The McDonnell F-4 Phantom II has the unique distinction of being the first carrier aircraft to be eventually adopted by an air force as its principal fighter. More so, it became the first US aircraft to be selected as the main fighter for a British armed service, serving both with the Royal Navy and the RAF. The selection of the Phantom for British service came as a result of the cancellation of the Hawker P.1154 project (later revived as the Harrier) at a time when the Royal Navy was in need of a new fleet defense fighter and the RAF a modern tactical strike and reconnaissance aircraft. The adoption of a foreign aircraft was controversial and as a result, British Phantoms were equipped with considerable domestic input, notably a pair of Rolls-Royce Spey engines which were more powerful than their US counterparts. Their size necessitated a redesigned rear fuselage but they provided British Phantoms with superior low-level performance though they struggled at higher altitudes. Ferranti-produced variants of the AN/AWG-10 radar were also installed. Operation on Britain's smaller carriers posed a considerable challenge and in the end, Phantoms were only operational on HMS Ark Royal and take-off had to be assisted by a strengthened, extendible landing gear. Eventually the scrapping of the carriers resulted in all RN aircraft being transferred to the RAF where they were increasingly used for air defense alongside the Lightning before being phased out in the early 1990s by the Tornado ADV. Despite being a foreign aircraft, the Phantom in British service ended up endearing itself to both its pilots and the public as a classic Cold War aircraft, albeit one that never saw combat.

The prototype YF-4K first flew on 27 June 1966 and was based on the USN's F-4J variant which at the time was the most advanced naval version of the Phantom. Royal Navy Phantoms were given the US designation F-4K (Phatnom FG.1 in the UK) and were the first to enter service. RAF Phantoms were designated F-4M (FGR.2) and were broadly similar to their naval counterparts, albeit with some equipment and avionics changes to make them more suitable for land-based use. These were procured in much larger numbers. Following the Falklands War, the need to provide an air defence component in the disputed islands resulted in the RAF procuring a squadron's worth of second-hand USN F-4Js (brought up to nearly F-4S standard), these were known as the F-4J(UK) (F.3).