Rolls Royce Merlin III, c 1940.
© Science Museum / Science & Society Picture Library
The Rolls Royce Merlin was the most important aero engine of World War II. Designed in 1932, the Merlin powered the Spitfire and the Hurricane fighters during the Battle of Britain in 1940 as well as other well-known aircraft such as the Lancaster and Mosquito. When the Merlin first entered service it produced 750 horse power, which was more than doubled over the period of the war, mainly through ever improving supercharged design, reaching well over 2000 horse power.