Its really critical, if you’re going to try to pursue a KJF strategy, to contain and then destroy the IJN. Total naval superiority is necessary to defeat the Germans out of Eurasia in the 4 man endgame. Basically the goal in that sort of endgame is to take over Japan’s “shucking into Asia” role, but just doing it with USA instead!
I think your best repeating purchase with UK is likely 1 fighter 1 bomber 3 infantry.
The 3 infantry fulfills your requirement to max place ground in Calcutta each round, but the bomber (as opposed to 2 fighters and artillery standard) will give you a more potent threat versus the Japanese fleet.
UK is in a position where they are usually collecting the same 31 ipcs for a while. If you make that Bomber+Fighter build 3 times in a row, (provided you don’t lose a bunch of aircraft initially) that gives you a really strong royal air force to keep the Japanese away from Suez by the 4th round. You’ll still have some fighter cover for the Russian capital, but the bombers can also move deeper out of UK, and cover a broader range from their positions behind the Russian lines.
A fun play is to keep that Australian sub active vs Japan on UK1, floating it around somewhere in the Indian ocean, to eventually join with this British air armada that you’ll be buying in subsequent rounds. Basically you use this sub and your bombers to keep Japan fearful of British airstrike capabilities out of South Asia. During the endgamge these strategic bombers will help bomb Tokyo in the critical rounds when USA is really stepping up, but in the meantime, the British bomber presence can also make it much harder for Japan to profitably engage the USN. They’ll be fearful of what UK might do in the aftermath of any naval battle, like say one that occurs near the money islands, and may chose to avoid sailing out beyond their comfort zones.
I suggested earlier today in another thread, the “sz37 Dive to Survive” move with your Aussie sub, which can work well with this type of build strategy. A single sub (sneak striking or absorbing a hit in place of a fighter or bomber) can make the threat of an airstrike too scary, and Japan might just decide to stay home instead of bringing their fleet too far from Tokyo.