The Rolls-Royce Merlin is one of the most celebrated piston aero engines of all time. The 12-cylinder, 27-litre engine powered the defending British Hurricane and Spitfire fighters during the Battle of Britain in 1940. This battle was one of the pivotal military contests in human history and the power and reliability of the Merlin was an important factor in the success of the British defence against the Luftwaffe. As a result, German invasion plans were shelved and Britain survived to become a springboard for the Anglo-American 'Second Front' - the invasion of France and Germany after the D-Day landings in June 1944.

The Merlin was the culmination of a long line of piston aero engine development at Derby, dating back to the Rolls-Royce Eagle of the First World War. All these engines embodied the rigour, perfectionism and the outstanding attention to detail which characterised Henry Royce, the founder of the company. Rolls-Royce performed astonishing feats of development engineering on the Merlin, taking it from 1000 hp in 1939 to over 2000 hp by the end of the war in 1945.

This shows a Merlin III from the Museum's 1940 Mk 1a Spitfire and is a replacement unit fitted in 1943.

Inv. 1954-659 Pt 10