I don’t really try to keep up with the US’s navy, I usually have the two AC’s and two BS’s that Istart with post in the pacific, ready to pick off any new additional US naval units. If they start building a fleet, I buy more fighter and bombers to hit them at range.
In short I use the Japanese to clear Asia and assist in Germany’s destruction of the Soviet Union.
A huge navy is great if you plan a landing, however there have been numerious games where I have an enormous navy and still to manage to lose massive numbers of land squares.
Occupy his time in the Atlantic, force the US to aid the UK.