I know nothing of The Pacific War but I am a big fan of Black Powder. It is readily adaptable to suit a wide range of periods - the core rules are very simple but designed to allow you to slot in special rules to modify it to suit the period of your choice.
It uses "units" that are usually battalions, but you could scale down to companies if you wish. It has a big emphasis on command and control and troop quality over the specifics of often trivial differences in armament. As casualties are represented by an accumulation of hits on the unit rather than by removing figures it also gives you huge flexibility in the number of figures that you want to use for units.