Convoy Interception Methods

[bigbear948]

1.How do you intercept convoys on the navigation map ?

2.And what is the maxium range you should intercept from ?

Intercepting seems really hard, I have no idea how to intercept, use the map tools(except managing the Sub's own course), and how do you take into acount the convoy's and your own speed ?

The navigation Turtorial in Submarine school is far too simple.

[Pacific_Ace]

Ive always found this works extremely well in SH3 and pretty well in SH4. The reason for the difference seems to be that in SH4 when a contact is listed as going for example East that doesnt necessarily mean its traveling at a heading of 90 degrees. It could be going 80, it could be going 110.

http://alexbret.perso.cegetel.net/index25c4.html?title=Intercepting_Targets

[SteamWake]

Biggest thing is to get ahead of them. Determine their course then lay in wait.

Simple as that.

Realize that often you cannot accomplish this simple task. To do so would burn way to much fuel and you just have to sigh and let it go.

[Rockin Robbins]

The real subs without radar had it worse than we do and still managed to intercept, so let's do it their way. First decide whether they are moving left to right or versa visa. Let's say they are tending to the right. Then turn right and put them on your 270º bearing. Hit the gas (assume they are going fast to begin with.)

Now observe. If their bearing stays the same over time you are on a collision course, keep it up. You're going to have a very short encounter with about one shot if you're lucky but you will be able to intercept them.

If the bearing changes more toward stern, in this case decreasing as time goes by, then you will pass in front of them. Keep it up. You want to get ahead and submerge off the track to shoot them as they come up on you.

If the bearing is getting larger than 270º, changing more toward the bow, that means that they will pass the point where your courses cross ahead of you. You will have a hard time getting in position for a shot. Change your angle of attack to put them at 270º again and see what happens. If you continue this you will eventually end up on a parallel course. Then if you are faster than they are, maintaining the 270 bearing will put you on a more and more converging course to end up ahead of them. Submerge off-track and wait for your shot.

These are VERY GENERAL guidelines which assume you know nothing more about them than "there they are." You can do much better than that if you can establish their course and speed. Basically if you are behind them, you want to end around at a range where you will not be detected, but you can maintain contact with them until you get far enough ahead to converge on their track, submerge and ambush them.

[Frederf]

First I'd like to call an "intercept" the process of going from intelligence about a contact (Flash traffic, navigation map square mark, whatever) to when you actually acquire the contact using your own sensors (visual, sonar, radar). Approaches are maneuvering with a contact followed by own sensors to the critical point (4000yd or so) and attacks are from critical point to torpedo launch. It's good not to confuse these phases with each other since their goals and means are quite different.

The nature of a contact intercept depends on quite a few things, none the least of which is the quality and style of contact information. In RSRD campaign (a mod) I very, very rarely get the stock square-with-tail contacts. More often it is the Flash radio message something like "Intel reports convoy traversing Formosa Strait AM Dec 21." This can be 1 to 3 days before Dec 21. The time frame could be from 12:01am to 11:59am that day. I'm going to assume though that you're working with the standard stock-type navmap contact square. Sometimes you'll get tail, no tail (depending on mod) or even pretty accurate course and speed info through a radio message.

How far depends on your patrol schedule, fuel, and confidence at intercepting. If you're confident and can see that the contact has to pass through a specific narrow waterway in just the right place you can have success at long, long ranges.

At the most basic, the interception problem comes down to predicting where the target's going to be and traveling there to show up at the same time or perhaps earlier. There are a great many choices of where to go as the target's going to be different places at different times. Just as there are different choices of meeting location, there are different reasons why you would choose one over the other.

More often you want to get to the contact as soon as possible. This will reduce the area the contact might be due to uncertainty in the speed and course as well as reduce the chance that the contact changes course. Submarine speed will be high so fuel use will be drastic for long distances. Encountering aircraft can ruin your average speed as well.

The math/geometry in the wiki link looks like black magic but it's nothing terribly special. What you're doing is setting up a mini-triangle where the length of two sides are known (your speed, contact speed) and the angle between those two sides. After you figure out the "intercept triangle" you merely scale it up so that two points are your position and the contact position. The last corner is the "meeting point." It's easy to check the math once constructed as the time for the contact to reach the meeting point and for the sub to reach the meeting point should be the same.

Given a speed and course range you end up getting windows at each time beyond the contact time. (Beware that the contact time can be much older than the time the marker popped up on the map) If the contact is moving 5-9 knots Westerly you can draw a window that has edges that are courses 247.5° and 292.5° (any more and it would be SW or NW instead of W) and ranges 5nm and 9nm. After an hour the contact could be anywhere inside this curvy angley box. If the boxes start to get bigger than your sensor range or how much ocean you can cover in an hour the chance of intercept goes down accordingly.

