Fred, great post! Much appreciated. I remember my Dad describing how they dropped the torpedo from a Hampden - also very low and slow to prevent it from tumbling and/or breaking up from impact. Often took heavy fire as they could not take evasive action while lining up the attack.
Why would you they instruct you NOT to attack a sited U-boat?
For example, we would be told we could attack anything in areas G8, H7. In areas C4, D7, H4, we could only attack U-boats on the surface or showing a periscope, not if completely submerged. In other areas we were NOT to attack submarines on the surface
Rodger