America's submachinegun by excellence during WW2 was the Thompson M1A1 chambered in .45 ACP, seeing combat in every region of Earth. Its defining characteristics were a 30-round magazine (instead of the earlier 20-round ones, or the 50-round drum magazines) and the reduction of unnecessary parts. Due to its increased simplicity, the M1A1 could be produced at a fraction of an original M1921's cost, though it remained significantly more expensive than its foreign contemporaries.
