High Quality Content by WIKIPEDIA articles! A submachine gun (SMG) is an automatic carbine, designed to fire pistol cartridges. It combines the automatic fire of a machine gun with the cartridge of a pistol. The submachine gun was invented during World War I (1914–1918), but the apex of its use was during World War II (1939–1945) when millions of the weapon type were manufactured. Today the submachine gun has mostly been replaced by the assault rifle for military use. (The assault rifle uses an intermediate-power cartridge with more power than a pistol but less than a standard rifle or battle rifle.)