The Rolls-Royce Experimental Machine Gun was a prototype British heavy machine gun, designed by Rolls-Royce during World War II. Rolls-Royce commenced design of a heavy machine gun in early 1940, intended for use in aircraft. The result was a recoil operated weapon firing .50 Browning cartridges. This was evaluated in March 1941 and proved prone to stoppages. A revised gas-operated weapon was designed and built to try and solve these problems.