I often will set course for the far corner (fastest possible contact speed, least-desirable contact course) of the box that I can reach in time (maybe it's the 5 hr box) so that if I guess wrong I've pretty much trapped the contact and likely will have stumbled across him on the way to his "worst position" if approaching from the rear. You can also shoot for "center of window" or "center of fast edge" and then search from there. I like to very quickly dive and sonar sweep every 30 minutes once in the current window, especially if the visibility is limited.

Forget the temptation to try to get well ahead of the target and wait. It is almost always better to contact the target immediately even if from a poor angle and maneuver keeping the smoke on the horizon. Trying to be clever can lead to the target changing course or being far from your estimates and completely bypassing you.

[Pisces]

Here is a classic tutorial on how it can be done with SH3:

http://www.subsim.com/radioroom/showthread.php?t=88961

(whoops, the same technique as that wiki link)

Look for post 41 on the second page. A good summary picture of the procedure. Allways make these kind of drawings based on where the contact should be right now!. Especially if the contact report is hours old.

Allways go as fast as you can, top-speed, or flank if fuel is not an issue. But readjust the drawing if weather is slowing you down. Then the contact has the least amount of time to move away and the search area stays limited in size.

As for how far away you can depends on experience, the capabilities of your boat, and on the situation. Knowing his speed accurately is most important for long range intercepts. But if you got just a speedrange it's wise to use a worst-case speed. Then you'll allways end up infront of it, and can turn to meet the contact along it's course if it isn't there. Also meet him at top speed since you can loose it if it makes a course, or speed, change in the meanwhile. If you can't find him at all, though luck, but you did your best.

Whenever you arrive at the intercept location, and the contact actually did have the assumed speed, the target may still be outside of visual range due to it having a course slightly off from the reported course. So you will have to rely on radar or hydrophone (sonar is too short) to extend your detectionrange. The reported course (N,NNE,NE,ENE,E, etc. ) are all in steps of 22.5 degrees, which means that the actual course can be 11.25 degrees on either side of reported. You need to fit your best sensor range (circle) within such a 22.5 degree wedge to determine how far you can let the contact move (since time-stamp of contact report) before he might sneak past undetected on the fringes of detection range. Roughly speaking this is 5 times your maximum detection radius. So if your radar has a range of 30nm (60k yds) make sure you can be at the intercept point before he has moved 150nm or don't bother to intercept at all. Beyond that his chances of of a lucky undetected escape increases.

To make that visual: Draw a courseline for the contact of 5-times-sensor-range from it's origin point. Draw a circle centered at the end of the line with a radius the same as your best sensor. Draw another 2 lines starting from the contact origin point with the ends touching on either side of the circle. You should get a drawing that looks like an ice-cone. If your intercept course doesn't intersect it before the center of the circle you should forget about it.

The above drawing also solves the issue of whether or not to intercept a contact that is allready moving away from you. If the intercept drawing (with the ice-cone) says you can get it in time, don't second guess it, but GO FOR IT.

[Rockin Robbins]

Now, technically, what I wrote about above is approach tactics, meaning that you have sensor contact with the target, and Frederf has written about intercept tactics, meaning you have no sensor contact with the target. My piece was based on the Submarine Torpedo Fire Control Manual (http://hnsa.org/doc/attack/index.htm), Chapter 9, Submerged Approach and Attack Practices. This is applicable also to surfaced approaches, but since it was written for the much more restricted battery powered submerged submarine, incorporates the most efficient methods for obtaining proper firing position and transitioning from the approach phase to the attack phase.


Always begin the approach by heading directly at the target. Then observe whether the bearing opens up to the left or right. That will determine whether to put the target on your starboard or port beam.

The normal approach course (NAC) of your submarine should be keeping the target on your beam and moving in the same direction as the target. If you determine the AoB is large you can open that up to a 100 or 110º angle to allow for possible high speed of the target. If the AoB is below 45º you'll want to reduce that approach angle to compensate for the fact that the target is headed more directly toward you. Remember that if the target is moving from right to left, you'll have to subtract that desired angle of approach from 360º to yield the course to steer. Let's say your target bears 0º, your NAC will be 360-90=270º. Then you find the AoB is close to 90º or even larger, so you open that up by 10º to course 260º or even 250º. Clear as mud?

