Rolls-Royce’s 1929 Schneider Trophy racing engine was called the R engine.
The R was a supercharged V-12 piston engine developed specifically for high-speed air racing. Rolls-Royce engineers created it by substantially revising the company’s Buzzard engine, increasing power and adapting the design for demanding short-duration competition.
The engine powered the Supermarine S.6 and S.6B racing aircraft. In 1931, an S.6B fitted with an R engine won the Schneider Trophy outright for Britain after achieving the required victories, and it also set a world air-speed record of 407.5 mph.
The R engine influenced later Rolls-Royce piston engines, including the Merlin. It is sometimes confused with the Merlin because both were liquid-cooled Rolls-Royce V-12s, but the R was an earlier racing design rather than a mass-produced wartime aircraft engine.