Volley gun
The Ribauldequin was a medieval version of the volley gun. It had its barrels set up in parallel. This early version was first employed during the Hundred Years' War by the army of Edward III of England, in 1339. Later on, the late Swiss army employed it.
Timeline of United States inventions (before 1890)
The machine gun is defined as a "fully automatic" firearm, usually designed to fire rifle cartridges in quick succession from an ammunition belt or large-capacity magazine. The world's first true machine gun, the Maxim gun, was invented in 1884 by the American inventor Hiram Stevens Maxim, who devised a recoil power of the previously fired bullet to reload rather than the crude method of a manually operated, hand-cranked firearm. With the ability to fire 750 rounds per minute, Maxim's other great innovation was the use of water cooling to reduce overheating. Maxim's gun was widely adopted and derivative designs were used on all sides during World War I.