I always played DiD (not counting the retirement), and my longest till now was IXB one; Jan41 to Apr43. Survived a really nasty ramming north of Scapa, with that one. Didn't really think i'd made it. But...hehe

. Didn't survive my last convoy attack!
MY shortest was a VIIC/41 one from Mai44 to Mai44

Sunk near the BoB. Got jumped by a task force. After i was spotted by a plane. DC'ed bad; really bad!