In the earlier days of me playing (not long ago) I used to sink them with AA. Until I got subs that didn't allow the AA to point below the horizon due to being in the nest at the back of the con-tower.
At the time they were plotted on the map for me too, but I seem to have lost that feature for some bizarre reason... now I can only find them by hunting for them with binocs.
I never blew one up with a torpedo though (never tried) and I never had anyone shoot at me.
In fact I pulled right up along side one for a journal once and danced with it for quite awhile trying to get a nice screenshot... it scraped along my side (kinda funny cuz it was all metallic sounding even though it was a rubber life raft) and if they were going to take a shot at me they would have. I ended up sailing off, having gotten the right screenshot for the storyline.
Could be they didn't shoot cuz they weren't armed cuz they came off a fishing boat maybe?
