The Thompson submachine gun, commonly known as the Tommy gun, was an automatic projectile weapon developed in the United States of America in the 1920s. It became particularly recognizable as a symbol of organized crime in the first half of the 20th century, and especially of the Chicago gangsters of the 1920s.
The natives of Sigma Iotia II, a world that modeled itself after the book Chicago Mobs of the Twenties, left behind by the crew of the starship Horizon, almost universally carried Tommy guns, including the women. (TOS: "A Piece of the Action")
Tommy guns were also used in several of the Dixon Hill novels favored by Captain Jean-Luc Picard, which were set late in the gangster era. (TNG: "Manhunt") In the year 2063, Captain Picard lured two Borg drones into a holodeck on the USS Enterprise-E, disabled the safety protocols, and used a Thompson submachine gun on the drones, killing them with the bullets. (Star Trek: First Contact)