20-mm M61 Vulcan Gatling gun

The six-barreled 20-mm M61A1 Vulcan Gatling gun has been the standard internal gun armament on most U.S. combat aircraft for more than 30 years (the self-powered GAU-4 is virtually identical).

The externally-powered M61 operates on the Gatling principle. Six 20-mm barrels are mounted on a geared rotor that is driven by a 20-hp electric motor. As the motor turns the rotor, the cam follower on the bolt of each rotating barrel follows a fixed cam path in the gun housing, opening and...