400 in the Australian army, there must have been some on airport duties somewhere!
Well ... on the website link below, there's a (reputedly) WW2 photo of an RAAF airfield in Tarakan, Borneo - which identifies a (reputedly) Austin Champ amongst the P-40's (W16).
Now, something is either wrong with the dating of the photo, or the ID of the vehicle - because according to John Mastrangelo's excellent Champ history page, development of the Champ did not commence until 1947, and full production was not commenced until 1952.
However, I note that he states that, "during World War Two, a prototype 4x2 'jeep' was produced in the United Kingdom".
Whether the vehicle amongst the P-40's has been mis-identified, or it actually was one of the 4x2 prototypes, is open to question.
Then there is the question of whether the dating of the Tarakan airfield photo is correct. As far as I knew, all RAAF aircraft had departed, and air operations were concluded at Tarakan by 1946 - thus making the likelihood of the vehicle being a Champ extremely unlikely.
Military Page 2