once ran into a convoy with one in the middle in 1940 - put two torps into bow before escorts took an interest so thought would surface and finish her off when they left. Well I surfaced to find it steaming in the middle of the convoy ,bow down at 8 kts
Second time was a troop convoy close to Gibralter - 8 troopships/liners and about same no of escorts doing about 14 kts
Sank two before being pounded to destruction by 3 black swans
There was a post on here a while ago with the route ( liner alley ) that they take from US to UK in the game but I never found one on it tho the author said he had sunk 1 then an hour later sunk another in same spot