Determining Enemy Course

[KingOfNothing22]

Now this may well have been asked before and if it has, I apologise. I've done a fair bit of searching both here and on Google but so far I've not really made any ground. I also apologise in advance if it seems like a stupid question!

Recently I've taken to trying to learn how to and actually do some of the calculations I need to do certain things like calculating an intercept course or getting set up for a shot with an AoB of 90° and the like. Very little trouble there so far despite me and maths generally not getting on at all...

So earlier I was cruising along when I stumbled on a lone merchant. Very calm conditions, clear skies, heading in a similar direction to me and about 9km out when my watch picked him up. No way am I letting this one get away... So I started planning how I'd go about my attack when I thought about working out what their exact course is. Seems strange because I've never thought about it until tonight, I've just made a very rough guess and gone with that. I know it's possible to plot ranges and bearings on the map and then draw a line through them to get a course that way, but when you aren't using map updates and your 1WO is only capable of giving you ranges to the nearest 500m (the joys of LSH3) you still end up with a very rough figure.

Long story short, I spent about two hours trying to work out different calculations that could fit using information I had to hand - my course (284°), AoB (1WO said 131° PRT), their bearing relative to my position (specifically 26° according to my 1WO) - but I couldn't get anything to add up in a way that made sense. The only thing that appeared to come close was just drawing a line based on the bearing out to the range, marking it, then taking the protractor and going from my boat to the mark then plotting out ahead of it until I got 131° - that gave me a line going through 260° which didn't seem too far off given I was on a course of 284°, but the range of the merchant still appeared to change noticeably even after altering to 260°.

If that does actually work and is one of the only (fairly) simple methods of doing it I'd be happy using that, but I was wondering whether or not there were actual formulas I could use to work it out on the fly as I've started doing with setting up attacks and the like. Maybe I'm just over-thinking it. I'd greatly appreciate any responses!

Sorry for the miniature essay,
A Kaleun with a loooot to learn

[GoldenRivet]

determining enemy course is very simple if you care to use the map screen as your drawing board.

if you have map contacts on follow this method:

***For ships on an easterly course 000° through 180° use this method***

1. on the map screen, locate the target ship on the map and use the pencil tool to mark it's present position with an "X"

2. after waiting a minute or two, repeat the process using the pencil tool to mark it's new position on the map with an "X"

3. use the ruler tool to connect these two "X" marks with a straight line, this gives you a course line.

4. Now, using the protractor tool, click north of the "course line" somewhere along a line of longitude (vertical) then and move the protractor tool southward along this line of longitude on the map until you meet the course line, click again, then move the protractor tool in the direction of ship travel along the course line a short distance and click a third time, an angle will be shown such as 64°. this creates an angle which represents the angle at which the course line intersects a line of longitude on the map. 64° for example would indicate that the target ship is holding a true course of 64°

because the SHIII world is a Mercator projection, and there is no variable like current, wind, or magnetic variation to account for, the true course of 064° is also the target ship's magnetic course.

this part is very important - IF your target ship is moving westerly 181° through 359° you would follow the above example exactly EXCEPT this time you would alter step 4 to read as follows:

4. Now, using the protractor tool, click north of the "course line" somewhere along a line of longitude (vertical) then and move the protractor tool southward along this line of longitude on the map until you meet the course line, click again, then move the protractor tool opposite the direction of ship travel (out its backside) along the course line a short distance and click a third time, an angle will be shown such as 64°. because the course is westerly, and the protractor tool in SHIII only goes up to 180° you will have to add 180° to come up with the westerly course... therefore if your course line indicates 64° add 180° for a total of 244° - the target ship has a course of 244°

**** with map contacts OFF follow this method ****

Now... if you are playing with map contacts OFF you have to add a couple of steps. this is easiest from a stationary position

1. Observe the target through the scope and gather bearing and range information to the target (for example bearing is 330° and range is 1KM

2. on the map screen, use the ruler tool and center it on your own sub icon, then advance a line outward along the bearing overlay outward on a bearing of 330° for 1,000 meters, then use the pencil tool to create your X mark

3. wait a minute or two and repeat step 2 using the new bearing information.

now that you have basically created a "map contact" for your target, you may now refer to step 3 in the "map contacts on directions" outlined earlier in this post.

hope this is clear to you. i can possibly work on screenshots later on

[siege00]

The math is pretty simple based on your parameters, you might be thinking about it too much.

