The F-4J was the final version of the Phantom II produced for the US Navy and US Marine Corps. It constituted an improved version of the F-4B and flew operationally for the first time in 1966. Of this version, 522 aircraft were constructed between 1966 and 1972. Because of increased weight and more demanding sink rates, the F-4J was fitted with a sturdier landing gear, which required modifications to the inner wings, as had been the case for the F-4C. F-4B aircraft were later converted to F-4N versions in a service life extension programme.
The squadron today known as VF-21 was first established in 1944 as VF-81, acquiring it's present designation in 1959, thus becoming the second US Navy squadron to be designated VF-21. The first Tomcats arrived in November 1983, replacing F-4N Phantoms. The transition was completed in March 1984. VF-21's aircraft are marked with a leaping panther, contained within a shark's fin shaped border. The background to the panther has been seen in many colours, ranging from a rainbow to no colour at all. One of the most persistent seems to be a yellow background. The aircraft also often sport black trim around the canopy.