Tommy Gun

The Thompson submachine gun was invented in 1919 by John T. Thompson and became infamous throughout the Prohibition era, used both by criminals and law enforcement. 
 
The gun was a favorite among soldiers, gangsters, and police for being ergonomic and compact, as well as having a .45 ACP cartridge and high rate of automatic fire.  Today, collectors value the weapon for its historical significance.
 
Early on, the Thompson M1921 had low sales due to its high price (A Thompson with one 20-round stick magazine cost $200, half the price of a Ford automobile at the time).  The gun was stocked by police departments throughout the US and minor use in armies and constabulary forces in Central and South America.  The Thompson was used by Marines in the Banana Wars and in China, with the weapon's firepower allowing for four-man teams to have as much strength as a nine-man rifle squad.  Despite this, the gun was put down for its inaccuracy and over 50 yards and lack of penetrating power despite the round being used.
 
Agents of the Irish Republican Army bought 653 Thompsons, though 495 were seized by US customs.  The remainder were used in the Irish War of Independence and the Irish Civil War.  The guns were not very effective in Ireland, with only 32% of attacks resulting in casualties.
 
The gun became a symbol of the prohibition and depression era, with the weapon used by gangsters, motorized bandits and the lawmen who chased them.  It was featured prominently in gangster films of the time, and came to be called "the gun that made the 20s roar."
 
1926 saw a recoil brake added as an option to the gun, designated as No. 21AC at the original $200 price, with the original version of the gun re-christened as No. 21A, at a price of $175.
 
 In 1938, the Thompson submachine gun was adopted as the main submachine gun of the US military.
 
There were two types of Thompsons used by the military:
 
The M1928A1 had support for box magazines and drums, as well as the recoil break, cooling fins on the barrel and the charging handle on top of the receiver.  Soldiers didn't like the drum magazine as it had a tendency to rattle and jam.  Due to the limited capacity of the original 20-round magazine, leading to the development of a 30-round magazine which is the magazine seen in most video games.
 
The M1 and M1A1 didn't have support for the drum and lacked the cooling fins, had a simplified rear sight and had its charging handle on the side of the receiver.
 
The gun would be used in the Korean War, and while the military would eventually move on to the M16, Thompsons were issued the South Vietnamese army units and militia during the Vietnam War.  In addition, the Vietcong employed both captured Thompsons and copies made in small jungle workshops.
 
In 1978, the gun was finally declared obsolete, with all Thompsons in US government possession were destroyed, save for a few museum pieces and training models.
 
The Thompson usually appears in WWII and mafia-themed games, with 30-round box magazines in the former and drum magazines in the latter, although the drum magazine can be unlocked in Call of Duty: World at War's multi-player by completing the Thompson Marksman III challenge.