Gatling gun

The Gatling gun is one of the best known early rapid-fire weapons and a forerunner of the modern machine gun. Invented by Richard Gatling, it is known for its use by the Union forces during the American Civil War in the 1860s, which was the first time it was employed in combat. Later it was used in the assault on San Juan Hill during the Spanish-American War.

The Gatling gun's operation centered on a cyclic multi-barrel design which facilitated cooling and synchronized the firing/reloading sequence. Each barrel fired a single shot when it reached a certain point in the cycle, after which it ejected the spent cartridge, loaded a new round, and in the process, cooled down somewhat. This configuration allowed higher rates of fire to be achieved without the barrel overheating.

Development of modern Gatling-type guns
After the Gatling gun was replaced in service by newer recoil- or gas-operated weapons, the approach of using multiple externally-powered rotating barrels fell into disuse for many decades although some examples were developed during the interwar years but only existed as prototypes, or rarely used. The concept resurfaced after World War II with the development of the M61 Vulcan.