Yep, I met one of those. SH3 Commander showed my nemesis to be the 'H.M.S. Whirlwind'... quite a fitting name :up:

I run around 50 meters deep (If I'm detected early I can get deep quicker and try to avoid the DD) at silent running until I get close enough to convoy, go to pd, fire and crash dive TOWARD convoy, go under passing ships, silent running again. That tactic is one that allows me to survive everytime. One; because DDs will know where I'm at but can't go right at me bacause of convoy ships, two; the convoy ship sounds help me slip away. Sometimes DDs will still dc me while scurrying around a convoy and I'll then run at near flank until DCs explode, as they explode I shut engines down and coast awhile. When it appears they're not sure where I'm at I then go silent running and slip away.

If I can get close enough to the convoy that also is a great tactic (hiding within the convoy) which also trolling along under a tanker is another great resource of hiding...but when im caught outside the safety of the targets and am being pestered...
Crash dive full ahead till the crapper is on top of me then hit silent and turn while coasting, drop a decoy or two....I like being more deeper than shallow as it allows a little reaction time to the charges being dropped or even at his pass made over you.
I try to get far enough away when I can, while he is looking for me, to pop up to PD and bust a cap in his ars...
course on the other hand I have had moments where the cat and mouse game goes on long enough that he calls for a buddy or two to come help out...thats when im creeping along at 210m...try not to have to much damage to the hull when that deep or your staying down there...