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

[AdamMil]

Hey, long time no post. I'm trying SH4 with the GFO (game fixes only) mod. I wanted to try playing without map contact updates, but it was hard because it even removed the sonar bearing lines. I tried finding some tutorials for playing without map contact updates, but I couldn't find any good ones. They all seem to be overly simplified. Either the target is plainly visible from the start or else radar or active sonar is used to get an absolute position or they ask the omniscient WO. But what about the case when you're too far away to see or ping it, and you don't have radar?

I played with it for the past 8 hours or so and found a couple of workable approaches. My first approach was to use the information from passive sonar to do a TMA (target motion analysis). I wrote a program to automate the TMA and spit out an intercept vector that would put me in a firing position 1000 yards off the target's side, and on the whole it works fairly well. The main benefit of this approach is that it gives you the target's absolute position, course, speed, AoB, etc. just from passive sonar readings, but it's a bit of a pain to write down the bearings on paper and alt-tab out of the game for a couple minutes to input the data. I also had trouble with my incompetent crew failing to report and track sound contacts despite them being clearly audible, and when that happened the approach degraded because it's hard to be a good sonarman and get accurate readings in addition to plotting on the map and everything else I have to do. Precision is important with this approach.

So my second approach was based on just using the rate of bearing change to find a lead pursuit course with the target. If you're on a lead pursuit vector (i.e. a straight-line course and speed on which you will intercept the target), then the target should remain at a constant bearing. (This is in contrast to a lag pursuit course where you simply keep your bow pointed at the target. Subs are too slow for that to be viable most of the time.) So what I did was:

1. Set my speed to the maximum that I feel is safe/stealthy and turn towards the target bearing.
2. Wait a little while and see how rapidly the bearing is changing.
3. If it's changing, turn in the direction it's changing in such a way as to "overshoot" and hopefully end up on a lead pursuit course, and repeat from step 2. Don't overshoot by more than 30 degrees or so.
4. Otherwise, if it's not changing, I'm on a lead pursuit course.
5. Sail until the target is in visual range (or range of other sensors). If you want, you can slow down as you get closer, for stealth. Just remember to find the intercept course for the new speed.

It's basically a rough version of Newton's method. Example:

• I'm traveling in some direction and hear a target far away on (relative) bearing 120.
• I order ahead standard and turn 120 degrees to starboard. (The target is now at bearing zero.)
• I wait for a little while. As I wait, the target bearing drifts from 0 to 354 (i.e. 0 to -6).
• I "overshoot" by turning 20 degrees to port (to bearing 340). (The target is now at bearing 14.)
• I wait some more. As I wait, the target bearing drifts from 14 to 11.
• It's still drifting towards port so I "overshoot" by turning ten more degrees to port. (The target is now at bearing 21.)
• I wait. The target bearing drifts from 21 to 22.
• Now it's drifting to starboard, so I turn 3 degrees to starboard. (The target is now at bearing 19.)
• I wait. The target stays on bearing 19. That means I'm on a lead pursuit intercept course.

After doing this, the target bearing may still drift very slowly, like one degree every five minutes, because you can't set an exact course in the game. In that case just adjust course again by two degrees maybe. But if the bearing keeps drifting substantially or if the range keeps increasing even though you're on an intercept course, then you're too slow to intercept the target. (You can either speed up or give up.)

The upside of this approach is that it's simpler than using TMA and doesn't require alt-tabbing out of the game. And you don't have to be very precise to get good results. The downside is that it doesn't give you the target's position, course, speed, or AoB, so you still have to figure that stuff out using other sensors and you can't directly sail to a firing position. But it's good to know how to do that anyway. Being on a lead pursuit course takes most of the guesswork out of interception, and when the target gets within 4-8 km or so you can begin roughly estimating its position and plotting its track using the following technique:

• Identify the target as soon as you can, but before then just pick a ship of its class (cargo, warship) with an average mast height.
• Every few minutes, take a stadimeter reading and note the target's bearing. It doesn't need to be perfect, but do the best you can. (In SH3 in rough seas it helps to pause the game when you're centered on the water line.) Radar or active sonar can also give you a position estimate, but may reveal your presence.
• Take the range and bearing and plot a line of that length along the target's bearing on the map, put a mark at the end of the line, and delete the line. (If you're moving or turning it's best to do this while paused, or else quickly mark the position/course of your boat.)
• When you have a few marks, draw a "best fit" line through the marks to estimate the target's track. Position yourself 90 degrees from the track at a good firing distance (say 500m).
• Repeat these steps and keep adjusting the track and your position relative to it. As the target gets closer and you take more readings, the estimated track will get progressively more accurate.
• If you want, you can start the stopwatch when the target is 2-3km away and measure the distance between marks to estimate speed. But if you're really close to the target track you can usually just guesstimate the torpedo lead angle. :-) 4-5 degrees works well for most cargo ships at 600m.

If the target detects you, is unarmed/unescorted, and starts zigzagging you can just surface and sail towards it at speed. If you get within 700 meters, it's relatively easy to score a hit - shoot just as the target starts to turn one way or the other and lead a little bit. Use the magnetic trigger if possible to avoid glancing impacts.

