In the mid to late 1950's the state rail system underwent a massive rehabilitation program. This effort was to repair and replace aging rolling stock rundown through the depression of the 1930's and war years in the 1940's.
Between 1956 and 1959, new steel First Class carriages were built. These were sitting cars of the saloon type. They were classed AZ and were numbered 1 to 13.
With the opening of the standard gauge through connection between Melbourne and Albury, five cars were converted to standard gauge cars coded VBK_, numbers 1 to 5. The VBK code was derived from V=Victoria, BK=the NSW code for the carriage type
This was for the through running of passenger trains between Melbourne and Sydney.
The remaining cars stayed on broad gauge for Victorian intrastate traffic.
In the mid to late 1980's, the cars were modified and fitted with guards/conductors van section. The cars were recoded to ACZ_ on conversion. At the same time they were renumbered into the '200' number range to reflect their steel construction.