The M197 Gatling Gun is a 20mm revolving cannon produced by General Dynamics Armament. Basically, it is a modification of the 6-barreled, M61 Vulcan rotating gun, which had been designed to be mounted on fixed-wing aircraft. The M61 Vulcan was simplified into a lighter, three-barreled variant, which was designated M197, to be fitted onto helicopters. It entered service with the US Marine Corps in 1967, being first used in combat in Vietnam, mounted on a UH-1 Huey gunship, in search and destroy missions. It would also be used on the AH-1 Cobra attack helicopter.
The M197 Gatling Gun consists of three, electrically-powered, rotating barrels, with each one of them being rifled with 9 grooves. It has a rate of fire of 730 round per minute, using 20x102mm armor-piercing ammunition.