I’m not sure how this initial strategy would play out on J3 (I’m guessing that’s when you would finally attack Australia) but it seems that Japan can reliably garrison sz54 on J1 by moving down its Caroline Islands fleet. This blocks Australia’s direct route to Dutch New Guinea (the transport can still go west around Australia) and pressures all three of Australia’s main centers.
The Aussie counterattack is: 1sub 1des 4ftr vs 1des 1tct 1ftr 1ac 1bb, but I’m not sure it’s one Australia would attempt. Even if Japan has to keep its destroyer around (to prevent Aus from getting a pop-shot at a tilted capital ship), they still can prevent the Aus destroyer from surviving. And once Australia attacks the Caroline fleet, Japan is free to land in Queensland – and possibly even Sydney – on J2 without declaring war on the U.S.
Round two of the battle looks like this, and only the 11 pips vs 12 result is a real danger (the forward slashes mean a capital ship is tilted):
42% = 1des 2ftr vs 1des 1ftr 1ac/ 1bb/ (8 pips vs 12)
42% = 1des 3ftr vs 1des 1ftr 1ac/ 1bb/ (11 vs 12)
8% = 1des 2ftr vs 1des 1tct 1ftr 1ac/ 1bb/ (8 vs 15)
8% = 1des 3ftr vs 1des 1tct 1ftr 1ac/ 1bb/ (11 vs 15)
But even with that bad result, Japan is likely to come to the final round with 1bb vs 1des. And if everything dies, Japan loses 65 in TUV and Australia loses 54 – but Japan still wins, because the goal is to keep sz54 open so that more Caroline Island reinforcements can come in on J2 (and matched with a J1 build of 3trn, I believe this is death for the Australians).
There are a few fuzzy rules that would affect this: 1) If an already-hit carrier is taken as a hit again, are the aircraft onboard also taken as casualties? Or is it just that they have to find another carrier to land on. 2) Does anyone know if there are capitals in this game? If Sydney is taken, do the Australians hand over all of their money?
Also, since I can’t quite run a full calc (I did some one-round checks with frood), my math may be a bit off, but if the worst result leads to victory, then we can say that the other round one results will just lead to more of a Japanese fleet presence.
Addendum: Since ANZAC does not start with ships in sz63, Japan should probably go there and leave the destroyer in sz54; it isn’t crucial to the fleet’s survival, since sz63 is out of range of the Aussie sub. This move prevents the Hawaiian transport from entering sz63 on US1 (US can’t attack Japan unless at war, right?) and prevents US2-3 reinforcements while still blocking sz54.