I see your point. It's a solvable problem and you have provided an answer.
I'm just thinking out loud...
Why do I need to use only one tool in my boat to make this kill.
Imagining a situation...
1. Target is part of the mission.
2. It's heavy rain and fog. So can't use Scope.
3. Target is escorted so can't come to surface.
4. Escorts have radar so can't use radar for range.
5. If they get detection, target serpentines and that would make the shot very hard and have to avoid destroyers.
The problem is... How can I maneuver the boat without the escorts hearing me. Certainly not with any speed.
If I didn't have escorts to worry about, why not just give surface chase and use radar to get range and when close to 1000 yards or meters, climb into the deck gun and get a little practice in. You can't see it at 1000 in heavy rain and fog, but you can get the accurate bearing from sonar tracking and 1000 is close enough to get a lot of hits. Chase him till he sinks.
The question is: When is it the best time to need this method of passive acoustics only?
Edited: I posted the above before seeing your message
Alcibiades