Maxim is a colorful character who claims to have invented everything from the asthma inhaler to automated fire sprinklers and even the lightbulb, despite Edison’s well documented account. He also experimented with helicopters, airplanes, and amusement park rides.
While on vacation in Vienna he claims another American told him “If you want to make a pile of money, invent something that will enable these Europeans to cut each others’ throats with greater facility.”
He went on to do exactly that, with the first truly portable machine gun.
Before Maxim’s machine gun the hand-cranked Gatling gun rapidly fired bullets. But, due to its size and weight, it was not especially portable.
Maxim’s gun used recoil motion to advance bullets. It was responsible for countless deaths, especially in WW1 trench warfare.