MP 40

The MP 40 (Maschinenpistole 40) is a submachine gun chambered for the 9×19mm Parabellum cartridge. Developed in Nazi Germany, it saw extensive service in the Axis forces during World War II.

Designed in 1938 by Heinrich Vollmer with inspiration from its predecessor the MP 38, it was heavily used by infantrymen (particularly by platoon- and squad-leaders), and by paratroopers, on the Eastern and Western Fronts as well as by the crews of armoured fighting vehicles. Its advanced and modern features made it a favorite among soldiers and popular in countries from various parts of the world after the war.

The Allies often referred to the MP 40 as the "Schmeisser", after the firearms-designer Hugo Schmeisser (1884-1953). In 1917 Schmeisser had designed the MP 18, which was the first mass-produced submachine gun. He did not, however, have anything to do with the design or development of the MP 40, although he held a patent on the magazine.

The MP 40's variants included the MP 40/I and the MP 41. Erma Werke produced an estimated 1.1 million MP 40s between 1940 and 1945.^{[citation needed]}

The Maschinenpistole 40 ("Machine pistol 40") descended from its predecessor the MP 38, which was in turn based on the MP 36, a prototype made of machined steel. The MP 36 was developed independently by Erma Werke's Berthold Geipel with funding from the German Army. It took design elements from Heinrich Vollmer's VPM 1930 and EMP. Vollmer then worked on Berthold Geipel's MP 36 and in 1938 submitted a prototype to answer a request from the Heereswaffenamt (Army Weapons Office) for a new submachine gun, which was adopted as MP 38. The MP 38 incorporated the simpler bolt design of Hugo Schmeisser's M.K.36,III as well as Schmeisser's magazine, but otherwise more closely followed Geipel's MP 36 design. The MP 38 was a simplification of the MP 36, and the MP 40 was a further simplification of the MP 38, with certain cost-saving alterations, most notably in the more extensive use of stamped steel rather than machined parts.

The MP 40 submachine guns are open-bolt, blowback-operated automatic arms. The only mode of fire is automatic, but the relatively low rate of fire permits single shots with controlled trigger pulls. The bolt features a telescoping return spring guide which serves as a pneumatic recoil buffer. The cocking handle was permanently attached to the bolt on early MP 38s, but on late-production MP 38s and MP 40s, the bolt handle was made as a separate part. It also serves as a safety by pushing the head of the handle into one of two separate notches above the main opening; this action locks the bolt in either the cocked (rear) or uncocked (forward) position. The absence of this feature on early MP 38s resulted in field expedients such as leather harnesses with a small loop that were used to hold the bolt in the forward position.

The MP 38 receiver was made of machined steel, but this was a time-consuming and expensive process. To save time and materials, and thus increase production, construction of the MP 40 receiver was simplified by using stamped steel and electro-spot welding as much as possible. The MP 38 also features longitudinal grooving on the receiver and bolt, as well as a circular opening on the magazine housing. These features were eliminated on the MP 40.

One feature found on most MP 38 and MP 40 submachine guns is an aluminum, steel, or Margolit (a variation of Bakelite) resting bar under the barrel. This was used to steady the weapon when firing over the side of open-top armored personnel carriers such as the Sd.Kfz. 251 half-track. A handguard, also made of Margolit, is located between the magazine housing and the Margolit pistol grip. The barrel lacked any form of insulation, which often resulted in burns on the supporting hand if it was incorrectly positioned. The MP 40 also has a forward-folding metal stock, the first for a submachine gun, resulting in a shorter overall weapon when folded. However, this stock design was at times insufficiently durable for hard combat use.