|Been thinking on this one for a while.
Post WWI Australia had one of the best militaries, man for man in the world. Our leaders, in particular Monash and Chauvel, were amoung the best. Even our soliders were well above average with many examples of individuals joining as Privates and ending up as Majors and Colonels (Percy Black and Harry Murray come to mind).
The AIF was already well on the way to becoming motorised with Service Corps posessing thousands of vehicles and combined arms operations well and truely proven during 1918 in battles such as Hamel.
Post war Chauvel pushed for mechanisation but instead it was decided, by polititians, that the true lesson of the Great War was that Australians were natural solidiers and as such there was no need to have a standing army. The assumption was than in the event of another war our citizens would simply take up arms and win the day. So instead of a Regular Army with Tanks, mechanised Infantry and Cavalry combat elements and motorised support echelons our army was gutted, the AIF disbanded and the greatest stupidity of all, Service Corps was forced to leave their vehicles in Europe and the hand full of units remaining in existance, reverted to horse drawn transport.
Considering the known threats of Japanese Imperialism and Communist Expansionism my what if is that common sense applied instead of jingoism and expediency.
-The RAR was formed in 1920 as motorised infantry using trucks as section vehicles and with Tankettes as support vehicles and all terrain tractors.
-An Australian Tank Regiment with a number of battalions was formed to provide organic armoured support to each Motor Brigade.
-The Cavalry was both motorised and mechanised with some units used as mounted infantry with armed trucks they could ride into battle and others were equiped with armoured cars to serve in the recc role.
-above all Service Corps would have retained and even upgraded their vehicles.
The other big change would be to dramatically increase the number of RAAF sqn's assigned to Army Cooperation.
Depending on responses to this post I wouldn't mind getting into the nitty gritty of ORBAT's and specific equipment selection, even Aust specific evolutions and developments.