Subs always shoot in opening fire and unless there is a DD for your side anything that would “sink” from the hits scored by the subs doesn’t get to shoot back. 2 subs getting two hits could sink the BB before it could fire back. You always need two hits to sink a BB no matter when they are applied.
Also note there is opening fire in every round of combat. Every round your subs have a shot at sinking something that won’t get to shoot back (unless an enemy DD is present.)
