High Quality Content by WIKIPEDIA articles! The Rolls-Royce Merlin is a British liquid-cooled, V-12, piston aero engine, of 27-litre (1,650 cu in) capacity. Rolls-Royce Limited designed and built the engine which was initially known as the PV-12: the PV-12 became known as the Merlin following the company convention of naming its piston aero engines after birds of prey.