In 1902 the Shell Oil Company introduced some tank wagons for service. VR 'registered' these as a tank wagon group 'Oil Tank' and started the number group from 1. As more tank wagons were placed into service the tank wagon numbers increased, no doubt due to the uprising popularity of the horseless carriage.
By 1928 there were 83 wagons in service, numbered 1 to 83. Tank wagons from any company and any description were then added to the same number group right up until the introduction of the TWX wagons in the mid 1970s when TWX 1, 2, 3 were placed on line for Heatane Gas traffic.
Tank 84 was the start of bogie tanks to service ( for oil / refined product traffic ). Through the 1930s to the 1950s more tanks were added in small groups to suit different companies and different uses. Occasionally some four wheelers were added for Oil Tank service or departmental oil service.
In the mid to late 1950s a group of 2300 gallon water carrying wagons were built. These were defined as 'tanks' and placed into the oil tank number block taking the next available numbers.
And in all this mix a group a steam engine tenders were converted for fuel oil traffic, coupled in pairs and placed into this oil tank group.
All in all a very good mix. By the 1970s the tank group was up to the high 600's with the last tanks to service being built by Indeng Qld for BXT (Benzinw Xylene, Toluene ) traffic to Melbourne. With some new gas traffic (South Australia to Bittern) and fertilser tank traffic via standarg gauge between NSW and Melbourne, tank numbers started at 1 and went up to about number 11 as TWF, TWX codes.
In the mid to late 1980s, V/line added to the tank fleet and kept renumbering from the 600's into the low 700's.
The main question that still needs to be answered is the subtle difference between a 'Tank' and a 'Truck'. This is the main division between the 'Water Tank' wagons in service within the Oil Tank group and the 'Water Truck' (WT) group. The author can only offer the following as conjecture:
Peter J. Vincent, updated 16/4/2008