I actually have the same question...how do you trail a [credible threat] submarine with his TA dangling in your face?
Back when I actually had time to play the game, I did one of those random missions in a 688 or Akula (can't remember which). There were three other subs out there, I bagged two of them and started trailing a third. I decided to see how close I could get to the third boat before he shot me, and I ended up riding right up to his screw.
But he turned out to be a Han, so no great achievement there I guess. All I did was drive right up on him, no more than 15kts if I remember. But it was funny, he was painted clear as a bell on my HF active sonar. I had to call all stop so I could drop back and shoot him.