In early 1918, in time for the great German Spring offensive of that year, the only widely used sub-machine gun deployed during the First World War - and the model for subsequent developments - was launched, the Bergmann Maschinenpistole 18/1 (MP18).  The MP18 used common but powerful 9mm ammunition rounds and was loaded via a 32-round magazine

This formidable weapon - in effect a machine pistol - was a genuinely effective forward infantry assault gun.  Its rate of fire was similar to heavy machine guns.

In the event - with Germany losing the war in the second half of 1918 - by the time the MP18 saw widespread service it was chiefly used as a defensive weapon.

The terms of the Treaty of Versailles specifically banned German possession of the MP18.  In post-war years the MP18 was used in the police service.