Between 1972 and 1974, 226 Navy and Marine F-4Bs were put through an update program with structural strengthening, new wiring, 30 kilowatt electrical power generators, and new avionics. The updated aircraft were known as "F-4Ns".

The Navy and Marines procured a variant similar to the F-4E, designated the "F-4J", with the following improvements:

Some new features like those of the F-4E, such as Martin-Baker Mark 7 zero-zero ejection seats; the slatted tailplane; and the number-7 fuel cell. The M61 cannon was not fitted, and in fact no production Navy or USMC Phantoms would ever have built-in gun armament.

Uprated J79-GE-10 engines, comparable to the F-4E's J79-GE-17 but without cartridge starting.

Strengthened airframe and landing gear, with Air-Force style tires.

New avionics, including an AN/AWG-10 fire control system with AN/APG-59 radar; an AN/AJB-7 bombing system; an AN/ASW-25 data-link for automatic carrier landings, developed as a follow-up from the F-4G experiments; and an AN/APR-32 RWR. The AN/APG-59 was a particular step forward, being a a solid-state system with multi-mode operation and "look-down" capabilities, allowing it to pick low-altitude targets out of ground clutter.

An uprated 30 kilowatt electric power generation system.

Three F-4Bs were rebuilt as "YF-4J" prototypes, with the first prototype performing its initial flight on 27 May 1966. 522 new-build F-4Js were manufactured into 1972, following the prototype conversions. A special version of the F-4J was proposed for the USMC but not built, this aircraft being intended to feature an enhanced fire-control system and F-4E-style leading-edge maneuvering slats.

Incidentally, the "F-4F" was a specialized Phantom variant flown only by the German Luftwaffe, while the "F-4H" designation was not used since it might cause confusion with the old "F4H" designation. The "F-4I" designation wasn't used either, since it could be misinterpreted as "F-41".