(covers information from several alternate timelines)
The M1921/28 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. The Thompson fired the .45 ACP cartridge and its rate of fire depended on the specific model.
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 the weapons, including the women. (TOS: "A Piece of the Action")
Thompson submachine 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 Tommy gun on the drones, killing them with the bullets. (Star Trek: First Contact)