 All of the single-seaters were later retired when the upgraded A-4SU began to enter service, the twin-seaters were upgraded instead and remained in service.A second batch of 70 airframes was ordered (mix of ex-US Navy A-4Bs and A-4Cs) in 1980, these were shipped directly to Singapore for rebuilding with the A-4Cs being rebuilt as the A-4S-1s while the A-4Bs was to remain in storage for use as spares.Along with a small number of TA-4S-1s, these newer Skyhawks (characterised by its straight refuelling probe instead of the cranked refuelling probe found on the original A-4S/TA-4S) would join the RSAF as attrition replacements from 1982.