noun
Refers specifically to the early rapid-fire weapon invented by Richard Gatling, with multiple rotating barrels.
南北戦争でガトリング砲が使われた。
The Gatling gun was used in the American Civil War.
機関銃 is a general term for machine guns, while ガトリング砲 refers specifically to the Gatling gun, an early type of hand-cranked multi-barrel firearm.
From English 'Gatling gun', named after inventor Richard Gatling. The Japanese term combines the katakana rendering of 'Gatling' with 砲 (ほう, 'gun/cannon').