953.{{sfn|Glasstone|Dolan|1977|page=179}}
A major effect of this kind of structural damage was that it created fuel for fires that were started simultaneously throughout the severe destruction region.
===Fire===
The first effect of the explosion was blinding light, accompanied by radiant heat from the fireball. The Hiroshima fireball was {{convert|1200|ft|m|order=flip|sp=us}} in diameter, with a surface temperature of {{convert|6000|C}}, about the same temperature as at the surface of the sun.{{sfn|Nuclear Weapon Thermal Effects|1998}} Near ground zero, everything flammable burst into flame. One famous, anonymous Hiroshima victim, sitting on stone steps {{convert|260|m}} from the hypocenter, left only a shadow, having absorbed the fireball heat that permanently bleached the surrounding stone.{{sfn|Human Shadow Etched in Stone}} Simultaneous fires were started throughout the blast-damaged area by fireball heat and by overturned stoves and furnaces, electrical shorts, etc. Twenty minutes after the detonation, these fires had merged into a [[firestorm]], pulling in surface air from all directions to feed an inferno which consumed everything flammable.{{sfn|Glasstone|Dolan|1977|pages=300–304}}
[[File: Hiroshima Damage Map.png|thumb|Hiroshima blast and fire damage, U.S. Strategic Bombing Survey map]]
The Hiroshima firestorm was roughly {{convert|2.0|mi|km|order=flip|sp=us}} in diameter, corresponding closely to the severe blast-damage zone. (See the USSBS{{sfn |D'Olier|1946|pp=22–25}} map, right.) Blast-damaged buildings provided fuel for the fire. Structural lumber and furniture were splintered and scattered about. Debris-choked roads obstructed firefighters. Broken gas pipes fueled the fire, and broken water pipes rendered hydrants useless.{{sfn|Glasstone|Dolan|1977|pages=300–304}} At Nagasaki, the fires failed to merge into a single firestorm, and the fire-damaged area was only one-quarter as great as at Hiroshima, due in part to a southwest wind that pushed the fires away from the city.{{sfn|Glasstone|Dolan|1977|page=304}}
As the map shows, the Hiroshima firestorm jumped natural firebreaks (river channels), as well as prepared firebreaks. The spread of fire stopped only when it reached the edge of the blast-damaged area, encountering less available fuel.{{sfn|The Atomic Bombings of Hiroshima and Nagasaki, 1946|pages=21–23}} The Manhattan Project report on Hiroshima estimated that 60% of immediate deaths were caused by fire, but with the caveat that "many persons near the center of explosion suffered fatal injuries from more than one of the bomb effects."{{sfn|The Atomic Bombings of Hiroshima and Nagasaki, 1946|page=21}}
===Radiation===
[[Nuclear fallout|Local fallout]] is dust and ash from a bomb crater, contaminated with radioactive fission products. It falls to earth downwind of the crater and can produce, with radiation alone, a lethal area much larger than that from blast and fire. With an [[air burst]], the fission products rise into the [[stratosphere]], where they dissipate and become part of the global environment. Because Little Boy was an air burst {{convert|1900|ft|m|order=flip|sp=us}} above the ground, there was no bomb crater and no local radioactive fallout.{{sfn|Glasstone|Dolan|1977|page=409 "An air burst, by definition, is one taking place at such a height above the earth that no appreciable quantities of surface material are taken up into the fireball. ... the deposition of early fallout from an air burst will generally not be significant. An air burst, however, may produce some induced radioactive contamination in the general vicinity of ground zero as a result of neutron capture by elements in the soil." p. 36, "at Hiroshima ... injuries due to fallout were completely absent."}}
However, a burst of intense [[neutron radiation|neutron]] and [[gamma radiation]] came directly from the fission of the uranium. Its lethal radius was approximately {{convert|0.8|mi|km|order=flip|sp=us}},{{sfn|Glasstone|Dolan|1977|pages=Chapter VIII and the 'Nuclear Bomb Effects Computer'}}<ref>{{cite web |url=https://nuclearsecrecy.com/nukemap/?&kt=15&lat=34.39468&lng=132.45462&hob_opt=2&hob_psi=5&hob_ft=1968&psi=20,5,1&zm=13 |title=NUKEMAP |last=Wellerstein |first=Alex |website=nuclearsecrecy.com |publisher=[[Alex Wellerstein]] |access-date=2021-07-28}}</ref> covering about half of the firestorm area. An estimated 30% of immediate fatalities were people who received lethal doses of this direct radiation, but died in the firestorm before their radiation injuries would have become apparent. Over 6,000 people survived the blast and fire, but died of radiation injuries.{{sfn|The Atomic Bombings of Hiroshima and Nagasaki, 1946|page=21}} Among injured survivors, 30% had radiation injuries{{sfn|Glasstone|Dolan|1977|pages=545, 546}} from which they recovered, but with a lifelong increase in [[Radiation-induced cancer|cancer]] risk.{{sfn|Richardson RR 2009}}<ref>{{cite news |url=http://www.radionetherlandsarchives.org/50th-anniversary-of-the-a-bomb-attacks-the-ongoing-research-into-the-effects-of-radiation/ |title=The ongoing research into the effects of radiation |newspaper=Radio Netherlands Archives |date=31 July 2005 |access-date=16 December 2018}}</ref> To date, no radiation-related evidence of heritable diseases has been observed among the survivors' children.{{sfn|Genetic Effects}}{{sfn|Izumi BJC 2003}}{{sfn|Izumi IJC 2003}}
After the surrender of Japan was finalized, Manhattan Project scientists began to immediately survey the city of Hiroshima to better understand the damage, and to communicate with Japanese physicians about radiation effects in particular. The collaboration became the [[Atomic Bomb Casualty Commission]] in 1946, a joint U.S.–Japanese project to track radiation injuries among survivors. In 1975 its work was superseded by the [[Radiation Effects Research Foundation]].<ref>{{cite journal |last=Putnam |first=F. W. |title=The Atomic Bomb Casualty Commission in retrospect|journal=Proceedings of the National Academy of Sciences of the United States of America |date=12 May 1998 |volume=95 |issue=10 |pages=5426–5431 |doi=10.1073/pnas.95.10.5426|pmid=9576898 |pmc=33857 |bibcode=1998PNAS...95.5426P |doi-access=free }}</ref>
In 1962, scientists at Los Alamos created a mockup of Little Boy known as "Project Ichiban" in order to answer some of the unanswered questions about the exact [[dosimetry|radiation output]] of the bomb, which would be useful for setting benchmarks for interpreting the relationship between radiation exposure and later health outcomes. But it failed to clear up all the issues. In 1982, Los Alamos created a replica Little Boy from the original drawings and specifications. This was then tested with enriched uranium but in a safe configuration that would not cause a nuclear explosion. A hydraulic lift was used to move the projectile, and experiments were run to assess neutron emission.{{sfn|Coster-Mullen|2012|pp=86–87}}
===Conventional weapon equivalent===
{{see also|Operation Meetinghouse}}
After hostilities ended, a survey team from the Manhattan Project that included [[William Penney]], Robert Serber, and [[George T. Reynolds]] was sent to Hiroshima to evaluate the effects of the blast. From evaluating the effects on objects and structures, Penney concluded that the yield was 12 ± 1 kilotons.{{sfn|Malik|1985|pp=18–20}} Later calculations based on charring pointed to a yield of 13 to 14 kilotons.{{sfn|Malik|1985|p=21}} In 1953, [[Frederick Reines]] calculated the yield as {{convert|15|ktonTNT}}.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=393}} Based on the Project Ichiban data, and the pressure-wave data from ''The Great Artiste'', the yield was estimated in the 1960s at 16.6 ± 0.3 kilotons.{{sfn|Malik|1985|p=16}} A review conducted by a scientist at Los Alamos in 1985 concluded, on the basis of existing blast, thermal, and radiological data, and then-current models of weapons effects, that the best estimate of the yield was {{convert|15|ktonTNT}} with an uncertainty of 20% (±3 kt). By comparison, the best value for the Nagasaki bomb was evaluated as {{convert|21|ktonTNT}} with an uncertainty of 10% (±2 kt), the difference in uncertainty owing to having better data on the latter. {{sfn|Malik|1985|p=1}}
Although Little Boy exploded with the energy equivalent of around 15 kilotons of TNT, in 1946 the [[Strategic Bombing Survey]] estimated that the same blast and fire effect could have been caused by 2.1 kilotons of [[conventional bomb]]s: "220 B-29s carrying 1.2 kilotons of [[incendiary bombs]], 400 tons of [[high-explosive]] bombs, and 500 tons of [[anti-personnel weapon|anti-personnel]] [[fragmentation bombs]]."{{sfn|D'Olier|1946|p=24}} Since the target was spread across a two-dimensional plane, the vertical component of a single spherical nuclear explosion was largely wasted. A [[cluster bomb]] pattern of smaller explosions would have been a more energy-efficient match to the target.{{sfn|D'Olier|1946|p=24}}
==Post-war==
[[File: Spare Little Boy atomic bomb casing at the Imperial War Museum in London in November 2015.jpg|thumb|One of five casings built for the Little Boy bomb used on Hiroshima on display at the [[Imperial War Museum]] in London during 2015]]
[[File:Cumuative Shipments of U-235 from Y-12 to Los Alamos 1944-1946.png|thumb|Graph of cumulative shipments of U-235 from the Y-12 electromagnetic enrichment plant at Oak Ridge to Los Alamos, 1944-1946]]
When the war ended, it was not expected that the inefficient Little Boy design would ever again be required, and many plans and diagrams were destroyed. However, by mid-1946 the Hanford Site reactors were suffering badly from the [[Wigner effect]]. Faced with the prospect of no more plutonium for new cores and no more [[polonium]] for the initiators for the cores that had already been produced, the Director of the Manhattan Project, [[Major general (United States)|Major General]] [[Leslie R. Groves]], ordered that some Little Boys be prepared as an interim measure until a solution could be found. No Little Boy assemblies were available, and no comprehensive set of diagrams of the Little Boy could be found, although there were drawings of the various components, and stocks of spare parts.{{sfn|Coster-Mullen|2012|p=85}}{{sfn|Abrahamson|Carew|2002|pp=41–42}}
At [[Sandia Base]], three Army officers, [[Captain (United States O-3)|Captains]] Albert Bethel, Richard Meyer, and Bobbie Griffin attempted to re-create the Little Boy. They were supervised by Harlow W. Russ, an expert on Little Boy who served with [[Project Alberta]] on Tinian, and was now leader of the Z-11 Group of the Los Alamos Laboratory's Z Division at Sandia. Gradually, they managed to locate the correct drawings and parts, and figured out how they went together. Eventually, they built six Little Boy assemblies. Although the casings, barrels, and components were tested, no enriched uranium was supplied for the bombs. By early 1947, the problem caused by the Wigner effect was on its way to solution, and the three officers were reassigned.{{sfn|Coster-Mullen|2012|p=85}}{{sfn|Abrahamson|Carew|2002|pp=41–42}}
The Navy [[Bureau of Ordnance]] began in 1947 to produce 25 "revised" Little Boy mechanical assemblies for use by the nuclear-capable [[Lockheed P2V Neptune]] [[aircraft carrier]] aircraft (which could be launched from, but not land, on the [[Midway-class aircraft carrier|''Midway''-class aircraft carriers]]). Components were produced by the Naval Ordnance Plants in [[Pocatello, Idaho]], and [[Louisville, Kentucky]]. Enough fissionable material was available by 1948 to build ten projectiles and targets, although there were only enough initiators for six. However, no actual fissionable components were produced by the end of 1948, and only two outer casings were available. {{sfn|Hansen|1995|pp=116–118}} By the end of 1950, only five complete Little Boy assemblies had been built. All were retired by November 1950.{{sfn|Hansen|1995|p=115}}
The [[Smithsonian Institution]] displayed a Little Boy (complete, except for enriched uranium), until 1986. The [[United States Department of Energy|Department of Energy]] took the weapon from the museum to remove its inner components, so the bomb could not be stolen and detonated with fissile material. The government returned the emptied casing to the Smithsonian in 1993. Three other disarmed bombs are on display in the United States; another is at the [[Imperial War Museum]] in London.{{sfn|Samuels|2008}}
{{Clear}}
==Notes==
{{reflist}}
==References==
{{refbegin|30em}}
* {{cite book |last1=Abrahamson |first1=James L. |last2=Carew |first2=Paul H. |title=Vanguard of American Atomic Deterrence |publisher=Praeger |location=Westport, Connecticut |year=2002 |isbn=0-275-97819-2 |oclc=49859889 }}
* {{cite web |title=The Atomic Bombings of Hiroshima and Nagasaki |publisher=The Manhattan Engineer District |date=29 Jun 1946 |url=http://www.cddc.vt.edu/host/atomic/hiroshim/hiro_med.pdf |ref={{Harvid|The Atomic Bombings of Hiroshima and Nagasaki, 1946}} |access-date=2013-11-06 |url-status=dead |archive-url=https://web.archive.org/web/20120406172413/http://www.cddc.vt.edu/host/atomic/hiroshim/hiro_med.pdf |archive-date=6 April 2012 |df=dmy-all }} This report can also be found [http://www.atomicarchive.com/Docs/MED/index.shtml here] and [http://avalon.law.yale.edu/subject_menus/mpmenu.asp here].
* {{cite book |last=Bernstein |first=Jeremy |authorlink=Jeremy Bernstein |title=Nuclear Weapons: What You Need to Know |year=2007 |publisher=Cambridge University Press |isbn=978-0-521-88408-2 |url-access=registration |url=https://archive.org/details/nuclearweaponswh0000bern }}
* {{cite book |last=Campbell |first=Richard H. |year=2005 |title=The Silverplate Bombers: A History and Registry of the Enola Gay and Other B-29s Configured to Carry Atomic Bombs |location=Jefferson, North Carolina |publisher=McFarland & Company |isbn=0-7864-2139-8 |oclc=58554961 }}
* {{cite book |last=Coster-Mullen |first=John |title=Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man |location=Waukesha, Wisconsin |publisher=J. Coster-Mullen |year=2012 |oclc=298514167 }}
* {{cite book |editor-first1=W. F. |editor-last1=Craven |editor-first2=J. L. |editor-last2=Cate |series=The Army Air Forces in World War II |volume=5 |title=The Pacific: Matterhorn to Nagasaki, June 1944 to August 1945 |date=1983 |publisher=Office of Air Force History |location=Washington, D.C. |url=https://www.ibiblio.org/hyperwar/AAF/V/AAF-V-23.html |access-date=28 March 2023 |oclc=9828710 }}
* {{cite book |last=Diacon |first=Diane |year=1984 |title=Residential Housing and Nuclear Attack |location=London |publisher=Croom Helm |url=https://books.google.com/books?id=nqYOAAAAQAAJ |isbn=978-0-7099-0868-5 }}
* {{cite book |editor-last=D'Olier |editor-first=Franklin |editor-link=Franklin D'Olier |year=1946 |title=United States Strategic Bombing Survey, Summary Report (Pacific War) |location=Washington |publisher=United States Government Printing Office |url=http://www.anesi.com/ussbs01.htm |access-date=6 November 2013 }} This report can also be found [http://marshall.csu.edu.au/Marshalls/html/WWII/USSBS_Summary.html here].
* {{cite web |title=Genetic Effects: Question #7 |publisher=Radiation Effects Research Foundation |url=http://rerf.or.jp/general/qa_e/qa7.html |ref={{Harvid|Genetic Effects}} |access-date=2013-11-06 }}
* {{cite book |last=Glasstone |first=Samuel |authorlink=Samuel Glasstone|title=The Effects of Nuclear Weapons, Revised Edition |location=United States |publisher=United States Department of Defense and United States Atomic Energy Commission |year=1962 |isbn=978-1258793555 }}
* {{cite book |last1=Glasstone |first1=Samuel |authorlink=Samuel Glasstone |last2=Dolan |first2=Philip J. |authorlink2=Philip J. Dolan |title=The Effects of Nuclear Weapons, Third Edition |location=United States |publisher=United States Department of Defense and United States Department of Energy |url=http://www.fourmilab.ch/etexts/www/effects/ |year=1977 |isbn=978-1603220163 }}
* {{cite book|last=Gosling|first=F. G.|title=The Manhattan Project: Making the Atomic Bomb|year=1999|publisher=Diane Publishing|isbn=978-0-7881-7880-1|url=https://archive.org/details/bub_gb_SKaSCzKs8ZsC<!--full view-->}}
* {{cite book |last=Groves |first=Leslie R. |authorlink=Leslie Groves |year=1962 |title=Now it Can Be Told: the Story of the Manhattan Project |location=New York |publisher=Da Capo Press (1975 reprint)|isbn=0-306-70738-1 }}
* {{cite book |last=Hansen |first=Chuck |authorlink=Chuck Hansen |series=Swords of Armageddon: US Nuclear Weapons Development since 1945 |title=Volume V: US Nuclear Weapons Histories |location=Sunnyvale, California |publisher=Chuckelea Publications |year=1995 |isbn=978-0-9791915-0-3|oclc=231585284 }}
* {{cite book |last=Hansen |first=Chuck |series=Swords of Armageddon: US Nuclear Weapons Development since 1945 |title=Volume VII: The Development of US Nuclear Weapons |location=Sunnyvale, California |publisher=Chuckelea Publications |year=1995a |isbn=978-0-9791915-7-2|oclc=231585284 }}
* {{cite book |last1=Hoddeson |first1=Lillian |authorlink=Lillian Hoddeson |first2=Paul W. |last2=Henriksen |first3=Roger A. |last3=Meade |first4=Catherine L. |last4=Westfall |authorlink4=Catherine Westfall |title=Critical Assembly: A Technical History of Los Alamos During the Oppenheimer Years, 1943–1945 |location=New York |publisher=Cambridge University Press |year=1993 |isbn=0-521-44132-3 |oclc=26764320 |url-access=registration |url=https://archive.org/details/criticalassembly0000unse }}
* {{cite web |title=Human Shadow Etched in Stone |work=Photographic Display |publisher=[[Hiroshima Peace Memorial Museum]] |url=http://www.pcf.city.hiroshima.jp/virtual/cgi-bin/museum.cgi?no=1001&l=e |ref={{harvid|Human Shadow Etched in Stone}} |access-date=6 November 2013 |archive-date=20 July 2021 |archive-url=https://web.archive.org/web/20210720110334/http://www.pcf.city.hiroshima.jp/virtual/cgi-bin/museum.cgi?no=1001&l=e |url-status=dead }}
* {{cite journal |vauthors=Izumi S, Koyama K, Soda M, Suyama A |title=Cancer incidence in children and young adults did not increase relative to parental exposure to atomic bombs |journal=British Journal of Cancer |volume=89 |issue=9 |pages=1709–1713 |date=November 2003 |pmid=14583774 |pmc=2394417 |ref={{Harvid|Izumi BJC 2003}} |doi=10.1038/sj.bjc.6601322}}
* {{cite journal |vauthors=Izumi S, Suyama A, Koyama K |title=Radiation-related mortality among offspring of atomic bomb survivors: a half-century of follow-up |journal=International Journal of Cancer |volume=107 |issue=2 |pages=292–297 |date=November 2003 |pmid=12949810 |ref={{Harvid|Izumi IJC 2003}} |doi=10.1002/ijc.11400|s2cid=23902907 |doi-access=free }}
* {{cite book |last=Jones |first=Vincent |title=Manhattan: The Army and the Atomic Bomb |publisher=United States Army Center of Military History |location=Washington, D.C. |year=1985 |url=http://www.history.army.mil/html/books/011/11-10/CMH_Pub_11-10.pdf |access-date=25 August 2013 |oclc=10913875 |archive-date=7 October 2014 |archive-url=https://web.archive.org/web/20141007074359/http://www.history.army.mil/html/books/011/11-10/CMH_Pub_11-10.pdf |url-status=dead }}
* {{cite web |last=Malik |first=John S. |title=The yields of the Hiroshima and Nagasaki nuclear explosions |publisher=Los Alamos National Laboratory report number LA-8819 |year=1985 |url=http://library.lanl.gov/cgi-bin/getfile?00313791.pdf |access-date=6 November 2013 }}
* {{cite book |last= Nichols |first= Kenneth |authorlink=Kenneth Nichols |title= The Road to Trinity: A Personal Account of How America's Nuclear Policies Were Made |year= 1987 |publisher= William Morrow |location= New York |isbn= 068806910X |oclc=15223648 }}
* {{cite web |title=Nuclear Weapon Thermal Effects |work=Special Weapons Primer, Weapons of Mass Destruction |publisher=[[Federation of American Scientists]] |year=1998 |url=https://fas.org/nuke/intro/nuke/thermal.htm |ref={{Harvid|Nuclear Weapon Thermal Effects|1998}} |access-date=2013-11-05 |url-status=dead |archive-url=https://web.archive.org/web/20130422224749/http://www.fas.org/nuke/intro/nuke/thermal.htm |archive-date=22 April 2013 |df=dmy-all }}
* {{cite book |last=Rhodes |first=Richard |authorlink=Richard Rhodes |year=1986 |title=The Making of the Atomic Bomb |url=https://archive.org/details/makingofatomicbo00rhod |url-access=registration |location=New York |publisher=Simon & Schuster |isbn=0-684-81378-5 |oclc=13793436 }}
* {{cite book |last=Rhodes |first=Richard |authorlink=Richard Rhodes |title=Dark Sun: The Making of the Hydrogen Bomb |publisher=Touchstone |year=1995 |location=New York |isbn=0-684-82414-0 |url-access=registration |url=https://archive.org/details/darksun00rich }}
* {{cite journal |last=Richardson |first=David |s2cid=12463437 |title=Ionizing Radiation and Leukemia Mortality among Japanese Atomic Bomb Survivors, 1950–2000 |journal=Radiation Research |volume=172 |issue=3 |pages=368–382 |date=September 2009 |pmid=19708786 |ref={{Harvid|Richardson RR 2009}} |doi=10.1667/RR1801.1 |display-authors=etal|bibcode=2009RadR..172..368R }}
* {{cite news |newspaper=[[The New Yorker]] |first=David |last=Samuels |date=15 December 2008 |url=http://www.newyorker.com/reporting/2008/12/15/081215fa_fact_samuels |title=Atomic John: A truck driver uncovers secrets about the first nuclear bombs |access-date=30 August 2013 }}
* {{cite book |last1=Serber |first1=Robert |authorlink=Robert Serber |first2=Robert P. |last2=Crease |title=Peace & War: Reminiscences of a Life on the Frontiers of Science |location=New York |publisher=Columbia University Press |year=1998 |isbn=978-0231105460 |oclc=37631186 |url-access=registration |url=https://archive.org/details/peacewarreminisc00serb }}
{{refend}}
==External links==
{{Commons|Little Boy}}
* [http://nuclearweaponarchive.org/Nwfaq/Nfaq8.html#nfaq8.1.3 Little Boy description] at Carey Sublette's NuclearWeaponArchive.org
* [http://www.nuclearfiles.org/menu/key-issues/nuclear-weapons/history/pre-cold-war/manhattan-project/littleboy.htm Nuclear Files.org] Definition and explanation of 'Little Boy'
* [http://nuclearweaponarchive.org/Usa/Med/Lbfm.html The Nuclear Weapon Archive]
* [http://beltoforion.de/article.php?a=little_boy Simulation of "Little Boy"] an interactive simulation of "Little Boy"
* [http://www.atomicarchive.com/Movies/index.shtml Little Boy 3D Model]
* [http://www.hiroshima-remembered.com/history/index.html Hiroshima & Nagasaki Remembered] information about preparation and dropping the Little Boy bomb
* [http://www.ssrichardmontgomery.com/download/littleboy.jpg Little boy Nuclear Bomb at Imperial War museum London UK (jpg)]
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Parsed HTML source of the new revision (new_html) | '<div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Atomic bomb dropped on Hiroshima</div>
<style data-mw-deduplicate="TemplateStyles:r1033289096">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}</style><div role="note" class="hatnote navigation-not-searchable">This article is about the type of atomic bomb that was dropped on Hiroshima. For other uses, see <a href="/https/en.wikipedia.org/wiki/Little_Boy_(disambiguation)" class="mw-disambig" title="Little Boy (disambiguation)">Little Boy (disambiguation)</a>.</div>
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<style data-mw-deduplicate="TemplateStyles:r1066479718">.mw-parser-output .infobox-subbox{padding:0;border:none;margin:-3px;width:auto;min-width:100%;font-size:100%;clear:none;float:none;background-color:transparent}.mw-parser-output .infobox-3cols-child{margin:auto}.mw-parser-output .infobox .navbar{font-size:100%}body.skin-minerva .mw-parser-output .infobox-header,body.skin-minerva .mw-parser-output .infobox-subheader,body.skin-minerva .mw-parser-output .infobox-above,body.skin-minerva .mw-parser-output .infobox-title,body.skin-minerva .mw-parser-output .infobox-image,body.skin-minerva .mw-parser-output .infobox-full-data,body.skin-minerva .mw-parser-output .infobox-below{text-align:center}</style><table class="infobox vcard" style="width:25.5em;border-spacing:2px;"><tbody><tr><th colspan="2" class="infobox-above hproduct" style="background-color:#C3D6EF;text-align:center;vertical-align:middle;font-size:110%;"><span class="fn org"> Little Boy </span></th></tr><tr><td colspan="2" class="infobox-image" style="text-align:center;border-bottom:1px solid #aaa;line-height:1.5em;"><figure class="mw-halign-center" typeof="mw:File"><a href="/https/en.wikipedia.org/wiki/File:Little_boy.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/6/6a/Little_boy.jpg/300px-Little_boy.jpg" decoding="async" width="300" height="190" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/6a/Little_boy.jpg/450px-Little_boy.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/6a/Little_boy.jpg/600px-Little_boy.jpg 2x" data-file-width="2860" data-file-height="1812" /></a><figcaption></figcaption></figure><div class="infobox-caption">A post-war Little Boy model</div></td></tr><tr><th scope="row" class="infobox-label" style="padding-right:1em">Type</th><td class="infobox-data"><a href="/https/en.wikipedia.org/wiki/Nuclear_weapon" title="Nuclear weapon">Nuclear weapon</a></td></tr><tr><th scope="row" class="infobox-label" style="padding-right:1em">Place of origin</th><td class="infobox-data">United States</td></tr><tr><th colspan="2" class="infobox-header" style="background-color:#C3D6EF;text-align:center;vertical-align:middle;font-size:110%;">Production history</th></tr><tr><th scope="row" class="infobox-label" style="padding-right:1em">Designer</th><td class="infobox-data"><a href="/https/en.wikipedia.org/wiki/Project_Y" title="Project Y">Los Alamos Laboratory</a></td></tr><tr><th scope="row" class="infobox-label" style="padding-right:1em">Manufacturer</th><td class="infobox-data"><div><ul><li><a href="/https/en.wikipedia.org/wiki/Naval_Gun_Factory" class="mw-redirect" title="Naval Gun Factory">Naval Gun Factory</a>,<br />Washington, D.C.</li><li>Naval Ordnance Plant,<br />Center Line, Michigan</li><li>Expert Tool and Die Company,<br />Detroit, Michigan</li></ul></div></td></tr><tr><th scope="row" class="infobox-label" style="padding-right:1em">Produced</th><td class="infobox-data">1945–1947</td></tr><tr><th scope="row" class="infobox-label" style="padding-right:1em"><abbr title="Number">No.</abbr> built</th><td class="infobox-data">1 wartime + 5 postwar</td></tr><tr><th colspan="2" class="infobox-header" style="background-color:#C3D6EF;text-align:center;vertical-align:middle;font-size:110%;">Specifications</th></tr><tr><th scope="row" class="infobox-label" style="padding-right:1em">Mass</th><td class="infobox-data">9,700 pounds (4,400 kg)</td></tr><tr><th scope="row" class="infobox-label" style="padding-right:1em">Length</th><td class="infobox-data">10 feet (3.0 m)</td></tr><tr><th scope="row" class="infobox-label" style="padding-right:1em">Diameter</th><td class="infobox-data">28 inches (71 cm)</td></tr><tr><td colspan="2" class="infobox-full-data"><hr /></td></tr><tr><th scope="row" class="infobox-label" style="padding-right:1em">Filling</th><td class="infobox-data"><a href="/https/en.wikipedia.org/wiki/Highly_enriched_uranium" class="mw-redirect" title="Highly enriched uranium">Highly enriched uranium</a></td></tr><tr><th scope="row" class="infobox-label" style="padding-right:1em">Filling weight</th><td class="infobox-data">64 kg</td></tr><tr><th scope="row" class="infobox-label" style="padding-right:1em">Blast yield</th><td class="infobox-data">15 kilotons of TNT (63 TJ)</td></tr></tbody></table>
<p><b>Little Boy</b> was the name of the type of <a href="/https/en.wikipedia.org/wiki/Atomic_bomb" class="mw-redirect" title="Atomic bomb">atomic bomb</a> used in the <a href="/https/en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki" title="Atomic bombings of Hiroshima and Nagasaki">bombing of the Japanese city of Hiroshima</a> on 6 August 1945 during <a href="/https/en.wikipedia.org/wiki/World_War_II" title="World War II">World War II</a>, making it the first nuclear weapon used in warfare. The bomb was dropped by the <a href="/https/en.wikipedia.org/wiki/Boeing_B-29_Superfortress" title="Boeing B-29 Superfortress">Boeing B-29 Superfortress</a> <i><a href="/https/en.wikipedia.org/wiki/Enola_Gay" title="Enola Gay">Enola Gay</a></i> piloted by <a href="/https/en.wikipedia.org/wiki/Colonel_(United_States)" title="Colonel (United States)">Colonel</a> <a href="/https/en.wikipedia.org/wiki/Paul_W._Tibbets_Jr." class="mw-redirect" title="Paul W. Tibbets Jr.">Paul W. Tibbets Jr.</a>, commander of the <a href="/https/en.wikipedia.org/wiki/509th_Composite_Group" title="509th Composite Group">509th Composite Group</a>, and Captain <a href="/https/en.wikipedia.org/wiki/Robert_A._Lewis" title="Robert A. Lewis">Robert A. Lewis</a>. It exploded with an energy of approximately 15 <a href="/https/en.wikipedia.org/wiki/TNT_equivalent" title="TNT equivalent">kilotons of TNT</a> (63 <a href="/https/en.wikipedia.org/wiki/Terajoule" class="mw-redirect" title="Terajoule">TJ</a>) and caused widespread death and destruction throughout the city. The Hiroshima bombing was the second nuclear explosion in history, after the <a href="/https/en.wikipedia.org/wiki/Trinity_nuclear_test" class="mw-redirect" title="Trinity nuclear test">Trinity nuclear test</a>.
