Jeesh, relax man. I got it the first time.
To be honest though, sending a sub in an out-of-control downward spiral doesn't strike me as proper procedure.
Ussually I go to flank, turn to get the incoming torpedo at my 90deg, either port or starboard, and turn into it hard when it's close, and order a change of depth.
If your method works, fine, but mine doesn't produce so much soiled underwear (70deg down-angle?!
).