Designed in 1938 by Heinrich Vollmer with inspiration from its predecessor the MP 38, it was heavily used by infantrymen (particularly platoon and squad leaders), and by paratroopers, on the Eastern and Western Fronts as well as armoured fighting vehicle crews.

[7][8] Its advanced and modern features made it a favorite among soldiers and popular in countries from various parts of the world after the war.

[12] 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.

[12] 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.

[14] 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.

[18] German soldiers were trained to grasp either the handguard on the underside of the weapon or the magazine housing with the supporting hand to avoid feed malfunctions.

[18] At the outbreak of World War II, the majority of German soldiers carried either Karabiner 98k rifles or MP 40s, both of which were regarded as the standard weapons of choice for an infantryman.

[19] However, later confrontations with Soviet troops such as the Battle of Stalingrad, where entire enemy units were armed with PPSh-41 submachine guns, the Germans found themselves out-gunned in short range urban combat which caused a shift in their tactics, and by the end of the war the MP 40 and its derivatives were sometimes issued to entire assault platoons.

[21] During and after the end of World War II, many MP 40s were captured or surrendered (upwards of 200,000) to the Allies and were then redistributed to the paramilitary and irregular forces of some developing countries.

[24] Later in 1941, rival company Erma Werke sued Haenel, at which Schmeisser was Chief Designer, for patent infringement.

This practice required proper registration of automatic weapons in accordance with the National Firearms Act before they could be imported, but this was curtailed later in the occupation, meaning a relatively small number of civilian-transferable original German MP 40s remain in circulation and are valued at around $20,000-37,500 as of 2021, with some selling for almost $50,000.

[61] As such, they are commonly used for recreational range shooting and WW2 historical reenactments, because the associated wear and tear (within reasonable limits) will not significantly diminish their value, as it would on original collectible examples.