I never knew the Australian Army had Austin Champs, but apparently they bought 400 of them. I never saw a single one anywhere, in any military depot in my travels whilst in the AMF during the period '69-'71.
I might add, there were still quite a number of WW2 warhorses such as Diamond T 981 trucks in use in that period in the AMF - and I sighted them, in use and in storage.
I can find no reference or even a single picture of any Australian Army Austin Champ on the AWM website - which is extremely unusual. However, it's possible there may be a picture or two of a Champ, but its mis-described or listed under its service classification.
I can only guess that the AMF disposed of all their Champs fairly rapidly in the late 1950's/early 1960's, when the Landrover became the standardised Australian Army GS vehicle. The cost of maintaining the Champs was possibly also a big factor.
The Champs weak point was the transmission. They blew up on a regular basis - you'd be lucky to get 20,000kms between major transmission repairs.
A entrepeneurial dealer bloke by the name of Arthur Marshall, based in Kenwick, a suburb of Perth, Western Australia, imported hundreds and hundreds of ex-British forces Austin Champs between about 1967 and the mid-1970's, for sale to farmers and station owners in Western Australia.
They were initially quite popular as they were cheap - and technically, quite advanced, with torsion bar suspension, rack and pinion steering and a fully sealed RR engine.
However, as soon as the weak transmission made itself obvious, sales dropped away - although many Champ owners purchased other civilian used Champs just for a supply of transmission spare parts.
They were also a nightmare to work on, and parts were difficult and slow to source. In addition, they were thirsty and slow. As soon as better Jap vehicles started appearing - such as Toyota Landcruisers and Nissan Patrols, the Champs soon became relegated to farm back paddocks.
Some useful Champ info -
1955 Austin Champ 4WD Review - mister-cars.com
An ongoing Champ restoration -
The Restoration of Austin Champ 1824