Originally Posted by Laconic

0 degree gyro does mean the torpedo won't turn; otherwise it would fire out a safe distance from the boat and then begin making its turn to the gyro angle that the TDC inputted to it. You just described the quick way to calculate a Fast-90 solution with the TDC by inputting the data as if the target were passing your bow and then rolling back the gyro to 0 degrees with your scope until you find the proper shoot bearing. I prefer to discover the shoot bearing and then manually lock my torpedoes to a 0 degree gyro so I don't have to worry about accidentally moving the scope and blowing up my solution.