During 1950/51 fifteen tank wagons were placed into service for weed spraying. The wagons were rebuilt long wheelbase _I__ and _IA_ trucks. The bodies were cutoff and tanks added to the underframes. The wagons were coded WX and the I/IA numbers were retained.
These wagons were numbered WX 7850, 8193, 8262, 8858, 9074, 9948, 10425, 10465, 11357, 11591, 12023, 12560, 13288, 13358, 13902.
Between 1955 and 1959, twenty five tank wagons were placed into service. Nine wagons were bogie tanks with _E__ underframes. The remainder were of a type with cylindrical tank mounted on a fixed wheel underframe. These wagons were to replace the existing WX wagons which were removed from service between 1955 and 1959.
The new WX tank wagons were numbered 1 - 25. They were attached in blocks and used in a weed spray train with then new weed spray van HZ ( WZ ).
WX 10-11, 12-13, 14-15, 16-17, 18-19 were issued to service coupled in pairs as numbered. It is presumed that the pairs were connected with some sort of piping to assist weed spraying. All these paired tanks were scrapped in 1959.
WX 20 - 26 were issued in 1959 as single fixed wheel tanks built from scrap underframes.
In 1963, the WX class was relettered to _WA_.