The First Class sitting cars for the "Spirit of Progress" train were coded 'AS' from 1939.
The cars were originally uncoded and numbered simply 1 to 5. However, they were known by the administration as "Steel AE" cars. With more construction due in 1940, the numbering system used was unsuitable. The cars were coded AS and kept their numbers.
Between 1940 and 1952 a further eleven cars were built. These entered service as AS 6 - 16.
Three cars were converted for "Overland" train service to provide a limited passenger service for Victorian passengers on an otherwise interstate service. The cars were modified to ABS_ in 1953/1959 and were converted back to AS in 1963.
Other conversions were to MBS_, BRS_ and _BS_.
With the adoption of a numbering system to identify steel passenger carriages, the remaining AS cars of 1984 had "200" added to their numbers.