The Maxim gun is a recoil-operated machine gun invented in 1884 by Hiram Stevens Maxim. It was the first fully automatic machine gun in the world.
Illustration of the Maxim Gun in Brockhaus and Efron Encyclopedic Dictionary
1895 .303 caliber tripod-mounted air-cooled variant
A large-bore Maxim on the USS Vixen c. 1898
Austro-Hungarian soldiers with a trophy Maxim machine gun in the High Alps, c. 1916
Recoil operation is an operating mechanism used to implement locked-breech autoloading firearms. Recoil operated firearms use the energy of recoil to cycle the action, as opposed to gas operation or blowback operation using the pressure of the propellant gas.
The barrel from a Para Ordnance P12.45, an M1911-derived design which uses short recoil operation. Under recoil, the barrel moves back in the frame, rotating the link (shown in the unlocked position), which causes the rear of the barrel to tip down and disengage from the slide.