The Gatling gun is one of the best known early rapid-fire weapons and a forerunner of the modern machine gun. 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.

The Gatling gun was designed by the American inventor Dr. Richard J. Gatling in 1861 and patented in 1862. Gatling wrote that he created it to reduce the size of armies and so reduce the number of deaths by combat and disease, and to show how futile war is.