|I like and always have liked Tank Destroyers but due to Australia's almost total lack of mechanisation at the start of WWII and the subsequent conversion of the bulk of the 2nd AIF into light infantry to fight the Japan in the Pacific there was never the opportunity to deploy this class of vehicle.
It is too bad that we weren't able to deploy a tank destroyer or assault gun early in the war in Greece, the Middle East or North Africa inplace of the towed AT guns and light field guns that (when available) supported the 2nd AIF's Rifle Battalions. They would have dramatically increased the fighting power of our Infantry providing direct fire support and may well have turned the course of some battles.
Having this kind of firepower, a platoon of 6 to 8 vehicles, embedded in each battalion would have had a lasting effect in the Army, perhaps resulting in a very different structure today. Instead of the ANZAC Legend being recast around Light or Jungle Infantry there is a real chance that the RAR would have had an effective armoured DFS capability from inception, working its way though generations of vehicles to ....?
Assuming we started with something akin to a Cruiser MkIII armed with a 3" 20cwt in a casemate we could have moved onto a Crusader with a 17 pounder serving until the late 40's, then a Comet with a 20 pounder for the 50's to mid 60's, finally the S Tank into the 90's.
The Tank Destroyers would replace tanks in the infantry and direct fire support role allowing tanks to be concentrated and used to best effect.