</p><p>Little Boy was developed by <a href="/https/en.wikipedia.org/wiki/Lieutenant_commander_(United_States)" title="Lieutenant commander (United States)">Lieutenant Commander</a> <a href="/https/en.wikipedia.org/wiki/Francis_Birch_(geophysicist)" title="Francis Birch (geophysicist)">Francis Birch</a>'s group at the <a href="/https/en.wikipedia.org/wiki/Manhattan_Project" title="Manhattan Project">Manhattan Project</a>'s <a href="/https/en.wikipedia.org/wiki/Los_Alamos_Laboratory" class="mw-redirect" title="Los Alamos Laboratory">Los Alamos Laboratory</a> during World War II, a reworking of their abandoned <a href="/https/en.wikipedia.org/wiki/Thin_Man_(nuclear_bomb)" title="Thin Man (nuclear bomb)">Thin Man</a> nuclear bomb. Like Thin Man, it was a <a href="/https/en.wikipedia.org/wiki/Gun-type_fission_weapon" title="Gun-type fission weapon">gun-type fission weapon</a>. It derived its explosive power from the <a href="/https/en.wikipedia.org/wiki/Nuclear_fission" title="Nuclear fission">nuclear fission</a> of <a href="/https/en.wikipedia.org/wiki/Uranium-235" title="Uranium-235">uranium-235</a>, whereas Thin Man was based on fission of <a href="/https/en.wikipedia.org/wiki/Plutonium-239" title="Plutonium-239">plutonium-239</a>. Fission was accomplished by shooting a hollow cylinder (the "bullet") onto a solid cylinder of the same material (the "target") by means of a charge of <a href="/https/en.wikipedia.org/wiki/Nitrocellulose" title="Nitrocellulose">nitrocellulose</a> propellant powder. Little Boy contained 64 kilograms (141 lb) of <a href="/https/en.wikipedia.org/wiki/Highly_enriched_uranium" class="mw-redirect" title="Highly enriched uranium">highly enriched uranium</a>, although less than a kilogram underwent nuclear fission. Its components were fabricated at three different plants so that no one would have a copy of the complete design. Unlike the implosion design, which required sophisticated coordination of shaped explosive charges, the gun-type design was considered almost certain to work so it was never tested before its first use at Hiroshima.
</p><p>After the war, a number of components for further Little Boy bombs were built. By 1950, only five complete weapons had been created, and these were retired by November 1950.
</p>
<div id="toc" class="toc" role="navigation" aria-labelledby="mw-toc-heading"><input type="checkbox" role="button" id="toctogglecheckbox" class="toctogglecheckbox" style="display:none" /><div class="toctitle" lang="en" dir="ltr"><h2 id="mw-toc-heading">Contents</h2><span class="toctogglespan"><label class="toctogglelabel" for="toctogglecheckbox"></label></span></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="#Naming"><span class="tocnumber">1</span> <span class="toctext">Naming</span></a></li>
<li class="toclevel-1 tocsection-2"><a href="#Development"><span class="tocnumber">2</span> <span class="toctext">Development</span></a>
<ul>
<li class="toclevel-2 tocsection-3"><a href="#Early_gun-type_design_work"><span class="tocnumber">2.1</span> <span class="toctext">Early gun-type design work</span></a></li>
<li class="toclevel-2 tocsection-4"><a href="#From_Thin_Man_to_Little_Boy"><span class="tocnumber">2.2</span> <span class="toctext">From Thin Man to Little Boy</span></a></li>
</ul>
</li>
<li class="toclevel-1 tocsection-5"><a href="#Design"><span class="tocnumber">3</span> <span class="toctext">Design</span></a>
<ul>
<li class="toclevel-2 tocsection-6"><a href="#Assembly_details"><span class="tocnumber">3.1</span> <span class="toctext">Assembly details</span></a></li>
<li class="toclevel-2 tocsection-7"><a href="#Counter-intuitive_design"><span class="tocnumber">3.2</span> <span class="toctext">Counter-intuitive design</span></a></li>
<li class="toclevel-2 tocsection-8"><a href="#Fuze_system"><span class="tocnumber">3.3</span> <span class="toctext">Fuze system</span></a></li>
</ul>
</li>
<li class="toclevel-1 tocsection-9"><a href="#Rehearsals"><span class="tocnumber">4</span> <span class="toctext">Rehearsals</span></a></li>
<li class="toclevel-1 tocsection-10"><a href="#Bombing_of_Hiroshima"><span class="tocnumber">5</span> <span class="toctext">Bombing of Hiroshima</span></a></li>
<li class="toclevel-1 tocsection-11"><a href="#Physical_effects"><span class="tocnumber">6</span> <span class="toctext">Physical effects</span></a>
<ul>
<li class="toclevel-2 tocsection-12"><a href="#Blast"><span class="tocnumber">6.1</span> <span class="toctext">Blast</span></a></li>
<li class="toclevel-2 tocsection-13"><a href="#Fire"><span class="tocnumber">6.2</span> <span class="toctext">Fire</span></a></li>
<li class="toclevel-2 tocsection-14"><a href="#Radiation"><span class="tocnumber">6.3</span> <span class="toctext">Radiation</span></a></li>
<li class="toclevel-2 tocsection-15"><a href="#Conventional_weapon_equivalent"><span class="tocnumber">6.4</span> <span class="toctext">Conventional weapon equivalent</span></a></li>
</ul>
</li>
<li class="toclevel-1 tocsection-16"><a href="#Post-war"><span class="tocnumber">7</span> <span class="toctext">Post-war</span></a></li>
<li class="toclevel-1 tocsection-17"><a href="#Notes"><span class="tocnumber">8</span> <span class="toctext">Notes</span></a></li>
<li class="toclevel-1 tocsection-18"><a href="#References"><span class="tocnumber">9</span> <span class="toctext">References</span></a></li>
<li class="toclevel-1 tocsection-19"><a href="#External_links"><span class="tocnumber">10</span> <span class="toctext">External links</span></a></li>
</ul>
</div>
<h2><span class="mw-headline" id="Naming">Naming</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=1" title="Edit section: Naming"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h2>
<figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/https/en.wikipedia.org/wiki/File:The_Thin_Man_1934_Poster.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/7/7e/The_Thin_Man_1934_Poster.jpg/220px-The_Thin_Man_1934_Poster.jpg" decoding="async" width="220" height="337" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/7e/The_Thin_Man_1934_Poster.jpg/330px-The_Thin_Man_1934_Poster.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/7/7e/The_Thin_Man_1934_Poster.jpg 2x" data-file-width="417" data-file-height="638" /></a><figcaption><a href="/https/en.wikipedia.org/wiki/Robert_Serber" title="Robert Serber">Robert Serber</a> claims that the original gun-type design, Thin Man, was named after the series of <a href="/https/en.wikipedia.org/wiki/Film_noir" title="Film noir">noir films</a> based on the work of <a href="/https/en.wikipedia.org/wiki/Dashiell_Hammett" title="Dashiell Hammett">Dashiell Hammett</a> that were popular in the 1930s and 1940s. "Little Boy" was itself derived from the earlier design codenames of "Thin Man" and "Fat Man".</figcaption></figure>
<p>There are two primary accounts of how the first atomic bombs got their names.
</p><p>Los Alamos and <a href="/https/en.wikipedia.org/wiki/Project_Alberta" title="Project Alberta">Project Alberta</a> physicist <a href="/https/en.wikipedia.org/wiki/Robert_Serber" title="Robert Serber">Robert Serber</a> claimed, many decades after the fact, to have named the first two <a href="/https/en.wikipedia.org/wiki/Atomic_bomb" class="mw-redirect" title="Atomic bomb">atomic bomb</a> designs during <a href="/https/en.wikipedia.org/wiki/World_War_II" title="World War II">World War II</a> based on their shapes: <a href="/https/en.wikipedia.org/wiki/Thin_Man_(nuclear_bomb)" title="Thin Man (nuclear bomb)">Thin Man</a> and <a href="/https/en.wikipedia.org/wiki/Fat_Man" title="Fat Man">Fat Man</a>. The "Thin Man" was a long, thin device and its name came from the <a href="/https/en.wikipedia.org/wiki/Dashiell_Hammett" title="Dashiell Hammett">Dashiell Hammett</a> detective novel and <a href="/https/en.wikipedia.org/wiki/The_Thin_Man_(film)" title="The Thin Man (film)">series of movies</a> about <i><a href="/https/en.wikipedia.org/wiki/The_Thin_Man" title="The Thin Man">The Thin Man</a></i>. The "Fat Man" was round and fat so it was named after Kasper Gutman, a rotund character in Hammett's 1930 novel <a href="/https/en.wikipedia.org/wiki/The_Maltese_Falcon_(novel)" title="The Maltese Falcon (novel)"><i>The Maltese Falcon</i></a>, played by <a href="/https/en.wikipedia.org/wiki/Sydney_Greenstreet" title="Sydney Greenstreet">Sydney Greenstreet</a> in the 1941 <a href="/https/en.wikipedia.org/wiki/The_Maltese_Falcon_(1941_film)" title="The Maltese Falcon (1941 film)">film version</a>. Little Boy was named by others as an allusion to Thin Man since it was based on its design.<sup id="cite_ref-FOOTNOTESerberCrease1998104_1-0" class="reference"><a href="#cite_note-FOOTNOTESerberCrease1998104-1">[1]</a></sup>
</p><p>In September 1945, another Project Alberta physicist, <a href="/https/en.wikipedia.org/wiki/Norman_F._Ramsey" class="mw-redirect" title="Norman F. Ramsey">Norman F. Ramsey</a>, claimed in his brief "History of Project A," that the early bomb ballistic test shapes designs were referred to as "Thin Man" and "Fat Man" by (unspecified) "Air Force representatives" for "security reasons," so that their communications over telephones sounded "as if they were modifying a plane to carry <a href="/https/en.wikipedia.org/wiki/Franklin_Delano_Roosevelt" class="mw-redirect" title="Franklin Delano Roosevelt">Roosevelt</a> (the Thin Man) and <a href="/https/en.wikipedia.org/wiki/Winston_Churchill" title="Winston Churchill">Churchill</a> (the Fat Man)," as opposed to modifying the <a href="/https/en.wikipedia.org/wiki/B-29" class="mw-redirect" title="B-29">B-29s</a> to carry the two atomic bomb shapes as part of Project <a href="/https/en.wikipedia.org/wiki/Silverplate" title="Silverplate">Silverplate</a> in the fall of 1943.<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993419_2-0" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993419-2">[2]</a></sup><sup id="cite_ref-3" class="reference"><a href="#cite_note-3">[3]</a></sup>
</p><p>Another explanation of the names, from a classified <a href="/https/en.wikipedia.org/wiki/United_States_Air_Force" title="United States Air Force">United States Air Force</a> history of Project Silverplate from the 1950s, implies a possible reconciliation of the two versions above: that the terms "Thin Man" and "Fat Man" were first developed by someone at or from Los Alamos (i.e., Serber), but were consciously adopted by the officers in Silverplate when they were adopting their own codenames for their own project (including "Silverplate"). As Silverplate involved modifying B-29s for a secret purpose, deliberately using codenames that would align with modifying vehicles for Roosevelt and Churchill would serve their needs well.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4">[4]</a></sup>
</p>
<h2><span class="mw-headline" id="Development">Development</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=2" title="Edit section: Development"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h2>
<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1033289096"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/https/en.wikipedia.org/wiki/Manhattan_Project" title="Manhattan Project">Manhattan Project</a></div>
<h3><span class="mw-headline" id="Early_gun-type_design_work">Early gun-type design work</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=3" title="Edit section: Early gun-type design work"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h3>
<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1033289096"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/https/en.wikipedia.org/wiki/Thin_Man_(nuclear_bomb)" title="Thin Man (nuclear bomb)">Thin Man (nuclear bomb)</a></div>
<figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/https/en.wikipedia.org/wiki/File:Los_Alamos_Primer_assembly_methods.png" class="mw-file-description"><img alt="A series of doodles" src="//upload.wikimedia.org/wikipedia/commons/thumb/4/4e/Los_Alamos_Primer_assembly_methods.png/170px-Los_Alamos_Primer_assembly_methods.png" decoding="async" width="170" height="348" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/4/4e/Los_Alamos_Primer_assembly_methods.png/255px-Los_Alamos_Primer_assembly_methods.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/4/4e/Los_Alamos_Primer_assembly_methods.png/340px-Los_Alamos_Primer_assembly_methods.png 2x" data-file-width="440" data-file-height="900" /></a><figcaption>Different fission bomb assembly methods explored during the July 1942 conference. The gun-type design was the first described; third from the top is an early concept of implosion, while the last shows an autocatalytic concept in which the process of the reaction would increase its own efficiency.</figcaption></figure>
<p>Because of its perceived simplicity, the <a href="/https/en.wikipedia.org/wiki/Gun-type_fission_weapon" title="Gun-type fission weapon">gun-type nuclear weapon design</a> was the first approach pursued by the scientists working on bomb design during the Manhattan Project. In 1942, it was not yet known which of the two <a href="/https/en.wikipedia.org/wiki/Fissile_material" title="Fissile material">fissile materials</a> pathways being simultaneously pursued — <a href="/https/en.wikipedia.org/wiki/Uranium-235" title="Uranium-235">uranium-235</a> or <a href="/https/en.wikipedia.org/wiki/Plutonium-239" title="Plutonium-239">plutonium-239</a> — would be successful, or if there were significant differences between the two fuels that would impact the design work. Coordination with British scientists in May 1942 convinced the American scientists, led by <a href="/https/en.wikipedia.org/wiki/J._Robert_Oppenheimer" title="J. Robert Oppenheimer">J. Robert Oppenheimer</a>, that the atomic bomb would not be difficult to design, and that the difficulty would lie only in the production of fuel. Early calculations in the summer of 1942 by theoretical physicists working on the project reinforced the idea that an ordinary artillery gun barrel would be able to impart sufficient velocity to the fissile material projectile.<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall199342–44_5-0" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall199342–44-5">[5]</a></sup>
</p><p>Several different weapon designs, including autocatalytic assembly, a nascent version of implosion, and alternative gun designs (e.g., using high explosives as a propellent, or creating a "double-gun" with two projectiles) were pursued in the early years of the project, while the facilities to manufacture fissile material were being constructed. The belief that the gun design would be an easy engineering task once fuel was available led to a sense of optimism at Los Alamos, although Oppenheimer established a small research group to study implosion as a fallback in early 1943.<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall199367,_75_6-0" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall199367,_75-6">[6]</a></sup> A full ordnance program for gun-design development was established by March 1943, with expertise provided by <a href="/https/en.wikipedia.org/w/index.php?title=E.L._Rose&action=edit&redlink=1" class="new" title="E.L. Rose (page does not exist)">E.L. Rose</a>, an experienced gun-designer and engineer. Work was begun to study the properties of barrels, internal and external ballistics, and tampers of gun weapons. Oppenheimer himself led aspects of the effort, telling Rose that "at the present time [May 1945] our estimates are so ill founded that I think it better for me to take responsibility for putting them forward." He would soon delegate the work to Naval Captain <a href="/https/en.wikipedia.org/wiki/William_Sterling_Parsons" title="William Sterling Parsons">William Sterling Parsons</a>, who, along with <a href="/https/en.wikipedia.org/wiki/Edwin_McMillan" title="Edwin McMillan">Ed McMillan</a>, <a href="/https/en.wikipedia.org/wiki/Charles_Critchfield" title="Charles Critchfield">Charles Critchfield</a>, and <a href="/https/en.wikipedia.org/wiki/Joseph_Hirschfelder" class="mw-redirect" title="Joseph Hirschfelder">Joseph Hirschfelder</a> would be responsible for rendering the theory into practice.<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall199382–84_7-0" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall199382–84-7">[7]</a></sup>
</p>
<figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/https/en.wikipedia.org/wiki/File:Thin_Man_plutonium_gun_bomb_casings.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/c/ce/Thin_Man_plutonium_gun_bomb_casings.jpg/220px-Thin_Man_plutonium_gun_bomb_casings.jpg" decoding="async" width="220" height="127" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/ce/Thin_Man_plutonium_gun_bomb_casings.jpg/330px-Thin_Man_plutonium_gun_bomb_casings.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/c/ce/Thin_Man_plutonium_gun_bomb_casings.jpg/440px-Thin_Man_plutonium_gun_bomb_casings.jpg 2x" data-file-width="898" data-file-height="520" /></a><figcaption>"Thin Man" plutonium gun test casings at <a href="/https/en.wikipedia.org/wiki/Wendover_Air_Force_Base" title="Wendover Air Force Base">Wendover Army Air Field</a>, as part of <a href="/https/en.wikipedia.org/wiki/Project_Alberta" title="Project Alberta">Project Alberta</a> in the <a href="/https/en.wikipedia.org/wiki/Manhattan_Project" title="Manhattan Project">Manhattan Project</a>, illustrating their relative length and size.</figcaption></figure>
<p>Concern that impurities in reactor-bred plutonium would make predetonation more likely meant that much of the gun-design work was focused on the plutonium gun. To achieve high projectile velocities, the plutonium gun was 17 feet (5.2 m) long with a narrow diameter — suggesting its code-name as the <a href="/https/en.wikipedia.org/wiki/Thin_Man_(nuclear_bomb)" title="Thin Man (nuclear bomb)">Thin Man</a> — which created considerable difficulty in its ballistics dropping from aircraft and fitting it into
the bomb bay of a <a href="/https/en.wikipedia.org/wiki/B-29" class="mw-redirect" title="B-29">B-29</a>.<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall199387,_114_8-0" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall199387,_114-8">[8]</a></sup>
</p><p>In the spring of 1944, <a href="/https/en.wikipedia.org/wiki/Emilio_G._Segr%C3%A8" class="mw-redirect" title="Emilio G. Segrè">Emilio G. Segrè</a> and his P-5 Group at Los Alamos received the first samples of plutonium produced from a nuclear reactor, the <a href="/https/en.wikipedia.org/wiki/X-10_Graphite_Reactor" title="X-10 Graphite Reactor">X-10 Graphite Reactor</a> at Oak Ridge. Analyzing it, they discovered that the presence of the isotope <a href="/https/en.wikipedia.org/wiki/Plutonium-240" title="Plutonium-240">plutonium-240</a> raised the rate of <a href="/https/en.wikipedia.org/wiki/Spontaneous_fission" title="Spontaneous fission">spontaneous fission</a> of the plutonium to an unacceptable amount. Previous analyses of plutonium had been made from samples created by <a href="/https/en.wikipedia.org/wiki/Cyclotron" title="Cyclotron">cyclotrons</a>, and did not have as much of the contaminating isotope. If reactor-bred plutonium were to be used in a gun-type design, they concluded, <a href="/https/en.wikipedia.org/wiki/Fizzle_(nuclear_test)" class="mw-redirect" title="Fizzle (nuclear test)">it would predetonate</a>, causing the weapon to destroy itself before achieving the conditions for a large-scale explosion.<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993228_9-0" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993228-9">[9]</a></sup>
</p>
<figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/https/en.wikipedia.org/wiki/File:Atombombe_Little_Boy.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/1/11/Atombombe_Little_Boy.jpg/220px-Atombombe_Little_Boy.jpg" decoding="async" width="220" height="169" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/11/Atombombe_Little_Boy.jpg/330px-Atombombe_Little_Boy.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/11/Atombombe_Little_Boy.jpg/440px-Atombombe_Little_Boy.jpg 2x" data-file-width="3000" data-file-height="2303" /></a><figcaption>As part of <a href="/https/en.wikipedia.org/wiki/Project_Alberta" title="Project Alberta">Project Alberta</a>, Commander <a href="/https/en.wikipedia.org/wiki/Francis_Birch_(geophysicist)" title="Francis Birch (geophysicist)">A. Francis Birch</a> (left) assembles the bomb while physicist <a href="/https/en.wikipedia.org/wiki/Norman_Ramsey" class="mw-redirect" title="Norman Ramsey">Norman Ramsey</a> watches. This is one of the rare photos where the inside of the bomb can be seen.</figcaption></figure>
<h3><span class="mw-headline" id="From_Thin_Man_to_Little_Boy">From Thin Man to Little Boy</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=4" title="Edit section: From Thin Man to Little Boy"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h3>
