The Thompson submachine gun, or "Tommy Gun", was the iconic weapon of the Prohibition Era. It was invented by General John T. Thomspson in 1919 as a replacement for the bolt action service rifles then in use. His idea was that it would be used as a "Trench Broom" to "sweep" out enemy trenches; but the war ended before his rifle could be put into production.
Although the United States Marine Corps bought a small quantity of Thompsons, which were used in small bush wars during the 1920s, and others were sold to local police forces, the Tommy Gun received it's chief notoriety in the hands of Prohibition and Depression-Era gangsters. (See also Mafia and Gun Moll.)
Although the iconic Tommy Gun from the 1930s gangster movies featured a distinctive drum-style ammunition magazine, the Thompson also came in models utilizing a stick-type magazine, which many soldiers preferred because the drum had a tendency to rattle and to jam as well as adding considerable weight to an already heavy weapon.
The Thompson was used by Allied forces during World War II for scouts, NCO's and patrol leaders. It was also used frequently by commandos because of it's compactness, it's high rate of fire and stopping power. It's penetration, however, left something to be desired; it was heavy, and not terribly accurate; and eventually the gun was superseded by lighter, more powerful semi-automatic rifles.
But the Thompson turned up in hot spots around the globe throughout the 20th Century. The IRA bought some of the first Thompsons made and used them throughout "The Troubles" in Northern Ireland. Chinese Communist forces used them during the Korean War and so did Viet Cong forces during the Vietnam War. They were also used by the FBI until 1976.