In 1966 the 12 U.S. Navy F-4G aircraft were to test a new tactical camouflage for embarked aircraft
In March, 1963, 12 F-4Bs were pulled from the McDonnell assembly line for the addition of special equipment.
These Phantoms were to test the new AN/ASW-21 air-to-ground data link. The new communication system and an approach power compensator were installed just aft of the rear cockpit in place of the No. 1 fuselage fuel cell. AN/ASW-21 data link communication system and approach power compensator coupled with the shipboard AN/SPN-10 radar and AN/USC-1 data link allowed hands off carrier landings to be accomplished. A radar reflector had to be attached to the nose in order to produce a larger radar target that would permit the AN/SPN-10 ship-borne radar to track the F-4 during automatic landings. Initially, the radar reflector was bolted onto the nose gear door, but in production versions the reflector retracted into a cavity underneath the nose immediately ahead of the landing gear.

The twelve modified aircraft were redesignated F-4Gs. Their serial numbers were BuNos 150481, 150484, 150487, 150489, 150492, 150625, 150629, 150633, 150636, 150639, 150642 and 150645. The first of these (150481) flew on 20 March 1963.
The data link system and approach power compensator were the only changes to an otherwise standard F-4B airframe.
According to Larry Davis book F-4 Phantom II In Action, when the U.S. Navy went to war in Vietnam, the F-4Gs were assigned to VF-213 Black Lions which had been deployed with Carrier Air Wing 11 (CVW-11) aboard the aircraft carrier USS Kitty Hawk (CVA-63) to Vietnam from 19 October 1965 to 13 June 1966. During the deployment F-4G 150645 was lost over North Vietnam.

In 1966 the service used the 12 F-4Gs to test a new tactical camouflage for Navy aircraft. The upper surfaces were painted overall in either 34102 or 34079 Green, or a combination of both; the undersurfaces remained White. Several other aircraft types were also tested the new camouflage colors including A-1s and A-6s. However, the U.S. Navy decided that camouflage paint did not hide the aircraft to any great extent, and was found to be a negative factor when attempting to move an aircraft under the carrier deck at night. Navy aircraft would remain in the standard scheme of 36440 Gull Gray upper surface, with Gloss White undersides and control surfaces, until 1970s.
Eventually the F-4Gs were returned to the U.S. and converted back to F-4B specifications.
The U.S. Navy dropped the F-4G designation but the AN/ASW-21 data link system became standard equipment on the F-4J.
The “F-4G” designation was later again used for U.S. Air Force (USAF) “Wild Weasel” conversions of F-4Es.

Photo credit: U.S. Navy