can the sub submerge immediately after hitting, without the chance of the battleship fighting back?
No, it has to suffer a shot from the battleship. If it survives, it can submerge, but why would you?
There’s Germans subs in a convoy zone and allies try to claim it back. The subs withdraw because the dice failed. And then, what happen with the (ipc) convoy, because there’s unit of both sides in it ?:??
Submerged subs don’t count as a presence, so the attacker would gain control of the convoy zone.