Starting with the fact that every triangle equals 180° total angle measure, and you have 2, you can figure out the 3rd.

Target bearing 26° with an AoB of 131° on the port side gives you a resultant angle of 23° (180 - (131 + 26)). Since he's headed from right to left, that will cause you to subtract from your True Heading of 284° (284-23) which gives you a heading of 261°. So your charting was more or less correct (+/- 1°) based on the input parameters but it's possible that your input parameters were off.

It's also possible that the contact changed course.

At any rate, that's the basic math behind it, solve for the angle that your contact and ownship make where the paths cross, then subtract or add based on which side the contact is headed. Of course if you have access to the attack disk, you can solve it without doing any math or charting.

You can also plug in your parameters into the TDC. Ie. Rotate your periscope to the target's bearing, set the AoB, lock the TDC and rotate your periscope to relative bearing of zero (straight ahead) and that will give you a new AoB, in this case 157°. Since he's headed away from you, subtract (180-157) equals 23°. Either way, still doing math I guess.

[KingOfNothing22]

Very informative and helpful answers, thanks to both

It's reassuring to know I was pretty close charting it with the protractor!

Using (180 - (AoB + Bearing)) suddenly makes a lot of sense after reading that So if the AoB is to port, which puts them heading right to left, you subtract it from your true heading - what would you do for a starboard AoB? I'm still not 100% sure on how you'd work that out.

[GoldenRivet]

the purpose of course of having a TDC was so that the commander and crew didn't have to spend precious minutes putting scratch pad to pencil to figure out information that the TDC could tell them instantly.

In shooting at a target with the TDC you really only need 3 parameters filled in

target bearing - angular difference between the front of your submarine and your target

target speed - how fast the target is going, which is super easy to determine once you figure out the ship class.

angle on bow - angular difference measured from the front of the target ship toward your submarine expressed as port side or starboard side (if the sub is on the port side of the target AOB is port and vise versa)

once you have those three things figured out you do not have to waste precious time conducting any superfluous calculations to find information you dont need - just turn the dials to the correct settings and pull the trigger.

you would need a fourth parameter - range - only if you wanted to know the estimated time of impact. i NEVER waste time figuring that one out

thing is... with the TDC - you only have to be reasonably close in your estimations in order to land a hit. in other words... if bearing is 100% accurate, there can be a pretty fair margin of error in your other variables (AOB and speed) - speed of course being the more critically accurate of the three and the accuracy of your speed calculation diminishes considerably with reduction in range.

for example. in the convoy attack tutorial... i know the exact variables to plug into the medium merchant are:

speed: 5kt
AOB: 42° Stb
Bearing: 319°

but if i alter the solution AOB anywhere from 35° to 55° and vary the speed anywhere from 4 to 6 knots... i still managed a hit in each case. thats an AOB margin of error of 20° so the TDC system is set up in such a way that it is meant to be used with quick observations, measurements taken on the fly etc

sure you could put pencil to paper and figure out all the exact variables mathematically, but in real world, the target is moving... so by the time you figured out the variables - most - if not all of them - have changed. additionally, a historical U-boat commander has already fired all of his bow tubes at between one and four targets in the amount of time it would have otherwise taken him to crunch the numbers on a single ship.

[siege00]

Originally Posted by KingOfNothing22

Very informative and helpful answers, thanks to both

It's reassuring to know I was pretty close charting it with the protractor!

Using (180 - (AoB + Bearing)) suddenly makes a lot of sense after reading that So if the AoB is to port, which puts them heading right to left, you subtract it from your true heading - what would you do for a starboard AoB? I'm still not 100% sure on how you'd work that out.

Glad to help. If he's moving left to right then you would add the result, instead of subtract it, to ownship course. Keep in mind that you've got to measure the angles that are inside of the triangle though.

