In 1972, the government of Singapore purchased 40 A-4Bs that were in storage at MASDC at Davis Monthan AFB in Arizona. They were refurbished by Lockheed Air Service to meet the particular requirements of the Singapore Air Force. This include the installation of the 8400 lb.s.t J65-W-20 turbojet, which was 20 percent more powerful that the earlier J65-W-16A. The wing lift spoilers of the later A-4F were incorporated. The 20-mm Mk. 12 cannon were replaced by 30-mm Aden cannon, and a Ferranti lead-computing optical gunsight was installed. A brake chute was added to reduce the landing roll. The communication electronics was replaced by more up-to-date equipment. Two additional underwing stores positions were added, bringing the total to 5. The aircraft were redesignated A-4S.
The first eight conversions (RSAF serials 600 to 607) were done by Lockheed at Ontario, California. The A-4S made its first flight on July 14, 1973. They were delivered to NAS Lemoore, California, where the initial training for RSAF Skyhawk crews was carried out. The remaining 32 conversions (RSAF serials 608 to 639) were performed by Lockheed Air Services of Singapore, using A-4B airframes that were shipped to Singapore.
Lockheed also produced a unique two-seater as part of the conversion contract. It was thought that it might be a good idea to standardize on the same engine for both single- and two-seat Skyhawks, and rather than convert factory-built two-seaters (which were all powered by J52 engines), Lockheed decided to modify J65-powered single-seat A-4Bs and turn them into two-seaters. This was done by adding a 28-inch fuselage plug and a second seat. However, unlike all of the other two-seat A-4s, a separate clamshell canopy was provided for the second crewman. The second canopy was immediately adjacent to the air intakes, and was raised in order to provide a better view. This modification was designated TA-4S. Seven A-4Bs were so modified, and were given the RSAF serials of 651 to 657.
The RSAF was quite happy with their A-4S aircraft, and ordered 70 more in 1980. To create these, A-4Cs were withdrawn from surplus stocks and shipped to the government-owned Singapore Aerospace Maintenance Company for rebuilding. These planes were modified in much the same manner as the earlier A-4Ss, but they retained the original 20-mm cannon, the shorter nose, and the straight inflight refueling probe of the A-4C. Another 16 A-4Bs were acquired for conversion into eight TA-4S two-seaters. They were issued to Nos 142 (Gryphon) and 145 (Hornet) Squadrons at Tengah, with No. 143 (Phoenix) Squadron acting as the training squadron.
In a major upgrade program in the mid-1980s, the RSAF fitted its A-4S versions with a new engine, an non-afterburning General Electric F404-GE-100D turbofan. The thrust of the engine was 10,000 lb.s.t, about 29 percent greater than that of the earlier J65. In addition, the fuel consumption was lower and the maintenance was easier. This version was designated A-4S-1. It first flew on September 19, 1986. The A-4S-1 became operational with No. 143 Squadron in 1988.
A second phase of the RSAF Skyhawk upgrade program involved an attempt to enhance the operational capabilities of the A-4S. A GEC-Marconi 4150 heads-up display was installed, a Litton LN-92 ring laser gyro inertial navigation system was added, and the aircraft was given the ability to launch the Maverick air-to-ground missile. The port side of the air intake had an extra air intake for an engine-mounted accessory drive. GEC Marconi was given the contract for the upgrade after Lear-Siegler had been ruled out because of technology transfer difficulties. The single-seat aircraft were redesignated A-4SU, the two-seaters TA-4SU, and were referred to as "Super Skyhawk". They re-entered service with No. 145 Squadron in early 1991, and became fully operational in February of 1992. in 1988.
Thr RSAF Skyhawk training unit (No. 143 Squadron) was disbanded in late 1997. Their planes were shipped to Cazaus Air Base in southwestern France, where RSAF No. 150 Squadron was set up to train pilots. This site was selected because it gives pilots access to bombing ranges and airspace over the North Atlantic.
The Black Knights RSAF flight demonstration team occasionally flies A-4SUs, drawn from Tengah-based units. The team has the unusal strategy of operating dissimilar types at the same time-- currently the team operates four A-4SUs and two F-16s.
The RSAF Skyhawks will probably continue to serve until 2003, when they will probably be replaced by F-16s.