The Rolls-Royce Merlin powered the Supermarine Spitfire. This British liquid-cooled V12 piston engine became one of the defining aero engines of the Second World War and is strongly associated with the Spitfire and Hawker Hurricane.
The Merlin first ran on 15 October 1933 and had a 27-litre capacity. Its combination of power, compact design and supercharging allowed fighter aircraft to perform effectively at different altitudes. Merlin variants powered many Spitfire marks, from the early Spitfire I to later versions such as the Merlin 61-equipped Spitfire Mk IX.
A common mix-up is the Rolls-Royce Griffon, which also powered later Spitfires. The Griffon was larger and more powerful, and replaced the Merlin in some late-war and post-war aircraft. The Merlin was not exclusive to fighters: more than 149,000 were built, and the four-engined Avro Lancaster used four of them.