<p>As a consequence of the discovery of the Pu-240 contamination problem, in July 1944 almost all research at Los Alamos was redirected to the implosion-type plutonium weapon, and the laboratory itself was entirely reorganized around the implosion problem. Work on the gun-type weapon continued under Person's Ordnance (O) Division, for use exclusively with highly-enriched uranium as a fuel. All the design, development, and technical work at Los Alamos was consolidated under <a href="/https/en.wikipedia.org/wiki/Lieutenant_Commander_(United_States)" class="mw-redirect" title="Lieutenant Commander (United States)">Lieutenant Commander</a> <a href="/https/en.wikipedia.org/wiki/Francis_Birch_(geophysicist)" title="Francis Birch (geophysicist)">Francis Birch</a>'s group.<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993245–249_10-0" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993245–249-10">[10]</a></sup> In contrast to the plutonium <a href="/https/en.wikipedia.org/wiki/Implosion-type_nuclear_weapon" class="mw-redirect" title="Implosion-type nuclear weapon">implosion-type nuclear weapon</a> and the plutonium gun-type fission weapon, the uranium gun-type weapon was much simpler to design. As a high-velocity gun was no longer required, the overall length of the gun barrel could be dramatically decreased, and this allowed the weapon to fit into a B-29 bomb bay without difficulty. Though not an optimal use of fissile material compared to the implosion design, it was seen as a nearly guaranteed weapon. Because of its smaller size compared to the Thin Man, it was given the code-name "Little Boy," while the plutonium implosion bomb was given the name "Fat Man."<sup id="cite_ref-FOOTNOTERhodes1986541_11-0" class="reference"><a href="#cite_note-FOOTNOTERhodes1986541-11">[11]</a></sup> It was also sometimes referred to as the "Mark I" nuclear bomb design, with "Mark II" referring to the abandoned Thin Man, and "Mark III" to the "Fat Man."<sup id="cite_ref-12" class="reference"><a href="#cite_note-12">[12]</a></sup>
</p><p>The design specifications were completed in February 1945, and contracts were let to build the components. Three different plants were used so that no one would have a copy of the complete design. The gun and breech were made by the <a href="/https/en.wikipedia.org/wiki/Naval_Gun_Factory" class="mw-redirect" title="Naval Gun Factory">Naval Gun Factory</a> in Washington, D.C.; the target case and some other components by the Naval Ordnance Plant in <a href="/https/en.wikipedia.org/wiki/Center_Line,_Michigan" title="Center Line, Michigan">Center Line, Michigan</a>; and the tail fairing and mounting brackets by the Expert Tool and Die Company in <a href="/https/en.wikipedia.org/wiki/Detroit,_Michigan" class="mw-redirect" title="Detroit, Michigan">Detroit, Michigan</a>.<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993257_13-0" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993257-13">[13]</a></sup> The bomb, except for the uranium payload, was ready at the beginning of May 1945.<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993262_14-0" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993262-14">[14]</a></sup> Manhattan District Engineer <a href="/https/en.wikipedia.org/wiki/Kenneth_Nichols" title="Kenneth Nichols">Kenneth Nichols</a> expected on 1 May 1945 to have enriched uranium "for one weapon before August 1 and a second one sometime in December", assuming the second weapon would be a gun type; designing an implosion bomb for enriched uranium was considered, and this would increase the production rate.<sup id="cite_ref-FOOTNOTENichols1987166,_175–176_15-0" class="reference"><a href="#cite_note-FOOTNOTENichols1987166,_175–176-15">[15]</a></sup> The enriched uranium projectile was completed on 15 June, and the target on 24 July.<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993265_16-0" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993265-16">[16]</a></sup> The target and bomb pre-assemblies (partly assembled bombs without the fissile components) left <a href="/https/en.wikipedia.org/wiki/Hunters_Point_Naval_Shipyard" title="Hunters Point Naval Shipyard">Hunters Point Naval Shipyard</a>, California, on 16 July aboard the <a href="/https/en.wikipedia.org/wiki/Heavy_cruiser" title="Heavy cruiser">heavy cruiser</a> <a href="/https/en.wikipedia.org/wiki/USS_Indianapolis_(CA-35)" title="USS Indianapolis (CA-35)">USS <i>Indianapolis</i></a>, arriving on 26 July.<sup id="cite_ref-FOOTNOTECoster-Mullen201230_17-0" class="reference"><a href="#cite_note-FOOTNOTECoster-Mullen201230-17">[17]</a></sup> The target inserts followed by air on 30 July.<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993265_16-1" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993265-16">[16]</a></sup>
</p><p>Although all of its components had been individually tested,<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993265_16-2" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993265-16">[16]</a></sup> no full test of a gun-type nuclear weapon occurred before the Little Boy was dropped over <a href="/https/en.wikipedia.org/wiki/Hiroshima" title="Hiroshima">Hiroshima</a>. The only <a href="/https/en.wikipedia.org/wiki/Nuclear_testing" class="mw-redirect" title="Nuclear testing">test explosion</a> of a nuclear weapon concept had been of an implosion-type device employing plutonium as its fissile material, and took place on 16 July 1945 at the <a href="/https/en.wikipedia.org/wiki/Trinity_nuclear_test" class="mw-redirect" title="Trinity nuclear test">Trinity nuclear test</a>. There were several reasons for not testing a Little Boy type of device. Primarily, there was the issue of fissile material. Oak Ridge was designed to produce around 30 kilograms of enriched uranium per month, and the Little Boy design used over 60 kilograms per bomb. So testing the weapon would incur a considerable delay in use of the weapon. (By comparison, the Hanford plant was designed to produced around 20 kilograms of plutonium per month, and each Fat Man bomb used only around 6 kilograms of material.)<sup id="cite_ref-FOOTNOTEHansen1995111–112_18-0" class="reference"><a href="#cite_note-FOOTNOTEHansen1995111–112-18">[18]</a></sup> Because of the simplicity of the gun-type design, laboratory testing could establish that its parts worked correctly on their own — for example, dummy projectiles could be shot down the gun barrel to make sure they were "seated" correctly onto a dummy target. By comparison, with the implosion design it was much more difficult to establish absence of a full-scale test whether the necessary simultaneity of compression had been achieved. While there was at least one prominent scientist (<a href="/https/en.wikipedia.org/wiki/Ernest_O._Lawrence" class="mw-redirect" title="Ernest O. Lawrence">Ernest O. Lawrence</a>) who advocated for a full-scale test, by the spring of 1945 Little Boy was regarded as nearly a sure-thing, and was expected to have a higher-yield than the first-generation implosion bombs.<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993293_19-0" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993293-19">[19]</a></sup>
</p><p>Though Little Boy incorporated various safety mechanisms, an accidental detonation of a fully-assembled weapon was very possible. For example, should the bomber carrying the device crash then the hollow "bullet" could be driven into the "target" cylinder, possibly detonating the bomb from gravity alone (though tests suggested this was unlikely), but easily creating a critical mass that would release dangerous amounts of radiation.<sup id="cite_ref-FOOTNOTEHansen1995113_20-0" class="reference"><a href="#cite_note-FOOTNOTEHansen1995113-20">[20]</a></sup> And crash of the B-29 and subsequent fire could trigger the explosives, causing the weapon to detonate.<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993333_21-0" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993333-21">[21]</a></sup> If immersed in water, the uranium components were subject to a <a href="/https/en.wikipedia.org/wiki/Neutron_moderator" title="Neutron moderator">neutron moderator</a> effect, which would not cause an explosion but would release <a href="/https/en.wikipedia.org/wiki/Radioactive_contamination" title="Radioactive contamination">radioactive contamination</a>. For this reason, pilots were advised to crash on land rather than at sea.<sup id="cite_ref-FOOTNOTEHansen1995113_20-1" class="reference"><a href="#cite_note-FOOTNOTEHansen1995113-20">[20]</a></sup> Ultimately, Parsons opted to keep the explosives out of the Little Boy bomb until after the B-29 had taken off, to avoid the risk of a crash that could destroy or damage the military base the weapon was being launched from.
</p>
<h2><span class="mw-headline" id="Design">Design</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=5" title="Edit section: Design"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h2>
<figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/https/en.wikipedia.org/wiki/File:Gun-type_fission_weapon_en-labels_thin_lines.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/b/b7/Gun-type_fission_weapon_en-labels_thin_lines.svg/220px-Gun-type_fission_weapon_en-labels_thin_lines.svg.png" decoding="async" width="220" height="144" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/b7/Gun-type_fission_weapon_en-labels_thin_lines.svg/330px-Gun-type_fission_weapon_en-labels_thin_lines.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/b7/Gun-type_fission_weapon_en-labels_thin_lines.svg/440px-Gun-type_fission_weapon_en-labels_thin_lines.svg.png 2x" data-file-width="670" data-file-height="440" /></a><figcaption>The "gun" assembly method. When the hollow <a href="/https/en.wikipedia.org/wiki/Uranium" title="Uranium">uranium</a> projectile was driven onto the target cylinder, a nuclear explosion resulted.</figcaption></figure>
<figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/https/en.wikipedia.org/wiki/File:Little_boy_casing_open.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/4/45/Little_boy_casing_open.png/220px-Little_boy_casing_open.png" decoding="async" width="220" height="151" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/4/45/Little_boy_casing_open.png/330px-Little_boy_casing_open.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/4/45/Little_boy_casing_open.png/440px-Little_boy_casing_open.png 2x" data-file-width="897" data-file-height="614" /></a><figcaption>Two Little Boy type bomb assemblies on Tinian, with casings open. For unit L-1, in the foreground, boxes containing hardware for the clock timers, radar fuzing units, and batteries are visible and arranged around the central gun tube. Pull-out wires are visible on top. L-1 was test-dropped without nuclear fuel on July 23, 1945, to gain experience in assembling, handling, and using the weapons prior to the actual strike (which used unit L-11).</figcaption></figure>
<p>The Little Boy was 120 inches (300 cm) in length, 28 inches (71 cm) in diameter and weighed approximately 9,700 pounds (4,400 kg).<sup id="cite_ref-FOOTNOTEGosling199951_22-0" class="reference"><a href="#cite_note-FOOTNOTEGosling199951-22">[22]</a></sup> The design used the gun method to explosively force a hollow sub-<a href="/https/en.wikipedia.org/wiki/Critical_mass_(nuclear)" class="mw-redirect" title="Critical mass (nuclear)">critical mass</a> of <a href="/https/en.wikipedia.org/wiki/Enriched_uranium" title="Enriched uranium">enriched uranium</a> and a solid target cylinder together into a super-critical mass, initiating a <a href="/https/en.wikipedia.org/wiki/Nuclear_chain_reaction" title="Nuclear chain reaction">nuclear chain reaction</a>.<sup id="cite_ref-FOOTNOTECoster-Mullen201218_23-0" class="reference"><a href="#cite_note-FOOTNOTECoster-Mullen201218-23">[23]</a></sup> This was accomplished by shooting one piece of the uranium onto the other by means of four cylindrical silk bags of <a href="/https/en.wikipedia.org/wiki/Cordite" title="Cordite">cordite</a> powder. This was a widely used smokeless propellant consisting of a mixture of 65 percent <a href="/https/en.wikipedia.org/wiki/Nitrocellulose" title="Nitrocellulose">nitrocellulose</a>, 30 percent <a href="/https/en.wikipedia.org/wiki/Nitroglycerine" class="mw-redirect" title="Nitroglycerine">nitroglycerine</a>, 3 percent <a href="/https/en.wikipedia.org/wiki/Petroleum_jelly" title="Petroleum jelly">petroleum jelly</a>, and 2 percent <a href="/https/en.wikipedia.org/wiki/Centralite" title="Centralite">carbamite</a> that was extruded into tubular granules. This gave it a high surface area and a rapid burning area, and could attain pressures of up to 40,000 pounds per square inch (280,000 kPa). Cordite for the wartime Little Boy was sourced from Canada; propellant for post-war Little Boys was obtained from the <a href="/https/en.wikipedia.org/wiki/Picatinny_Arsenal" title="Picatinny Arsenal">Picatinny Arsenal</a>.<sup id="cite_ref-FOOTNOTECoster-Mullen201227_24-0" class="reference"><a href="#cite_note-FOOTNOTECoster-Mullen201227-24">[24]</a></sup> The bomb contained 64 kilograms (141 lb) of enriched uranium. Most was enriched to 89% but some was only 50% uranium-235, for an average enrichment of 80%.<sup id="cite_ref-FOOTNOTECoster-Mullen201218_23-1" class="reference"><a href="#cite_note-FOOTNOTECoster-Mullen201218-23">[23]</a></sup> Less than a kilogram of uranium underwent <a href="/https/en.wikipedia.org/wiki/Nuclear_fission" title="Nuclear fission">nuclear fission</a>, and of this mass only 0.7 grams (0.025 oz) was transformed into several forms of energy, mostly <a href="/https/en.wikipedia.org/wiki/Kinetic_energy" title="Kinetic energy">kinetic energy</a>, but also heat and radiation.<sup id="cite_ref-FOOTNOTEGlasstoneDolan197712_25-0" class="reference"><a href="#cite_note-FOOTNOTEGlasstoneDolan197712-25">[25]</a></sup>
</p>
<h3><span class="mw-headline" id="Assembly_details">Assembly details</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=6" title="Edit section: Assembly details"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h3>
<p>Inside the weapon, the uranium-235 material was divided into two parts, following the gun principle: the "projectile" and the "target". The projectile was a hollow cylinder with 60% of the total mass (38.5 kilograms [85 lb]). It consisted of a stack of nine uranium rings, each 6.25 inches (159 mm) in diameter with a 4-inch (100 mm) bore in the center, and a total length of 7 inches (180 mm), pressed together into the front end of a thin-walled projectile 16.25 inches (413 mm) long. Filling in the remainder of the space behind these rings in the projectile was a <a href="/https/en.wikipedia.org/wiki/Tungsten_carbide" title="Tungsten carbide">tungsten carbide</a> disc with a steel back. At ignition, the projectile slug was pushed 42 inches (1,100 mm) along the 72-inch-long (1,800 mm), 6.5-inch-wide (170 mm) smooth-bore gun barrel. The slug "insert" was a 4-inch cylinder, 7 inches in length with a 1-inch (25 mm) axial hole. The slug comprised 40% of the total fissile mass (25.6 kilograms or 56 pounds). The insert was a stack of six washer-like uranium discs somewhat thicker than the projectile rings that were slid over a 1-inch rod. This rod then extended forward through the tungsten carbide tamper plug, impact-absorbing anvil, and nose plug backstop, eventually protruding out of the front of the bomb casing. This entire target assembly was secured at both ends with locknuts.<sup id="cite_ref-nukearchive_26-0" class="reference"><a href="#cite_note-nukearchive-26">[26]</a></sup><sup id="cite_ref-FOOTNOTECoster-Mullen201218–19,_27_27-0" class="reference"><a href="#cite_note-FOOTNOTECoster-Mullen201218–19,_27-27">[27]</a></sup>
</p><p>When the hollow-front projectile reached the target and slid over the target insert, the assembled super-critical mass of uranium would be completely surrounded by a tamper and neutron reflector of tungsten carbide and steel, both materials having a combined mass of 2,300 kilograms (5,100 lb).<sup id="cite_ref-FOOTNOTEBernstein2007133_28-0" class="reference"><a href="#cite_note-FOOTNOTEBernstein2007133-28">[28]</a></sup> <a href="/https/en.wikipedia.org/wiki/Neutron_initiator" class="mw-redirect" title="Neutron initiator">Neutron initiators</a> inside the assembly were activated by the impact of the projectile into the target.<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993263–265_29-0" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993263–265-29">[29]</a></sup>
</p>
<figure class="mw-default-size mw-halign-center" typeof="mw:File"><a href="/https/en.wikipedia.org/wiki/File:Little_Boy_Internal_Components.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/d/d1/Little_Boy_Internal_Components.png" decoding="async" width="735" height="675" class="mw-file-element" data-file-width="735" data-file-height="675" /></a><figcaption></figcaption></figure>
<h3><span class="mw-headline" id="Counter-intuitive_design">Counter-intuitive design</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=7" title="Edit section: Counter-intuitive design"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h3>
<p>The material was split almost in half, with at one end a group of rings of U-235 with 40% of the supercritical mass, and at the other end another group of slightly larger rings with 60% of the supercritical mass, which was fired onto onto the smaller group, with a polonium-breryllium “initiator” to make the supercritical mass explode. <sup id="cite_ref-FOOTNOTEMonk2012409,_410_30-0" class="reference"><a href="#cite_note-FOOTNOTEMonk2012409,_410-30">[30]</a></sup>
</p><p>A hole in the center of the larger piece dispersed the mass and increased the surface area, allowing more fission neutrons to escape, thus preventing a premature chain reaction.<sup id="cite_ref-FOOTNOTECoster-Mullen201223–24_31-0" class="reference"><a href="#cite_note-FOOTNOTECoster-Mullen201223–24-31">[31]</a></sup> But, for this larger, hollow piece to have minimal contact with the tamper, it must be the projectile, since only the projectile's back end was in contact with the tamper prior to detonation. The rest of the tungsten carbide surrounded the sub-critical mass target cylinder (called the "insert" by the designers) with air space between it and the insert. This arrangement packs the maximum amount of fissile material into a gun-assembly design.<sup id="cite_ref-FOOTNOTECoster-Mullen201223–24_31-1" class="reference"><a href="#cite_note-FOOTNOTECoster-Mullen201223–24-31">[31]</a></sup>
</p><p>For the first fifty years after 1945, every published description and drawing of the Little Boy mechanism assumed that a small, solid projectile was fired into the center of a larger, stationary target.<sup id="cite_ref-FOOTNOTESamuels2008_32-0" class="reference"><a href="#cite_note-FOOTNOTESamuels2008-32">[32]</a></sup> However, critical mass considerations dictated thAat in Little Boy the more extensive, hollow piece would be the projectile. The assembled fissile core had more than two <a href="/https/en.wikipedia.org/wiki/Critical_mass" title="Critical mass">critical masses</a> of uranium-235. This required one of the two pieces to have more than one critical mass, with the larger piece avoiding criticality prior to assembly by means of shape and minimal contact with the neutron-reflecting tungsten carbide tamper. In 2004 John Coster-Mullen a truck driver amd modelmaker from Illinois who had studied every photograph and document on the Hiroshima bomb to make an accurate model corrected earlier published accounts. <sup id="cite_ref-FOOTNOTEMonk2012409,_410_30-1" class="reference"><a href="#cite_note-FOOTNOTEMonk2012409,_410-30">[30]</a></sup>
</p>
<h3><span class="mw-headline" id="Fuze_system">Fuze system</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=8" title="Edit section: Fuze system"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h3>
<figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/https/en.wikipedia.org/wiki/File:Little_Boy_arming_plugs_in_October_2009.JPG" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/0/0c/Little_Boy_arming_plugs_in_October_2009.JPG/220px-Little_Boy_arming_plugs_in_October_2009.JPG" decoding="async" width="220" height="165" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/0/0c/Little_Boy_arming_plugs_in_October_2009.JPG/330px-Little_Boy_arming_plugs_in_October_2009.JPG 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/0/0c/Little_Boy_arming_plugs_in_October_2009.JPG/440px-Little_Boy_arming_plugs_in_October_2009.JPG 2x" data-file-width="1524" data-file-height="1146" /></a><figcaption>Arming plugs for a Little Boy type atomic bomb on display at the <a href="/https/en.wikipedia.org/wiki/National_Air_and_Space_Museum" title="National Air and Space Museum">National Air and Space Museum</a>'s <a href="/https/en.wikipedia.org/wiki/Steven_F._Udvar-Hazy_Center" title="Steven F. Udvar-Hazy Center">Steven F. Udvar-Hazy Center</a></figcaption></figure>
<p>The <a href="/https/en.wikipedia.org/wiki/Fuze" title="Fuze">fuzing</a> system was designed to trigger at the most destructive altitude, which calculations suggested was 580 meters (1,900 ft). It employed a three-stage interlock system:<sup id="cite_ref-FOOTNOTEHansen1995a2–5_33-0" class="reference"><a href="#cite_note-FOOTNOTEHansen1995a2–5-33">[33]</a></sup>
</p>
<ul><li>A timer ensured that the bomb would not explode until at least fifteen seconds after release, one-quarter of the predicted fall time, to ensure the safety of the aircraft. The timer was activated when the electrical <a href="/https/en.wikipedia.org/wiki/Arming_plug" title="Arming plug">pull-out plugs</a> connecting it to the airplane pulled loose as the bomb fell, switching it to its internal 24-volt battery and starting the timer. At the end of the 15 seconds, the bomb would be 3,600 feet (1,100 m) from the aircraft, and the radar altimeters were powered up and responsibility was passed to the <a href="/https/en.wikipedia.org/wiki/Barometric" class="mw-redirect" title="Barometric">barometric</a> stage.<sup id="cite_ref-FOOTNOTEHansen1995a2–5_33-1" class="reference"><a href="#cite_note-FOOTNOTEHansen1995a2–5-33">[33]</a></sup></li>
