The following situation needs clarification:
A German submarine and a British battleship are sharing a sea zone. As the UK, I want to attack that submarine with a destroyer and a fighter, but I would prefer to leave the battleship out of the battle so I can retreat it. However, if I am attacking that submarine, I am forced to use the battleship in the fight, correct? Or could I move the battleship out first as a combat move? There is the rule that says that a ship may move away from a hostile sea zone as a combat move, but technically a submarine does not make a sea zone hostile.
In short, I would not be able to send the battleship away, but instead it would have to fight, correct?