The designation OA-4M was assigned to 23 TA-4Fs that were reworked at NAS Pensacola to act as fast forward air controller aircraft for the Marine Corps. The OA-4M was basically a TA-4F equipped with the electronics of the A-4M, the main US Marine Corps close support aircraft
The modifications included a ground control bombing system, a KY-28 secure voice system, a canted midair refuelling probe, extra cockpit side armor plating, an APN-194 altimeter, and ARC-159 radio and ARC-114 VHF radio. Perhaps the most visible change was the fitting of the dorsal electronics hump, neatly faired into the rear of the two-seat canopy. The nose sensor group of the OA-4M was basically the same as that of the A-4M, but the Angle/Rate Bombing system was not fitted, and the laser spotting and tracking window was faired over, since neither of these were needed on an aircraft which was not to be employed in a pure bombing role.
Some consideration was given to fitting the 11,200 lb.s.t Pratt & Whitney J52-P-408 of the A-4M, but this turned out to be impractical, and the OA-4M retained the J52-P-8 of the TA-4F.
The first OA-4M, BuNo 165294 was tested at NATC Patuxent River, MD in July of 1978. The first squadron to receive the OA-4M was H&MS-52, based at MCAS Cherry Point, NC.