German MP40 "Maschinenpistole .40" submachine gun, .40 caliber.
General History
The Maschinenpistole 40, commonly known as the MP40, is similar to the Thompson, but uses a smaller 9-mm round. This submachine gun evolved out of the MP38, which was prone to misfirings that had sometimes lethal results. A simple technical innovation to the hammer eliminated the problem, and the MP40 was born. Total production is unknown but it is believed that more that one million of these weapons were produced between 1940 and 1944.