When the need arose for a form of motor car transportation between Melbourne and Adelaide in 1958, a new vehicle class was created.
Previous to this, cars had typically been lifted by crane and secured on flat wagons, but this method of loading was slow and wasted a lot of space.
Later wagons were built to altered, extended designs, and coded ALF, later ALX or ALP, with the "L" indicating the increased capacity and the final letter indicating the bogie type - F for freight trains, X for freight but convertible to standard gauge for runs to Sydney, and P for passenger trains at 70 mph.
The early usage of the wagon was for carrying finished motor cars from Melbourne to Sydney and Adelaide.
[1] The Ford plant at Broadmeadows was one major source of the traffic, with Holden being the other between Melbourne and Adelaide.
[3] The other traffic was the motorail service provided to passengers on long distance trains, allowing them to bring their car along with them.
The wagon was built by recycling the underframe of a scrapped Swing Door type locomotive-hauled carriage, with skeletal truss sides supporting an upper level deck.
[7] These wagons, which were 58 feet 9 inches (17.91 m) in length, were built at Newport Workshops and received the code 'AA'.
In the early 1970s, six wagons (2, 8, 9, 11, 17 and 20) were allocated to 'Motorail' service between Melbourne and Mildura on the overnight passenger train.
The other 16 vehicles were on standard gauge in freight motor car traffic between Melbourne and Sydney.
Over the course of 1985 these six wagons were recoded to VMAP series 5-10, though four of the vehicles spent a few months with the short-lived code VMPY.
The wagons were much like their shorter counterparts, with roll-on and roll-off ramps and track connectors and skeletal truss sides Twenty-two members of the new class were ordered at first.
The 'PY' showed that passenger speed bogies were fitted allowing 115 km/h operation, but that the cars were not gauge convertible.
A number of these wagons were sold to the National Rail Corporation in 1994, and those were reclassed to RMBX in 1994/95 to reflect that change in ownership.