[WernherVonTrapp]

I believe, if you point your periscope at a specific heading (during the heavy fog) and hit the "L" (lock) key, even though you don't see anything, your torp will follow the locked path of that track. So, theoretically speaking, you an do this by picking a spot ahead of your target (say 15 degrees) and fire, or just fire w/o locking anything (including sonar) when the target is about 12-15 degrees off.