The SAA Steel Carrier is a type of two axle flat wagon with a very specific use which would result in their life as the SAA designation being relatively short lived. Introduced in 1966, the first withdrawals took place in 1971 following an accident at the foot of Beattock summit in Scotland. 

By 1976 over half of the wagons found themselves rebuilt and redesignated as the FPA container flat wagons, in the ten years preceding this the SAAs were under used, warranting the rebuilds. No SAA container wagons remain in service in 2023, with only a handful of the rebuilt variants still in storage.