Here is my "device" to solve zero gyro angle shots:
Simply put, it's two angles and a circle drawn on the map (somewhere off in an area where you won't be sailing through. I draw it on an intersection of lines to keep things straight.)
The circle starts off at 4600 yards (MK14 fast torpedo speed is 46 knots. The size of this initial circle is different depending on the speed of the torpedo you are firing). Use this to position the first angle, one leg pointing to the center of the circle (representing your course), one leg pointing off wherever.
The second angle is centered on the circle, with one leg pointing south towards the first angle, and the other leg off elsewhere.
The center of the circle represents the torpedo impact point, the radius is the target speed, and the angles are the target course (relative to yours) and the lead angle.
It is now ready to be set up for the targeting problem.
First Exercise:
Target is traveling at 7 knots, with a course intersecting yours at an angle of 65 degrees. What is the lead for a 0 gyro shot?
Setup:
Adjust the circle to 700 yards (representing the 7 knot speed of the target).
Adjust the second angle to represent the the target course relative to yours. In this case, 115 degrees. (180 - 65 = 115)
Now, bring the second leg so that it crosses the intersection of the first angle and the circle. This intersection is your aiming point, where the target needs to be when you fire.
Read the angle at the bottom of the device. This is your lead angle, 8 degrees. Note that this is to port, so the actual angle is 352 (360 - 8 = 352).
Aim your scope down this bearing, and when parts of the ship (bow, stern, stack, bridge, etc.) cross the wire, launch the fish.
Second Exercise:
Target is traveling at 15 knots, with a course intersecting yours at an angle of 135 degrees. What is the lead for a 0 gyro shot?
Setup:
Adjust the circle to 1500 yards (15 knots).
Adjust the second angle to represent the the target course relative to yours, 45 degrees. (180 - 135 = 45)
Read your lead angle of 17 degrees. The target is crossing from starboard, so your actual firing bearing is 17 degrees. Aim, wait, and launch.
(Actual lead angles are 8.4 and 16.7, but the figures derived from this device are good enough to ensure a hit if the range is not excessively long.)