Stealth submarines would be doable. We once played with two boards and a Game Master. You could only “see” units adjacent too your units or if you did a pre-combat move which was a “scout” by sending a fighter up to two territories out and back to see what was there.
It was a good way to chew up fighters and prevent them from attacking because they were now “moved” and could not engage in combat or NCM.
It was a pain on the game master though. He had to do a lot of running back and forth to make sure things were correct on both boards.
But it was fun!
For instance, in one game, Japan conquered England! (And yes, England was the first to fall, Japan just sailed around Africa and up with 3 transports loaded with 4 infantry, 1 armor - this was classic, so that’s full transports)
I want a PDF of the rules. I’ll buy the dang game, I just don’t want to break the shrink wrap on it!