 The Army introduced the U.S. M3 and M3A1 submachine guns in 1943 with plans to produce the latter in numbers sufficient to cancel future orders for the Thompson, while gradually withdrawing it from the first-line service.However, due to unforeseen production delays and requests for modifications, the M3/M3A1 never replaced the Thompson, and purchases continued until February 1944.Though the M3 was considerably cheaper to produce, at the end of World War II, the Thompson, with a total wartime production of over 1.5 million, outnumbered the M3/M3A1 submachine guns in service by nearly three to one.