Rotary cannon

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 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.

The cyclic multi-barrel design synchronizes the firing/reloading sequence. Each barrel fires a single shot when it reaches a certain point in the cycle, after which the spent cartridge is ejected and then a new round loaded. During the cycle, the barrel transfers some heat to the surrounding air.

Due to the size and weight of rotary cannons, they are typically mounted on aircraft or ships.

The Gatling gun was the first gun to use rotating barrels. It was designed by the American inventor Dr. Richard J. Gatling in 1861 and patented in 1862. Hand cranked and hopper fed, it could fire at a rate of 200 rounds per minute. The Gatling gun was a field weapon, first used in warfare during the American Civil War and subsequently by European and Russian armies.

The design was steadily improved; by 1876 the Gatling gun had a theoretical rate of fire of 1,200 rounds per minute, although 400 rounds per minute was more readily achievable in combat. By 1893, the M1893 Gatling gun was capable of a maximum rate of fire of some 800–900 rounds per minute. Ultimately the Gatling's weight and cumbersome artillery carriage hindered its ability to keep up with infantry forces over difficult ground and was superseded by lighter and more mobile machine-guns such as the Maxim gun. All models of Gatling guns were declared obsolete by the U.S. Army in 1911, after 45 years of service.

After the Gatling gun was replaced in service by newer recoil- or gas-operated non-rotating machine guns, the approach of using multiple rotating barrels fell into disuse for many decades. However, some examples were developed during the interwar years but only existed as prototypes, or rarely used. During World War I, Imperial Germany was working on the Fokker-Leimberger, an externally powered 12-barrel Gatling gun in the 7.92×57mm round capable of firing over 7200 rounds per minute.

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