Japan is m fav country to play and like many other players I try not to get into static purchaces, as its easy to counter. I employ this strat to quickly balance the navy between the US and Japan, forcing US to build more on the pacific side. Generally the first 2 or 3 turns i play with japan I purchace transports and ground units, I try to get as many troops to the main land so by turn 3 you have so many troops you can afford to slowly filter planes off the mainland to newly bought carriers. I also load the land up because I find when I go to take the DEI this usually weakens my mainland leaving openings for China an UK.