The Gatling gun is one of the best known early rapid-fire weapons and a forerunner of the modern machine gun. It is well 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 also famously 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.
Although the first Gatling gun was capable of firing continuously, it required a person to crank it; therefore it was not a true automatic weapon.
The Maxim gun, invented in 1884, was the first true fully automatic weapon, making use of the fired projectile's recoil force to reload the weapon. Nonetheless, the Gatling gun represented a huge leap in firearm technology. Prior to the Gatling gun, the only rapid-fire firearms available to militaries were mass-firing volley weapons as the French Reffyemitrailleuse in 1870–71 or grapeshot as fired from field cannons, similarly to a very large shotgun. The latter were widely used during and since the Napoleonic Wars.
Although the rate of fire was increased by firing multiple projectiles simultaneously, these weapons still needed to be reloaded after each discharge, which for multi-barrel systems like the mitrailleuse was cumbersome and time-consuming. This negated their high rate of fire per discharge thus making them impractical for use on the battlefield. In comparison, the Gatling gun offered a rapid and continuous rate of fire without having to manually reload by opening it.
Richjard 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.