finding, intercepting, and engaging targets without automap, radar, or active sonar

[TorpX]

Originally Posted by AdamMil

Perhaps I'm dense, but I just don't see it. If they taught it, then I imagine it must have worked, so I'm probably misunderstanding you. But what about these cases?



In both cases, the sub turns to put the target on its beam, and in both cases it can adjust its speed to keep the target there, but in neither case will it ever intercept, no matter how slow the target is going.

You are right about the cases you illustrated. Neither of these would permit an interception with the Normal Approach Course. If the target had been detected earlier, the situation would be very different.

Here, I took your first case and extended the target track backwards to show how the Normal Approach Course could be used:

Your second case is just like the first, except the target is even farther past.

Here is a diagram which illustrates the problem. The target is shown at an early position, A, and later positions, B, C, D, and E are marked. The gray line is the normal course, and is the shortest distance to the target track. If the sub is close to the target track and detects the target early, the NAC is nearly the same (as in case A).

The target can be easily intercepted if detected at A, with just a fraction of the targets speed (assuming the diagram is drawn to scale). It can be intercepted at B, with a little more speed, or even at C. The farther along towards D the target reaches, the harder it is to intercept (that is, it requires more speed).

If the target reaches D before detection, the NAC will not accomplish anything, as you stated. Once the target has reached D, or E (or any point to the right of D), no course will permit an interception without having a greater speed than the target. For submerged submarines in WWII, this was generally an impossibility.

That would be in the nature of chasing after and overtaking a passed target, and was considered a different problem.

The geometry here shows why, in submerged operations, it was considered important to detect potential targets as early as possible. It also shows why many targets were detected, but still 'got by'.

[AdamMil]

Ahh, I guess that's what you meant when you originally said "if ... it has already passed". Of course, without knowing the target's course, there's no way to know whether the target has passed or not, but as Warren Peace said, I can just try it out and see if the target is getting closer. (Thankfully SH3 sonarmen can discern that instantly. :-)

So it does seem like a good approach to know, since it's simple and when it works it does give the slowest possible interception as you said, and slower means stealthier. In some cases (e.g. when the target is close to point D) it could take 'forever' but I believe you when you say it works pretty well in practice.

In fact, our two approaches seem quite similar in that they both attempt to find a lead pursuit course based on zeroing the rate of bearing change. Yours (NAC) fixes course and adjusts speed to find the minimum speed required, but fails if the target isn't 'behind' you. Mine fixes speed and adjusts course to find the minimum time required, but fails if the chosen speed is too low. Since I'm early in the war I can afford to zip around on the surface and just want the fastest intercept. Later, when I have to be stealthier, I might switch to NAC to find the stealthiest intercept. :-) I appreciate the explanation, in any case! I learned something.