<li>The purpose of the barometric stage was to delay activating the radar altimeter firing command circuit until near detonation altitude. A thin metallic membrane enclosing a vacuum chamber (a similar design is still used today in old-fashioned wall barometers) gradually deformed as ambient air pressure increased during descent. The barometric fuze was not considered accurate enough to detonate the bomb at the precise ignition height, because air pressure varies with local conditions. When the bomb reached the design height for this stage (reportedly 2,000 meters; 6,600 ft), the membrane closed a circuit, activating the radar altimeters. The barometric stage was added because of a worry that external radar signals might detonate the bomb too early.<sup id="cite_ref-FOOTNOTEHansen1995a2–5_33-2" class="reference"><a href="#cite_note-FOOTNOTEHansen1995a2–5-33">[33]</a></sup></li>
<li>Two or more <a href="/https/en.wikipedia.org/wiki/Redundancy_(engineering)" title="Redundancy (engineering)">redundant</a> <a href="/https/en.wikipedia.org/wiki/Radar_altimeter" title="Radar altimeter">radar altimeters</a> were used to reliably detect final altitude. When the altimeters sensed the correct height, the firing switch closed, igniting the three BuOrd Mk15, Mod 1 Navy gun primers in the breech plug, which set off the charge consisting of four silk powder bags each containing 2 pounds (910 g) of WM slotted-tube <a href="/https/en.wikipedia.org/wiki/Cordite" title="Cordite">cordite</a>. This launched the uranium projectile towards the opposite end of the gun barrel at an eventual <a href="/https/en.wikipedia.org/wiki/Muzzle_velocity" title="Muzzle velocity">muzzle velocity</a> of 300 meters per second (980 ft/s). Approximately 10 milliseconds later the chain reaction occurred, lasting less than 1 microsecond. The radar altimeters used were modified U.S. Army Air Corps <a href="/https/en.wikipedia.org/wiki/Monica_(radar)" title="Monica (radar)">APS-13</a> <a href="/https/en.wikipedia.org/wiki/Tail_warning_radar" title="Tail warning radar">tail warning radars</a>, nicknamed "Archie", normally used to warn a fighter pilot of another plane approaching from behind.<sup id="cite_ref-FOOTNOTEHansen1995a2–5_33-3" class="reference"><a href="#cite_note-FOOTNOTEHansen1995a2–5-33">[33]</a></sup></li></ul>
<h2><span class="mw-headline" id="Rehearsals">Rehearsals</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=9" title="Edit section: Rehearsals"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h2>
<figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/https/en.wikipedia.org/wiki/File:Atombombe_Little_Boy_2.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e0/Atombombe_Little_Boy_2.jpg/220px-Atombombe_Little_Boy_2.jpg" decoding="async" width="220" height="245" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e0/Atombombe_Little_Boy_2.jpg/330px-Atombombe_Little_Boy_2.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e0/Atombombe_Little_Boy_2.jpg/440px-Atombombe_Little_Boy_2.jpg 2x" data-file-width="2354" data-file-height="2618" /></a><figcaption>Little Boy in the bomb pit on <a href="/https/en.wikipedia.org/wiki/Tinian" title="Tinian">Tinian</a> island, before being loaded into <i>Enola Gay</i><span class="nowrap" style="padding-left:0.1em;">'</span>s bomb bay. A section of the bomb bay door is visible on the top right.</figcaption></figure>
<p>The Little Boy pre-assemblies were designated L-1, L-2, L-3, L-4, L-5, L-6, L-7, and L-11. Of these, L-1, L-2, L-5, and L-6 were expended in test drops. The first drop test was conducted with L-1 on 23 July 1945. It was dropped over the sea near Tinian in order to test the radar altimeter by the B-29 later known as <i><a href="/https/en.wikipedia.org/wiki/Big_Stink_(aircraft)" title="Big Stink (aircraft)">Big Stink</a></i>, piloted by <a href="/https/en.wikipedia.org/wiki/Colonel_(United_States)" title="Colonel (United States)">Colonel</a> <a href="/https/en.wikipedia.org/wiki/Paul_W._Tibbets" class="mw-redirect" title="Paul W. Tibbets">Paul W. Tibbets</a>, the commander of the <a href="/https/en.wikipedia.org/wiki/509th_Composite_Group" title="509th Composite Group">509th Composite Group</a>. Two more drop tests over the sea were made on 24 and 25 July, using the L-2 and L-5 units in order to test all components. Tibbets was the pilot for both missions, but this time the bomber used was the one subsequently known as <i><a href="/https/en.wikipedia.org/wiki/Jabit_III" title="Jabit III">Jabit</a></i>. L-6 was used as a dress rehearsal on 29 July. The B-29 <i><a href="/https/en.wikipedia.org/wiki/Next_Objective" title="Next Objective">Next Objective</a></i>, piloted by <a href="/https/en.wikipedia.org/wiki/Major_(rank)" title="Major (rank)">Major</a> <a href="/https/en.wikipedia.org/wiki/Charles_W._Sweeney" class="mw-redirect" title="Charles W. Sweeney">Charles W. Sweeney</a>, flew to <a href="/https/en.wikipedia.org/wiki/Iwo_Jima" title="Iwo Jima">Iwo Jima</a>, where emergency procedures for loading the bomb onto a standby aircraft were practiced. This rehearsal was repeated on 31 July, but this time L-6 was reloaded onto a different B-29, <i><a href="/https/en.wikipedia.org/wiki/Enola_Gay" title="Enola Gay">Enola Gay</a></i>, piloted by Tibbets, and the bomb was test dropped near Tinian. L-11 was the assembly used for the Hiroshima bomb, and was fully assembled with its nuclear fuel by 31 July.<sup id="cite_ref-FOOTNOTECampbell200546,_80_34-0" class="reference"><a href="#cite_note-FOOTNOTECampbell200546,_80-34">[34]</a></sup><sup id="cite_ref-FOOTNOTECoster-Mullen2012100–101_35-0" class="reference"><a href="#cite_note-FOOTNOTECoster-Mullen2012100–101-35">[35]</a></sup>
</p>
<h2><span class="mw-headline" id="Bombing_of_Hiroshima">Bombing of Hiroshima</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=10" title="Edit section: Bombing of Hiroshima"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h2>
<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1033289096"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/https/en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki#Bombing_of_Hiroshima" title="Atomic bombings of Hiroshima and Nagasaki">Atomic bombings of Hiroshima and Nagasaki § Bombing of Hiroshima</a></div>
<figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/https/en.wikipedia.org/wiki/File:Enola_Gay_(plane).jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/6/66/Enola_Gay_%28plane%29.jpg/350px-Enola_Gay_%28plane%29.jpg" decoding="async" width="350" height="149" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/66/Enola_Gay_%28plane%29.jpg/525px-Enola_Gay_%28plane%29.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/66/Enola_Gay_%28plane%29.jpg/700px-Enola_Gay_%28plane%29.jpg 2x" data-file-width="1392" data-file-height="594" /></a><figcaption><i>Enola Gay</i> after Hiroshima mission, entering <a href="/https/en.wikipedia.org/wiki/Hardstand" title="Hardstand">hardstand</a>. It is in its 6th Bombardment Group livery, with <a href="/https/en.wikipedia.org/wiki/USAAF_unit_identification_aircraft_markings" title="USAAF unit identification aircraft markings">victor number</a> 82 visible on fuselage just forward of the tail fin.</figcaption></figure>
<p>Parsons, the <i>Enola Gay</i><span class="nowrap" style="padding-left:0.1em;">'</span>s weaponeer, was concerned about the possibility of an accidental detonation if the plane crashed on takeoff, so he decided not to load the four cordite powder bags into the gun breech until the aircraft was in flight. After takeoff, Parsons and his assistant, <a href="/https/en.wikipedia.org/wiki/Second_Lieutenant" class="mw-redirect" title="Second Lieutenant">Second Lieutenant</a> <a href="/https/en.wikipedia.org/wiki/Morris_R._Jeppson" title="Morris R. Jeppson">Morris R. Jeppson</a>, made their way into the bomb bay along the narrow catwalk on the port side. Jeppson held a flashlight while Parsons disconnected the primer wires, removed the breech plug, inserted the powder bags, replaced the breech plug, and reconnected the wires. Before climbing to altitude on approach to the target, Jeppson switched the three safety plugs between the electrical connectors of the internal battery and the firing mechanism from green to red. The bomb was then fully armed. Jeppson monitored the bomb's circuits.<sup id="cite_ref-FOOTNOTECoster-Mullen201234–35_36-0" class="reference"><a href="#cite_note-FOOTNOTECoster-Mullen201234–35-36">[36]</a></sup>
</p>
<figure class="mw-default-size mw-halign-left" typeof="mw:File/Thumb"><a href="/https/en.wikipedia.org/wiki/File:Atomic_cloud_over_Hiroshima_-_NARA_542192_-_Edit.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/2f/Atomic_cloud_over_Hiroshima_-_NARA_542192_-_Edit.jpg/260px-Atomic_cloud_over_Hiroshima_-_NARA_542192_-_Edit.jpg" decoding="async" width="260" height="306" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/2f/Atomic_cloud_over_Hiroshima_-_NARA_542192_-_Edit.jpg/390px-Atomic_cloud_over_Hiroshima_-_NARA_542192_-_Edit.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/2f/Atomic_cloud_over_Hiroshima_-_NARA_542192_-_Edit.jpg/520px-Atomic_cloud_over_Hiroshima_-_NARA_542192_-_Edit.jpg 2x" data-file-width="2498" data-file-height="2943" /></a><figcaption>The <a href="/https/en.wikipedia.org/wiki/Mushroom_cloud" title="Mushroom cloud">mushroom cloud</a> over <a href="/https/en.wikipedia.org/wiki/Hiroshima" title="Hiroshima">Hiroshima</a> after the detonation of Little Boy on 6 August 1945. A separation between the upper mushroom head and the stem is visible. This photograph and its vaguely <a href="/https/en.wikipedia.org/wiki/Question_mark" title="Question mark">question mark</a> appearance was used as the inspiration for the <a href="/https/en.wikipedia.org/wiki/File:Manhattan_District.svg" title="File:Manhattan District.svg">insignia of the Manhattan Engineer District</a>, and was widely reprinted globally within days of the attack.</figcaption></figure>
<p>The bomb was dropped at approximately 08:15 (JST) on 6 August 1945. After falling for 44.4 seconds, the time and barometric triggers started the firing mechanism. The detonation happened at an altitude of 1,968 ± 50 feet (600 ± 15 m). It was less powerful than the <a href="/https/en.wikipedia.org/wiki/Fat_Man" title="Fat Man">Fat Man</a>, which was dropped on <a href="/https/en.wikipedia.org/wiki/Nagasaki" title="Nagasaki">Nagasaki</a>, but the damage and the number of victims at Hiroshima were much higher, as Hiroshima was on flat terrain, while the <a href="/https/en.wikipedia.org/wiki/Hypocenter" title="Hypocenter">hypocenter</a> of Nagasaki lay in a small valley. According to figures published in 1945, 66,000 people were killed as a direct result of the Hiroshima blast, and 69,000 were injured to varying degrees.<sup id="cite_ref-37" class="reference"><a href="#cite_note-37">[37]</a></sup> Later estimates put the deaths as high as 140,000 people.<sup id="cite_ref-38" class="reference"><a href="#cite_note-38">[38]</a></sup> The <a href="/https/en.wikipedia.org/wiki/United_States_Strategic_Bombing_Survey" title="United States Strategic Bombing Survey">United States Strategic Bombing Survey</a> estimated that out of 24,158 <a href="/https/en.wikipedia.org/wiki/Imperial_Japanese_Army" title="Imperial Japanese Army">Imperial Japanese Army</a> soldiers in Hiroshima at the time of the bombing, 6,789 were killed or missing as a result of the bombing.<sup id="cite_ref-FOOTNOTECravenCate1983723_39-0" class="reference"><a href="#cite_note-FOOTNOTECravenCate1983723-39">[39]</a></sup>
</p><p>
The exact measurement of the explosive yield of the bomb was problematic since the weapon had never been tested. <a href="/https/en.wikipedia.org/wiki/President_of_the_United_States" title="President of the United States">President</a> <a href="/https/en.wikipedia.org/wiki/Harry_S._Truman" title="Harry S. Truman">Harry S. Truman</a> officially announced that the yield was 20 kilotons of TNT (84 TJ). This was based on Parsons's visual assessment that the blast was greater than what he had seen at the <a href="/https/en.wikipedia.org/wiki/Trinity_nuclear_test" class="mw-redirect" title="Trinity nuclear test">Trinity nuclear test</a>. Since that had been estimated at 18 kilotons of TNT (75 TJ), speech writers rounded up to 20 kilotons. Further discussion was then suppressed, for fear of lessening the impact of the bomb on the Japanese. Data had been collected by <a href="/https/en.wikipedia.org/wiki/Luis_Walter_Alvarez" title="Luis Walter Alvarez">Luis Alvarez</a>, <a href="/https/en.wikipedia.org/wiki/Harold_Agnew" title="Harold Agnew">Harold Agnew</a>, and <a href="/https/en.wikipedia.org/wiki/Lawrence_H._Johnston" title="Lawrence H. Johnston">Lawrence H. Johnston</a> on the instrument plane, <i><a href="/https/en.wikipedia.org/wiki/The_Great_Artiste" title="The Great Artiste">The Great Artiste</a></i>, but this was not used to calculate the yield at the time.<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993393_40-0" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993393-40">[40]</a></sup> More rigorous estimates of the bomb yield and conventional bomb equivalent were made when more data was acquired following the end of the war. A 1985 study estimated the bomb's yield was around 15 kilotons of TNT (63 TJ).<sup id="cite_ref-FOOTNOTEMalik19851_41-0" class="reference"><a href="#cite_note-FOOTNOTEMalik19851-41">[41]</a></sup> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1033289096"></p><div role="note" class="hatnote navigation-not-searchable">Further information: <a href="/https/en.wikipedia.org/wiki/Little_boy#Conventional_weapon_equivalent" class="mw-redirect" title="Little boy">Little boy § Conventional weapon equivalent</a></div>
<p><br />
</p>
<h2><span class="mw-headline" id="Physical_effects">Physical effects</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=11" title="Edit section: Physical effects"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h2>
<figure class="mw-default-size mw-halign-left" typeof="mw:File/Thumb"><span><video id="mwe_player_0" poster="//upload.wikimedia.org/wikipedia/commons/thumb/b/b1/General_Effects_of_Atomic_Bomb_on_Hiroshima_and_Nagasaki.ogv/220px--General_Effects_of_Atomic_Bomb_on_Hiroshima_and_Nagasaki.ogv.jpg" controls="" preload="none" class="mw-file-element" width="220" height="165" data-durationhint="1321" data-mwtitle="General_Effects_of_Atomic_Bomb_on_Hiroshima_and_Nagasaki.ogv" data-mwprovider="wikimediacommons" resource="/wiki/File:General_Effects_of_Atomic_Bomb_on_Hiroshima_and_Nagasaki.ogv"><source src="//upload.wikimedia.org/wikipedia/commons/b/b1/General_Effects_of_Atomic_Bomb_on_Hiroshima_and_Nagasaki.ogv" type="video/ogg; codecs="theora, vorbis"" data-width="400" data-height="300" /><source src="//upload.wikimedia.org/wikipedia/commons/transcoded/b/b1/General_Effects_of_Atomic_Bomb_on_Hiroshima_and_Nagasaki.ogv/General_Effects_of_Atomic_Bomb_on_Hiroshima_and_Nagasaki.ogv.m3u8" type="application/vnd.apple.mpegurl" data-transcodekey="m3u8" data-width="0" data-height="0" /><source src="//upload.wikimedia.org/wikipedia/commons/transcoded/b/b1/General_Effects_of_Atomic_Bomb_on_Hiroshima_and_Nagasaki.ogv/General_Effects_of_Atomic_Bomb_on_Hiroshima_and_Nagasaki.ogv.240p.vp9.webm" type="video/webm; codecs="vp9, opus"" data-transcodekey="240p.vp9.webm" data-width="320" data-height="240" /></video></span><figcaption><i>The General Effects of the Atomic Bombs on Hiroshima and Nagasaki</i>, a U.S. Air Force film</figcaption></figure>
<p>After being selected in April 1945, Hiroshima was spared conventional bombing to serve as a pristine target, where the effects of a nuclear bomb on an undamaged city could be observed.<sup id="cite_ref-FOOTNOTEGroves1962267,_"To_enable_us_to_assess_accurately_the_effects_of_the_[nuclear]_bomb,_the_targets_should_not_have_been_previously_damaged_by_air_raids."_Four_cities_were_chosen,_including_Hiroshima_and_Kyoto._War_Secretary_Stimson_vetoed_Kyoto,_and_Nagasaki_was_substituted._p._275,_"When_our_target_cities_were_first_selected,_an_order_was_sent_to_the_Army_Air_Force_in_Guam_not_to_bomb_them_without_special_authority_from_the_War_Department."_42-0" class="reference"><a href="#cite_note-FOOTNOTEGroves1962267,_"To_enable_us_to_assess_accurately_the_effects_of_the_[nuclear]_bomb,_the_targets_should_not_have_been_previously_damaged_by_air_raids."_Four_cities_were_chosen,_including_Hiroshima_and_Kyoto._War_Secretary_Stimson_vetoed_Kyoto,_and_Nagasaki_was_substituted._p._275,_"When_our_target_cities_were_first_selected,_an_order_was_sent_to_the_Army_Air_Force_in_Guam_not_to_bomb_them_without_special_authority_from_the_War_Department."-42">[42]</a></sup> While damage could be studied later, the energy yield of the untested Little Boy design could be determined only at the moment of detonation, using instruments dropped by parachute from a plane flying in formation with the one that dropped the bomb. Radio-transmitted data from these instruments indicated a yield of about 15 kilotons.<sup id="cite_ref-FOOTNOTEMalik19851_41-1" class="reference"><a href="#cite_note-FOOTNOTEMalik19851-41">[41]</a></sup>
</p><p>Comparing this yield to the observed damage produced a rule of thumb called the 5 <a href="/https/en.wikipedia.org/wiki/Pound_per_square_inch" title="Pound per square inch">pounds per square inch</a> (34 <a href="/https/en.wikipedia.org/wiki/Pascal_(unit)" title="Pascal (unit)">kPa</a>) lethal area rule. Approximately all the people inside the area where the shock wave carried such an overpressure or greater would be killed.<sup id="cite_ref-FOOTNOTEGlasstone1962629_43-0" class="reference"><a href="#cite_note-FOOTNOTEGlasstone1962629-43">[43]</a></sup> At Hiroshima, that area was 3.5 kilometers (2.2 mi) in diameter.<sup id="cite_ref-FOOTNOTEGlasstoneDolan1977Nuclear_Bomb_Effects_Computer_44-0" class="reference"><a href="#cite_note-FOOTNOTEGlasstoneDolan1977Nuclear_Bomb_Effects_Computer-44">[44]</a></sup>
</p><p>The damage came from three main effects: blast, fire, and radiation.<sup id="cite_ref-FOOTNOTEGlasstoneDolan19771_45-0" class="reference"><a href="#cite_note-FOOTNOTEGlasstoneDolan19771-45">[45]</a></sup>
</p>
<h3><span class="mw-headline" id="Blast">Blast</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=12" title="Edit section: Blast"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h3>
<p>The blast from a nuclear bomb is the result of <a href="/https/en.wikipedia.org/wiki/X-ray" title="X-ray">X-ray</a>-heated air (the fireball) sending a shock wave or pressure wave in all directions, initially at a velocity greater than the speed of sound,<sup id="cite_ref-FOOTNOTEDiacon198418_46-0" class="reference"><a href="#cite_note-FOOTNOTEDiacon198418-46">[46]</a></sup> analogous to thunder generated by lightning. Knowledge about urban blast destruction is based largely on studies of Little Boy at Hiroshima. Nagasaki buildings suffered similar damage at similar distances, but the Nagasaki bomb detonated 3.2 kilometers (2.0 mi) from the city center over hilly terrain that was partially bare of buildings.<sup id="cite_ref-FOOTNOTEGlasstoneDolan1977300,_301_47-0" class="reference"><a href="#cite_note-FOOTNOTEGlasstoneDolan1977300,_301-47">[47]</a></sup>
</p>
<figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/https/en.wikipedia.org/wiki/File:House_1953_Nevada_Nuclear_Test_5_psi.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/d/db/House_1953_Nevada_Nuclear_Test_5_psi.jpg/220px-House_1953_Nevada_Nuclear_Test_5_psi.jpg" decoding="async" width="220" height="165" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/d/db/House_1953_Nevada_Nuclear_Test_5_psi.jpg/330px-House_1953_Nevada_Nuclear_Test_5_psi.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/d/db/House_1953_Nevada_Nuclear_Test_5_psi.jpg/440px-House_1953_Nevada_Nuclear_Test_5_psi.jpg 2x" data-file-width="1024" data-file-height="768" /></a><figcaption>Frame house in 1953 nuclear test, 5 <a href="/https/en.wikipedia.org/wiki/Pound_per_square_inch" title="Pound per square inch">psi</a> overpressure</figcaption></figure>
<p>In Hiroshima, almost everything within 1.6 kilometers (1.0 mi) of the point directly under the explosion was completely destroyed, except for about 50 heavily reinforced, earthquake-resistant concrete buildings, only the shells of which remained standing. Most were completely gutted, with their windows, doors, sashes, and frames ripped out.<sup id="cite_ref-FOOTNOTEThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_194614_48-0" class="reference"><a href="#cite_note-FOOTNOTEThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_194614-48">[48]</a></sup> The perimeter of severe blast damage approximately followed the 5 pounds per square inch (34 kPa) contour at 1.8 kilometers (1.1 mi).
</p><p>Later test explosions of nuclear weapons with houses and other test structures nearby confirmed the 5 psi overpressure threshold. Ordinary urban buildings experiencing it were crushed, toppled, or gutted by the force of air pressure. The picture at right shows the effects of a nuclear bomb-generated 5 psi pressure wave on a test structure in Nevada in 1953.<sup id="cite_ref-FOOTNOTEGlasstoneDolan1977179_49-0" class="reference"><a href="#cite_note-FOOTNOTEGlasstoneDolan1977179-49">[49]</a></sup>
</p><p>A major effect of this kind of structural damage was that it created fuel for fires that were started simultaneously throughout the severe destruction region.
