[joegrundman]

90 degree shots are not actually that difficult so long as you are competent at estimating target length and range -and with one of those you can calculate it all easily enough with a slide rule.

Torpedo parallax is much less of an issue at 90 degrees than at other large gyro solutions.

You already know, with a fixed 90 degree shot what the gyro is and that it is running perfectly perpendicular to your course, so all you need to know is the total forward distance the torpedo will travel from the position of the periscope before it settles on the 90 degree track.

Let's say the scope is exactly at the midpoint of the submarine, then the forward motion of the torpedo is half the length of the submarine, plus the straight run it makes to clear the submarine, and then the turning radius to get onto a 90 degree track.

So with a 100m sub, and a 10 m reach (the straight run) and a turning radius of 10 m, the total diference from the submarine point of view and the torp is 50+20=70m

So with the scope pointed at 90 degrees, the torp will hit a parallel point 70 m further forward.

So to setup your shot and add the 70 m at the target. For a 140m target, for example, to hit dead center you aim for a point at the bow/stern depending.

anyway it's how i used to do it when messing around with no tdc targetting