First true automatic weapon

In 1883, Sir Hiram Maxim built and developed his first self-powered, single-barreled machine gun and demonstrated it in 1884 for the first time.   It used the recoil force of the fired round to extract the fired case and place another in the chamber, cocking the action in the process.  By holding the trigger down, the gun fired continuously or until it overheated or jammed. Various designs of the Maxim gun were used in the First World War by Britain, Russia and Germany, and it continued in service in various guises throughout the Second World War too.