2 cm Flak 30, Flak 38 and Flakvierling 38

The Flak 30 (Flugzeugabwehrkanone 30) and improved Flak 38 were 20 mm anti-aircraft guns used by various German forces throughout World War II. It was not only the primary German light anti-aircraft gun but by far the most numerously produced German artillery piece throughout the war. It was produced in a variety of models, notably the Flakvierling 38 which combined four Flak 38 autocannons onto a single carriage.

Source: Wikipedia — 2 cm Flak 30, Flak 38 and Flakvierling 38 (CC BY-SA 4.0)