For those who don't play paradox games or Hearts of Iron 4, I did a difficult achievement, which is starting as communist china and proclaiming the People's republic of china. You have to fight an uphill battle starting from a single province. I managed to consolidate, drive out the japanese, and turn on the Kuomintang in a few years. This last year has been researching and preparing a naval invasion to fully defeat Japan. Of course, I had to keep Mao as the head, otherwise how could I really claim to have created the PRC?
Its not the best but its supposed to work in that battleships kill cruisers who kill destroyers who kill subs who kill battleships IIRC. If you are a small country just build subs. If you are a large country its good to build some heavy cruisers and destroyers also. Battleships take too long to build to be of much use imo.