The Q class were introduced as bogie flatwagons in the 1870's. Large Q wagons as shown were built to the 1920's
In the early 1900's, some Q wagons were modified for Pintsch Gas traffic with a small pump motor cabin at one end and a tank for carrying the gas. Other conversions for traffic were as required. Examples were: sheet glass, skeletal underframes between workshops
In 1926 the railways built two narrow gauge Garratt locomotives. As normal wagons were unsuitable for moving these locomotives a special skeletal wagon was built. The engines were split into units for transportation. It featured axle bearings and boxes from steam engines, had hinged buffers that could drop out of the way during loading/unloading. It also featured 'strap' rail along the deck. The wagon was Q 129. This wagon was also available for general narrow gauge rolling stock.
Q wagons were numbered from 1 to 136.
The class was reduced by scrapping, conversion or recoding to QAB_, _QF_, _QH_ or VFAA.
The gas traffic wagons Q 26 and Q 30 in storage at Newport Workshops had their numbers swapped in the mid 1980's.