It was during the mid-19th century that a successful machine-gun design was first introduced. The modern machine guns were based on the Model 1862 Gatling gun, with the key characteristics being their relatively high rate of fire and mechanical loading. The Gatling gun, patented by Richard Jordan Gatling in 1861, was the first firearm to offer controlled, sequential firing with mechanical loading. The United States Navy first adopted this machine gun, and were later sold to various armies in the late 19th century. They saw limited action in the American Civil War and subsequent, improved designs of this early machine gun were later used in the Franco-Prussian war and the North West-Rebellion. However, these weapons were powered by hand and were gradually replaced after Hiram Maxim introduced the idea of harnessing recoil energy to power reloading, used in the Maxim machine gun.
The Maxim gun, invented by Sir Hiram Maxi in 1884, was the first practical self-powered machine gun. It used the recoil power of the previously fired bullet to reload rather than being hand-powered, thus allowing for a much higher rate of fire than was possible using earlier designs. To reduce heat, Sir Maxim also introduced the use of water cooling, via a water jacket around the barrel. Maxim’s gun was widely adopted and various designs were used by all sides during the First World War. Combat experience from The Great War, greatly increased the importance of the machine gun. The United States Army issued four machine guns per regiment in 1912, but that allowance increased to 336 machine guns per regiment by 1919.
While there have been varied definitions for the term machine gun, the modern definition used by the Sports Arms and Ammunition Manufactures Institution of America is, a fully automatic firearm that loads, fires and ejects continuously when the trigger is held to the rear until the ammunition is exhausted or pressure on the trigger is released. The current definition then excludes the most of the early manually operated repeating firearms such as the Gatling gun. The development of conventional machine guns has been slowed due to the fact that existing machine gun designs are adequate for most purposes.