First of all, I want to say that USA committing any purchases to the pacific is a mistake. For the same amount of resources, the USA can always pressure Germany more than Japan. This is from my experience playing hundreds of revised games, many at a high level.
That said, assuming the US commits to the Pacific…
1. Japan should always sink the US fleet at pearl harbor. If this is done, Japan generally starts with a 1 battleship, 2 carrier, 3 fighter advantage compared to the USA that will take 5+ turns of buildup for the US to overcome.
2. The US can’t make significant advances unless the Japan fleet is destroyed. The best way to stall the USA is to place your fleet in the sea zone off the phillipines or china and deadzone all sea zone within 2 spaces of Japan’s fleet. Have the carriers filled with fighters AND try to have an equal number of fighters in a land territory that can reach all the sz within 2 spaces of Japan’s fleet. For example, 2 carriers can support 8 fighters attacking a sea zone.
3. Japan can continue pushing land units into asia, even with all US purchases going to the pacific. My typical purchases are like 6 inf and 2 fighters. With the Japan fleet off of China
1. R1 best purchase is 3 transports and 2 inf. This maximizes Japan’s land deployment into Asia and the transports serve a double purpose of strengthening your navy.
2. R2+ The only purchases you should consider for naval battles are fighters, subs, and carriers. Fighters are significantly better than subs mainly because fighters have a potential striking range of 4. Cruisers, destroyers, bombers, and battleships are too expensive for what they provide. Never buy these. I can elaborate if people are interested.
3. Don’t buy a factory. With just Japan production, Japan can push 6 land units into Asia without a factory. Japan with 35-45 income simply can’t afford to produce more land units while defending against US naval builds. If Japan doesn’t buy enough fighters/subs to deadzone the sea zones, US can move in and take east indies, borneo, and phillipines.
In summary: Don’t lose the Japan fleet, and buy mostly infantry and fighters.