OK, here's the deal on Frederf's chart above. If you think about it, your lead angle changes, depending on the angle on the bow of the target. To take an extreme example, when the AoB is zero he's headed straight toward you. There is no lead angle at all! You just set speed to zero or AoB to zero and if your bow is pointed at the target, out comes a zero gyro angle shot.
However, when you are at AoB 90, the target has the highest apparent motion from left to right or right to left and you must make a maximum lead angle ahead of the target bearing to achieve the boom.
So you can see that as the target approaches, the lead angle is constantly changing. However, the graph doesn't graph target bearing. It graphs torpedo track angle. You may swear now. Oh, they're not tracking real torpedo track angle, but pseudo torpedo track angle! @#$@#$%@#$ I'm going to have to pull out a chart here.....
Now your sub is on the right end of the sub's course line. Yeah, I know that's not obvious. Why didn't they just SAY SO???
. Point P is the periscope. The middle line between M and P is the bow of the submarine. Point M is the end of the torpedo's straight run, where it turns to its set gyro angle along the curved course to the torpedo track toward the target. Kapeesh?
Actually that's not going to matter much, because in the special case these graphs show, the deflection angle is exactly equal to the periscope lead angle. They don't explain that in the Submarine Torpedo Fire Control Manual, they just claim that "From a study of the curves it is evident that..."
NO, IT"S NOT EVIDENT!!! THAT"S WHY WE"RE LEFT WITH THESE FREAKIN' QUESTIONS!!! Thank you, I feel much better now.
To further muddy the waters, the manual doesn't say what the optimum periscope bearing to fire is, it relates everything to the resulting angle the torpedo takes when striking the target, measured from zero at the bow to 180 at the stern. So to make any sense out of what they say you have to reverse engineer all the gobbledygook.
I've done that. You're going to laugh. All the charts can be used to start campfires or something. Let's take the chart you used above.
Let's take the bottom curve, for 8 knots. The deflection angle is the exact same as our lead angle because they're all zero gyro shots. It says if the track angle is zero (you are shooting directly at the bow), the deflection (lead) angle is zero, you don't have to lead the target at all.
But as the angle on the bow, which is a bit less than the deflection angle, increases and the target bears more and more boadside the lead angle increases until you get to the optimum track angle, where the curve levels off and starts to fall again.
In the shaded area, between a 90º track angle and the next radial line over, where the lead angle is again the same as a 90º track angle, the lead angle changes least for each degree of target bearing. So shooting a torpedo track angle in that range will give you the most error tolerance possible. Gee, I think I've talked about building error tolerance into our attack plans before!
Well, all thse graphs are very fine and great for impressing girlfriends over dinner if you've run out of things to talk about, but what in sam hill do they mean? You're gonna die...
Shoot from a course at right angles to the target track, ala Dick O'Kane and
fire when the target bears 0º. The torpedo will automatically (if your TDC is set for AoB 90º and correct target speed) take the optimum track angle toward the target. If you care about the resulting 10º to 20º gyro angle (you shouldn't worry about gyro angles of less than 30º) you can alter your course to about 110º from the target track instead of 90º. This will reduce your gyro angles in all reasonable circumstances to less than 5º. I'm not going to worry about it myself.
Now you can go make paper airplanes from those pretty graphs and use them to entertain children. Yup, there's the right way, the wrong way and the military way. Welcome to the military way to make the simple into brain surgery...
