Rolls-Royce Merlin

The Rolls-Royce Merlin is a British liquid-cooled V-12 piston aero engine of 27-litre (1,650 cu in) capacity. Developed as a private venture by Rolls-Royce and first run in 1933, the engine became one of the most successful aircraft engines of World War II, most closely associated with the Hawker Hurricane and Supermarine Spitfire, although the majority of the production run was for the four-engined Avro Lancaster heavy bomber.

Initially known as the PV-12, it was dubbed Merlin after the company convention of naming its four-stroke piston aero engines for birds of prey. The engine benefitted from the racing experiences of precursor engines in the 1930s. After several modifications, the first production variants of the PV-12 were completed in 1936. The first operational aircraft to enter service using the Merlin were the Fairey Battle, Hurricane, and Spitfire. Experience in use led to a series of rapidly applied developments that markedly improved the engine's performance and durability. Starting at 1,000 horsepower (750 kW) for the first production models, most late-war versions produced just under 1,800 horsepower (1,300 kW). The final version, used in the de Havilland Hornet, had over 2,000 horsepower (1,500 kW).

Some 50 versions of the Merlin were built by Rolls-Royce in Derby, Crewe, and Glasgow, as well as by Ford of Britain at their Trafford Park factory near Manchester. The Packard V-1650 was a version of the Merlin built in the United States. A de-rated version was the basis of the Rolls-Royce/Rover Meteor tank engine. After the war, the Merlin was largely superseded by the Rolls-Royce Griffon for military use, although new variants were designed and built for airliners and military transport aircraft. Production ceased in 1950 after a total of almost 150,000 engines had been delivered.

Merlin engines remain in Royal Air Force service today with the Battle of Britain Memorial Flight, and power many restored aircraft in private ownership worldwide.