There is much more detailed information in the manual itself, linked above.

OK, Fred, am I blind? Where's that wiki link?http://i196.photobucket.com/albums/aa293/RockinRobbins13/smileys/clueless.gif

[Pacific_Ace]

He's talking about the one I posted. It is to the SH3 Community Wiki.

@ Fred (or RR even)
"Intel reports convoy traversing Formosa Strait AM Dec 21."
The game simulates Ultra's? I cant say Ive noticed this, but then I really dont pay much attention to the messages, I just look at the Nav plots

[Rockin Robbins]

Yes, that specific type of report simulates Ultra and its reports are generally reliable. Unfortunately, most remote sightings aren't done that way by intelligence report, but by random sighting by "another unit." These tend to be so unreliable that it really isn't worth the time to chase them unless you're VERY near and it won't impede your progress to your destination to complete your mission.

So in the game intelligence reports are pretty reliable and worth chasing. Sightings by "other units" are a lot less reliable and most of the time aren't worth an extended travel out of your way.

[Frederf]

Pacific_Ace, the Flash Traffic messages are unique to RSRD campaign (mod). I don't believe they are in stock at all. With RFB+RSRD, getting the little black square contacts are very rare (once a month?) and the Ultra messages are much more common (once a week on average?).

I've never seen any lack reliability in either Flash or the square contacts. I wouldn't consider either to be more reliable than the other.

//Aside

NACs and OACs are approach phase terms and sort of out of the scope of intercepting. However, small correction as a NAC puts the target on the 090/270 bearing line ("normal" being a synonym for "orthogonal" or "right angle" instead of the more common "usual" or "every day"). The OAC is technically a NAC on the firing position at limiting torpedo run range abreast of the target and on the near side and therefore is usually places the target closer to 000 bearing instead of exactly on the 090/270 line. The approximation for OAC without doing all the geometry is 10 degrees less lead which would mean putting the target on 080/280 bearing.

Technically the OAC and NAC are the same if you're directly beside a target and only when you are aft of the target's beam would the OAC dictate a course that places the target on a bearing more aft than 090/270 which would be silly because being behind the target means you're in an end run situation and OAC is not helpful as in end around maneuvering you care about getting to the target's beam and forward without being seen so the location of the firing position is best ignored. I would smoothly transition from NAC to OAC when at the target's beam.

Approaches with bearings to target of >90° I only use if I'm uncomfortable with how close I am to the target and want it to disappear into the distance a little more or if I am really trying to stretch my range to a target that I knew was nearly as fast or faster than me and I had a very good idea of its motion. Turning away could mean that you and the target are driving apart which is counterproductive.

Anyway, enough of that nonsense.
//Aside

The method used in the wiki link is perfectly sound. I guess I could generate a table from this method that used the ratio of submarine and target speed and the angle between the contact bearing and contact course as the two inputs and have the lead angle be spat out as the output. It would save you having to do the method (which honestly is handier than referencing a table in my opinion).

If the contact information is 100% precise and the contact travels in a straight line then interception is a breeze and isn't all that exciting. The tricky bits come when dealing with uncertainty.

[Armistead]

Some great info Fred and RR. I play with contacts off and what you guys say is right on.

The one method I think Fred mentioned is if you get a contact close enough after checking that heading, try to see if there is a probable pass you can cut them off at. I've caught many this way rather than chasing them in a big ocean.

[Rockin Robbins]

It's absolutely necessary, especially in real life, to be aggressive and cut them off in the shortest period of time. Time brings more variables into play and half of them (examples, change in weather that slows you down, change in target course and speed) are bad. Cut 'em off as quick as you can to eliminate as many possibilities for bad things to happen as you can.

[Armistead]

I agree with cutting them off in the shortest time, but that's hard with contacts off. Why I agree contacts off is not really realistic, but contacts on gives too much info. Hard thing with them off is not being able to see all the escorts, so I take time finding a way in. The bad thing is often you get caught doing this.

I ran into a 8 ship convoy last night that had 8 escorts...little rare. Tryin to find the right way in takes time and usually is what gives me problems.
If it's getting close to dark, I'll just flank and wait. I also hate attacking in calm waters. Course I want to identify all escorts and attack the side that has weaker escorts, less charges, ect....I love it when I can be seen, but escape on the surface bringing escorts searchin, then leaving them behind on the surface having a total weak sector to attack on the surface, run, do it again. Did I say surface enough.
Even with TMO, I find this works great..I prefer to be a surface raider

Frankly contacts off is hard as heck for me anyway. Getting much better and attack half the time with success, sometimes spend hours getting in position. Still have a problem with fast TF.....then I do just go for it if I'm in position. Contacts off can wear you out fast......

