During the pre-war and early period of the war, medium anti-aircraft guns (3.7cm and 4cm calibres) were relegated to a relatively minor role in Germany’s air defence. Instead, emphasis was placed on the light 2cm calibre weapons such as the FlaK30, FlaK38 and Flakvierling 38 (quad 2cm).

As the Allies imposed their dominance in the skies the need for medium anti-aircraft weapons became greater. The 2cm weapons hitting power and range were not always up to the task, the 3.7cm weapons offered greater range and hitting power without a dramatic decrease in the rate of fire.

The original 3.7 cm Flugzeugabwehrkanone 18 gun was developed by Rheinmetall in 1935 and was essentially an enlarged version of the 2cm FlaK30.