In 1937, a group of steel rivetted cars were built for the 'Spirit of Progress' train. The cars were uncoded and placed into a number group. By 1940 when more cars were to be added, this system did not work.
The Second Class cars were numbered 6 to 9. In 1939 they were classed 'BS' and renumbered 1 to 4.
Three more cars were built in 1940: BS 5 - 7; three more in 1955: 8 - 10; four in 1956: 11 - 14.
With the start of standard gauge passenger operations, eight cars were transferred to S.G. for the Melbourne - Sydney 'Spirit of Progress' service.
The cars became VAC_, VFS_, VFX_ classes.
In 1966, a mini buffet service was introduced. Two BS cars were modified and recoded to MBS_.
In 1972, BS 15 entered service, modified from ABS_ 2.
In 1977, two cars were modified and recoded to MRS_, a mini refreshment service.
In 1982, most of the remaining _AS_ cars were modified and recoded to BS. As most of the BS numbers were not in use, opportunity was taken to refill unused numbers.
From 1984, a new passenger car numbering system saw steel cars numbered into the '200' range. Conversions from this time saw new numbers adopted. BS became BRS 224, a refreshment car. BS 9 became BS 209, etc.
By 1990, the BS cars were grouped 201 - 219, 273.