The Merlin, the design of which started in 1933, was a development based on the Rolls Royce history of high performance engines, such as the Kestrel, Buzzard, and R. Most famous for World War II use in Hawker Hurricanes, Supermarine Spitfires, and North American P-51s, the Merlin developed more horsepower for its displacement than any other engine in production during the war. By the end of the war, it was developing 1,641 kW (2,200 shp), up from its initial 768 kW (1,030 shp). Packard and Continental built over 58,000 of these engines in the U.S. under license. Many were shipped to England and others powered later versions of the Curtiss P-40 and most versions of the North American P-51.

This is a Packard-built, Rolls-Royce-designed Merlin engine. It powered the North American P-51B, C, D, and K models, and the armed tactical reconnaissance version known as the F-6B, C, D, and K.