Basic Information
The Gatling gun - named after the inventor Richard Gatling is a repeating firearm usually classified as a type of machine gun - although opinions vary.
Distinguishing features are multiple barrels cycling by rotation, sustained feed (historically by hopper) and a driven (rather than automatic) action. The original Gatling guns were driven by a hand-crank but subsequent models were driven by compressed air, electric or combustion motors or belt drives from an external engine.
The multiple barrels help to resist overheating and reduce wear on any one barrel (thus protecting the rifling) and external drive can help in preventing stoppages resulting from the complexities of an automatic action and can allow precise control of the rate of fire.
Gatling's innovation was mainly in the use of the hopper fed reloading mechanism and although his creation was not a true automatic weapon it was the first weapon to allow cyclic fire.
Weapons were built in a variety of calibres from standard rifle ammunition up to cannon calibres - the Royal Navy used 1.5" (37mm) Gatling Guns for anti-torpedo-boat defence for many years. Early utility was limited by the fact that the guns were deployed on artillery carriges to begin with and, given that they used black powder ammunition, had a tendency to block their own sightlines with smoke if the wind blew in the wrong direction.
The concept was more or less sidelined by the appearance of true automatic weapons (starting with the Maxim MMG) but revived after WW2 as the quest for ever faster rates of fire lead to barrel wear and overheating once more becoming major considerations.
In the modern era the Gatling concept is used in a variety of weapons in more or less the same range of calibres that they have always been - everything from small arms up to light cannon. Despite some experiments they remain non-man-portable anywhere outside the film industry.