The MP 38 and MP 40 (MP designates Maschinenpistole.), often wrongly called Schmeisser were submachine guns developed in Nazi Germany and used extensively by Fallschirmjäger, tank crews, platoon and squad leaders, and other troops during World War II.
Despite the impression given by popular culture, particularly in war films and video games, MP 40s were generally issued only to paratroopers and platoon and squad leaders; the majority of German soldiers carried Karabiner 98k rifles. However, later experience with Soviet tactics - such as the Battle of Stalingrad where entire units armed with submachine guns outgunned their German counterparts in short range urban combat - caused a shift in tactics, and by the end of the war the MP 40 and its derivatives were being issued to entire assault platoons on a limited basis.
Although the MP 40 was generally reliable, a major weakness was its 32-round magazine. Unlike the double-column, dual-feed magazine insert found on the Thompson M1921-28 variants, the MP 38 and MP 40 used a double-column, single-feed insert. The single-feed insert resulted in increased friction against the remaining cartridges moving upwards towards the feed lips, occasionally resulting in feed failures; this problem was exacerbated by the presence of dirt or other debris. Another problem was that the magazine was also sometimes misused as a handhold. This could cause the weapon to malfunction when hand pressure on the magazine body caused the magazine lips to move out of the line of feed, since the magazine well did not keep the magazine firmly locked. German soldiers were trained to grasp either the handhold on the underside of the weapon or the magazine housing with the supporting hand to avoid feed malfunctions.