</p>
<h3><span class="mw-headline" id="Fire">Fire</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=13" title="Edit section: Fire"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h3>
<p>The first effect of the explosion was blinding light, accompanied by radiant heat from the fireball. The Hiroshima fireball was 370 meters (1,200 ft) in diameter, with a surface temperature of 6,000 °C (10,830 °F), about the same temperature as at the surface of the sun.<sup id="cite_ref-FOOTNOTENuclear_Weapon_Thermal_Effects1998_50-0" class="reference"><a href="#cite_note-FOOTNOTENuclear_Weapon_Thermal_Effects1998-50">[50]</a></sup> Near ground zero, everything flammable burst into flame. One famous, anonymous Hiroshima victim, sitting on stone steps 260 metres (850 ft) from the hypocenter, left only a shadow, having absorbed the fireball heat that permanently bleached the surrounding stone.<sup id="cite_ref-FOOTNOTEHuman_Shadow_Etched_in_Stone_51-0" class="reference"><a href="#cite_note-FOOTNOTEHuman_Shadow_Etched_in_Stone-51">[51]</a></sup> Simultaneous fires were started throughout the blast-damaged area by fireball heat and by overturned stoves and furnaces, electrical shorts, etc. Twenty minutes after the detonation, these fires had merged into a <a href="/https/en.wikipedia.org/wiki/Firestorm" title="Firestorm">firestorm</a>, pulling in surface air from all directions to feed an inferno which consumed everything flammable.<sup id="cite_ref-FOOTNOTEGlasstoneDolan1977300–304_52-0" class="reference"><a href="#cite_note-FOOTNOTEGlasstoneDolan1977300–304-52">[52]</a></sup>
</p>
<figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/https/en.wikipedia.org/wiki/File:Hiroshima_Damage_Map.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/5/56/Hiroshima_Damage_Map.png/220px-Hiroshima_Damage_Map.png" decoding="async" width="220" height="210" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/56/Hiroshima_Damage_Map.png/330px-Hiroshima_Damage_Map.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/56/Hiroshima_Damage_Map.png/440px-Hiroshima_Damage_Map.png 2x" data-file-width="1024" data-file-height="976" /></a><figcaption>Hiroshima blast and fire damage, U.S. Strategic Bombing Survey map</figcaption></figure>
<p>The Hiroshima firestorm was roughly 3.2 kilometers (2.0 mi) in diameter, corresponding closely to the severe blast-damage zone. (See the USSBS<sup id="cite_ref-FOOTNOTED'Olier194622–25_53-0" class="reference"><a href="#cite_note-FOOTNOTED'Olier194622–25-53">[53]</a></sup> map, right.) Blast-damaged buildings provided fuel for the fire. Structural lumber and furniture were splintered and scattered about. Debris-choked roads obstructed firefighters. Broken gas pipes fueled the fire, and broken water pipes rendered hydrants useless.<sup id="cite_ref-FOOTNOTEGlasstoneDolan1977300–304_52-1" class="reference"><a href="#cite_note-FOOTNOTEGlasstoneDolan1977300–304-52">[52]</a></sup> At Nagasaki, the fires failed to merge into a single firestorm, and the fire-damaged area was only one-quarter as great as at Hiroshima, due in part to a southwest wind that pushed the fires away from the city.<sup id="cite_ref-FOOTNOTEGlasstoneDolan1977304_54-0" class="reference"><a href="#cite_note-FOOTNOTEGlasstoneDolan1977304-54">[54]</a></sup>
</p><p>As the map shows, the Hiroshima firestorm jumped natural firebreaks (river channels), as well as prepared firebreaks. The spread of fire stopped only when it reached the edge of the blast-damaged area, encountering less available fuel.<sup id="cite_ref-FOOTNOTEThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_194621–23_55-0" class="reference"><a href="#cite_note-FOOTNOTEThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_194621–23-55">[55]</a></sup> The Manhattan Project report on Hiroshima estimated that 60% of immediate deaths were caused by fire, but with the caveat that "many persons near the center of explosion suffered fatal injuries from more than one of the bomb effects."<sup id="cite_ref-FOOTNOTEThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_194621_56-0" class="reference"><a href="#cite_note-FOOTNOTEThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_194621-56">[56]</a></sup>
</p>
<h3><span class="mw-headline" id="Radiation">Radiation</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=14" title="Edit section: Radiation"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h3>
<p><a href="/https/en.wikipedia.org/wiki/Nuclear_fallout" title="Nuclear fallout">Local fallout</a> is dust and ash from a bomb crater, contaminated with radioactive fission products. It falls to earth downwind of the crater and can produce, with radiation alone, a lethal area much larger than that from blast and fire. With an <a href="/https/en.wikipedia.org/wiki/Air_burst" title="Air burst">air burst</a>, the fission products rise into the <a href="/https/en.wikipedia.org/wiki/Stratosphere" title="Stratosphere">stratosphere</a>, where they dissipate and become part of the global environment. Because Little Boy was an air burst 580 meters (1,900 ft) above the ground, there was no bomb crater and no local radioactive fallout.<sup id="cite_ref-FOOTNOTEGlasstoneDolan1977409_"An_air_burst,_by_definition,_is_one_taking_place_at_such_a_height_above_the_earth_that_no_appreciable_quantities_of_surface_material_are_taken_up_into_the_fireball._..._the_deposition_of_early_fallout_from_an_air_burst_will_generally_not_be_significant._An_air_burst,_however,_may_produce_some_induced_radioactive_contamination_in_the_general_vicinity_of_ground_zero_as_a_result_of_neutron_capture_by_elements_in_the_soil."_p._36,_"at_Hiroshima_..._injuries_due_to_fallout_were_completely_absent."_57-0" class="reference"><a href="#cite_note-FOOTNOTEGlasstoneDolan1977409_"An_air_burst,_by_definition,_is_one_taking_place_at_such_a_height_above_the_earth_that_no_appreciable_quantities_of_surface_material_are_taken_up_into_the_fireball._..._the_deposition_of_early_fallout_from_an_air_burst_will_generally_not_be_significant._An_air_burst,_however,_may_produce_some_induced_radioactive_contamination_in_the_general_vicinity_of_ground_zero_as_a_result_of_neutron_capture_by_elements_in_the_soil."_p._36,_"at_Hiroshima_..._injuries_due_to_fallout_were_completely_absent."-57">[57]</a></sup>
</p><p>However, a burst of intense <a href="/https/en.wikipedia.org/wiki/Neutron_radiation" title="Neutron radiation">neutron</a> and <a href="/https/en.wikipedia.org/wiki/Gamma_radiation" class="mw-redirect" title="Gamma radiation">gamma radiation</a> came directly from the fission of the uranium. Its lethal radius was approximately 1.3 kilometers (0.8 mi),<sup id="cite_ref-FOOTNOTEGlasstoneDolan1977Chapter_VIII_and_the_'Nuclear_Bomb_Effects_Computer'_58-0" class="reference"><a href="#cite_note-FOOTNOTEGlasstoneDolan1977Chapter_VIII_and_the_'Nuclear_Bomb_Effects_Computer'-58">[58]</a></sup><sup id="cite_ref-59" class="reference"><a href="#cite_note-59">[59]</a></sup> covering about half of the firestorm area. An estimated 30% of immediate fatalities were people who received lethal doses of this direct radiation, but died in the firestorm before their radiation injuries would have become apparent. Over 6,000 people survived the blast and fire, but died of radiation injuries.<sup id="cite_ref-FOOTNOTEThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_194621_56-1" class="reference"><a href="#cite_note-FOOTNOTEThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_194621-56">[56]</a></sup> Among injured survivors, 30% had radiation injuries<sup id="cite_ref-FOOTNOTEGlasstoneDolan1977545,_546_60-0" class="reference"><a href="#cite_note-FOOTNOTEGlasstoneDolan1977545,_546-60">[60]</a></sup> from which they recovered, but with a lifelong increase in <a href="/https/en.wikipedia.org/wiki/Radiation-induced_cancer" title="Radiation-induced cancer">cancer</a> risk.<sup id="cite_ref-FOOTNOTERichardson_RR_2009_61-0" class="reference"><a href="#cite_note-FOOTNOTERichardson_RR_2009-61">[61]</a></sup><sup id="cite_ref-62" class="reference"><a href="#cite_note-62">[62]</a></sup> To date, no radiation-related evidence of heritable diseases has been observed among the survivors' children.<sup id="cite_ref-FOOTNOTEGenetic_Effects_63-0" class="reference"><a href="#cite_note-FOOTNOTEGenetic_Effects-63">[63]</a></sup><sup id="cite_ref-FOOTNOTEIzumi_BJC_2003_64-0" class="reference"><a href="#cite_note-FOOTNOTEIzumi_BJC_2003-64">[64]</a></sup><sup id="cite_ref-FOOTNOTEIzumi_IJC_2003_65-0" class="reference"><a href="#cite_note-FOOTNOTEIzumi_IJC_2003-65">[65]</a></sup>
</p><p>After the surrender of Japan was finalized, Manhattan Project scientists began to immediately survey the city of Hiroshima to better understand the damage, and to communicate with Japanese physicians about radiation effects in particular. The collaboration became the <a href="/https/en.wikipedia.org/wiki/Atomic_Bomb_Casualty_Commission" title="Atomic Bomb Casualty Commission">Atomic Bomb Casualty Commission</a> in 1946, a joint U.S.–Japanese project to track radiation injuries among survivors. In 1975 its work was superseded by the <a href="/https/en.wikipedia.org/wiki/Radiation_Effects_Research_Foundation" title="Radiation Effects Research Foundation">Radiation Effects Research Foundation</a>.<sup id="cite_ref-66" class="reference"><a href="#cite_note-66">[66]</a></sup>
</p><p>In 1962, scientists at Los Alamos created a mockup of Little Boy known as "Project Ichiban" in order to answer some of the unanswered questions about the exact <a href="/https/en.wikipedia.org/wiki/Dosimetry" title="Dosimetry">radiation output</a> of the bomb, which would be useful for setting benchmarks for interpreting the relationship between radiation exposure and later health outcomes. But it failed to clear up all the issues. In 1982, Los Alamos created a replica Little Boy from the original drawings and specifications. This was then tested with enriched uranium but in a safe configuration that would not cause a nuclear explosion. A hydraulic lift was used to move the projectile, and experiments were run to assess neutron emission.<sup id="cite_ref-FOOTNOTECoster-Mullen201286–87_67-0" class="reference"><a href="#cite_note-FOOTNOTECoster-Mullen201286–87-67">[67]</a></sup>
</p>
<h3><span class="mw-headline" id="Conventional_weapon_equivalent">Conventional weapon equivalent</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=15" title="Edit section: Conventional weapon equivalent"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h3>
<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1033289096"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/https/en.wikipedia.org/wiki/Operation_Meetinghouse" class="mw-redirect" title="Operation Meetinghouse">Operation Meetinghouse</a></div>
<p>After hostilities ended, a survey team from the Manhattan Project that included <a href="/https/en.wikipedia.org/wiki/William_Penney" class="mw-redirect" title="William Penney">William Penney</a>, Robert Serber, and <a href="/https/en.wikipedia.org/wiki/George_T._Reynolds" title="George T. Reynolds">George T. Reynolds</a> was sent to Hiroshima to evaluate the effects of the blast. From evaluating the effects on objects and structures, Penney concluded that the yield was 12 ± 1 kilotons.<sup id="cite_ref-FOOTNOTEMalik198518–20_68-0" class="reference"><a href="#cite_note-FOOTNOTEMalik198518–20-68">[68]</a></sup> Later calculations based on charring pointed to a yield of 13 to 14 kilotons.<sup id="cite_ref-FOOTNOTEMalik198521_69-0" class="reference"><a href="#cite_note-FOOTNOTEMalik198521-69">[69]</a></sup> In 1953, <a href="/https/en.wikipedia.org/wiki/Frederick_Reines" title="Frederick Reines">Frederick Reines</a> calculated the yield as 15 kilotons of TNT (63 TJ).<sup id="cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993393_40-1" class="reference"><a href="#cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993393-40">[40]</a></sup> Based on the Project Ichiban data, and the pressure-wave data from <i>The Great Artiste</i>, the yield was estimated in the 1960s at 16.6 ± 0.3 kilotons.<sup id="cite_ref-FOOTNOTEMalik198516_70-0" class="reference"><a href="#cite_note-FOOTNOTEMalik198516-70">[70]</a></sup> A review conducted by a scientist at Los Alamos in 1985 concluded, on the basis of existing blast, thermal, and radiological data, and then-current models of weapons effects, that the best estimate of the yield was 15 kilotons of TNT (63 TJ) with an uncertainty of 20% (±3 kt). By comparison, the best value for the Nagasaki bomb was evaluated as 21 kilotons of TNT (88 TJ) with an uncertainty of 10% (±2 kt), the difference in uncertainty owing to having better data on the latter. <sup id="cite_ref-FOOTNOTEMalik19851_41-2" class="reference"><a href="#cite_note-FOOTNOTEMalik19851-41">[41]</a></sup>
</p><p>Although Little Boy exploded with the energy equivalent of around 15 kilotons of TNT, in 1946 the <a href="/https/en.wikipedia.org/wiki/Strategic_Bombing_Survey" class="mw-redirect" title="Strategic Bombing Survey">Strategic Bombing Survey</a> estimated that the same blast and fire effect could have been caused by 2.1 kilotons of <a href="/https/en.wikipedia.org/wiki/Conventional_bomb" class="mw-redirect" title="Conventional bomb">conventional bombs</a>: "220 B-29s carrying 1.2 kilotons of <a href="/https/en.wikipedia.org/wiki/Incendiary_bombs" class="mw-redirect" title="Incendiary bombs">incendiary bombs</a>, 400 tons of <a href="/https/en.wikipedia.org/wiki/High-explosive" class="mw-redirect" title="High-explosive">high-explosive</a> bombs, and 500 tons of <a href="/https/en.wikipedia.org/wiki/Anti-personnel_weapon" title="Anti-personnel weapon">anti-personnel</a> <a href="/https/en.wikipedia.org/wiki/Fragmentation_bombs" class="mw-redirect" title="Fragmentation bombs">fragmentation bombs</a>."<sup id="cite_ref-FOOTNOTED'Olier194624_71-0" class="reference"><a href="#cite_note-FOOTNOTED'Olier194624-71">[71]</a></sup> Since the target was spread across a two-dimensional plane, the vertical component of a single spherical nuclear explosion was largely wasted. A <a href="/https/en.wikipedia.org/wiki/Cluster_bomb" class="mw-redirect" title="Cluster bomb">cluster bomb</a> pattern of smaller explosions would have been a more energy-efficient match to the target.<sup id="cite_ref-FOOTNOTED'Olier194624_71-1" class="reference"><a href="#cite_note-FOOTNOTED'Olier194624-71">[71]</a></sup>
</p>
<h2><span class="mw-headline" id="Post-war">Post-war</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=16" title="Edit section: Post-war"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h2>
<figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/https/en.wikipedia.org/wiki/File:Spare_Little_Boy_atomic_bomb_casing_at_the_Imperial_War_Museum_in_London_in_November_2015.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/0/04/Spare_Little_Boy_atomic_bomb_casing_at_the_Imperial_War_Museum_in_London_in_November_2015.jpg/220px-Spare_Little_Boy_atomic_bomb_casing_at_the_Imperial_War_Museum_in_London_in_November_2015.jpg" decoding="async" width="220" height="165" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/0/04/Spare_Little_Boy_atomic_bomb_casing_at_the_Imperial_War_Museum_in_London_in_November_2015.jpg/330px-Spare_Little_Boy_atomic_bomb_casing_at_the_Imperial_War_Museum_in_London_in_November_2015.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/0/04/Spare_Little_Boy_atomic_bomb_casing_at_the_Imperial_War_Museum_in_London_in_November_2015.jpg/440px-Spare_Little_Boy_atomic_bomb_casing_at_the_Imperial_War_Museum_in_London_in_November_2015.jpg 2x" data-file-width="4238" data-file-height="3182" /></a><figcaption>One of five casings built for the Little Boy bomb used on Hiroshima on display at the <a href="/https/en.wikipedia.org/wiki/Imperial_War_Museum" title="Imperial War Museum">Imperial War Museum</a> in London during 2015</figcaption></figure>
<figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/https/en.wikipedia.org/wiki/File:Cumuative_Shipments_of_U-235_from_Y-12_to_Los_Alamos_1944-1946.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/20/Cumuative_Shipments_of_U-235_from_Y-12_to_Los_Alamos_1944-1946.png/220px-Cumuative_Shipments_of_U-235_from_Y-12_to_Los_Alamos_1944-1946.png" decoding="async" width="220" height="171" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/20/Cumuative_Shipments_of_U-235_from_Y-12_to_Los_Alamos_1944-1946.png/330px-Cumuative_Shipments_of_U-235_from_Y-12_to_Los_Alamos_1944-1946.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/20/Cumuative_Shipments_of_U-235_from_Y-12_to_Los_Alamos_1944-1946.png/440px-Cumuative_Shipments_of_U-235_from_Y-12_to_Los_Alamos_1944-1946.png 2x" data-file-width="924" data-file-height="718" /></a><figcaption>Graph of cumulative shipments of U-235 from the Y-12 electromagnetic enrichment plant at Oak Ridge to Los Alamos, 1944-1946</figcaption></figure>
<p>When the war ended, it was not expected that the inefficient Little Boy design would ever again be required, and many plans and diagrams were destroyed. However, by mid-1946 the Hanford Site reactors were suffering badly from the <a href="/https/en.wikipedia.org/wiki/Wigner_effect" title="Wigner effect">Wigner effect</a>. Faced with the prospect of no more plutonium for new cores and no more <a href="/https/en.wikipedia.org/wiki/Polonium" title="Polonium">polonium</a> for the initiators for the cores that had already been produced, the Director of the Manhattan Project, <a href="/https/en.wikipedia.org/wiki/Major_general_(United_States)" title="Major general (United States)">Major General</a> <a href="/https/en.wikipedia.org/wiki/Leslie_R._Groves" class="mw-redirect" title="Leslie R. Groves">Leslie R. Groves</a>, ordered that some Little Boys be prepared as an interim measure until a solution could be found. No Little Boy assemblies were available, and no comprehensive set of diagrams of the Little Boy could be found, although there were drawings of the various components, and stocks of spare parts.<sup id="cite_ref-FOOTNOTECoster-Mullen201285_72-0" class="reference"><a href="#cite_note-FOOTNOTECoster-Mullen201285-72">[72]</a></sup><sup id="cite_ref-FOOTNOTEAbrahamsonCarew200241–42_73-0" class="reference"><a href="#cite_note-FOOTNOTEAbrahamsonCarew200241–42-73">[73]</a></sup>
</p><p>At <a href="/https/en.wikipedia.org/wiki/Sandia_Base" title="Sandia Base">Sandia Base</a>, three Army officers, <a href="/https/en.wikipedia.org/wiki/Captain_(United_States_O-3)" title="Captain (United States O-3)">Captains</a> Albert Bethel, Richard Meyer, and Bobbie Griffin attempted to re-create the Little Boy. They were supervised by Harlow W. Russ, an expert on Little Boy who served with <a href="/https/en.wikipedia.org/wiki/Project_Alberta" title="Project Alberta">Project Alberta</a> on Tinian, and was now leader of the Z-11 Group of the Los Alamos Laboratory's Z Division at Sandia. Gradually, they managed to locate the correct drawings and parts, and figured out how they went together. Eventually, they built six Little Boy assemblies. Although the casings, barrels, and components were tested, no enriched uranium was supplied for the bombs. By early 1947, the problem caused by the Wigner effect was on its way to solution, and the three officers were reassigned.<sup id="cite_ref-FOOTNOTECoster-Mullen201285_72-1" class="reference"><a href="#cite_note-FOOTNOTECoster-Mullen201285-72">[72]</a></sup><sup id="cite_ref-FOOTNOTEAbrahamsonCarew200241–42_73-1" class="reference"><a href="#cite_note-FOOTNOTEAbrahamsonCarew200241–42-73">[73]</a></sup>
</p><p>The Navy <a href="/https/en.wikipedia.org/wiki/Bureau_of_Ordnance" title="Bureau of Ordnance">Bureau of Ordnance</a> began in 1947 to produce 25 "revised" Little Boy mechanical assemblies for use by the nuclear-capable <a href="/https/en.wikipedia.org/wiki/Lockheed_P2V_Neptune" class="mw-redirect" title="Lockheed P2V Neptune">Lockheed P2V Neptune</a> <a href="/https/en.wikipedia.org/wiki/Aircraft_carrier" title="Aircraft carrier">aircraft carrier</a> aircraft (which could be launched from, but not land, on the <a href="/https/en.wikipedia.org/wiki/Midway-class_aircraft_carrier" title="Midway-class aircraft carrier"><i>Midway</i>-class aircraft carriers</a>). Components were produced by the Naval Ordnance Plants in <a href="/https/en.wikipedia.org/wiki/Pocatello,_Idaho" title="Pocatello, Idaho">Pocatello, Idaho</a>, and <a href="/https/en.wikipedia.org/wiki/Louisville,_Kentucky" title="Louisville, Kentucky">Louisville, Kentucky</a>. Enough fissionable material was available by 1948 to build ten projectiles and targets, although there were only enough initiators for six. However, no actual fissionable components were produced by the end of 1948, and only two outer casings were available. <sup id="cite_ref-FOOTNOTEHansen1995116–118_74-0" class="reference"><a href="#cite_note-FOOTNOTEHansen1995116–118-74">[74]</a></sup> By the end of 1950, only five complete Little Boy assemblies had been built. All were retired by November 1950.<sup id="cite_ref-FOOTNOTEHansen1995115_75-0" class="reference"><a href="#cite_note-FOOTNOTEHansen1995115-75">[75]</a></sup>
</p><p>The <a href="/https/en.wikipedia.org/wiki/Smithsonian_Institution" title="Smithsonian Institution">Smithsonian Institution</a> displayed a Little Boy (complete, except for enriched uranium), until 1986. The <a href="/https/en.wikipedia.org/wiki/United_States_Department_of_Energy" title="United States Department of Energy">Department of Energy</a> took the weapon from the museum to remove its inner components, so the bomb could not be stolen and detonated with fissile material. The government returned the emptied casing to the Smithsonian in 1993. Three other disarmed bombs are on display in the United States; another is at the <a href="/https/en.wikipedia.org/wiki/Imperial_War_Museum" title="Imperial War Museum">Imperial War Museum</a> in London.<sup id="cite_ref-FOOTNOTESamuels2008_32-1" class="reference"><a href="#cite_note-FOOTNOTESamuels2008-32">[32]</a></sup>
</p>
<div style="clear:both;"></div>
<h2><span class="mw-headline" id="Notes">Notes</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=17" title="Edit section: Notes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h2>
<style data-mw-deduplicate="TemplateStyles:r1011085734">.mw-parser-output .reflist{font-size:90%;margin-bottom:0.5em;list-style-type:decimal}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist">
<div class="mw-references-wrap mw-references-columns"><ol class="references">
<li id="cite_note-FOOTNOTESerberCrease1998104-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTESerberCrease1998104_1-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFSerberCrease1998">Serber & Crease 1998</a>, p. 104.</span>
</li>
<li id="cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993419-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993419_2-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHoddesonHenriksenMeadeWestfall1993">Hoddeson et al. 1993</a>, p. 419.</span>
</li>
<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1133582631">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free a,.mw-parser-output .citation .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited a,.mw-parser-output .id-lock-registration a,.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription a,.mw-parser-output .citation .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:#d33}.mw-parser-output .cs1-visible-error{color:#d33}.mw-parser-output .cs1-maint{display:none;color:#3a3;margin-left:0.3em}.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}</style><cite id="CITEREFRamsey2012" class="citation book cs1"><a href="/https/en.wikipedia.org/wiki/Norman_F._Ramsey" class="mw-redirect" title="Norman F. Ramsey">Ramsey, N. F.</a> (2012). "History of Project A". In Coster-Mullen, John (ed.). <i>Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man</i>. United States: J. Coster-Mullen. <a href="/https/en.wikipedia.org/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://www.worldcat.org/oclc/298514167">298514167</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=History+of+Project+A&rft.btitle=Atom+Bombs%3A+The+Top+Secret+Inside+Story+of+Little+Boy+and+Fat+Man&rft.place=United+States&rft.pub=J.+Coster-Mullen&rft.date=2012&rft_id=info%3Aoclcnum%2F298514167&rft.aulast=Ramsey&rft.aufirst=N.+F.&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></span>
</li>
<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFBowen1959" class="citation book cs1">Bowen, Lee (1959). <i>A History of the Air Force Atomic Energy Program, 1943-1953, Volume I (Project Silverplate, 1943-1946)</i>. United States Air Force Historical Division. p. 96.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=A+History+of+the+Air+Force+Atomic+Energy+Program%2C+1943-1953%2C+Volume+I+%28Project+Silverplate%2C+1943-1946%29&rft.pages=96&rft.pub=United+States+Air+Force+Historical+Division&rft.date=1959&rft.aulast=Bowen&rft.aufirst=Lee&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></span>
</li>
<li id="cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall199342–44-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall199342–44_5-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHoddesonHenriksenMeadeWestfall1993">Hoddeson et al. 1993</a>, pp. 42–44.</span>
</li>
<li id="cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall199367,_75-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall199367,_75_6-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHoddesonHenriksenMeadeWestfall1993">Hoddeson et al. 1993</a>, pp. 67, 75.</span>
</li>
<li id="cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall199382–84-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall199382–84_7-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHoddesonHenriksenMeadeWestfall1993">Hoddeson et al. 1993</a>, pp. 82–84.</span>
</li>
<li id="cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall199387,_114-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall199387,_114_8-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHoddesonHenriksenMeadeWestfall1993">Hoddeson et al. 1993</a>, pp. 87, 114.</span>
</li>
<li id="cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993228-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993228_9-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHoddesonHenriksenMeadeWestfall1993">Hoddeson et al. 1993</a>, p. 228.</span>
</li>
<li id="cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993245–249-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993245–249_10-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHoddesonHenriksenMeadeWestfall1993">Hoddeson et al. 1993</a>, pp. 245–249.</span>
</li>
<li id="cite_note-FOOTNOTERhodes1986541-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTERhodes1986541_11-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFRhodes1986">Rhodes 1986</a>, p. 541.</span>
</li>
<li id="cite_note-12"><span class="mw-cite-backlink"><b><a href="#cite_ref-12">^</a></b></span> <span class="reference-text">While "Mark III" has always referred to "Fat Man" designs, there is inconsistency in the historical record as to the weapons referred to as "Mark I" and "Mark II", with some documents referring to the "Mark II" as an low-efficiency, lensless implosion concept that was pursued as a fallback concept. The "Mark" nomenclature did not become standardized until the postwar period.</span>
</li>
<li id="cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993257-13"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993257_13-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHoddesonHenriksenMeadeWestfall1993">Hoddeson et al. 1993</a>, p. 257.</span>
</li>
<li id="cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993262-14"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993262_14-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHoddesonHenriksenMeadeWestfall1993">Hoddeson et al. 1993</a>, p. 262.</span>
</li>
<li id="cite_note-FOOTNOTENichols1987166,_175–176-15"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTENichols1987166,_175–176_15-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFNichols1987">Nichols 1987</a>, pp. 166, 175–176.</span>
</li>
<li id="cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993265-16"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993265_16-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993265_16-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993265_16-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFHoddesonHenriksenMeadeWestfall1993">Hoddeson et al. 1993</a>, p. 265.</span>
</li>
<li id="cite_note-FOOTNOTECoster-Mullen201230-17"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTECoster-Mullen201230_17-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFCoster-Mullen2012">Coster-Mullen 2012</a>, p. 30.</span>
</li>
<li id="cite_note-FOOTNOTEHansen1995111–112-18"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHansen1995111–112_18-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHansen1995">Hansen 1995</a>, pp. 111–112.</span>
</li>
<li id="cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993293-19"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993293_19-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHoddesonHenriksenMeadeWestfall1993">Hoddeson et al. 1993</a>, p. 293.</span>
</li>
<li id="cite_note-FOOTNOTEHansen1995113-20"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEHansen1995113_20-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEHansen1995113_20-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFHansen1995">Hansen 1995</a>, p. 113.</span>
</li>