Example: You are traveling true heading 020°. You have a contact that is at relative bearing 300° with an AoB of 70° to STB. The equation would be 180-(70+60) = 50. 70 from the AoB, and 60 from the bearing (300 would be the angle outside of the triangle, 60 would be the angle inside (360-300). Your course + 50° or 20° + 50° = 70° target course. So for bearing you need the degrees from your bow using the shortest path (60° to port points to the target).

Does that make sense? Hell I think I confused myself while re-reading it. It's a lot easier to illustrate.

[siege00]

What GoldenRivet says is true though. The tools you have on board, TDC, maybe you have attack disk as well, etc. are designed to help you solve the equations without doing the math. I posted just so that you could see the math because I like to know how things work. I'm a bit geeky like that.

If you want the true course because you're working on plotting an intercept, parallel course, or something the math could help, or you could chart it, or use the attack disk. Attack disk is the fastest method IMHO and has several uses as exampled in the Angriffsscheibe Handbuch. It also shows the formulae for the calculations.

[Bilge_Rat]

as others pointed out, it is a lot more productive if you plot all the data on the map, as you put down the various data points, you can easily determine target course, speed, range and AOB using the in game tools,

for example, here, by plotting two data points, measuring the time in between, we have target course 68 degrees east, speed 5 knots.






Here by measuring where I want to shoot, i.e. on a bearing of 350, I get a range of 950 meters and AOB of 76 degrees.






obviously the closer you are, the less precise you have to be, in part because the target will cover several degrees.

[KingOfNothing22]

Originally Posted by siege00

Glad to help. If he's moving left to right then you would add the result, instead of subtract it, to ownship course. Keep in mind that you've got to measure the angles that are inside of the triangle though.

Example: You are traveling true heading 020°. You have a contact that is at relative bearing 300° with an AoB of 70° to STB. The equation would be 180-(70+60) = 50. 70 from the AoB, and 60 from the bearing (300 would be the angle outside of the triangle, 60 would be the angle inside (360-300). Your course + 50° or 20° + 50° = 70° target course. So for bearing you need the degrees from your bow using the shortest path (60° to port points to the target).

Does that make sense? Hell I think I confused myself while re-reading it. It's a lot easier to illustrate.

Confused me a bit at first as well but yes it's making sense at last! If I'm following correctly I just have to remember that if the bearing is 180 - 359 I subtract it from 360 to give me a number to fit within 180. Thanks siege

It turns out I actually did this when getting ready to attack a cruiser a few months ago, without realising I was actually doing it. It also doesn't seem too different from when I was learning how to adjust your course to get a 90° AoB shot. I've written the two examples down and I'll keep practising them whenever I encounter a ship to make sure I'm doing it right.

Also, GoldenRivet and Bilge_Rat, thanks for your responses too. Some handy info there for attacks which I'll be sure to keep in mind, but here I was only looking for a precise way of working out a target's exact heading so I can travel parallel to them. In theory I'll find this useful when tracking or shadowing a convoy, since any previous efforts I've made to do so have me constantly changing course due to the distance between us either closing or opening significantly.

[siege00]

Originally Posted by KingOfNothing22

Confused me a bit at first as well but yes it's making sense at last! If I'm following correctly I just have to remember that if the bearing is 180 - 359 I subtract it from 360 to give me a number to fit within 180. Thanks siege

It turns out I actually did this when getting ready to attack a cruiser a few months ago, without realising I was actually doing it. It also doesn't seem too different from when I was learning how to adjust your course to get a 90° AoB shot. I've written the two examples down and I'll keep practising them whenever I encounter a ship to make sure I'm doing it right.

Also, GoldenRivet and Bilge_Rat, thanks for your responses too. Some handy info there for attacks which I'll be sure to keep in mind, but here I was only looking for a precise way of working out a target's exact heading so I can travel parallel to them. In theory I'll find this useful when tracking or shadowing a convoy, since any previous efforts I've made to do so have me constantly changing course due to the distance between us either closing or opening significantly.

Sounds like you've got it exactly right. Good hunting!