Aut cum scuto aut in scuto
I don't know precisely how they work, but I do know that they work very well. But a DDG against a torpedo with a nuclear warhead wouldn't provide a satisfying outcome. Subs and targets...
First thing we were thought in Sub school was that boats are black and targets are grey!
Active sonar is great for fishing too:)
If I had it to do all over, shipfitting would definitely be vying for commercial pilot as the course I'd venture onto.