<li id="cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993333-21"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993333_21-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHoddesonHenriksenMeadeWestfall1993">Hoddeson et al. 1993</a>, p. 333.</span>
</li>
<li id="cite_note-FOOTNOTEGosling199951-22"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEGosling199951_22-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFGosling1999">Gosling 1999</a>, p. 51.</span>
</li>
<li id="cite_note-FOOTNOTECoster-Mullen201218-23"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTECoster-Mullen201218_23-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTECoster-Mullen201218_23-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFCoster-Mullen2012">Coster-Mullen 2012</a>, p. 18.</span>
</li>
<li id="cite_note-FOOTNOTECoster-Mullen201227-24"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTECoster-Mullen201227_24-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFCoster-Mullen2012">Coster-Mullen 2012</a>, p. 27.</span>
</li>
<li id="cite_note-FOOTNOTEGlasstoneDolan197712-25"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEGlasstoneDolan197712_25-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFGlasstoneDolan1977">Glasstone & Dolan 1977</a>, p. 12.</span>
</li>
<li id="cite_note-nukearchive-26"><span class="mw-cite-backlink"><b><a href="#cite_ref-nukearchive_26-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFSublette" class="citation web cs1">Sublette, Carey. <a rel="nofollow" class="external text" href="http://nuclearweaponarchive.org/Nwfaq/Nfaq8.html">"Nuclear Weapons Frequently Asked Questions, Section 8.0: The First Nuclear Weapons"</a><span class="reference-accessdate">. Retrieved <span class="nowrap">29 August</span> 2013</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Nuclear+Weapons+Frequently+Asked+Questions%2C+Section+8.0%3A+The+First+Nuclear+Weapons&rft.aulast=Sublette&rft.aufirst=Carey&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttp%2Fnuclearweaponarchive.org%2FNwfaq%2FNfaq8.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></span>
</li>
<li id="cite_note-FOOTNOTECoster-Mullen201218–19,_27-27"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTECoster-Mullen201218–19,_27_27-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFCoster-Mullen2012">Coster-Mullen 2012</a>, pp. 18–19, 27.</span>
</li>
<li id="cite_note-FOOTNOTEBernstein2007133-28"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEBernstein2007133_28-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFBernstein2007">Bernstein 2007</a>, p. 133.</span>
</li>
<li id="cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993263–265-29"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993263–265_29-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHoddesonHenriksenMeadeWestfall1993">Hoddeson et al. 1993</a>, pp. 263–265.</span>
</li>
<li id="cite_note-FOOTNOTEMonk2012409,_410-30"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEMonk2012409,_410_30-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEMonk2012409,_410_30-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFMonk2012">Monk 2012</a>, pp. 409, 410.<span class="error harv-error" style="display: none; font-size:100%"> sfn error: no target: CITEREFMonk2012 (<a href="/https/en.wikipedia.org/wiki/Category:Harv_and_Sfn_template_errors" title="Category:Harv and Sfn template errors">help</a>)</span></span>
</li>
<li id="cite_note-FOOTNOTECoster-Mullen201223–24-31"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTECoster-Mullen201223–24_31-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTECoster-Mullen201223–24_31-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFCoster-Mullen2012">Coster-Mullen 2012</a>, pp. 23–24.</span>
</li>
<li id="cite_note-FOOTNOTESamuels2008-32"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTESamuels2008_32-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTESamuels2008_32-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFSamuels2008">Samuels 2008</a>.</span>
</li>
<li id="cite_note-FOOTNOTEHansen1995a2–5-33"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEHansen1995a2–5_33-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEHansen1995a2–5_33-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-FOOTNOTEHansen1995a2–5_33-2"><sup><i><b>c</b></i></sup></a> <a href="#cite_ref-FOOTNOTEHansen1995a2–5_33-3"><sup><i><b>d</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFHansen1995a">Hansen 1995a</a>, pp. 2–5.</span>
</li>
<li id="cite_note-FOOTNOTECampbell200546,_80-34"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTECampbell200546,_80_34-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFCampbell2005">Campbell 2005</a>, pp. 46, 80.</span>
</li>
<li id="cite_note-FOOTNOTECoster-Mullen2012100–101-35"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTECoster-Mullen2012100–101_35-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFCoster-Mullen2012">Coster-Mullen 2012</a>, pp. 100–101.</span>
</li>
<li id="cite_note-FOOTNOTECoster-Mullen201234–35-36"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTECoster-Mullen201234–35_36-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFCoster-Mullen2012">Coster-Mullen 2012</a>, pp. 34–35.</span>
</li>
<li id="cite_note-37"><span class="mw-cite-backlink"><b><a href="#cite_ref-37">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFThe_Manhattan_Engineer_District1946" class="citation web cs1">The Manhattan Engineer District (29 June 1946). <a rel="nofollow" class="external text" href="https://www.gutenberg.org/cache/epub/685/pg685.html">"The Atomic Bombings of Hiroshima and Nagasaki"</a>. p. 3 – via <a href="/https/en.wikipedia.org/wiki/Project_Gutenberg" title="Project Gutenberg">Project Gutenberg</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=The+Atomic+Bombings+of+Hiroshima+and+Nagasaki&rft.pages=3&rft.date=1946-06-29&rft.au=The+Manhattan+Engineer+District&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Fwww.gutenberg.org%2Fcache%2Fepub%2F685%2Fpg685.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></span>
</li>
<li id="cite_note-38"><span class="mw-cite-backlink"><b><a href="#cite_ref-38">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFWellerstein2020" class="citation web cs1"><a href="/https/en.wikipedia.org/wiki/Alex_Wellerstein" title="Alex Wellerstein">Wellerstein, Alex</a> (4 August 2020). <a rel="nofollow" class="external text" href="https://thebulletin.org/2020/08/counting-the-dead-at-hiroshima-and-nagasaki/">"Counting the Dead at Hiroshima and Nagasaki"</a>. <i><a href="/https/en.wikipedia.org/wiki/Bulletin_of_the_Atomic_Scientists" title="Bulletin of the Atomic Scientists">Bulletin of the Atomic Scientists</a></i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Bulletin+of+the+Atomic+Scientists&rft.atitle=Counting+the+Dead+at+Hiroshima+and+Nagasaki&rft.date=2020-08-04&rft.aulast=Wellerstein&rft.aufirst=Alex&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Fthebulletin.org%2F2020%2F08%2Fcounting-the-dead-at-hiroshima-and-nagasaki%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></span>
</li>
<li id="cite_note-FOOTNOTECravenCate1983723-39"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTECravenCate1983723_39-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFCravenCate1983">Craven & Cate 1983</a>, p. 723.</span>
</li>
<li id="cite_note-FOOTNOTEHoddesonHenriksenMeadeWestfall1993393-40"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993393_40-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEHoddesonHenriksenMeadeWestfall1993393_40-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFHoddesonHenriksenMeadeWestfall1993">Hoddeson et al. 1993</a>, p. 393.</span>
</li>
<li id="cite_note-FOOTNOTEMalik19851-41"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEMalik19851_41-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEMalik19851_41-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-FOOTNOTEMalik19851_41-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFMalik1985">Malik 1985</a>, p. 1.</span>
</li>
<li id="cite_note-FOOTNOTEGroves1962267,_"To_enable_us_to_assess_accurately_the_effects_of_the_[nuclear]_bomb,_the_targets_should_not_have_been_previously_damaged_by_air_raids."_Four_cities_were_chosen,_including_Hiroshima_and_Kyoto._War_Secretary_Stimson_vetoed_Kyoto,_and_Nagasaki_was_substituted._p._275,_"When_our_target_cities_were_first_selected,_an_order_was_sent_to_the_Army_Air_Force_in_Guam_not_to_bomb_them_without_special_authority_from_the_War_Department."-42"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEGroves1962267,_"To_enable_us_to_assess_accurately_the_effects_of_the_[nuclear]_bomb,_the_targets_should_not_have_been_previously_damaged_by_air_raids."_Four_cities_were_chosen,_including_Hiroshima_and_Kyoto._War_Secretary_Stimson_vetoed_Kyoto,_and_Nagasaki_was_substituted._p._275,_"When_our_target_cities_were_first_selected,_an_order_was_sent_to_the_Army_Air_Force_in_Guam_not_to_bomb_them_without_special_authority_from_the_War_Department."_42-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFGroves1962">Groves 1962</a>, p. 267, "To enable us to assess accurately the effects of the [nuclear] bomb, the targets should not have been previously damaged by air raids." Four cities were chosen, including Hiroshima and Kyoto. War Secretary Stimson vetoed Kyoto, and Nagasaki was substituted. p. 275, "When our target cities were first selected, an order was sent to the Army Air Force in Guam not to bomb them without special authority from the War Department.".</span>
</li>
<li id="cite_note-FOOTNOTEGlasstone1962629-43"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEGlasstone1962629_43-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFGlasstone1962">Glasstone 1962</a>, p. 629.</span>
</li>
<li id="cite_note-FOOTNOTEGlasstoneDolan1977Nuclear_Bomb_Effects_Computer-44"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEGlasstoneDolan1977Nuclear_Bomb_Effects_Computer_44-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFGlasstoneDolan1977">Glasstone & Dolan 1977</a>, p. Nuclear Bomb Effects Computer.</span>
</li>
<li id="cite_note-FOOTNOTEGlasstoneDolan19771-45"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEGlasstoneDolan19771_45-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFGlasstoneDolan1977">Glasstone & Dolan 1977</a>, p. 1.</span>
</li>
<li id="cite_note-FOOTNOTEDiacon198418-46"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEDiacon198418_46-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFDiacon1984">Diacon 1984</a>, p. 18.</span>
</li>
<li id="cite_note-FOOTNOTEGlasstoneDolan1977300,_301-47"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEGlasstoneDolan1977300,_301_47-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFGlasstoneDolan1977">Glasstone & Dolan 1977</a>, pp. 300, 301.</span>
</li>
<li id="cite_note-FOOTNOTEThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_194614-48"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_194614_48-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_1946">The Atomic Bombings of Hiroshima and Nagasaki, 1946</a>, p. 14.</span>
</li>
<li id="cite_note-FOOTNOTEGlasstoneDolan1977179-49"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEGlasstoneDolan1977179_49-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFGlasstoneDolan1977">Glasstone & Dolan 1977</a>, p. 179.</span>
</li>
<li id="cite_note-FOOTNOTENuclear_Weapon_Thermal_Effects1998-50"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTENuclear_Weapon_Thermal_Effects1998_50-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFNuclear_Weapon_Thermal_Effects1998">Nuclear Weapon Thermal Effects 1998</a>.</span>
</li>
<li id="cite_note-FOOTNOTEHuman_Shadow_Etched_in_Stone-51"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHuman_Shadow_Etched_in_Stone_51-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHuman_Shadow_Etched_in_Stone">Human Shadow Etched in Stone</a>.</span>
</li>
<li id="cite_note-FOOTNOTEGlasstoneDolan1977300–304-52"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEGlasstoneDolan1977300–304_52-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEGlasstoneDolan1977300–304_52-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFGlasstoneDolan1977">Glasstone & Dolan 1977</a>, pp. 300–304.</span>
</li>
<li id="cite_note-FOOTNOTED'Olier194622–25-53"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTED'Olier194622–25_53-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFD'Olier1946">D'Olier 1946</a>, pp. 22–25.</span>
</li>
<li id="cite_note-FOOTNOTEGlasstoneDolan1977304-54"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEGlasstoneDolan1977304_54-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFGlasstoneDolan1977">Glasstone & Dolan 1977</a>, p. 304.</span>
</li>
<li id="cite_note-FOOTNOTEThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_194621–23-55"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_194621–23_55-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_1946">The Atomic Bombings of Hiroshima and Nagasaki, 1946</a>, pp. 21–23.</span>
</li>
<li id="cite_note-FOOTNOTEThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_194621-56"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_194621_56-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_194621_56-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_1946">The Atomic Bombings of Hiroshima and Nagasaki, 1946</a>, p. 21.</span>
</li>
<li id="cite_note-FOOTNOTEGlasstoneDolan1977409_"An_air_burst,_by_definition,_is_one_taking_place_at_such_a_height_above_the_earth_that_no_appreciable_quantities_of_surface_material_are_taken_up_into_the_fireball._..._the_deposition_of_early_fallout_from_an_air_burst_will_generally_not_be_significant._An_air_burst,_however,_may_produce_some_induced_radioactive_contamination_in_the_general_vicinity_of_ground_zero_as_a_result_of_neutron_capture_by_elements_in_the_soil."_p._36,_"at_Hiroshima_..._injuries_due_to_fallout_were_completely_absent."-57"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEGlasstoneDolan1977409_"An_air_burst,_by_definition,_is_one_taking_place_at_such_a_height_above_the_earth_that_no_appreciable_quantities_of_surface_material_are_taken_up_into_the_fireball._..._the_deposition_of_early_fallout_from_an_air_burst_will_generally_not_be_significant._An_air_burst,_however,_may_produce_some_induced_radioactive_contamination_in_the_general_vicinity_of_ground_zero_as_a_result_of_neutron_capture_by_elements_in_the_soil."_p._36,_"at_Hiroshima_..._injuries_due_to_fallout_were_completely_absent."_57-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFGlasstoneDolan1977">Glasstone & Dolan 1977</a>, p. 409 "An air burst, by definition, is one taking place at such a height above the earth that no appreciable quantities of surface material are taken up into the fireball. ... the deposition of early fallout from an air burst will generally not be significant. An air burst, however, may produce some induced radioactive contamination in the general vicinity of ground zero as a result of neutron capture by elements in the soil." p. 36, "at Hiroshima ... injuries due to fallout were completely absent.".</span>
</li>
<li id="cite_note-FOOTNOTEGlasstoneDolan1977Chapter_VIII_and_the_'Nuclear_Bomb_Effects_Computer'-58"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEGlasstoneDolan1977Chapter_VIII_and_the_'Nuclear_Bomb_Effects_Computer'_58-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFGlasstoneDolan1977">Glasstone & Dolan 1977</a>, pp. Chapter VIII and the 'Nuclear Bomb Effects Computer'.</span>
</li>
<li id="cite_note-59"><span class="mw-cite-backlink"><b><a href="#cite_ref-59">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFWellerstein" class="citation web cs1">Wellerstein, Alex. <a rel="nofollow" class="external text" href="https://nuclearsecrecy.com/nukemap/?&kt=15&lat=34.39468&lng=132.45462&hob_opt=2&hob_psi=5&hob_ft=1968&psi=20,5,1&zm=13">"NUKEMAP"</a>. <i>nuclearsecrecy.com</i>. <a href="/https/en.wikipedia.org/wiki/Alex_Wellerstein" title="Alex Wellerstein">Alex Wellerstein</a><span class="reference-accessdate">. Retrieved <span class="nowrap">28 July</span> 2021</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=nuclearsecrecy.com&rft.atitle=NUKEMAP&rft.aulast=Wellerstein&rft.aufirst=Alex&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Fnuclearsecrecy.com%2Fnukemap%2F%3F%26kt%3D15%26lat%3D34.39468%26lng%3D132.45462%26hob_opt%3D2%26hob_psi%3D5%26hob_ft%3D1968%26psi%3D20%2C5%2C1%26zm%3D13&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></span>
</li>
<li id="cite_note-FOOTNOTEGlasstoneDolan1977545,_546-60"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEGlasstoneDolan1977545,_546_60-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFGlasstoneDolan1977">Glasstone & Dolan 1977</a>, pp. 545, 546.</span>
</li>
<li id="cite_note-FOOTNOTERichardson_RR_2009-61"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTERichardson_RR_2009_61-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFRichardson_RR_2009">Richardson RR 2009</a>.</span>
</li>
<li id="cite_note-62"><span class="mw-cite-backlink"><b><a href="#cite_ref-62">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite class="citation news cs1"><a rel="nofollow" class="external text" href="http://www.radionetherlandsarchives.org/50th-anniversary-of-the-a-bomb-attacks-the-ongoing-research-into-the-effects-of-radiation/">"The ongoing research into the effects of radiation"</a>. <i>Radio Netherlands Archives</i>. 31 July 2005<span class="reference-accessdate">. Retrieved <span class="nowrap">16 December</span> 2018</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Radio+Netherlands+Archives&rft.atitle=The+ongoing+research+into+the+effects+of+radiation&rft.date=2005-07-31&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttp%2Fwww.radionetherlandsarchives.org%2F50th-anniversary-of-the-a-bomb-attacks-the-ongoing-research-into-the-effects-of-radiation%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></span>
</li>
<li id="cite_note-FOOTNOTEGenetic_Effects-63"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEGenetic_Effects_63-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFGenetic_Effects">Genetic Effects</a>.</span>
</li>
<li id="cite_note-FOOTNOTEIzumi_BJC_2003-64"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEIzumi_BJC_2003_64-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFIzumi_BJC_2003">Izumi BJC 2003</a>.</span>
</li>
<li id="cite_note-FOOTNOTEIzumi_IJC_2003-65"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEIzumi_IJC_2003_65-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFIzumi_IJC_2003">Izumi IJC 2003</a>.</span>
</li>
<li id="cite_note-66"><span class="mw-cite-backlink"><b><a href="#cite_ref-66">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFPutnam1998" class="citation journal cs1">Putnam, F. W. (12 May 1998). <a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC33857">"The Atomic Bomb Casualty Commission in retrospect"</a>. <i>Proceedings of the National Academy of Sciences of the United States of America</i>. <b>95</b> (10): 5426–5431. <a href="/https/en.wikipedia.org/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/1998PNAS...95.5426P">1998PNAS...95.5426P</a>. <a href="/https/en.wikipedia.org/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="cs1-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1073%2Fpnas.95.10.5426">10.1073/pnas.95.10.5426</a></span>. <a href="/https/en.wikipedia.org/wiki/PMC_(identifier)" class="mw-redirect" title="PMC (identifier)">PMC</a> <span class="cs1-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC33857">33857</a></span>. <a href="/https/en.wikipedia.org/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/9576898">9576898</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Proceedings+of+the+National+Academy+of+Sciences+of+the+United+States+of+America&rft.atitle=The+Atomic+Bomb+Casualty+Commission+in+retrospect&rft.volume=95&rft.issue=10&rft.pages=5426-5431&rft.date=1998-05-12&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC33857%23id-name%3DPMC&rft_id=info%3Apmid%2F9576898&rft_id=info%3Adoi%2F10.1073%2Fpnas.95.10.5426&rft_id=info%3Abibcode%2F1998PNAS...95.5426P&rft.aulast=Putnam&rft.aufirst=F.+W.&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC33857&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></span>
</li>
<li id="cite_note-FOOTNOTECoster-Mullen201286–87-67"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTECoster-Mullen201286–87_67-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFCoster-Mullen2012">Coster-Mullen 2012</a>, pp. 86–87.</span>
</li>
<li id="cite_note-FOOTNOTEMalik198518–20-68"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEMalik198518–20_68-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFMalik1985">Malik 1985</a>, pp. 18–20.</span>
</li>
<li id="cite_note-FOOTNOTEMalik198521-69"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEMalik198521_69-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFMalik1985">Malik 1985</a>, p. 21.</span>
</li>
<li id="cite_note-FOOTNOTEMalik198516-70"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEMalik198516_70-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFMalik1985">Malik 1985</a>, p. 16.</span>
</li>
<li id="cite_note-FOOTNOTED'Olier194624-71"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTED'Olier194624_71-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTED'Olier194624_71-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFD'Olier1946">D'Olier 1946</a>, p. 24.</span>
</li>
<li id="cite_note-FOOTNOTECoster-Mullen201285-72"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTECoster-Mullen201285_72-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTECoster-Mullen201285_72-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFCoster-Mullen2012">Coster-Mullen 2012</a>, p. 85.</span>
</li>
<li id="cite_note-FOOTNOTEAbrahamsonCarew200241–42-73"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEAbrahamsonCarew200241–42_73-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEAbrahamsonCarew200241–42_73-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFAbrahamsonCarew2002">Abrahamson & Carew 2002</a>, pp. 41–42.</span>
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<li id="cite_note-FOOTNOTEHansen1995116–118-74"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHansen1995116–118_74-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHansen1995">Hansen 1995</a>, pp. 116–118.</span>
</li>
<li id="cite_note-FOOTNOTEHansen1995115-75"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHansen1995115_75-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHansen1995">Hansen 1995</a>, p. 115.</span>
</li>
</ol></div></div>
<h2><span class="mw-headline" id="References">References</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=18" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h2>
<style data-mw-deduplicate="TemplateStyles:r1054258005">.mw-parser-output .refbegin{font-size:90%;margin-bottom:0.5em}.mw-parser-output .refbegin-hanging-indents>ul{margin-left:0}.mw-parser-output .refbegin-hanging-indents>ul>li{margin-left:0;padding-left:3.2em;text-indent:-3.2em}.mw-parser-output .refbegin-hanging-indents ul,.mw-parser-output .refbegin-hanging-indents ul li{list-style:none}@media(max-width:720px){.mw-parser-output .refbegin-hanging-indents>ul>li{padding-left:1.6em;text-indent:-1.6em}}.mw-parser-output .refbegin-columns{margin-top:0.3em}.mw-parser-output .refbegin-columns ul{margin-top:0}.mw-parser-output .refbegin-columns li{page-break-inside:avoid;break-inside:avoid-column}</style><div class="refbegin refbegin-columns references-column-width" style="column-width: 30em">
<ul><li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFAbrahamsonCarew2002" class="citation book cs1">Abrahamson, James L.; Carew, Paul H. (2002). <i>Vanguard of American Atomic Deterrence</i>. Westport, Connecticut: Praeger. <a href="/https/en.wikipedia.org/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/https/en.wikipedia.org/wiki/Special:BookSources/0-275-97819-2" title="Special:BookSources/0-275-97819-2"><bdi>0-275-97819-2</bdi></a>. <a href="/https/en.wikipedia.org/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://www.worldcat.org/oclc/49859889">49859889</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Vanguard+of+American+Atomic+Deterrence&rft.place=Westport%2C+Connecticut&rft.pub=Praeger&rft.date=2002&rft_id=info%3Aoclcnum%2F49859889&rft.isbn=0-275-97819-2&rft.aulast=Abrahamson&rft.aufirst=James+L.&rft.au=Carew%2C+Paul+H.&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFThe_Atomic_Bombings_of_Hiroshima_and_Nagasaki,_1946" class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20120406172413/http://www.cddc.vt.edu/host/atomic/hiroshim/hiro_med.pdf">"The Atomic Bombings of Hiroshima and Nagasaki"</a> <span class="cs1-format">(PDF)</span>. The Manhattan Engineer District. 29 June 1946. Archived from <a rel="nofollow" class="external text" href="http://www.cddc.vt.edu/host/atomic/hiroshim/hiro_med.pdf">the original</a> <span class="cs1-format">(PDF)</span> on 6 April 2012<span class="reference-accessdate">. Retrieved <span class="nowrap">6 November</span> 2013</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=The+Atomic+Bombings+of+Hiroshima+and+Nagasaki&rft.pub=The+Manhattan+Engineer+District&rft.date=1946-06-29&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttp%2Fwww.cddc.vt.edu%2Fhost%2Fatomic%2Fhiroshim%2Fhiro_med.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span> This report can also be found <a rel="nofollow" class="external text" href="http://www.atomicarchive.com/Docs/MED/index.shtml">here</a> and <a rel="nofollow" class="external text" href="http://avalon.law.yale.edu/subject_menus/mpmenu.asp">here</a>.</li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFBernstein2007" class="citation book cs1"><a href="/https/en.wikipedia.org/wiki/Jeremy_Bernstein" title="Jeremy Bernstein">Bernstein, Jeremy</a> (2007). <span class="cs1-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/nuclearweaponswh0000bern"><i>Nuclear Weapons: What You Need to Know</i></a></span>. Cambridge University Press. <a href="/https/en.wikipedia.org/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/https/en.wikipedia.org/wiki/Special:BookSources/978-0-521-88408-2" title="Special:BookSources/978-0-521-88408-2"><bdi>978-0-521-88408-2</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Nuclear+Weapons%3A+What+You+Need+to+Know&rft.pub=Cambridge+University+Press&rft.date=2007&rft.isbn=978-0-521-88408-2&rft.aulast=Bernstein&rft.aufirst=Jeremy&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Farchive.org%2Fdetails%2Fnuclearweaponswh0000bern&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFCampbell2005" class="citation book cs1">Campbell, Richard H. (2005). <i>The Silverplate Bombers: A History and Registry of the Enola Gay and Other B-29s Configured to Carry Atomic Bombs</i>. Jefferson, North Carolina: McFarland & Company. <a href="/https/en.wikipedia.org/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/https/en.wikipedia.org/wiki/Special:BookSources/0-7864-2139-8" title="Special:BookSources/0-7864-2139-8"><bdi>0-7864-2139-8</bdi></a>. <a href="/https/en.wikipedia.org/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://www.worldcat.org/oclc/58554961">58554961</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+Silverplate+Bombers%3A+A+History+and+Registry+of+the+Enola+Gay+and+Other+B-29s+Configured+to+Carry+Atomic+Bombs&rft.place=Jefferson%2C+North+Carolina&rft.pub=McFarland+%26+Company&rft.date=2005&rft_id=info%3Aoclcnum%2F58554961&rft.isbn=0-7864-2139-8&rft.aulast=Campbell&rft.aufirst=Richard+H.&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFCoster-Mullen2012" class="citation book cs1">Coster-Mullen, John (2012). <i>Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man</i>. Waukesha, Wisconsin: J. Coster-Mullen. <a href="/https/en.wikipedia.org/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://www.worldcat.org/oclc/298514167">298514167</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Atom+Bombs%3A+The+Top+Secret+Inside+Story+of+Little+Boy+and+Fat+Man&rft.place=Waukesha%2C+Wisconsin&rft.pub=J.+Coster-Mullen&rft.date=2012&rft_id=info%3Aoclcnum%2F298514167&rft.aulast=Coster-Mullen&rft.aufirst=John&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFCravenCate1983" class="citation book cs1">Craven, W. F.; Cate, J. L., eds. (1983). <a rel="nofollow" class="external text" href="https://www.ibiblio.org/hyperwar/AAF/V/AAF-V-23.html"><i>The Pacific: Matterhorn to Nagasaki, June 1944 to August 1945</i></a>. The Army Air Forces in World War II. Vol. 5. Washington, D.C.: Office of Air Force History. <a href="/https/en.wikipedia.org/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://www.worldcat.org/oclc/9828710">9828710</a><span class="reference-accessdate">. Retrieved <span class="nowrap">28 March</span> 2023</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+Pacific%3A+Matterhorn+to+Nagasaki%2C+June+1944+to+August+1945&rft.place=Washington%2C+D.C.&rft.series=The+Army+Air+Forces+in+World+War+II&rft.pub=Office+of+Air+Force+History&rft.date=1983&rft_id=info%3Aoclcnum%2F9828710&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Fwww.ibiblio.org%2Fhyperwar%2FAAF%2FV%2FAAF-V-23.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFDiacon1984" class="citation book cs1">Diacon, Diane (1984). