Staff Writer (Updated: 7/18/2016):
The Phantom II was initially envisioned as an all-weather attack platform and began as a McDonnell company study project. The design, the F3H-G/H was an advanced navy fighter proposal powered by twin Wright J65 turbojet engines, an armament suite of 4 x 20mm cannons and seating for one. At the time, the United States Navy was looking for a replacement of their core F3H Demon series with a more viable and capable type and took notice of the McDonnell attempt. The project began in 1954 and the USN ordered the F3H as two evaluation YAH-1 (AH-1) prototypes, though these fitted with the new General Electric J79 afterburning turbojet (x2). In 1955 the USN turned the AH-1 requirement into a new two-seat, all-missile fighter design - and along with it, the designation of F4H Phantom II was born. Two XF4H-1 Phantom II prototypes were built with the first one flying on May 27, 1958 and quickly outclassing any other aircraft in the skies at the time. These prototypes featured an early form of - what was to become - the legendary General Electric J79 afterburning turbojet engines. F4H-1 (later redesignated the F-4A) was produced in 45 examples, these with the General Electric J79-GE-2/2A turbojet engines. This batch is oft-regarded as a pre-production version of the main aircraft series for the United States Navy, leading up to the first true operational production examples in the F-4B model series, which was essentially the second half of the initial F4H-1 production batch. Full production began in 1957.
The F-4B "fleet defense" model was fitted with the J79-GE-8 series engines, this being an improved form of the A-model' powerplant. The first operational squadron of F-4 operators became the VF-114 of the United States Navy, whom received the F-4B model series in October of 1961, after successful trials off the deck of a carrier the year prior. The United States Marine Corps soon followed suit, seeing the multi-role capabilities of the aircraft, and received their order in 1962 with the intention of utilizing the platform as their primary close air support fighter-bomber. F-4A and F-4B models were quick to land in the aviation record books. Throughout the late 1950's and early 1960's, the two variants went on to set several records in maximum altitude (98,556 feet on December 6th, 1959), time-to-altitude and overall speed (1,606 miles per hour on November 22,1961) among others.
Not to be left behind, the USAF took notice of the aircraft and received 29 on loan from the USN for evaluation - an unprecedented step in itself considering the historical "competition" between these branches of service. The USAF jumped on the Phantom II bandwagon and ordered their own batch as the F-110A (in an effort to replace their slower Lockheed F-104 Starfighters), though this designation was later changed, officially becoming the F-4C Phantom II model. The first USAF F-4C was received in 1963 making the F-4 Phantom II the first such aircraft to serve in the three major military branches at the same time (USAF, USN and USMC). The F-4D was later added to the mix, this variant - with a redesigned radome and improved internal systems - was generally similar to the USAF F-4C series but with USAF electronics instead of US Navy.
The definitive F-4 model came in the form of the F-4E Phantom II, production of which totaled over 1,400 aircraft. F-4E's featured the J79-GE-17 series engines as well as other additions that included an internal 20mm rotary-barrel cannon, leading edge slats and an improved radar system. The radar comprised of an APQ-120 system and the last Phantom II (5,057th example) was an F-4E model for South Korea, delivered in October of 1979.
Numerous other variants followed such as the F-4F - a dedicated air-superiority fighter exported to West Germany (they would later also take deliveries of F-4E models in 1971). These F-4F's would later be upgraded via the Improved Combat Efficiency upgrade with compatibility with the medium range AIM-120 AMRAAM missile and APG-65 radar functionality. The US Navy utilized the F-4J (beginning in June of 1976) and their J79-GE-10 series engines with a redesigned wing and tail section with improved ground attack capability and replaced their F-4B models. The USMC followed their lead and upgraded their F-4B models with F-4J as well. The Royal Navy operated the F-4K model (received in 1968) which was based on the USN F-4J series though these with the British Rolls-Royce RB168-25R Spey 201 turbofan engines. The Royal Air Force also utilized the F-4 Phantom II in their F-4M FGR.2 models, these based on the Royal Navy's F-4K. F-4M FGR.2 models fulfilled a variety of roles for the RAF including reconnaissance and ground strike along with the typical air defense role. Royal Navy F-4K aircraft were later passed on to the RAF to which they were redesignated as Phantom FG.1 and slated for use in dedicated air defense. Britain was, in fact, the first foreign nation to receive the F-4 Phantom II into their inventories.