Just remember defensive builds are far cheaper in navy than offense.
Japan starts with 6 FIGs, right? and 2 AC’s.
Build 1 more AC, and base all 6 FIGs onm AC’s
That immediately gives you a defensive force of 36.
Flesh out with at least 1 DST (to remove the sneak aspect of the enemy subs), and then subs of your own to serve as fodder and additional strike forces, plus your starting 2 BB’s…
In just 2 rounds you can have a fleet with a defensive score over 60… that is 10 hits a round against the US when they attack you. It would take a LONG time for the US to build up THAT kind of force, move it to Japan, and then strike with it.
And as for Germany…
Base FIGs in Western, build INF initially, then ARM and INF, and push toward Moscow. Keep your forces massed and take and keep.
Sure, Japan may not be pushing hard, but you said Russia was keeping forces posted on Japan’s norders, which means some of their money is heading east.
With no US support in the Atlantic, it is a pretty easy matter to secure against what UK can send… and if you sent any forces to Africa initially, by G5 you should OWN all of it and be battling over Persia. This will really hurt UK’s income, dropping them to mostly INF to fill their tranny’s, and little offesnive punch to attack Germany.
And just keep driving on Moscow. You killed it once, you got bonus income, so build more tanks, keep moving your INF toward Moscow and take it again in 2 turns, this time for good.