The Rolls-Royce Merlin powered the North American P-51 Mustang in its famous Merlin-powered form.
The P-51 originally used the Allison V-1710 engine, but later Mustang variants adopted the Packard-built version of the Rolls-Royce Merlin. The change gave the fighter much stronger performance at high altitude, where the original engine was less effective.
This combination helped turn the Mustang into a long-range escort fighter during the Second World War. Its range allowed it to accompany bomber formations deep into enemy territory, while its speed and altitude performance made it an effective fighter.
The Merlin also powered aircraft such as the Supermarine Spitfire, Hawker Hurricane and Avro Lancaster. Packard manufactured the engine under licence in the United States, so references may describe the Mustang’s engine as either a Merlin or a Packard Merlin.