3 cm MK 303 (Br)
3cm MK 303 Flakzwilling, two 3 cm MK 303 in the twin mount
Type	Anti-aircraft cannon
Place of origin	Nazi Germany
Service history
In service	unknown
Used by	Nazi Germany
Wars	World War II
Production history
Manufacturer	Krieghoff[1]
Produced	1944–1945
No. built	222 (32 in 1944 and 190 in 1945)[1]
Variants	3 cm Flakzwilling MK 303 (Br)
Specifications
Mass	185 kg (408 lbs)[2]
Length	3.145 m (10 ft 3.8 in)
Barrel length	2.2 m (7 ft 3 in) L/73
Shell	30×210mm
Caliber	30 mm (1.18 in)
Elevation	-10°to ±85°
Traverse	360°
Rate of fire	400 rpm (cyclic)
Muzzle velocity	1100 m/s (3,609 ft/s) M-Schos 900 m/s (2,953 ft/s) HE 950 m/s (3,117 ft/s) AP/HE[2]
Feed system	15 cartridge clip

The 3 cm MK 303 Flak and twin-mounted 3 cm MK 303 Flakzwilling (M44) were experimental 30 mm anti-aircraft guns developed in Nazi Germany. They fired the powerful 30x210mm round and only 222 were produced.^[1] The gun was to be installed on Type XXI submarines as AA defense^[3] and its use as AA defense replacing 2 cm Flak and 3.7 cm Flak weapons was also considered. The use of 3 cm M.K. 303 Flakzwilling on Flakpanzer IV "Kugelblitz" was considered, but rejected. The development began in late 1941^[1] and production started in late 1944.

In the 50s, the MK 303 was produced in Czechoslovakia under the designation M53, with the clip feed replaced by a 10-round box magazine.^[1] It was also used as armament of SPAAG M53/59 Praga.