The Thompson submachine gun was developed by Brig. Gen. John T. Thompson for use in the trenches during World War I, but the first models were not ready by war's end. It fired .45 ACP cartridges at about 850 rounds per minute. The model 1921AC, which came out in 1926, featured a Cutts Compensator, a muzzle brake, which helped prevent the muzzle from rising during automatic fire.