Originally Posted by Albrecht Von Hesse

One thing I wanted to point out, though. There have been more than a few occassions where I've had tin cans start pinging, even though I'm several hundred to over a thousand meters directly behind them. I'm certainly not in their active sonar cone at that point.

I think what happens is that an escort won't, without any reason, just begin actively pinging unless your doing A, B and C (which is how I'm interpreting your post). However, once they've twigged onto a U-boat in the vicinity, or have lost passive contact with you for a number of minutes, they'll start actively pinging seeking to re-acquire contact again.