A rotary cannon, rotary autocannon, or Gatling-type cannon is a rapid-firing weapon that utilizes multiple barrels in a rotating cluster to provide a sustained rate of fire greater than single-barreled machine guns or automatic cannon of equivalent caliber. The loading, firing, and unloading functions are performed simultaneously in different barrels as they rotate, and the rotation also permits the barrels some time to cool. The rotating barrel cluster on most Gatling-type guns is powered by an external force such as an electric motor, although gas-operated versions have also been developed.