Somewhere.. the evil torpedo gods are doing their best Dr.Evil impersonation
I really feel for you, I had a similar experience but managed to escape with my life. I fired off a group of 4 torps at a large passenger liner and the 4th was an end-a-rounder, but for some strange bit of luck it was a dud as well. It bounced off the aft of my sub... once I started breathing again I managed to submerge and count my lucky stars.