Designed during World War I by General John T. Thompson, the Tommy gun was available in the .45 Caliber ACP (Automatic Colt Pistol) cartridge, and was used by the U.S. Army and British Commandos through World War II. The means of operation is direct blow-back, although early models made use of the Blish lock, turning the mechanism into a delayed blow-back system. After WWII it saw limited service in Korea, and was carried unofficially by a smattering of soldiers in Vietnam.
In the United States, it was used by law enforcement, most prominently by the FBI, until 1976 when it was declared obsolete, and all Thompsons in government possession were destroyed, except for a few token museum pieces and training models. Owing to both its gangster and WWII connections, Thompsons are highly sought after collector's items. An original 1928 gun in working condition can easily fetch $15,000. Semi-auto replicas are currently produced by the Auto-Ordnance Company, which is operated as a division of Kahr firearms.