Last night I ran into a 9 ship convoy with 3 DD screen. Managed to get a snap shot on a Cimmaron tanker that blew her nose off. Other 3 torpedo's took out the other tankers and merchants.
Dove deep and waited with silent running for the screen to move off with the remaining ships. Surfaced probably 4 hours later (in game time) to take in my external torpedo's and reload when I see the tanker burning off in the distance. She's stopped, burning from aft to what's left of her bow and just sitting there in the heavy seas.
Took about 40 rounds from the deck gun to finally get her to go under
Have screenshots but not here on the work PC lol