The McDonnell Douglas Phantom is one of the most versatile and effective combat jets ever to enter service and it enjoyed the longest production run of any supersonic fighter built in the USA. Some 50 years after its first flight, the Phantom still flies in front line squadrons of a number of nations' air arms. The Royal Navy were looking for a fixed-wing replacement for their De Havilland Sea Vixen aircraft and a number of aircraft in development were being considered. After endless stalling and the cancelation of the P.1154 (Royal Navy) RN Programme (a supersonic variant of the Harrier), the navy decided to go with an aircraft that was already successfully in service - the American Mc Donnell Douglas Phantom. The British did insist on a number of specific alterations! Based on the F-4J, the UK versions were designated F-4K (Royal Navy) and F-4M (RAF). Perhaps the major difference with the British machines was the use of the Rolls Royce Spey engines. These units yielded greater power and efficiency than the US General Electric J79s, without the signature of smoke trails. This did, however, come at a price - the UK Phantoms required extensive re-design work to the entire rear section of the fuselage and the engines needed larger intakes, amongst a host of design challenges to allow this mighty aircraft to be used from Britains dimunative aircraft carriers. In the end, of the 140 Phantoms originally intended for the Royal Navy, only 48 were ordered and 20 of these were diverted to the RAF.