The 3.7 cm Flak 43 was a light anti-aircraft (AA) gun used by Nazi Germany during World War II.

It was provided with single- and twin-gun mounts, the latter being designated as the 3.7 cm Flak 43 Zwilling and was in service from 1944 to 1945.

In addition to versions used by the Kriegsmarine (German Navy), it served as the main armament of the Ostwind and Möbelwagen and was proposed for use in the Flakpanzer Coelian self-propelled AA guns.

Rheinmetall-Borsig redesigned the Flak 36/37 to incorporate the gas-operated breech mechanism of the 3-centimeter (1.18 in) MK 103[1] and to reduce the number of man-hours required to manufacture it from 4320 to 1000.

[3] The first Flak 43s were reported in Luftwaffe service in August 1944, 431 single guns and 41 Zwilling mounts.