Colt Mk 12 cannon

The Colt Mk 12 is a 20 mm autocannon that was widely used by the United States Navy after World War II. Wikipedia

Caliber: 20 mm (0.787 in)

Cartridge: 20×110mm USN

In service: 1950s – present

Muzzle velocity: 1,010 m/s (3,300 ft/s)

Rate of fire: 1,000 rpm