The MP 40 (Maschinenpistole 40, "machine pistol 40") is a German-made submachine gun chambered in 9×19mm Parabellum. It is famous for its use by the Wehrmacht during World War II.
The MP 40 descended from its predecessor the MP 38, which was in turn based on the MP 36, a prototype made of machined steel. Each was a progressive simplification of the last, with design changes such as the more extensive use of stamped steel rather than machined parts to make manufacturing both easier and faster. The MP 40 was often called the "Schmeisser" by the Allies, after the weapon designer Hugo Schmeisser. Schmeisser had designed the MP 18, which was the first mass-produced submachine gun in the world and carried some slight resemblance to the MP 40, although he did not have anything to do with the design or development of the MP 40.
Popular culture has fuelled the image that the vast majority of Wehrmacht soldiers during World War II were armed with MP 40s, when in fact the weapon was only issued to select individuals and was actually far less common than the bolt-action Kar 98k rifle, which was standard issue. However, towards the end of the war whole platoons were being issued with MP 40s on a limited basis in response to lessons learned by the German army on the Eastern Front, where the Russians would equip entire units with PPSh-41 and PPS-43 submachine guns, and as a consequence German troops would find themselves totally outgunned at close range.
- The MP 40 was one of three World War II weapons used in the construction of the (mostly fictional) firearms seen in Aliens. The others were the MG 42 (another German weapon) and the Thompson submachine gun (used by the Allies). The use of mostly WWII-era weapons on the production was probably for practical reasons — large numbers of such weapons are in existence (Aliens armorers Bapty & Co. has a huge selection of working WWII firearms), ammunition is generally cheap and plentiful, and their typically solid-steel construction means they can be easily fitted with cosmetic modifications.