Short answers, pulled from the story.
Richard Jordan Gatling of North Carolina invented the rapid-firing multiple-barrel firearm in 1861. He patented his revolving battery gun on the 4th of November 1862 under U.S. Patent No. 36,386.
The original design used multiple rotating barrels turned by a hand crank with fibrous matting stuffed among them that could be soaked with water to cool them down. Later models eliminated this matting jacketing as being unnecessary.
On the 17th of July 1863 Gatling guns were purportedly used to overawe New York anti-draft rioters. Twelve of the guns were purchased personally by Union commanders and used in the trenches during the Siege of Petersburg Virginia from June 1864 to April 1865.
The Russians tested two Gatlings in 1865 and organized 400 Gatlings into eight batteries by 1876 for use in the Russo-Turkish War from 1877 to 1878. The British Army first deployed the Gatling gun in 1873-74 during the Anglo-Ashanti wars and extensively used it during the last actions of the 1879 Anglo-Zulu war.
By 1911 all models of Gatling guns were declared obsolete by the U.S. military after 45 years of service due to their weight and cumbersome artillery carriage hindering movement over difficult ground. The Maxim gun invented and patented in 1883 became the first true fully-automatic weapon making use of the fired projectile's recoil force to reload the weapon.