The Merlin is one of the best known and most significant liquid-cooled piston aero engines ever produced. It evolved from the Rolls-Royce PV12 of 1933 which was a development the Rolls-Royce Kestrel. Early versions of the Merlin powered the Hurricane and Spitfire fighter aircraft flown by the Royal Air Force (RAF) during the Battle of Britain. It was developed continuously throughout the Second World War at factories including Derby and Crewe in the UK and was built in the USA by Packard. It powered numerous British service aircraft types including most versions of the Avro Lancaster bomber and also enabled the US-designed P-51 Mustang to fulfill its potential as a long-range escort fighter over Germany.
The Merlin was used in aircraft flown and serviced by Royal Australian Air Force (RAAF) personnel in Europe, Africa and the Mediterranean as part of RAF Bomber, Fighter, Training and Coastal Commands. It was also used in Australia to power aircraft including the Fairy Battle trainer and Supermarine Spitfire fighter. Locally-made and imported RAAF Mosquito and Mustangs used Packard-built Merlins imported from the USA. The Commonwealth Aircraft Corporation assembled the Merlin 102 at Lidcombe, NSW using some imported parts for the post-war GAF Lincoln bomber built at the Government Aircraft Factory, Port Melbourne. The Merlin was also modified for use in tanks such as the Centurion where it was named the Meteor. Overhauled 60-Series Merlins from ex-RAAF Mk VIII Spitfires were fitted to some of the new Mustangs built by the Commonwealth Aircraft Corporation in Port Melbourne after the war.