In 1938, the Thompson submachine gun was adopted by the U.S. military, serving during World War II and beyond.
There were two military types of Thompson SMG.
The M1928A1 had provisions for box and drum magazines. It had a Cutts compensator, cooling fins on the barrel, employed a delayed blowback action and its charging handle was on the top of the receiver. The M1 and M1A1 had a barrel without cooling fins, a simplified rear sight, provisions only for box magazines, employed a straight blowback action and the charging handle was on the side of the receiver. Over 1.5 million military Thompson submachine guns were produced during World War II.