I use this overall approach with success in SH3 + GWX. (I went back to it because SH4 crashed and corrupted my saved games on 2 out of 3 patrols. :-|)

[TorpX]

I like that you worked this out and all, but there is a way that achieves the same essential result with less maneuvering. [I'm not familiar with Newton's method so I can't say anything about that.]

The last time I was in such a situation I used the Normal Approach Course. This means setting a course normal to the bearing of the target.

Using your example:

I am running submerged at 2 kt. and detect screws bearing 120 deg. relative. I wait a little while and the bearing moves to 119 deg.

Now I order 4 knots and turn 90 deg. to port from his bearing. He will then be at 90 deg. relative.

This is a Normal Approach Course. It allows an intercept with a minimum of speed, provided an interception is possible. If the target is too fast, the target track is too far away, or it has already passed, you cannot intercept it this way.

I continue to monitor the sound. If I am gaining bearing, I can reduce speed. If I am loosing bearing, I can increase speed to 6 knots, but going higher isn't really an option, unless the target is already close. If I am still loosing bearing at 6 kt., I must either consider surface pursuit options, or let it go.

Like your method, this isn't intended to provide detailed target data (nor is it necessary), but rather to get you within attack range. You then have the standard problem of a submerged periscope approach.

The NAC lacks the fancy geometry of sophisticated sonar-only methods, but in practical terms works just as well (at least imo).

[AdamMil]

Originally Posted by TorpX

I ... detect screws bearing 120 deg. relative... Now I order 4 knots and turn 90 deg. to port from his bearing. He will then be at 90 deg. relative... It allows an intercept with a minimum of speed, provided an interception is possible.

Thanks for the example, but are you sure this works reliably? Let's say that after putting him on your starboard beam (90 deg. relative), you and him are now on similar courses. When you adjust your speed to maintain bearing, you'd end up adjusting your speed to be nearly the same as his. Thus you'd be traveling nearly parallel, which seems to me like the longest way to intercept.

[TorpX]

I'm sure it will work within the constraints I mentioned. It was taught in the US Navy, and Dick O'Kane describes it in his book, CLEAR THE BRIDGE.

As far as being "longest way to intercept", that could be, but consider, intercepting at max. speed, intercepting at min. speed, and intercepting at X speed, are different options.

Let's say that after putting him on your starboard beam (90 deg. relative), you and him are now on similar courses.

This isn't really the case. The NAC is 90 deg. off the bearing, the target's course could be almost anything, nor do we need to know what it is.

This diagram shows what the NAC is:

The target track(s) is red, the sub is blue, the bearing line is green.

The bearing line is moving in the direction of the green arrow, so we set the course indicated by the blue line. Let's say the target track is the red line A. The NAC allows an intercept with a minimum speed. Another course with a shorter path may allow an intercept, but would require a greater speed.

If the target is on course B, we are farther off the target track, and must move faster to intercept. If the target is on course C, it is the opposite. We are closer to the track, and can intercept with less speed. In every case, the NAC gives us the best chance for an interception (that is with the least speed).

Note, that it is possible that we start on a NAC, at our best speed, and still loose bearing. This means an interception is not possible.

By monitoring the bearing of the target as time progresses, we will know if we can intercept or not. Gaining bearing means we would reach the point, where our tracks cross, ahead of the target. Loosing bearing means we would reach that point behind the target.

If you knew the target's course and speed, it would make sense to calculate a specific intercept course, but lacking such data, a NAC gives you the best chance to prevent the target getting by.

[Aktungbby]

AdamMil! after two+ years of silent running and a first rate diagrammed lesson from TorpX...you're well up on the DAY!

[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.

Anyway, these examples call into question my own approach as well, since they show that it's possible to keep the target on a constant bearing without being on a lead pursuit course, even if one exists. If you overshoot by too much you might wind up on homing in on one of the constant-bearing courses that isn't an intercept course. (But I think it's less likely to occur with my 'algorithm' since you start out pointing yourself at the target.)

@Aktungbby: Thanks for the welcome. :-)

[Warren Peace]

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.

Anyway, these examples call into question my own approach as well, since they show that it's possible to keep the target on a constant bearing without being on a lead pursuit course, even if one exists. If you overshoot by too much you might wind up on homing in on one of the constant-bearing courses that isn't an intercept course. (But I think it's less likely to occur with my 'algorithm' since you start out pointing yourself at the target and adjust course rather than speed.)

@Aktungbby: Thanks for the welcome. :-)

In either of those situations, hydrophone checks will give you all the information you need. In the case of your first example, checking for his screw noise will reveal one of two things; a) no change, meaning you are on the same course at the same speed, or b) his contact will begin gaining bearing and becoming quieter, indicating he is pulling away.

In regards to example 2; you'll hear his screws become quieter as you open the range, indicating you are moving away from him and need to readjust your course if you wish to still intercept (which would turn into a tail-chase, not something I typically recommend).

[AdamMil]

Originally Posted by Warren Peace

In either of those situations, hydrophone checks will give you all the information you need.

