In late 1964 three F-4Bs were converted to test numerous improvements to the basic design and designated YF-4J. Improved aerodynamics to lower take-off distances and decrease landing speeds, improved engines, upgraded radar, and better ground attack ability were the primary changes. Over 500 of this version of the Phantom were built between 1966 and 1972. Markings shown on this airframe: Naval Air Test Facility, Naval Air Station, New Jersey, 1974