What I'm thinking of is like German U-boats like in the movie U-571 if you've seen this movie you will know what I'm talking about but what would be cooler than having your own submarine it would make destroying the carriers and battleships simpler i know and it might make the game unfair but if you put depth charges into the game then were back to even playing fields. Also, maybe throw in some features like water pressure to it which would make the player think more about what he/she is doing so they don't capsize their boat. and etc! let me know what you think