Additional balance note:
On TripleA I set all sides to the Fast AI to guarantee equal players. As you can see, the Allies clearly won:
A U.S sub uses a suprise stike on a hostile Japanese seazone containing 1 BS and a crusier. The subs attack succeeds and the cruiser is removed. Question Does the battleship get a deffencive roll even though there is no destroyer.
Yes.
Wouldn’t this belong in the pacific area?
You are thinking to the rule for the aircraft; the aircraft cannot attack a sub if there is no destroyer in the water or else all naval units except the transport can defend against a sub and obviously on the first strike the boat if hit is removed and any other naval unit can defend.
and instead of taking the hit on the cruiser… take it on the battleship, and because the battleship is two hits, you get 2 defending shots at the submarine.