In the world of video games, nothing improves a tank with a big gun more than strapping another cannon on top of it. Whether a fictional Leman Russ battle tank, or the historical M3 Lee in a more realistic game like Steel Panthers, it’s hard to argue that two shot aren’t better than one.
But while most tanks have machine guns complementing their main guns, historical experience has shown that having multiple cannons (weapons firing shells 20 millimeter-diameter shells or larger) had major shortcomings. But that didn’t stop engineers from trying to make it work.
In fact, in 1916, the first ever tank to roll into combat was the UK’s rhombus-shaped Mark I. It was armed with two Hotchkiss 6-pounder (57-millimeter) naval guns in side-mounted swiveling sponsons, and supplemented by three Vickers machine guns in its ‘male’ configuration. (The ‘female’ variant had machine gun-only armament.)
The Mark I was the product of the UK’s secretive Landship Committee, which included then-future prime minister Winston Churchill. Later renamed the Tank Supply Committee, its original name and Royal Navy origins hinted at its goal—seeking to build a 1,000- or 300-ton ‘land ironclad’ with multiple turrets. Eventually, engineering constraints forced it to settle on the 31-ton Mark I, which could barely achieve a walking speed of 3.7 miles per hour on road.
Though revolutionary, the Mark I’s configuration—and that of successors and rivals like the British Mark IV, French Schneider CA and German A7V—all shared a common problem: the inability of hull-mounted guns to all point towards the same target in many circumstances. Thus, it was France’s dinky, mass-produced, 6.5-ton FT-17 light tank with its fully-rotating gun turret that set the paradigm for nearly all tanks that followed it.
Still, engineers between the World Wars stubbornly tried to create large ‘super heavy tanks’ with multiple gun turrets. Most, like the prototype Vickers A1E1 Independent, Japan’s Type 95 heavy tank, and France's massive 76-ton Char 2C, had one cannon turret supported by smaller machine gun turrets.
However, the only multi-cannon turret tank to see combat was the Soviet Union’s massive 50-ton T-35 tank. Its crew of 10 operated one fully-rotating central turret with a low-velocity 76-millimeter howitzer, two turrets with high-velocity 45-millimeter anti-tank guns (covering opposing 90-degree quadrants), and two more small machine gun turrets.
However, the T-35’s large surface area made it hard to maintain dense armor across the vehicle’s flanks without excessive weight gain. While 10 of the 61 T-35s built received 4 tons of extra armor, that worsened the design’s true Achille’s heel—a combination of heavy weight and underpowered engines.
When the Red Army committed its 48 still-functional T-35 tanks to counterattacking invading Nazis in June of 1941, 38 were lost on the march to breakdowns, bog-downs, and (in two cases) falling through bridges. In the Battle of Brody, the remaining T-35s managed to engage and briefly drive out German forces in Verba, Ukraine, before being dispatched by anti-tank fire, swarming infantry, and Stuka dive bombers.
Russia also combat-tested smaller but better-armored T-100 and SMK prototype multi-turret tanks—both featuring a 76-millimeter turret situated in tandem with a 45-millimeter turret. While assaulting the fortified Finnish Mannerheim Line in 1940, the SMK was immobilized by a mine. The T-100 faired better, surviving 14 hits by anti-tank artillery. The Red Army chose to build single-turret KV-1 heavy tanks instead.
Tanks with hull and turret cannons
A more successful multi-cannon configuration involved combining a smaller turret anti-tank cannon with a bigger 75- or 76-millimeter gun situated in the hull. France’s heavy Char B1 bis, the U.S. M3 Grant/Lee tank, and the British Churchill Mark 1 all featured this setup.
These were successful, in part, because medium-velocity 75-millimeter tanks guns were uncommon—yet very effective against both tanks and infantry—early in World War II. The Churchill and Char B1 bis were both also heavily armored—the latter’s 60-millimeter plate was nearly impenetrable by most German tank guns in the 1940 Battle of France.
While the 400 Char B1 bis bloodied German armor and infantry on several occasions in 1940, poor mobility, inadequate maintenance and fuel logistics, and a lack of support from infantry and artillery prevented them from stemming the German tide.
Likewise, the M3’s 75-millimeter gun gave British forces in North Africa a temporary long-range overmatch against Rommel’s Panzers in the first half of 1942.