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=nqYOAAAAQAAJ"><i>Residential Housing and Nuclear Attack</i></a>. London: Croom Helm. <a href="/https/en.wikipedia.org/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/https/en.wikipedia.org/wiki/Special:BookSources/978-0-7099-0868-5" title="Special:BookSources/978-0-7099-0868-5"><bdi>978-0-7099-0868-5</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Residential+Housing+and+Nuclear+Attack&rft.place=London&rft.pub=Croom+Helm&rft.date=1984&rft.isbn=978-0-7099-0868-5&rft.aulast=Diacon&rft.aufirst=Diane&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Fbooks.google.com%2Fbooks%3Fid%3DnqYOAAAAQAAJ&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFD'Olier1946" class="citation book cs1"><a href="/https/en.wikipedia.org/wiki/Franklin_D%27Olier" title="Franklin D'Olier">D'Olier, Franklin</a>, ed. (1946). <a rel="nofollow" class="external text" href="http://www.anesi.com/ussbs01.htm"><i>United States Strategic Bombing Survey, Summary Report (Pacific War)</i></a>. Washington: United States Government Printing Office<span class="reference-accessdate">. Retrieved <span class="nowrap">6 November</span> 2013</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=United+States+Strategic+Bombing+Survey%2C+Summary+Report+%28Pacific+War%29&rft.place=Washington&rft.pub=United+States+Government+Printing+Office&rft.date=1946&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttp%2Fwww.anesi.com%2Fussbs01.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span> This report can also be found <a rel="nofollow" class="external text" href="http://marshall.csu.edu.au/Marshalls/html/WWII/USSBS_Summary.html">here</a>.</li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFGenetic_Effects" class="citation web cs1"><a rel="nofollow" class="external text" href="http://rerf.or.jp/general/qa_e/qa7.html">"Genetic Effects: Question #7"</a>. Radiation Effects Research Foundation<span class="reference-accessdate">. Retrieved <span class="nowrap">6 November</span> 2013</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Genetic+Effects%3A+Question+%237&rft.pub=Radiation+Effects+Research+Foundation&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttp%2Frerf.or.jp%2Fgeneral%2Fqa_e%2Fqa7.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFGlasstone1962" class="citation book cs1"><a href="/https/en.wikipedia.org/wiki/Samuel_Glasstone" title="Samuel Glasstone">Glasstone, Samuel</a> (1962). <i>The Effects of Nuclear Weapons, Revised Edition</i>. United States: United States Department of Defense and United States Atomic Energy Commission. <a href="/https/en.wikipedia.org/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/https/en.wikipedia.org/wiki/Special:BookSources/978-1258793555" title="Special:BookSources/978-1258793555"><bdi>978-1258793555</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+Effects+of+Nuclear+Weapons%2C+Revised+Edition&rft.place=United+States&rft.pub=United+States+Department+of+Defense+and+United+States+Atomic+Energy+Commission&rft.date=1962&rft.isbn=978-1258793555&rft.aulast=Glasstone&rft.aufirst=Samuel&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFGlasstoneDolan1977" class="citation book cs1"><a href="/https/en.wikipedia.org/wiki/Samuel_Glasstone" title="Samuel Glasstone">Glasstone, Samuel</a>; <a href="/https/en.wikipedia.org/wiki/Philip_J._Dolan" title="Philip J. Dolan">Dolan, Philip J.</a> (1977). <a rel="nofollow" class="external text" href="http://www.fourmilab.ch/etexts/www/effects/"><i>The Effects of Nuclear Weapons, Third Edition</i></a>. United States: United States Department of Defense and United States Department of Energy. <a href="/https/en.wikipedia.org/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/https/en.wikipedia.org/wiki/Special:BookSources/978-1603220163" title="Special:BookSources/978-1603220163"><bdi>978-1603220163</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+Effects+of+Nuclear+Weapons%2C+Third+Edition&rft.place=United+States&rft.pub=United+States+Department+of+Defense+and+United+States+Department+of+Energy&rft.date=1977&rft.isbn=978-1603220163&rft.aulast=Glasstone&rft.aufirst=Samuel&rft.au=Dolan%2C+Philip+J.&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttp%2Fwww.fourmilab.ch%2Fetexts%2Fwww%2Feffects%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFGosling1999" class="citation book cs1">Gosling, F. G. (1999). <a rel="nofollow" class="external text" href="https://archive.org/details/bub_gb_SKaSCzKs8ZsC"><i>The Manhattan Project: Making the Atomic Bomb</i></a>. Diane Publishing. <a href="/https/en.wikipedia.org/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/https/en.wikipedia.org/wiki/Special:BookSources/978-0-7881-7880-1" title="Special:BookSources/978-0-7881-7880-1"><bdi>978-0-7881-7880-1</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+Manhattan+Project%3A+Making+the+Atomic+Bomb&rft.pub=Diane+Publishing&rft.date=1999&rft.isbn=978-0-7881-7880-1&rft.aulast=Gosling&rft.aufirst=F.+G.&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Farchive.org%2Fdetails%2Fbub_gb_SKaSCzKs8ZsC&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFGroves1962" class="citation book cs1"><a href="/https/en.wikipedia.org/wiki/Leslie_Groves" title="Leslie Groves">Groves, Leslie R.</a> (1962). <i>Now it Can Be Told: the Story of the Manhattan Project</i>. New York: Da Capo Press (1975 reprint). <a href="/https/en.wikipedia.org/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/https/en.wikipedia.org/wiki/Special:BookSources/0-306-70738-1" title="Special:BookSources/0-306-70738-1"><bdi>0-306-70738-1</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Now+it+Can+Be+Told%3A+the+Story+of+the+Manhattan+Project&rft.place=New+York&rft.pub=Da+Capo+Press+%281975+reprint%29&rft.date=1962&rft.isbn=0-306-70738-1&rft.aulast=Groves&rft.aufirst=Leslie+R.&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFHansen1995" class="citation book cs1"><a href="/https/en.wikipedia.org/wiki/Chuck_Hansen" title="Chuck Hansen">Hansen, Chuck</a> (1995). <i>Volume V: US Nuclear Weapons Histories</i>. Swords of Armageddon: US Nuclear Weapons Development since 1945. Sunnyvale, California: Chuckelea Publications. <a href="/https/en.wikipedia.org/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/https/en.wikipedia.org/wiki/Special:BookSources/978-0-9791915-0-3" title="Special:BookSources/978-0-9791915-0-3"><bdi>978-0-9791915-0-3</bdi></a>. <a href="/https/en.wikipedia.org/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://www.worldcat.org/oclc/231585284">231585284</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Volume+V%3A+US+Nuclear+Weapons+Histories&rft.place=Sunnyvale%2C+California&rft.series=Swords+of+Armageddon%3A+US+Nuclear+Weapons+Development+since+1945&rft.pub=Chuckelea+Publications&rft.date=1995&rft_id=info%3Aoclcnum%2F231585284&rft.isbn=978-0-9791915-0-3&rft.aulast=Hansen&rft.aufirst=Chuck&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFHansen1995a" class="citation book cs1">Hansen, Chuck (1995a). <i>Volume VII: The Development of US Nuclear Weapons</i>. Swords of Armageddon: US Nuclear Weapons Development since 1945. Sunnyvale, California: Chuckelea Publications. <a href="/https/en.wikipedia.org/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/https/en.wikipedia.org/wiki/Special:BookSources/978-0-9791915-7-2" title="Special:BookSources/978-0-9791915-7-2"><bdi>978-0-9791915-7-2</bdi></a>. <a href="/https/en.wikipedia.org/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://www.worldcat.org/oclc/231585284">231585284</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Volume+VII%3A+The+Development+of+US+Nuclear+Weapons&rft.place=Sunnyvale%2C+California&rft.series=Swords+of+Armageddon%3A+US+Nuclear+Weapons+Development+since+1945&rft.pub=Chuckelea+Publications&rft.date=1995&rft_id=info%3Aoclcnum%2F231585284&rft.isbn=978-0-9791915-7-2&rft.aulast=Hansen&rft.aufirst=Chuck&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFHoddesonHenriksenMeadeWestfall1993" class="citation book cs1"><a href="/https/en.wikipedia.org/wiki/Lillian_Hoddeson" title="Lillian Hoddeson">Hoddeson, Lillian</a>; Henriksen, Paul W.; Meade, Roger A.; <a href="/https/en.wikipedia.org/wiki/Catherine_Westfall" title="Catherine Westfall">Westfall, Catherine L.</a> (1993). <span class="cs1-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/criticalassembly0000unse"><i>Critical Assembly: A Technical History of Los Alamos During the Oppenheimer Years, 1943–1945</i></a></span>. New York: Cambridge University Press. <a href="/https/en.wikipedia.org/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/https/en.wikipedia.org/wiki/Special:BookSources/0-521-44132-3" title="Special:BookSources/0-521-44132-3"><bdi>0-521-44132-3</bdi></a>. <a href="/https/en.wikipedia.org/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://www.worldcat.org/oclc/26764320">26764320</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Critical+Assembly%3A+A+Technical+History+of+Los+Alamos+During+the+Oppenheimer+Years%2C+1943%E2%80%931945&rft.place=New+York&rft.pub=Cambridge+University+Press&rft.date=1993&rft_id=info%3Aoclcnum%2F26764320&rft.isbn=0-521-44132-3&rft.aulast=Hoddeson&rft.aufirst=Lillian&rft.au=Henriksen%2C+Paul+W.&rft.au=Meade%2C+Roger+A.&rft.au=Westfall%2C+Catherine+L.&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Farchive.org%2Fdetails%2Fcriticalassembly0000unse&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFHuman_Shadow_Etched_in_Stone" class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20210720110334/http://www.pcf.city.hiroshima.jp/virtual/cgi-bin/museum.cgi?no=1001&l=e">"Human Shadow Etched in Stone"</a>. <i>Photographic Display</i>. <a href="/https/en.wikipedia.org/wiki/Hiroshima_Peace_Memorial_Museum" title="Hiroshima Peace Memorial Museum">Hiroshima Peace Memorial Museum</a>. Archived from <a rel="nofollow" class="external text" href="http://www.pcf.city.hiroshima.jp/virtual/cgi-bin/museum.cgi?no=1001&l=e">the original</a> on 20 July 2021<span class="reference-accessdate">. Retrieved <span class="nowrap">6 November</span> 2013</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Photographic+Display&rft.atitle=Human+Shadow+Etched+in+Stone&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttp%2Fwww.pcf.city.hiroshima.jp%2Fvirtual%2Fcgi-bin%2Fmuseum.cgi%3Fno%3D1001%26l%3De&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFIzumi_BJC_2003" class="citation journal cs1">Izumi S, Koyama K, Soda M, Suyama A (November 2003). <a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2394417">"Cancer incidence in children and young adults did not increase relative to parental exposure to atomic bombs"</a>. <i>British Journal of Cancer</i>. <b>89</b> (9): 1709–1713. <a href="/https/en.wikipedia.org/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1038%2Fsj.bjc.6601322">10.1038/sj.bjc.6601322</a>. <a href="/https/en.wikipedia.org/wiki/PMC_(identifier)" class="mw-redirect" title="PMC (identifier)">PMC</a> <span class="cs1-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2394417">2394417</a></span>. <a href="/https/en.wikipedia.org/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/14583774">14583774</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=British+Journal+of+Cancer&rft.atitle=Cancer+incidence+in+children+and+young+adults+did+not+increase+relative+to+parental+exposure+to+atomic+bombs&rft.volume=89&rft.issue=9&rft.pages=1709-1713&rft.date=2003-11&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC2394417%23id-name%3DPMC&rft_id=info%3Apmid%2F14583774&rft_id=info%3Adoi%2F10.1038%2Fsj.bjc.6601322&rft.aulast=Izumi&rft.aufirst=S&rft.au=Koyama%2C+K&rft.au=Soda%2C+M&rft.au=Suyama%2C+A&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC2394417&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFIzumi_IJC_2003" class="citation journal cs1">Izumi S, Suyama A, Koyama K (November 2003). <a rel="nofollow" class="external text" href="https://doi.org/10.1002%2Fijc.11400">"Radiation-related mortality among offspring of atomic bomb survivors: a half-century of follow-up"</a>. <i>International Journal of Cancer</i>. <b>107</b> (2): 292–297. <a href="/https/en.wikipedia.org/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="cs1-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1002%2Fijc.11400">10.1002/ijc.11400</a></span>. <a href="/https/en.wikipedia.org/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/12949810">12949810</a>. <a href="/https/en.wikipedia.org/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:23902907">23902907</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=International+Journal+of+Cancer&rft.atitle=Radiation-related+mortality+among+offspring+of+atomic+bomb+survivors%3A+a+half-century+of+follow-up&rft.volume=107&rft.issue=2&rft.pages=292-297&rft.date=2003-11&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Fapi.semanticscholar.org%2FCorpusID%3A23902907%23id-name%3DS2CID&rft_id=info%3Apmid%2F12949810&rft_id=info%3Adoi%2F10.1002%2Fijc.11400&rft.aulast=Izumi&rft.aufirst=S&rft.au=Suyama%2C+A&rft.au=Koyama%2C+K&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Fdoi.org%2F10.1002%252Fijc.11400&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFJones1985" class="citation book cs1">Jones, Vincent (1985). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20141007074359/http://www.history.army.mil/html/books/011/11-10/CMH_Pub_11-10.pdf"><i>Manhattan: The Army and the Atomic Bomb</i></a> <span class="cs1-format">(PDF)</span>. Washington, D.C.: United States Army Center of Military History. <a href="/https/en.wikipedia.org/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://www.worldcat.org/oclc/10913875">10913875</a>. Archived from <a rel="nofollow" class="external text" href="http://www.history.army.mil/html/books/011/11-10/CMH_Pub_11-10.pdf">the original</a> <span class="cs1-format">(PDF)</span> on 7 October 2014<span class="reference-accessdate">. Retrieved <span class="nowrap">25 August</span> 2013</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Manhattan%3A+The+Army+and+the+Atomic+Bomb&rft.place=Washington%2C+D.C.&rft.pub=United+States+Army+Center+of+Military+History&rft.date=1985&rft_id=info%3Aoclcnum%2F10913875&rft.aulast=Jones&rft.aufirst=Vincent&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttp%2Fwww.history.army.mil%2Fhtml%2Fbooks%2F011%2F11-10%2FCMH_Pub_11-10.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFMalik1985" class="citation web cs1">Malik, John S. (1985). <a rel="nofollow" class="external text" href="http://library.lanl.gov/cgi-bin/getfile?00313791.pdf">"The yields of the Hiroshima and Nagasaki nuclear explosions"</a> <span class="cs1-format">(PDF)</span>. Los Alamos National Laboratory report number LA-8819<span class="reference-accessdate">. Retrieved <span class="nowrap">6 November</span> 2013</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=The+yields+of+the+Hiroshima+and+Nagasaki+nuclear+explosions&rft.pub=Los+Alamos+National+Laboratory+report+number+LA-8819&rft.date=1985&rft.aulast=Malik&rft.aufirst=John+S.&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttp%2Flibrary.lanl.gov%2Fcgi-bin%2Fgetfile%3F00313791.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFNichols1987" class="citation book cs1"><a href="/https/en.wikipedia.org/wiki/Kenneth_Nichols" title="Kenneth Nichols">Nichols, Kenneth</a> (1987). <i>The Road to Trinity: A Personal Account of How America's Nuclear Policies Were Made</i>. New York: William Morrow. <a href="/https/en.wikipedia.org/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/https/en.wikipedia.org/wiki/Special:BookSources/068806910X" title="Special:BookSources/068806910X"><bdi>068806910X</bdi></a>. <a href="/https/en.wikipedia.org/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://www.worldcat.org/oclc/15223648">15223648</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+Road+to+Trinity%3A+A+Personal+Account+of+How+America%27s+Nuclear+Policies+Were+Made&rft.place=New+York&rft.pub=William+Morrow&rft.date=1987&rft_id=info%3Aoclcnum%2F15223648&rft.isbn=068806910X&rft.aulast=Nichols&rft.aufirst=Kenneth&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFNuclear_Weapon_Thermal_Effects1998" class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20130422224749/http://www.fas.org/nuke/intro/nuke/thermal.htm">"Nuclear Weapon Thermal Effects"</a>. <i>Special Weapons Primer, Weapons of Mass Destruction</i>. <a href="/https/en.wikipedia.org/wiki/Federation_of_American_Scientists" title="Federation of American Scientists">Federation of American Scientists</a>. 1998. Archived from <a rel="nofollow" class="external text" href="https://fas.org/nuke/intro/nuke/thermal.htm">the original</a> on 22 April 2013<span class="reference-accessdate">. Retrieved <span class="nowrap">5 November</span> 2013</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Special+Weapons+Primer%2C+Weapons+of+Mass+Destruction&rft.atitle=Nuclear+Weapon+Thermal+Effects&rft.date=1998&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Ffas.org%2Fnuke%2Fintro%2Fnuke%2Fthermal.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFRhodes1986" class="citation book cs1"><a href="/https/en.wikipedia.org/wiki/Richard_Rhodes" title="Richard Rhodes">Rhodes, Richard</a> (1986). <span class="cs1-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/makingofatomicbo00rhod"><i>The Making of the Atomic Bomb</i></a></span>. New York: Simon & Schuster. <a href="/https/en.wikipedia.org/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/https/en.wikipedia.org/wiki/Special:BookSources/0-684-81378-5" title="Special:BookSources/0-684-81378-5"><bdi>0-684-81378-5</bdi></a>. <a href="/https/en.wikipedia.org/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://www.worldcat.org/oclc/13793436">13793436</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+Making+of+the+Atomic+Bomb&rft.place=New+York&rft.pub=Simon+%26+Schuster&rft.date=1986&rft_id=info%3Aoclcnum%2F13793436&rft.isbn=0-684-81378-5&rft.aulast=Rhodes&rft.aufirst=Richard&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Farchive.org%2Fdetails%2Fmakingofatomicbo00rhod&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFRhodes1995" class="citation book cs1"><a href="/https/en.wikipedia.org/wiki/Richard_Rhodes" title="Richard Rhodes">Rhodes, Richard</a> (1995). <span class="cs1-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/darksun00rich"><i>Dark Sun: The Making of the Hydrogen Bomb</i></a></span>. New York: Touchstone. <a href="/https/en.wikipedia.org/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/https/en.wikipedia.org/wiki/Special:BookSources/0-684-82414-0" title="Special:BookSources/0-684-82414-0"><bdi>0-684-82414-0</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Dark+Sun%3A+The+Making+of+the+Hydrogen+Bomb&rft.place=New+York&rft.pub=Touchstone&rft.date=1995&rft.isbn=0-684-82414-0&rft.aulast=Rhodes&rft.aufirst=Richard&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Farchive.org%2Fdetails%2Fdarksun00rich&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFRichardson_RR_2009" class="citation journal cs1">Richardson, David; et al. (September 2009). "Ionizing Radiation and Leukemia Mortality among Japanese Atomic Bomb Survivors, 1950–2000". <i>Radiation Research</i>. <b>172</b> (3): 368–382. <a href="/https/en.wikipedia.org/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2009RadR..172..368R">2009RadR..172..368R</a>. <a href="/https/en.wikipedia.org/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1667%2FRR1801.1">10.1667/RR1801.1</a>. <a href="/https/en.wikipedia.org/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/19708786">19708786</a>. <a href="/https/en.wikipedia.org/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:12463437">12463437</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Radiation+Research&rft.atitle=Ionizing+Radiation+and+Leukemia+Mortality+among+Japanese+Atomic+Bomb+Survivors%2C+1950%E2%80%932000&rft.volume=172&rft.issue=3&rft.pages=368-382&rft.date=2009-09&rft_id=info%3Adoi%2F10.1667%2FRR1801.1&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Fapi.semanticscholar.org%2FCorpusID%3A12463437%23id-name%3DS2CID&rft_id=info%3Apmid%2F19708786&rft_id=info%3Abibcode%2F2009RadR..172..368R&rft.aulast=Richardson&rft.aufirst=David&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFSamuels2008" class="citation news cs1">Samuels, David (15 December 2008). <a rel="nofollow" class="external text" href="http://www.newyorker.com/reporting/2008/12/15/081215fa_fact_samuels">"Atomic John: A truck driver uncovers secrets about the first nuclear bombs"</a>. <i><a href="/https/en.wikipedia.org/wiki/The_New_Yorker" title="The New Yorker">The New Yorker</a></i><span class="reference-accessdate">. Retrieved <span class="nowrap">30 August</span> 2013</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=The+New+Yorker&rft.atitle=Atomic+John%3A+A+truck+driver+uncovers+secrets+about+the+first+nuclear+bombs&rft.date=2008-12-15&rft.aulast=Samuels&rft.aufirst=David&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttp%2Fwww.newyorker.com%2Freporting%2F2008%2F12%2F15%2F081215fa_fact_samuels&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li>
<li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1133582631"><cite id="CITEREFSerberCrease1998" class="citation book cs1"><a href="/https/en.wikipedia.org/wiki/Robert_Serber" title="Robert Serber">Serber, Robert</a>; Crease, Robert P. (1998). <span class="cs1-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/peacewarreminisc00serb"><i>Peace & War: Reminiscences of a Life on the Frontiers of Science</i></a></span>. New York: Columbia University Press. <a href="/https/en.wikipedia.org/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/https/en.wikipedia.org/wiki/Special:BookSources/978-0231105460" title="Special:BookSources/978-0231105460"><bdi>978-0231105460</bdi></a>. <a href="/https/en.wikipedia.org/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://www.worldcat.org/oclc/37631186">37631186</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Peace+%26+War%3A+Reminiscences+of+a+Life+on+the+Frontiers+of+Science&rft.place=New+York&rft.pub=Columbia+University+Press&rft.date=1998&rft_id=info%3Aoclcnum%2F37631186&rft.isbn=978-0231105460&rft.aulast=Serber&rft.aufirst=Robert&rft.au=Crease%2C+Robert+P.&rft_id=https%3A%2F%2F1.800.gay%3A443%2Fhttps%2Farchive.org%2Fdetails%2Fpeacewarreminisc00serb&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALittle+Boy" class="Z3988"></span></li></ul>
</div>
<h2><span class="mw-headline" id="External_links">External links</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/https/en.wikipedia.org/w/index.php?title=Little_Boy&action=edit&section=19" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></h2>
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<div class="side-box-text plainlist">Wikimedia Commons has media related to <a href="https://commons.wikimedia.org/wiki/Little_Boy" class="extiw" title="commons:Little Boy"><span style="font-style:italic; font-weight:bold;">Little Boy</span></a>.</div></div>
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<ul><li><a rel="nofollow" class="external text" href="http://nuclearweaponarchive.org/Nwfaq/Nfaq8.html#nfaq8.1.3">Little Boy description</a> at Carey Sublette's NuclearWeaponArchive.org</li>
<li><a rel="nofollow" class="external text" href="http://www.nuclearfiles.org/menu/key-issues/nuclear-weapons/history/pre-cold-war/manhattan-project/littleboy.htm">Nuclear Files.org</a> Definition and explanation of 'Little Boy'</li>
<li><a rel="nofollow" class="external text" href="http://nuclearweaponarchive.org/Usa/Med/Lbfm.html">The Nuclear Weapon Archive</a></li>
<li><a rel="nofollow" class="external text" href="http://beltoforion.de/article.php?a=little_boy">Simulation of "Little Boy"</a> an interactive simulation of "Little Boy"</li>
<li><a rel="nofollow" class="external text" href="http://www.atomicarchive.com/Movies/index.shtml">Little Boy 3D Model</a></li>
<li><a rel="nofollow" class="external text" href="http://www.hiroshima-remembered.com/history/index.html">Hiroshima & Nagasaki Remembered</a> information about preparation and dropping the Little Boy bomb</li>
<li><a rel="nofollow" class="external text" href="http://www.ssrichardmontgomery.com/download/littleboy.jpg">Little boy Nuclear Bomb at Imperial War museum London UK (jpg)</a></li></ul>
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transparent;border:none;box-shadow:none;padding:0;">v</abbr></a></li><li class="nv-talk"><a href="/https/en.wikipedia.org/wiki/Template_talk:United_States_nuclear_devices" title="Template talk:United States nuclear devices"><abbr title="Discuss this template" style=";;background:none transparent;border:none;box-shadow:none;padding:0;">t</abbr></a></li><li class="nv-edit"><a href="/https/en.wikipedia.org/wiki/Special:EditPage/Template:United_States_nuclear_devices" title="Special:EditPage/Template:United States nuclear devices"><abbr title="Edit this template" style=";;background:none transparent;border:none;box-shadow:none;padding:0;">e</abbr></a></li></ul></div><div id="United_States_nuclear_devices" style="font-size:114%;margin:0 4em"><a href="/https/en.wikipedia.org/wiki/List_of_nuclear_weapons#United_States" title="List of nuclear weapons">United States nuclear devices</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/https/en.wikipedia.org/wiki/Nuclear_weapon" title="Nuclear weapon">Fission<br />(including<br />boosted)</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:8em"><a href="/https/en.wikipedia.org/wiki/Unguided_bomb" title="Unguided bomb">Gravity bombs</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a class="mw-selflink selflink">Little Boy</a> (Mark 1)</li>
<li><a href="/https/en.wikipedia.org/wiki/Thin_Man_(nuclear_bomb)" title="Thin Man (nuclear bomb)">Thin Man</a> (Mark 2)</li>
<li><a href="/https/en.wikipedia.org/wiki/Fat_Man" title="Fat Man">Fat Man</a> (Mark 3)</li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_4_nuclear_bomb" title="Mark 4 nuclear bomb">Mark 4</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_5_nuclear_bomb" title="Mark 5 nuclear bomb">Mark 5</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_6_nuclear_bomb" title="Mark 6 nuclear bomb">Mark 6</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_7_nuclear_bomb" title="Mark 7 nuclear bomb">Mark 7</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_8_nuclear_bomb" title="Mark 8 nuclear bomb">Mark 8</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_10_nuclear_bomb" title="Mark 10 nuclear bomb">Mark 10</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_11_nuclear_bomb" title="Mark 11 nuclear bomb">Mark 11</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_12_nuclear_bomb" title="Mark 12 nuclear bomb">Mark 12</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_13_nuclear_bomb" title="Mark 13 nuclear bomb">Mark 13</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_18_nuclear_bomb" title="Mark 18 nuclear bomb">Mark 18</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_13_nuclear_bomb#Mark_20" title="Mark 13 nuclear bomb">Mark 20</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mk_105_Hotpoint" title="Mk 105 Hotpoint">Mk 105</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B57_nuclear_bomb" title="B57 nuclear bomb">B57</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:8em">Warheads</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/Mark_4_nuclear_bomb" title="Mark 4 nuclear bomb">W4</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_5_nuclear_bomb" title="Mark 5 nuclear bomb">W5</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_7_nuclear_bomb" title="Mark 7 nuclear bomb">W7</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_8_nuclear_bomb" title="Mark 8 nuclear bomb">W8</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_12_nuclear_bomb" title="Mark 12 nuclear bomb">W12</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_13_nuclear_bomb" title="Mark 13 nuclear bomb">W13</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W25_(nuclear_warhead)" title="W25 (nuclear warhead)">W25</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W30_(nuclear_warhead)" title="W30 (nuclear warhead)">W30</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W31" title="W31">W31</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W34_(nuclear_warhead)" title="W34 (nuclear warhead)">W34</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W31" title="W31">W37</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W40_(nuclear_warhead)" title="W40 (nuclear warhead)">W40</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W42_(nuclear_warhead)" title="W42 (nuclear warhead)">W42</a></li>
<li><a href="/https/en.wikipedia.org/wiki/RUR-5_ASROC#W44_nuclear_depth_charge" title="RUR-5 ASROC">W44</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W45_(nuclear_warhead)" title="W45 (nuclear warhead)">W45</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W54" title="W54">XW-51</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W54" title="W54">W54</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W54" title="W54">W72</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W76" title="W76">W76-2</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W81" title="W81">W81</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:8em">Depth bombs</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/Mark_90_nuclear_bomb" title="Mark 90 nuclear bomb">Mark 90</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mk_101_Lulu" title="Mk 101 Lulu">Mk 101</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mk_105_Hotpoint" title="Mk 105 Hotpoint">Mk 105</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B57_nuclear_bomb" title="B57 nuclear bomb">B57</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:8em">Artillery</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/W9_(nuclear_warhead)" title="W9 (nuclear warhead)">W9</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W19_(nuclear_artillery_shell)" title="W19 (nuclear artillery shell)">W19</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W19_(nuclear_artillery_shell)" title="W19 (nuclear artillery shell)">W23</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W33_(nuclear_warhead)" title="W33 (nuclear warhead)">W33</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W48" title="W48">W48</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W54" title="W54">W54</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W74_(nuclear_warhead)" title="W74 (nuclear warhead)">W74</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W74_(nuclear_warhead)" title="W74 (nuclear warhead)">W75</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W79_Artillery-Fired_Atomic_Projectile" title="W79 Artillery-Fired Atomic Projectile">W79</a>-1</li>
