Background
The United Kingdom bought versions based on the U.S. Navy's F-4J for use with the Royal Air Force and the Royal Navy's Fleet Air Arm. The UK was the only country outside the United States to operate the Phantom at sea, launching them from HMS Ark Royal. The main differences were the use of the British Rolls-Royce Spey engines and of British-made avionics. The RN and RAF versions were given the designation F-4K and F-4M respectively, and entered service with the British military aircraft designations Phantom FG.1 (fighter/ground attack) and Phantom FGR.2 (fighter/ground attack/reconnaissance).