The Thompson submachine gun is a firearm invented by US Brigadier General John T. Thompson in 1918. It was a signature weapon of various American organized crime syndicates and remembered often in the media, being used by both police officials & criminals of that era.

The Thompson submachine gun had many different nicknames, including the 'Tommy Gun', 'Chicago Typewriter' and simply, 'The Thompson'. It weighed almost 10 pounds (4.5 kg) empty and fired .45-caliber ammunition. The magazine was a circular drum that held 50 or 100 rounds.

Some of the first 'Tommy Guns' were bought by agents of the Irish Republican Army (IRA). The first test of a 'Thompson' in Ireland was performed by a local brigade commander in the presence of the IRA leader, Michael Collins. Some made their way to the IRA through Liverpool and were used in the Irish War of Independence (1919–21). After a truce with the British, the IRA imported more 'Tommys' and used them in the Irish Civil War in 1923. The Thompson submachine gun saw further use in Korea & Vietnam. But by that time the weapon’s design was considered a relic.

'Tommy Guns' achieved most of their notoriety with Prohibition & Great Depression-era gangsters and movies about their exploits, such as the St Valentine's Day Massacre. They have since gained popularity among collectors for their historical significance, especially in works about the Prohibition era & World War II. 'Tommys' are among the most iconic firearm in history.

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