 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 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). Initially, the FGR.2 was used in the ground attack and reconnaissance role, primarily with RAF Germany, while 43 Squadron was formed in the air defence role using the FG.1s that had been intended for the Fleet Air Arm for use aboard HMS Eagle. The superiority of the Phantom over the English Electric Lightning in terms of both range and weapon load, combined with the successful introduction of the SEPECAT Jaguar, meant that, during the mid-1970s, most of the ground attack Phantoms in Germany were redeployed to the UK to replace air defence Lightning squadrons. A second RAF squadron, 111 Squadron, was formed on the FG.1 in 1979 after the disbandment of 892 NAS.