By contrast, the Churchill Mark I’s 3” (76-millimeter) hull howitzer was limited to smoke and anti-personnel rounds, leaving anti-tank duties to the turret’s 40-millimeter 2-pounder anti-tank gun. It (and the M3’s 37-millimeter gun) were both underpowered for their antitank role by mid-World War II. Though some of the 303 Churchill Mark 1s saw combat in North Africa and the disastrous Dieppe amphibious raid, the 5,300 succeeding Churchill marks ditched the hull howitzer.
Though all three remained in second-line service through the end of World War II, the hull-cannon concept didn’t endure. The multi-tasking required of tank crews to aim, fire, and reload multiple cannons reduced firing rates substantially. Their position’s limited field fire frequently required turning the entire tank, and left them unable to shoot from behind cover (‘hull down’ position). Even the hull-mounted ‘bow’ machine guns that werecommon on World War II tanks gradually disappeared post-war.
In effect, the M3 and Churchill Mark 1’s were stopgaps awaiting the production of larger-diameter turrets supporting 57- or 75-millimeter guns. Indeed, nearly every successful mid-to-late war medium tank—such as the M4 Sherman, Panther, Cromwell, and T-34—used a 75- or 75-millimeter medium- or high-velocity turret gun.
Side-by-side: Coaxial Tank Cannons
Yet another multi-cannon configuration involved mounting a lighter co-axial cannon beside the main gun in the turret, replacing or supplementing the standard coaxial machine gun. This meant that the extra gun had the main gun’s full 360-degree firing arc, but lost the option to engage separate targets.
Side-by-side turret cannons featured in Germany’s five slow and thinly-armored 26-ton Neubaufahrzeug heavy tanks built between 1933 and 1934. Used largely for propaganda, three saw brief combat use in Germany’s invasion of Norway in 1940 (with mixed success) before being scrapped.
Germany later paired a 128-millimeter gun with a coaxial long-barrel 75-millimeter cannon in its two humongous 207-ton Maus and 123-ton E100 prototype super-heavy tanks.
The UK’s Centurion Mark I featured a co-axial 20-millimeter Polsten anti-aircraft cannon, though it was swiftly deleted in subsequent variants. More enduringly, France’s AMX-30B series tanks were refit in the 1970s with coaxial 20-millimeter M693 F2 cannons, each of which boasted up to 40 degrees vertical traverse to counter helicopters.
But the most important contemporary armored vehicle to feature coaxial cannons isn’t a tank. The turret on Russia’s BMP-3 infantry fighting vehicle combines a 30-millimeter 2A42 autocannon with a low-velocity 2A70 100-millimeter rifled gun armed with anti-personnel shells and a few anti-tank missiles. The still-in-production BMP-3’s fearsome armament was copied in Russia’s BMD-4 airborne fighting vehicle and China’s ZBD-04, but has not tempted Western imitations.
While the BMP-3 remains in production, as of June of 2024, Russia has lost over 480 of the thinly armored IFVs, and its proposed successors ditch the secondary 2A70 gun for improved protection.
Setting aside anti-aircraft gun vehicles, which often employ multiple small autocannons, several other kinds of armored vehicle designs have flirted with big multi-cannon armament.
For example, Russia tested two twin-gun 2S35 Koalitsya self-propelled artillery prototypes—combining a T-80 tank chassis with two long-barrel 2A86 152-millimeter howitzers stacked one atop the other in a huge, unmanned turret. Though allegedly able to fire 16 rounds per minute, it was discarded in 2010 in favor of a different single-barrel design with the same name.
The Marine Corp’s bizarre M50 ONTOS tank destroyer had a turret mounting six 106-millimeter M40A1 recoilless rifles—in part because there was no way to safely reload them mid-combat. Though ONTOSs did knock out three light tanks in the Dominican civil war, it thereafter served in an anti-personnel role during the Vietnam War (particularly in the brutal urban Battle of Hue).
In the 1970s, Germany also tested VT1-1 and 1-2 turret-less tank destroyers, armed with twin 105- or 120-millimeter guns in the hull. These were designed to discharge while vehicles drove in zig-zags towards enemy forces. But tests found Leopard 2 tanks at least as effective.
Turrets upon turrets and automated autocannons?
The current renaissance of multi-cannon tanks (though, all strictly prototypes for now) relates to the evolution of the turret-top heavy machine gun. This usually .50cal/12.7- millimeter weapon supplements the tank’s coaxial machine gun against soft targets and lightly armored vehicles, but is primarily intended for air defense—particularly with the development of anti-tank helicopters in the 1960s-1970s.
