The Thompson submachine gun is a .45 caliber American submachine gun, invented by John T. Thompson in 1919, that became infamous during the Prohibition era. It was a common sight of the time, being used by both law enforcement officers and criminals (being marketed to the former as "Thompson's anti-bandit gun"). The Thompson was also known informally as the "Tommy Gun," the "Trench Broom," the "Trench Sweeper," the "Chicago Piano," the "Chicago Typewriter," and the "Chopper." The Thompson was eventually picked up by the US Army during the World War II, and remained in service until the Vietnam War.
Though soldiers loved the heavy weapon for its reliability and rate of fire, the Thompson was hated by the logistical corps due to the high cost and long time it took to make, and over time many of the distinctive features of the gangster-era weapon (muzzle brake, finned barrel, pistol foregrip, drum magazines, etc) were stripped away in an effort to reduce cost and speed up production.
Both the War and Navy Departments would embark on separate, equally disastrous projects to replace the Thompson. The Army based its project, the m3_submachine_gun, on the stamped-metal process seen in the German mp40, but initial tolerances were too loose and resulted in a host of failures up to and including the weapon disassembling itself while firing. The Navy's project, the m50_reising, performed better on the display grounds, but on combat deployment proved highly susceptible to jamming. The Army would stick with the Grease Gun and turn it into a functional if unspectacular weapon, while the Navy abandoned submachine guns altogether and issued the m1_carbine in their place.
The weapon is most commonly depicted using drum magazines as was the norm during the 20s; the World War II model, however, used regular box magazines.