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Originally Posted by Bosk
Another thing that interests me is setting the torpedo bearing in manual TDC.
I'm aware that to ensure maximum accuracy the bearing should ideally be as close to 0 as possible to ensure 000 gyro angle, making the torpedo head do as little work as possible.
The thing is though, when coming to periscope depth near (or in the middle of) a convoy it is often very, very difficult to perfectly line the sub up with the approaching target to guarantee a 'perfect shot' in time before the escorts spot you. It would often be very useful to "slingshot" torpedos using a gyro angle much greater/less than 000 to attack targets to the far left or right of the submarine without having to come around.
My question is, does taking this sort of approach compromise the accuracy of one's torpedoes unecessarily?
And does it lead to an anacceptable percentage of dud's due to the shallower angles at which they strike their targets?
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You don't want to fire on a bearing of 000, you want to fire on a gyro angle of 000. It maybe that you mean the same thing here, but generally speaking the gyro angle is the angle the torpedo will adopt relative to the heading of the submarine, whereas the bearing is the bearing to target. They are not the same thing at all.
Assuming you have a track angle of 90 (that is your submarine is perpendicular to the track of the target), then the bearing to the target at which there will be a gyro angle of 000 is a function of the torpedo speed settings and the target speed. Typically for a fast running torpedo against a target moving at 7 kts, the bearing to target is +/- 9 degrees from dead ahead. For a target moving at 18kts, it's around +/-22 degrees.
The mathematics of it mean that when you are positioned perpendicualr to the target track, and fire on the 000 gyro angle, range becomes irrelevant. The further you are from that ideal situation, the more critical range becomes.
In the extreme case, you are travelling parallel to the target track and intending to fire more or less at a gyro angle of 90 degrees. it is fine to do this, but you must have a very good range estimate. The reason range suddenly becomes so critical is because of torpedo tube parallax, which is to say the difference between the position of the scope view and the torpedo once it has completed its turning circle. With a 90 degree shot this is significant. The TDC will have programmed a converging course for the torpedo to meet at the range you have given. Unless that range is accruate, it could easily follow a very different angle and miss the target altogether.