A modification of the Flak (Flugabwehrkanone) 30 anti-aircraft cannon, the 20mm Flak 38 featured a higher rate of fire that was needed to take into account the increasing speed of aircraft. Although the Flak 30 had been produced by Rheinmetall-Borsig, the Flak 38 was manufactured by Mauser.
The Flak 38 entered service in late 1940 and was the most common light anti-aircraft cannon used by the German army, navy and air force. The Sonderanhanger 51 trailer was used to tow the Flak 38. In order to increase firepower, a four-barrelled version, the Flakvierling 38, was also created.