However, manually operating turret heavy machine guns required the tank commander to ‘unbutton’ his hatch and expose himself to enemy fire—an often fatal risk, especially in close-range urban battles.
A solution lay in the adoption of remote controlled/operated weapons (going by the acronyms RCWS, ROWS, or RWS), which were aimed using high-quality optical video feeds. Though Germany first deployed remote-control machine guns on its World War II Sturmgeschutz III and IV assault guns, RCWSs didn’t enter wider usage until the 2000s, when tanks were increasingly being used for counter-insurgency in urban areas.
Notably, Kongsberg’s M153 CROWS II system became standard equipment for many Abrams tanks, including the M1A2 SEP(V)2, SEP(V)3, and TUSK variants. This gyro-stabilized gun mount can carry 5.56-, 7.62-, and 12.7-millimeter machine guns or 40-millimeter automatic grenade launchers, can depress 20 degrees and elevate up to 60 degrees, and is aimed via camera.
However, initial attempts to produce main battle tanks with turret-top autocannons were unsuccessful. For example, the planned U.S.-German MBT70 tank was intended to sport a remote-controlled Rh-202 20-millimeter autocannon with 660 rounds in a retractable ‘capsule’ atop the left turret.
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Other unsuccessful attempts followed. Another example is the sole 1990s-vintage Slovakian T-72M2 with a 2A42 30-millimeter cannon.
And in 2011, Turkish company StandartBio teamed with L3Harris to unsuccesfully propose an “Affordable Main Battle Tank” (a.k.a. M60AMBT or L3 Destroyer). This refurbished aging M60 Patton tanks with a bigger 120-millimeter M256 cannon and a 25-millimeter LW25 chain gun with 300 rounds, new turret cage armor, and a 66% more powerful 1,200-horsepower engine.
But now, tanks, sensors, and computers have evolved to improve the automation of both detecting, identifying, and tracking targets, and the ability to slew the main gun to shoot at them. Furthermore, tank commanders received independently rotatable sights called the Commander’s Independent Thermal Viewer (CITV) that double a tank’s spotting capability and allow rapid handover of multiple targets to the gunner via a ‘hunter-killer’ engagement mode.
The maturation of automated hunter-killer engagement and remote-control weapons with 360-degrees traverse enabled the upsizing of the top-turret weapon to an autocannon with greater range and hitting power—and with the potential to autonomously engage air or ground targets tagged by the tank commander independently of the main gun.
Smaller autocannons can’t penetrate a main battle tank’s frontal armor, but multiple hits may disable exposed sights—blinding and possibly panicking the crew.
More intriguingly, a turret autocannon could merge sensors alongside the radars and optical sensors of automated hard-kill Active Protection Systems (APSs) designed to detect incoming missiles, shells, or drones and automatically shoot them down. Perhaps APSs could even harness autocannons to dispatch some drone, rocket, and missile intercepts at longer range before they enter the shorter reach of the APS’s hard-kill counter-munitions.
Presently, German firm KNDS has proposed three tanks with turret-top autocannons—the Leopard 2 A-RC3.0, the Leclerc Evolution, and the ADT-140—while General Dynamics has proposed the comparable AbramsX. Time will tell if the services seize upon these new concepts.
Skeptics may argue that main battle tanks are already too difficult to deploy due to excessive weight, cost, and complexity—and adding autocannons worsens all three factors. Proponents, on the other hand, will insist that new unmanned turrets and smaller crews will create weight savings allocatable to secondary cannons and additional sensors.
Critics also worry that remote-control turret weapons and the optical sensors they depend upon may prove too easily damaged by non-anti-tank weapons like heavy machine guns, small-caliber autocannons, and snipers with anti-material rifles.
But for now, improved sensors, better automation, and a pressing need for counter-drone defenses are bringing multi-cannon tank designs back to the forefront of cutting-edge design—as was the case a century ago.
Sébastien Roblin has written on the technical, historical, and political aspects of international security and conflict for publications including 19FortyFive, The National Interest, MSNBC, Forbes.com, Inside Unmanned Systems and War is Boring. He holds a Master’s degree from Georgetown University and served with the Peace Corps in China. You can follow his articles on Twitter.