[Rockin Robbins]

And I'll second the motion on evaluating, pulling out, leaving the escorts searching one side of the convoy while you do an end around to the other side. Actually, with a heavily guarded TMO convoy, that is sometimes the only way that works.

After awhile your spider senses just say, "This isn't working out just right. Time to scram." It's best to listen carefully to that small voice. It can pay off bigtime on the other side of the convoy!

[Frederf]

Anyone here decent at trig? I'm actually trying to make that manual lead table value but I keep coming up sour mathematically. The setup is pretty simple, three dots on a page, submarine position, target position, and intercept location. I know that all you need to find out your lead angle is the ratio of target/submarine speeds and the AoB angle.

An example would be something like "Target is half my speed, AoB is 120 degrees... lead angle solution is 22 degrees." You point 22 degrees from directly at the target in the direction it's moving and you run into it some time later with a big clang of metal.

[Rockin Robbins]

You end up with a sheaf of multi-column pages (it's been done). As a matter of fact, it was the reason for my developing the Dick O'Kane targeting technique. The complexity of picking the correct page, then the correct line and column opens up hundreds of possibilities for error and what seems at first to have been a good idea devolves into a litany of frustrating misses.

You're better off using the graphic solution of vector analysis, which can be done in seconds with much fewer opportunities for human error. Minimization of human error and mitigation of their inevitable effects is the hallmark of good attack practice.

War is fought by imperfect people who must be victorious anyway.:D

[Frederf]

I went through the math again and my page of equations was replaced by a simple few lines of better equations. It's simply:

EDIT
L = ArcSin ( C/S Sin A )

Where L is the lead angle, C is the speed of the target, S is the speed of the submarine, and A is AoB (0-180°). A very complete table would be huge but for reasonable speeds it could be small. A graph with several curves would be more compact, readable, and usable for common scenarios. I figure it's pretty useful as it works for both intercept and torpedo problems. It's nice to have a backup solution in case a juicy target starts slipping out of view and the TDC solution is discovered to be bad.

It's of note that such a graph or table might be slightly easier and faster to figure out the speed based on the angle instead of the usual reverse. Mostly I did it just to see if I could do the math still.

[Pisces]

I went through the math again and my page of equations was replaced by a simple few lines of better equations. It's simply:

L = ArcSin ( C/S Tan A )Sorry, that is not entirely correct. Calculating "tan 90" for an AOB of 90 degrees is not possible because the result would be an infinately high number, yet arcsin can only handle numbers between -1 and 1. It's supposed to be "Sin A", not "Tan A". Because it is completely based on the "Law of sines" in a triangle of any shape:

edge_opposite_to_angle1/sin(angle1) =
edge_opposite_to_angle2/sin(angle2) =
edge_opposite_to_angle3/sin(angle3)

So the above formula would be:

L= Arcsin( C / S * Sin(A) ) [or: multiply C with Sin(A) , then divide result by S, then take Arcsin of next result ]

Also, for leading a torpedo C would be the speed of the target, but S would be the speed of the torpedo. S would only be the speed of the uboat incase you wanted to intercept the target yourself.

[Frederf]

You know I had it with 2 sines the first time when I actually worked it out but Subsim.com went down right when I tried to press the reply button. The second time (a day later) I typed it from memory and got it wrong.

Certainly C and S don't have to be the contact and the submarine. They can be anything where "C" is the speed of the "interceptee" and "S" is the speed of the "interceptor." Torpedo shooting is assumed to not be a factor since this thread is all about intercepting which is done at ranges far exceeding torpedo range.

Eventually I did end up using the law of sines to solve it rather quickly. You should see the 8 pages of very pretty and probably correct trigonometry that was leading me into madness.

[Rockin Robbins]

Yes, the underlying trig is actually fun when you're doing something destructive with it!:har:

Similar trig functions were the genesis the the Dick O'Kane and John P Cromwell attacks. You should see all Nisgeis' and my e-mails back and forth in the development of that one! It all started out with a deceptively simple (evil) drawing he sent me one day, asking if there could be a rule of thumb attack similar to Dick O'Kane for that situation.

Here came the proverbial five pages of trigonometry! And at the end of that, a short list of rules for that precise angle setup, so that the user of the method didn't need my five pages of trig!

It's funny that when I was in school I was intimidated by math and now it almost qualifies as a hobby. How far the "mighty" have fallen!:doh: