Harbour raid in (I think) Harwich early years saw me face to face with a couple of them. They seemed extremely passive until I hit one with an eel, then they brought their guns to the party with extreme accuracy - It's relatively shallow and I couldn't go deep! Luckily after I'd fired the torpedoes I'd turned around expecting as much.
Ahead Flank!
I've yet to bump into one in the open that wasn't part of a convoy.