<li><a href="/https/en.wikipedia.org/wiki/W82" title="W82">W82</a>-1</li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:8em"><a href="/https/en.wikipedia.org/wiki/Atomic_demolition_munition" title="Atomic demolition munition">Atomic demolition<br />munitions</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/Mark_6_nuclear_bomb#XM1_Atomic_Demolition_Munition" title="Mark 6 nuclear bomb">XM1 ADM</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_7_nuclear_bomb#T2_Atomic_Demolition_Munition" title="Mark 7 nuclear bomb">T2 ADM</a></li>
<li><a href="/https/en.wikipedia.org/wiki/T-4_Atomic_Demolition_Munition" title="T-4 Atomic Demolition Munition">T4</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Medium_Atomic_Demolition_Munition" title="Medium Atomic Demolition Munition">Medium Atomic Demolition Munition</a> (MADM)</li>
<li><a href="/https/en.wikipedia.org/wiki/Special_Atomic_Demolition_Munition" title="Special Atomic Demolition Munition">Special Atomic Demolition Munition</a> (SADM)</li>
<li><a href="/https/en.wikipedia.org/wiki/Tactical_Atomic_Demolition_Munition" class="mw-redirect" title="Tactical Atomic Demolition Munition">Tactical Atomic Demolition Munition</a> (TADM)</li></ul>
</div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/https/en.wikipedia.org/wiki/Thermonuclear_weapon" title="Thermonuclear weapon">Thermonuclear</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:8em">Gravity bombs</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/Mark_14_nuclear_bomb" title="Mark 14 nuclear bomb">Mark 14</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_15_nuclear_bomb" title="Mark 15 nuclear bomb">Mark 15</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_16_nuclear_bomb" title="Mark 16 nuclear bomb">TX16</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_17_nuclear_bomb" title="Mark 17 nuclear bomb">Mark 17</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_21_nuclear_bomb" title="Mark 21 nuclear bomb">Mark 21</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_22_nuclear_bomb" title="Mark 22 nuclear bomb">TX22</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_24_nuclear_bomb" title="Mark 24 nuclear bomb">Mark 24</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_26_nuclear_bomb" title="Mark 26 nuclear bomb">Mark 26</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_27_nuclear_bomb" title="Mark 27 nuclear bomb">Mark 27</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B28_nuclear_bomb" title="B28 nuclear bomb">B28</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_36_nuclear_bomb" title="Mark 36 nuclear bomb">Mark 36</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_39_nuclear_bomb" title="Mark 39 nuclear bomb">Mark 39</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B41_nuclear_bomb" title="B41 nuclear bomb">B41</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B43_nuclear_bomb" title="B43 nuclear bomb">B43</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B46_nuclear_bomb" title="B46 nuclear bomb">TX46</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B53_nuclear_bomb" title="B53 nuclear bomb">B53</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B61_nuclear_bomb" title="B61 nuclear bomb">B61</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B77_nuclear_bomb" title="B77 nuclear bomb">B77</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B83_nuclear_bomb" title="B83 nuclear bomb">B83</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B90_nuclear_bomb" title="B90 nuclear bomb">B90</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:8em">Depth bombs</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/B90_nuclear_bomb" title="B90 nuclear bomb">B90</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:8em">Warheads</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/Mark_15_nuclear_bomb" title="Mark 15 nuclear bomb">W15</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_27_nuclear_bomb" title="Mark 27 nuclear bomb">W27</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B28_nuclear_bomb" title="B28 nuclear bomb">W28</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W29_(nuclear_warhead)" class="mw-redirect" title="W29 (nuclear warhead)">TX29</a></li>
<li><a href="/https/en.wikipedia.org/wiki/XW-35" title="XW-35">XW-35</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W38_(nuclear_warhead)" title="W38 (nuclear warhead)">W38</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_39_nuclear_bomb" title="Mark 39 nuclear bomb">W39</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B41_nuclear_bomb" title="B41 nuclear bomb">W41</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B46_nuclear_bomb" title="B46 nuclear bomb">XW-46</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W47" title="W47">W47</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W49" title="W49">W49</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W50_(nuclear_warhead)" title="W50 (nuclear warhead)">W50</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W52_(nuclear_warhead)" title="W52 (nuclear warhead)">W52</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B53_nuclear_bomb" title="B53 nuclear bomb">W53</a></li>
<li><a href="/https/en.wikipedia.org/wiki/UUM-44_SUBROC" title="UUM-44 SUBROC">W55</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W56" title="W56">W56</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W58" title="W58">W58</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W59" title="W59">W59</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W60_(nuclear_warhead)" title="W60 (nuclear warhead)">W60</a></li>
<li><a href="/https/en.wikipedia.org/wiki/B61_nuclear_bomb#W61_Earth_Penetrator_Warhead" title="B61 nuclear bomb">W61</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W62" title="W62">W62</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W63_(nuclear_warhead)" title="W63 (nuclear warhead)">W63</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W64_(nuclear_warhead)" title="W64 (nuclear warhead)">W64</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W67_(nuclear_warhead)" title="W67 (nuclear warhead)">W67</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W68" title="W68">W68</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W69" title="W69">W69</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W70" title="W70">W70</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W71" title="W71">W71</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W73_(nuclear_warhead)" title="W73 (nuclear warhead)">W73</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W76" title="W76">W76</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W78" title="W78">W78</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W80_(nuclear_warhead)" title="W80 (nuclear warhead)">W80</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W84" title="W84">W84</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W85_(nuclear_warhead)" title="W85 (nuclear warhead)">W85</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W86" title="W86">W86</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W87" title="W87">W87</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W88" title="W88">W88</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W89" title="W89">W89</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W91" title="W91">W91</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Reliable_Replacement_Warhead" title="Reliable Replacement Warhead">Reliable Replacement Warhead</a> (RRW)</li>
<li><a href="/https/en.wikipedia.org/wiki/W93" title="W93">W93</a></li></ul>
</div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/https/en.wikipedia.org/wiki/Neutron_bomb" title="Neutron bomb">Enhanced<br />radiation</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:8em">Warheads</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/W63_(nuclear_warhead)" title="W63 (nuclear warhead)">W63</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W64_(nuclear_warhead)" title="W64 (nuclear warhead)">W64</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W65_(nuclear_warhead)" title="W65 (nuclear warhead)">W65</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W66_(nuclear_warhead)" title="W66 (nuclear warhead)">W66</a></li>
<li><a href="/https/en.wikipedia.org/wiki/W70" title="W70">W70</a>-3</li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:8em">Artillery</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/W79_Artillery-Fired_Atomic_Projectile" title="W79 Artillery-Fired Atomic Projectile">W79</a>-0</li>
<li><a href="/https/en.wikipedia.org/wiki/W82" title="W82">W82</a>-0</li></ul>
</div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Primary stages</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/Robin_(nuclear_primary)" title="Robin (nuclear primary)">Robin</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Swan_(nuclear_primary)" title="Swan (nuclear primary)">Swan</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Python_(nuclear_primary)" title="Python (nuclear primary)">Python</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Tsetse_(nuclear_primary)" title="Tsetse (nuclear primary)">Tsetse</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Kinglet_(nuclear_primary)" title="Kinglet (nuclear primary)">Kinglet</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Starling_(nuclear_primary)" title="Starling (nuclear primary)">Starling</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Experimental</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/Trinity_(nuclear_test)" title="Trinity (nuclear test)">Gadget</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Ivy_Mike" title="Ivy Mike">Sausage</a></li>
<li><a href="/https/en.wikipedia.org/wiki/RACER_IV" title="RACER IV">RACER IV</a></li></ul>
</div></td></tr></tbody></table></div>
<div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1061467846"></div><div role="navigation" class="navbox" aria-labelledby="Manhattan_Project" style="padding:3px"><table class="nowraplinks mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="3"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1063604349"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/https/en.wikipedia.org/wiki/Template:Manhattan_Project" title="Template:Manhattan Project"><abbr title="View this template" style=";;background:none transparent;border:none;box-shadow:none;padding:0;">v</abbr></a></li><li class="nv-talk"><a href="/https/en.wikipedia.org/wiki/Template_talk:Manhattan_Project" title="Template talk:Manhattan Project"><abbr title="Discuss this template" style=";;background:none transparent;border:none;box-shadow:none;padding:0;">t</abbr></a></li><li class="nv-edit"><a href="/https/en.wikipedia.org/wiki/Special:EditPage/Template:Manhattan_Project" title="Special:EditPage/Template:Manhattan Project"><abbr title="Edit this template" style=";;background:none transparent;border:none;box-shadow:none;padding:0;">e</abbr></a></li></ul></div><div id="Manhattan_Project" style="font-size:114%;margin:0 4em"><a href="/https/en.wikipedia.org/wiki/Manhattan_Project" title="Manhattan Project">Manhattan Project</a></div></th></tr><tr><td class="navbox-abovebelow" colspan="3"><div><a href="/https/en.wikipedia.org/wiki/Timeline_of_the_Manhattan_Project" title="Timeline of the Manhattan Project">Timeline</a></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Sites</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/Ames_Project" title="Ames Project">Ames</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Calutron" title="Calutron">Berkeley</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Metallurgical_Laboratory" title="Metallurgical Laboratory">Chicago</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Dayton_Project" title="Dayton Project">Dayton</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Hanford_Engineer_Works" title="Hanford Engineer Works">Hanford</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Project_Camel" title="Project Camel">Inyokern</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Project_Y" title="Project Y">Los Alamos</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Montreal_Laboratory" title="Montreal Laboratory">Montreal</a></li>
<li><a href="/https/en.wikipedia.org/wiki/K-25" title="K-25">New York</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Clinton_Engineer_Works" title="Clinton Engineer Works">Oak Ridge</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Salt_Wells_Pilot_Plant" title="Salt Wells Pilot Plant">Salt Wells Pilot Plant</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Trinity_(nuclear_test)" title="Trinity (nuclear test)">Trinity</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Wendover_Air_Force_Base" title="Wendover Air Force Base">Wendover</a></li>
<li><a href="/https/en.wikipedia.org/wiki/P-9_Project" title="P-9 Project">Heavy water sites</a></li></ul>
</div></td><td class="noviewer navbox-image" rowspan="6" style="width:1px;padding:0 0 0 2px"><div><span typeof="mw:File"><a href="/https/en.wikipedia.org/wiki/File:Nagasakibomb.jpg" class="mw-file-description" title="The rising mushroom cloud from the Nagasaki "Fat Man" bomb, August 9, 1945"><img alt="The rising mushroom cloud from the Nagasaki "Fat Man" bomb, August 9, 1945" src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e0/Nagasakibomb.jpg/120px-Nagasakibomb.jpg" decoding="async" width="120" height="143" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e0/Nagasakibomb.jpg/180px-Nagasakibomb.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e0/Nagasakibomb.jpg/240px-Nagasakibomb.jpg 2x" data-file-width="3245" data-file-height="3877" /></a></span></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Administrators</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/Vannevar_Bush" title="Vannevar Bush">Vannevar Bush</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Arthur_Compton" title="Arthur Compton">Arthur Compton</a></li>
<li><a href="/https/en.wikipedia.org/wiki/James_B._Conant" title="James B. Conant">James B. Conant</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Priscilla_Duffield" title="Priscilla Duffield">Priscilla Duffield</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Thomas_Farrell_(United_States_Army_officer)" title="Thomas Farrell (United States Army officer)">Thomas Farrell</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Leslie_Groves" title="Leslie Groves">Leslie Groves</a></li>
<li><a href="/https/en.wikipedia.org/wiki/John_Lansdale_Jr." title="John Lansdale Jr.">John Lansdale</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Ernest_Lawrence" title="Ernest Lawrence">Ernest Lawrence</a></li>
<li><a href="/https/en.wikipedia.org/wiki/James_C._Marshall" title="James C. Marshall">James Marshall</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Franklin_Matthias" title="Franklin Matthias">Franklin Matthias</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Dorothy_McKibbin" title="Dorothy McKibbin">Dorothy McKibbin</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Kenneth_Nichols" title="Kenneth Nichols">Kenneth Nichols</a></li>
<li><a href="/https/en.wikipedia.org/wiki/J._Robert_Oppenheimer" title="J. Robert Oppenheimer">Robert Oppenheimer</a></li>
<li><a href="/https/en.wikipedia.org/wiki/William_Sterling_Parsons" title="William Sterling Parsons">Deak Parsons</a></li>
<li><a href="/https/en.wikipedia.org/wiki/William_R._Purnell" title="William R. Purnell">William Purnell</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Frank_Spedding" title="Frank Spedding">Frank Spedding</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Charles_Allen_Thomas" title="Charles Allen Thomas">Charles Thomas</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Paul_Tibbets" title="Paul Tibbets">Paul Tibbets</a></li>
<li><a href="/https/en.wikipedia.org/wiki/William_L._Uanna" title="William L. Uanna">Bud Uanna</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Harold_Urey" title="Harold Urey">Harold Urey</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Stafford_L._Warren" title="Stafford L. Warren">Stafford Warren</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Ed_Westcott" title="Ed Westcott">Ed Westcott</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Roscoe_Charles_Wilson" title="Roscoe Charles Wilson">Roscoe Wilson</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Scientists</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/Luis_Walter_Alvarez" title="Luis Walter Alvarez">Luis Alvarez</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Robert_Bacher" title="Robert Bacher">Robert Bacher</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Hans_Bethe" title="Hans Bethe">Hans Bethe</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Aage_Bohr" title="Aage Bohr">Aage Bohr</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Niels_Bohr" title="Niels Bohr">Niels Bohr</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Norris_Bradbury" title="Norris Bradbury">Norris Bradbury</a></li>
<li><a href="/https/en.wikipedia.org/wiki/James_Chadwick" title="James Chadwick">James Chadwick</a></li>
<li><a href="/https/en.wikipedia.org/wiki/John_Cockcroft" title="John Cockcroft">John Cockcroft</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Charles_Critchfield" title="Charles Critchfield">Charles Critchfield</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Harry_Daghlian" title="Harry Daghlian">Harry Daghlian</a></li>
<li><a href="/https/en.wikipedia.org/wiki/John_R._Dunning" title="John R. Dunning">John R. Dunning</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Enrico_Fermi" title="Enrico Fermi">Enrico Fermi</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Richard_Feynman" title="Richard Feynman">Richard Feynman</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Val_Logsdon_Fitch" title="Val Logsdon Fitch">Val Fitch</a></li>
<li><a href="/https/en.wikipedia.org/wiki/James_Franck" title="James Franck">James Franck</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Klaus_Fuchs" title="Klaus Fuchs">Klaus Fuchs</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Maria_Goeppert_Mayer" title="Maria Goeppert Mayer">Maria Goeppert Mayer</a></li>
<li><a href="/https/en.wikipedia.org/wiki/George_Kistiakowsky" title="George Kistiakowsky">George Kistiakowsky</a></li>
<li><a href="/https/en.wikipedia.org/wiki/George_Koval" title="George Koval">George Koval</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Willard_Libby" title="Willard Libby">Willard Libby</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Edwin_McMillan" title="Edwin McMillan">Edwin McMillan</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Mark_Oliphant" title="Mark Oliphant">Mark Oliphant</a></li>
<li><a href="/https/en.wikipedia.org/wiki/George_B._Pegram" title="George B. Pegram">George B. Pegram</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Norman_Ramsey_Jr." title="Norman Ramsey Jr.">Norman Ramsey Jr.</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Isidor_Isaac_Rabi" title="Isidor Isaac Rabi">Isidor Isaac Rabi</a></li>
<li><a href="/https/en.wikipedia.org/wiki/James_Rainwater" title="James Rainwater">James Rainwater</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Bruno_Rossi" title="Bruno Rossi">Bruno Rossi</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Glenn_T._Seaborg" title="Glenn T. Seaborg">Glenn Seaborg</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Emilio_Segr%C3%A8" title="Emilio Segrè">Emilio Segrè</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Louis_Slotin" title="Louis Slotin">Louis Slotin</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Henry_DeWolf_Smyth" title="Henry DeWolf Smyth">Henry DeWolf Smyth</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Leo_Szilard" title="Leo Szilard">Leo Szilard</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Edward_Teller" title="Edward Teller">Edward Teller</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Stanis%C5%82aw_Ulam" title="Stanisław Ulam">Stanisław Ulam</a></li>
<li><a href="/https/en.wikipedia.org/wiki/John_von_Neumann" title="John von Neumann">John von Neumann</a></li>
<li><a href="/https/en.wikipedia.org/wiki/John_Archibald_Wheeler" title="John Archibald Wheeler">John Wheeler</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Eugene_Wigner" title="Eugene Wigner">Eugene Wigner</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Robert_R._Wilson" title="Robert R. Wilson">Robert Wilson</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Leona_Woods" title="Leona Woods">Leona Woods</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Chien-Shiung_Wu" title="Chien-Shiung Wu">Chien-Shiung Wu</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Operations</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/Alsos_Mission" title="Alsos Mission">Alsos Mission</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki" title="Atomic bombings of Hiroshima and Nagasaki">Bombings of Hiroshima and Nagasaki</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Operation_Crossroads" title="Operation Crossroads">Operation Crossroads</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Operation_Peppermint" title="Operation Peppermint">Operation Peppermint</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Project_Alberta" title="Project Alberta">Project Alberta</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Silverplate" title="Silverplate">Silverplate</a></li>
<li><a href="/https/en.wikipedia.org/wiki/509th_Composite_Group" title="509th Composite Group">509th Composite Group</a></li>
<li><i><a href="/https/en.wikipedia.org/wiki/Enola_Gay" title="Enola Gay">Enola Gay</a></i></li>
<li><i><a href="/https/en.wikipedia.org/wiki/Bockscar" title="Bockscar">Bockscar</a></i></li>
<li><i><a href="/https/en.wikipedia.org/wiki/The_Great_Artiste" title="The Great Artiste">The Great Artiste</a></i></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Weapons</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/Fat_Man" title="Fat Man">Fat Man</a></li>
<li><a class="mw-selflink selflink">Little Boy</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Pumpkin_bomb" title="Pumpkin bomb">Pumpkin bomb</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Thin_Man_(nuclear_bomb)" title="Thin Man (nuclear bomb)">Thin Man</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Related topics</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="/https/en.wikipedia.org/wiki/Atomic_Energy_Act_of_1946" title="Atomic Energy Act of 1946">Atomic Energy Act of 1946</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Bismuth_phosphate_process" title="Bismuth phosphate process">Bismuth phosphate process</a></li>
<li><a href="/https/en.wikipedia.org/wiki/British_contribution_to_the_Manhattan_Project" title="British contribution to the Manhattan Project">British contribution</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Calutron_Girls" title="Calutron Girls">Calutron Girls</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Chicago_Pile-1" title="Chicago Pile-1">Chicago Pile-1</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Demon_core" title="Demon core">Demon core</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Einstein%E2%80%93Szilard_letter" title="Einstein–Szilard letter">Einstein–Szilard letter</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Franck_Report" title="Franck Report">Franck Report</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Interim_Committee" title="Interim Committee">Interim Committee</a></li>
<li><i><a href="/https/en.wikipedia.org/wiki/Los_Alamos_Primer" title="Los Alamos Primer">Los Alamos Primer</a></i></li>
<li><a href="/https/en.wikipedia.org/wiki/Oppenheimer_security_hearing" title="Oppenheimer security hearing">Oppenheimer security hearing</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Plutonium" title="Plutonium">Plutonium</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Quebec_Agreement" title="Quebec Agreement">Quebec Agreement</a></li>
<li><a href="/https/en.wikipedia.org/wiki/RaLa_Experiment" title="RaLa Experiment">RaLa Experiment</a></li>
<li><a href="/https/en.wikipedia.org/wiki/S-1_Executive_Committee" title="S-1 Executive Committee">S-1 Executive Committee</a></li>
<li><a href="/https/en.wikipedia.org/wiki/S-50_(Manhattan_Project)" title="S-50 (Manhattan Project)">S-50 Project</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Smyth_Report" title="Smyth Report">Smyth Report</a></li>
<li><a href="/https/en.wikipedia.org/wiki/Uranium" title="Uranium">Uranium</a></li>
<li><a href="/https/en.wikipedia.org/wiki/X-10_Graphite_Reactor" title="X-10 Graphite Reactor">X-10 Graphite Reactor</a></li></ul>
</div></td></tr><tr><td class="navbox-abovebelow" colspan="3"><div><span class="noviewer" typeof="mw:File"><span title="Category"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/16px-Symbol_category_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/23px-Symbol_category_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/31px-Symbol_category_class.svg.png 2x" data-file-width="180" data-file-height="185" /></span></span> <a href="/https/en.wikipedia.org/wiki/Category:Manhattan_Project" title="Category:Manhattan Project">Manhattan Project</a></div></td></tr></tbody></table></div>
<style data-mw-deduplicate="TemplateStyles:r1130092004">.mw-parser-output .portal-bar{font-size:88%;font-weight:bold;display:flex;justify-content:center;align-items:baseline}.mw-parser-output .portal-bar-bordered{padding:0 2em;background-color:#fdfdfd;border:1px solid #a2a9b1;clear:both;margin:1em auto 0}.mw-parser-output .portal-bar-related{font-size:100%;justify-content:flex-start}.mw-parser-output .portal-bar-unbordered{padding:0 1.7em;margin-left:0}.mw-parser-output .portal-bar-header{margin:0 1em 0 0.5em;flex:0 0 auto;min-height:24px}.mw-parser-output .portal-bar-content{display:flex;flex-flow:row wrap;flex:0 1 auto;padding:0.15em 0;column-gap:1em;align-items:baseline;margin:0;list-style:none}.mw-parser-output .portal-bar-content-related{margin:0;list-style:none}.mw-parser-output .portal-bar-item{display:inline-block;margin:0.15em 0.2em;min-height:24px;line-height:24px}@media screen and (max-width:768px){.mw-parser-output .portal-bar{font-size:88%;font-weight:bold;display:flex;flex-flow:column wrap;align-items:baseline}.mw-parser-output .portal-bar-header{text-align:center;flex:0;padding-left:0.5em;margin:0 auto}.mw-parser-output .portal-bar-related{font-size:100%;align-items:flex-start}.mw-parser-output .portal-bar-content{display:flex;flex-flow:row wrap;align-items:center;flex:0;column-gap:1em;border-top:1px solid #a2a9b1;margin:0 auto;list-style:none}.mw-parser-output .portal-bar-content-related{border-top:none;margin:0;list-style:none}}.mw-parser-output .navbox+link+.portal-bar,.mw-parser-output .navbox+style+.portal-bar,.mw-parser-output .navbox+link+.portal-bar-bordered,.mw-parser-output .navbox+style+.portal-bar-bordered,.mw-parser-output .sister-bar+link+.portal-bar,.mw-parser-output .sister-bar+style+.portal-bar,.mw-parser-output .portal-bar+.navbox-styles+.navbox,.mw-parser-output .portal-bar+.navbox-styles+.sister-bar{margin-top:-1px}</style><div class="portal-bar noprint metadata noviewer portal-bar-bordered" role="navigation" aria-label="Portals"><span class="portal-bar-header"><a href="/https/en.wikipedia.org/wiki/Wikipedia:Contents/Portals" title="Wikipedia:Contents/Portals">Portals</a>:</span><ul class="portal-bar-content"><li class="portal-bar-item"><span typeof="mw:File"><span><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/b/b5/Radioactive.svg/21px-Radioactive.svg.png" decoding="async" width="21" height="18" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/b5/Radioactive.svg/32px-Radioactive.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/b5/Radioactive.svg/42px-Radioactive.svg.png 2x" data-file-width="512" data-file-height="446" /></span></span> <a href="/https/en.wikipedia.org/wiki/Portal:Nuclear_technology" title="Portal:Nuclear technology">Nuclear technology</a></li><li class="portal-bar-item"><span typeof="mw:File"><span><img alt="image" src="//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Newton%27s_reflecting_telescope.jpg/17px-Newton%27s_reflecting_telescope.jpg" decoding="async" width="17" height="19" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Newton%27s_reflecting_telescope.jpg/26px-Newton%27s_reflecting_telescope.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Newton%27s_reflecting_telescope.jpg/34px-Newton%27s_reflecting_telescope.jpg 2x" data-file-width="1140" data-file-height="1276" /></span></span> <a href="/https/en.wikipedia.org/wiki/Portal:History_of_science" title="Portal:History of science">History of science</a></li></ul></div>
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