Once underground, workers would frequently pause to try to hear the scrape of shovels on earth that could be the enemy. When two tunnels met, vicious fighting would ensue.
Over time, tunnel warfare had its ups and downs. It became almost non-existent during the Napoleonic era, mainly because Napoleon lacked the patience or desire for long sieges. Military sappers were revived during the siege of Sevastopol in 1854–1855. Tunnel warfare advanced considerably following the industrial revolution as new mining technology and more and more powerful explosives became available. Underground warfare was seen in the latter parts of the American Civil War; some historians view the siegeworks of the ACW as practice for WWI.
Tunnel warfare saw a ‘renaissance’ during WWI, as both sides tried to break the deadlock by burrowing under each other’s defensive lines, to blow up enemy trenches, or, as at Arras, to launch attacks from behind