Of course, but my point regards an easy procedure to establish a good intercept course. I'm trying to understand this Normal Approach Course technique, which given my (mis)understanding of it seems to produce weird results in these cases.

[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.

[TG626]

I'll add my thanks as well. A good read. One item I notice isn't being expressly remarked on it fuel conservation, which would have been a very real consideration. Along with everything else, making your intercept in the most fuel efficient manner would have been important I would think.

[AdamMil]

Originally Posted by TG626

One item I notice isn't being expressly remarked on it fuel conservation, which would have been a very real consideration.

Especially if you're submerged and your "fuel" is battery charge. :-) I was thinking about it, but it's hard to say anything concrete. Fuel usage increases proportionately more rapidly than speed, which implies that you'd want to go as slow as possible. However, going as slow as possible (e.g. with NAC) can lead to you sailing a much longer distance than necessary, which may result in a much greater overall fuel usage than taking a shorter path at a higher speed. Battery charge also affects speed, which adds another complication. And it probably all depends on the specific parameters of the batteries, engines, and submarine. A mathematical analysis to arrive at a general rule is surely possible, but too time-consuming for me. :-P

What I personally do, though, is cruise around at "ahead slow" speed, giving me about double the range of "ahead standard" while only reducing speed by about 25-35%, so I don't have to worry about fuel usage in combat. I try to intercept on the surface at standard or full and only submerge once I get within 3-4 km or so. But I'm still early in the war...

[TorpX]

Originally Posted by AdamMil

Especially if you're submerged and your "fuel" is battery charge.

Yes. The Normal Approach Course was mainly something applied to submerged approaches.

Here is a quote from the 1950 Submarine Fire Control Manual, which speaks for itself:

310. FLEET TYPE SUBMARINE:

(a) The Fleet Type Submarine will make the following speeds submerged for the length of time indicated, if it starts with a full battery charge:

Knots Time
3.0 48 hours
6.0 3 hours
8.0 1 hour
9.0 1/2 hour

(b) Thus it can readily be seen that a major consideration when making an approach is conservation of the battery capacity.

If you have liberty to maneuver on the surface, you have much better speed, and many more options, to make an approach.

If the people who own the convoy, have aircraft out flying ahead (as they often did), then surface maneuvers become problematic. It occurs to me, that aircraft make a convoy much more secure. They don't need to even make attacks; their mere presence would hold down submarines and frustrate attacks.



Also, I didn't mean to imply the NAC is some kind of rigid method. You don't need to adjust speed to the minimum, or follow any specific plan. You could increase speed for a short time to gain bearing (and a better position), then reduce speed when you know you are close enough to the target track to be assured of getting an attack opportunity.

Often, a NAC would be taken when a target was first spotted, and later when they were within several thousand yards, change course and speed to meet tactical requirements.

I like the Normal Approach Course, because it has that elegant combination of simplicity and effectiveness. However, the Navy also had what they called the Optimum Approach Course:

I've never really used the OAC, but I've certainly used the NAC many times.

[AdamMil]

Originally Posted by TorpX

(paraphrasing) 3 knots = 48 hours, 6 knots = 3 hours

I don't know how accurate Silent Hunter is in this regard, but that's a huge difference in endurance: 144 nm @ 3 kn versus 18 nm @ 6 kn. I expected a large difference, but not that large, so if you're submerged, choosing the intercept that lets you go as slow as possible (i.e. NAC) seems like it would outweigh other considerations much of the time.

The OAC seems to require knowing the target's course, so I imagine it's one of those things you'd use after you get close enough to see which way the target's headed.

I didn't get the impression that you were presenting an overly rigid method, by the way. :-) These are all good tools to have in one's toolkit, to use and adapt as best fits the situation...

[banryu79]

First of all many thanks for this most interesting and educational thread. I really appreciate it.

Originally Posted by AdamMil

The OAC seems to require knowing the target's course, so I imagine it's one of those things you'd use after you get close enough to see which way the target's headed.

Actually you could work out a very good estimation of target course/speed/range while conducting a passive sonar only approach.

Maybe I'm not telling you anything newer, but worth mentioning.
Once you have found and set your boat on the NAC, you have at least two methods that I'm aware of.

1) First ther is the "four bearing method". It involves sampling the bearing to tgt in temporal steps and plotting. TMA done by hand, requires times and patience, but gives out good results. I rarely use this.

2) Then there is the "Using the [Is-Was disk] [Mk13 submarine attack course finder] to conduct a passive sonar only approach" method. This requires time and practice, and the use of the Is-Was disk (you can make one yourself or use a mod that give you that in-game).
This method is the one I almost always use when first detecting long range hydrophone contacts. I do not use the "whole" methods, just the first three-four steps to obtain 3 estimated possible courses and speeds of tgt.
In this way I can plot them and so get a visual aid that help me much in analyzing the different tatical options at hand and finally choose an approach course that suit me the most.
I find it reasonable fast to use and "less annoying" than the four bearings method.

You can find detailed documents about this methods (and others) inside the [hsGUI v3.1] mod for SHIII.

I think that if you already had work out out and egaged the NAC to your tgt, then you could easly make a gross estimation of the OAC simply using the second method cited above while your are waiting to close range.