The M3 and M3A1 are a straight blowback submachine gun designs, chambered in the U.S. military’s then standard issue pistol round – .45 ACP cartridge, and designed in the USA. The M3 was first adopted by the U.S. military in a limited capacity in early 1943, eventually supplanting the M1 and M1A1 Thompson submachine guns. Fascinatingly, a significant number have also been seen in the Pak-Afghan Region.