The Rolls Royce Merlin is the world's most recognizable aero engine. It powered the Battle of Britain aircraft, the Spitfire, and Hurricane. It is the engine that powered the Lancaster and Halifax of Bomber Command. The Merlin was the power plant of the Mustang escort fighter. The Mosquito, was also powered by the Merlin. The Merlin worked day and night to secure the eventual Allied victory. This book tells the human story of the development of the engine and its operational use during the war featuring the voices of air crew who relied on the Merlin.