One of the original Q bogie wagons made from wood and wire with SEM bogies, with a crawler tractor and Milicast Rolls Royce Armoured Car (1920 model) as alternate loads.
Historical Accuracy Note: Some of the original Q wagons remained in use through the period of the layout, however no proof is to hand they were used for military loading at this time. While the Australian Army used RR Armoured Cars in WW1, I can find no evidence they brought them back home after use in the Middle East theatre. In any case the model here (1920) is a later version and I can't find records this version was imported, though they were common throughout the Commonwealth. However Australia did possess and develop several kinds of armoured cars during the layout period, to which the RR here is visually similar. So this pairing is plausible but not probable, rather it has been assembled to represent the era.