 These aircraft would later emerge as the A-4S single-seater (44 airframes) and the TA-4S two-seat trainer (three airframes), all having more than 100 changes incorporated (these included a slightly longer nose to house a new avionics package, five stores hardpoints instead of the usual three, a saddle-style Automatic Direction Finder dorsal hump, cockpit armour plating, spoilers, a cranked refuelling probe, AIM-9 Sidewinder capability, a brake parachute housing below the jetpipe into the standard A-4B airframes.As with the Israeli A-4Hs which were armed with a pair of 30 mm DEFA cannons, these were similarly armed with the ADEN cannons in place of the original 20 mm Colt Mk 12 cannons.A later order of four two-seat trainer airframes was placed in 1976, and these joined the RSAF in 1977.