M1917 Browning machine gun
The M1917 Browning machine gun is a heavy machine gun used by the United States armed forces in World War I, World War II, the Korean War, and the Vietnam War; it has also been used by other nations. It was a crew-served, belt-fed, water-cooled machine gun that served alongside the much lighter air-cooled Browning M1919.
Source: Wikipedia — M1917 Browning machine gun (CC BY-SA 4.0)