How do I get inside a convoy?

[bsalyers]

I was once waiting in the path of a convoy in - I want to say 1941 - with engines off at periscope depth. As the lead escort drew nearer and nearer, I ordered silence. My hydrophone man whispered that the destroyer was closing at short range. In this game, short range means really close. I knew then we would be killed; I just wanted to watch it happen. On a whim, I put up my scope; not all the way so it broke the surface, just enough to see the cans when they were dropped. Within seconds I actually saw the hull of the destoyer pass over my bow. We were probably less than 2 meters under him. He never detected me. BTW, I was playing at full realism.
I don't know if this is remotely authentic, but in the world of the game, "silent running" seems to make a huge difference. I've used it ever since, not just when evading, but when lying in wait just before my attack, too.