[magic452]

Torpedo doors will not effect the dud ratio.
What happens is if you don't open the doors first it will ruin your firing solution. The fish will launch later than the solution is set for, you will miss aft.

This is true anytime you use auto targeting or are using the PK.
The PK will have a gyro angle set to the time of pushing the fire button but the torpedo will launch several seconds later. "Torpedo missed sir"

Magic

Edit the same holds true even if your using a constant bearing method. You'll actually shoot later than you want.