The Johnston machine gun was a machine gun of united states origin. It was an unusual tripod mounted weapon that used rotating barrels to enable rapid firing without fouling and overheating during a firefight. The weapon was intended as a mounted on heavy artillery/vehicles and was patented under 1328230 in 1920.
The Johnston machine gun internally was a simpler design than the Gatling gun as it had no chambers but 3 chain driven feeding rollers with grooves to chamber the round when firing from ratchet actuated firing pins when the feeding rollers aligned. External power source was from either a hand crank or electric motor and could be fired at virtually any rate of fire. Its compensator came with an internal propellor to extract the heat from the barrels. The Johnston machine gun was fed from a belt and fired from 2 barrels as well as 1 depending if both sides of the weapon was loaded from.