As a defense force why? Tanks are offensive weapons...why would a defense force need any more than that? The Australian military is so small do they even have enough troops to man the 59 they have?
Edit: You have 26,611 troops in your Army and one Battalion (59 tanks of M1A1s - the old stuff); At Fort Hood Texas alone we have and entired Armored Corps of 60,000 Soldiers and over 1800 M1A2 SEPs (the latest stuff)...on one base.
Ooooh..103 you don't say...