As the original German Army MP38 submachine gun series proving a success, it was also too expensive for war time production. As such, the MP40 was offered up as a slightly reworked design featuring more in the way of welded steel construction and pressed components. Modifications to the internal components were also made that attempted to decrease the number of jamming incidences being reported with operational use of the original MP38.
With these changes in hand, the MP40 became the definitive submachine gun for the German Army in the latter stages of World War 2. The weapon continued the revolutionary thinking behind the original German submachine gun approach including its folding stock and long magazine that doubled as the forward grip. The relatively compact size of the gun proved ideal for forces on the march, in particular, the German mechanized forces on all fronts. Its use, however, was not restricted as such for the submachine gun could stock the inventories of special operatives and logistical, second-line personnel as well.
Various attempts to produce specialized versions of the MP40 were made though few of these developments actually saw large-scale production. A dual-magazine version (MP40/II) did enter limited manufacture but did not see extensive action. A wooden butt version also existed as the MP41. The MP40, as success dictated, would go on to see service on a global scale after the war, a testament to its sound design and manufacturing. Some may even be encountered in operational service in far off places on the globe. Axis-aligned forces benefitted from the relationship by receiving stocks of MP40 submachine guns during World War 2 and many German victim-nations also took up the type in the post-war years.
Manufacturers of the Maschinenpistole 40 (MP40) submachine gun included Erfurter Maschinenfabrik B. Geipel GmbH, C.G. C.G. Haenel Waffen - und Fahrradfabrik AG and Osterreichische Waffenfabrik-Gesellschaft.
Features specific to the MP38/40 series (long magazine/foregrip, simple production measures and folding metal stock) went on to be utilized in foreign developments during the war, principally the American M3 Grease Gun and the Soviet PPS-43.