Realistic modern sub tactic?

Is this scenario realistic?

Your target is a civilian surface vessel being escorted by one warship. There is civilian traffic close to your target. You only have one chance at a shot. At this point...do you raise the periscope and use that for targetting? Or do you still use TMA? Bear in mind, there is a small chance of the enemy spotting the periscope....though you know that as the sole escort, he wont be too bothered about hunting you and leaving his escort, unless you fire off a fish.

So would using the periscope (WW2 style) in this situation be realistic....?