I like it, though warfare would certainly be harder for your people than others. All that water and extra equipment would be costly on ship equipment, I would suspect prove to be a little tricky with electrical systems? No gravity would also, I think, mess up a ship. And the requirements for atmospheric and for underwater use would, I think, require a good deal more activity-specific equipment, which means that warships would have to be quite large just to do everything you had in your application.