I call this maneuver "Tickling the Dragon's Tail," (the name refers to fooling around with nuclear reactor cores almost ready to go critical). I do it when a destroyer or some other ASW boat is disabled but still deadly. Here, you can see the Clemson is down by the stern and dead in the water. I cannot surface for obvious reasons and I don't want to waste another torpedo... I try to trick it into depth charging the surface, damaging it more.
Failing that, ramming works too. I tore the deck gun off, since it was already out of ammo.
Ran across a U-Flak far away from the Biscay area. Shouted "THOMSEEEEEEN" as she went by.