Using the Submarine Attack Course Finder to conduct a passive sonar only approach

[joegrundman]

Conducting a passive sonar only approach

Introduction

I have made this tutorial to describe an effective way to make submerged approaches when all you have is a sonar bearing. It takes advantage of the Mk1.Mod3 Submarine Attack Course Finder (SACF) (http://www.subsim.com/radioroom/showthread.php?t=106923) and the accompanying manual (http://www.hnsa.org/doc/attackfinder/index.htm ). This tutorial will only make sense if you have built yourself a SACF and have read and understood the manual. Generally, trying to intercept a ship which is moving much faster than you are is an unreliable process whose success depends on the speed and course of the target as well as the strength of your own tactics. However, assuming the target is reachable, then this approach will get you close to a firing position without using the periscope, even if you are targeting warships.

Without active sonar, some periscope sightings are still necessary. At least one is necessary for your range for the firing solution, but of course all periscope observations that can be made are useful and will improve the reliability of this method. However, even if the seas are very heavy or fog and rain have reduced visibility to 1000m or less this method will have you in a position to make an effective attack very quickly after the first periscope sighting is made.

This also promotes quite a different style of play. My most rewarding moments using this method have been lying in the English Channel or any other crowded waterway darting at sonar contacts, letting uncatchable ones go but killing those within your grasp, and all the while only surfacing for the minimum amount of time needed to recharge batteries.

Contact phase – establish general heading of target

Once your sonar officer has given you a contact report, take a note of type, relative bearing, whether or not closing, speed and range. Unless it is closing, forget about it. If it is moving fast, then you will require more luck to catch it. Set your true course on the Submarine Attack Course Finder (SACF) and position the periscope on the bearing given by the sonar officer. Read off the target true bearing and draw this on your map.

To establish whether the target will show you its port of starboard side, either come to a stop, turn directly towards the target or directly away from it, whichever is quickest. Once stable, if the relative bearing to target increases it will show you its starboard side, if it decreases it will show you its port side. In addition, you can also take advantage of known characteristics regarding shipping lanes and access to ports to help you determine the general heading of the target.

Approach course

Set normal approach course

Using the SACF, or working it out yourself, set a course for your submarine that will bring the target to a relative bearing of 90 or 270 degrees, whichever will intercept the target. If it is a merchant stay slow, if a warship speed up to 6kts.

Once on the new course, set your submarine’s true course and the target relative bearing on the SACF.

Estimate AOB and target speed

You now have to guess the target speed. Ships often travel at predictable speeds.

Merchant at slow speed: 6 or 7 knots
Merchant at medium speed: 8 or 9 knots
Warship at medium speed: 12 – 14 knots

So, a reasonably accurate guess is quite feasible. If your guess proves wildly wrong, you will find out eventually and you will likely not have a good opportunity to hit it. Lucky for him.

Set your speed so that your target maintains a constant relative bearing from you, close to the 90/270 degree relative bearing for a period of 2 or 3 minutes. Once you have a constant bearing to the target, you and it are on a collision course.

As you know your own speed, the following formula will provide an estimate of AOB

Own speed /Target speed = sine AOB

The following table has the range of values you will need for a type VII U-boat, I have this stuck to the side of my monitor. Read off sub speed from the top and target speeds down the side to provide the AOB in the middle cells


Sub speed
x --------------3kts ----4kts---- 5kts ----6kts ----7kts
Target speed

5kts ----------AOB37 ---53 ------90 --------------- -
6kts------------ 30 -----42------ 56 -----90 ---------
7kts------------ 25 -----35------ 46 -----59------ 90
8kts ------------22 -----30 ------39----- 49 ------61
9kts ------------19 -----26 ------34 -----42------ 51
10kts -----------17 -----24 ------30 -----37 ------44
11kts -----------16 -----21 ------27 -----33 ------40
12kts -----------15 -----20 ------25 -----30 ------36
13kts -----------13 -----18 ------23 -----27------ 33
14kts -----------12 -----17 ------21 -----25 ------30
15kts -----------11.5 ---15 ------19 -----24 ------28
16kts -----------11----- 14 ------17----- 22 ------26


It is optimal if you have an AOB between 20 and 35 degrees.

If you find you can’t get a quite stable AOB, make micro adjustments to your course to return the target to a relative bearing of 90/270 degrees until it stabilizes. If the target appears to be off the scale you can manage, then it is too fast or has turned away from you or is otherwise uncatchable. Forget about it and return to waiting for a better contact.

If you find you can only get a constant speed match at very low speeds (1 or 2 knots) then it appears that you have a very small AOB. In that case you should try approaching maintaining a relative bearing of 60/300 degrees or less, but the table above will not work.

Read off the appropriate AOBs for your chosen target speed and the speeds either side of it. Eg. Your speed 4kts, estimated target speed 8 kts, AOB 30. Note also 7kts give AOB 35 and 9kts gives AOB 26.

Double check that the periscope marker on the SACF is set to the target relative bearing, and then set the enemy wheel to show the correct AOB and note down the target true courses for the three AOBs given. Mark these down on your map for quick visual reference.

Estimate target range

Reset your stopwatch and drop the sub’s speed by 3 knots, eg from 6 to 3 knots or from 3 to 0. Use power back to increase deceleration if traveling at slow speeds. (Alternatively, if feasible, you could speed up 3kts and subtract instead of add for the speed calculations)

Once at your new speed, take note of the present target relative bearing as reported by the sonar officer and start the stopwatch.

Now you need to use the range finder on the reverse side of your SACF. Set the arm to your current speed and set the degree wheel to the estimated AOB (use the median value of the three) and read off from the 90 degree mark the estimated target speed assuming no change in bearing. For example, if dropping speed from 6kts to 3 kts with an estimated AOB of 30 and target speed of 12kts, we note the predicted target speed of 6kts.

Then wait for the relative bearing to move forward 3 degrees, and note the exact time when this point has been reached. Place the arm on the range solver side of the SACF on to the speed that represents the difference between your estimated speed and the predicted speed noted just before. In our example, with the estimated speed of 12kts and a predicted speed of 6 kts, 12-6=6, we place the arm on 6kts. We then rotate the degree wheel until the 3 degrees mark is in line with the exact time passed, in our case 4min50sec. We then read off the range in line with the angle on bow - in our case 30 degrees gives a range of 9100 yds.

As we are playing SH3, ranges need to be converted to meters. Just knock off 10% for an acceptable conversion, so 9100 yds gives 8200 meters range to target.

Mark range to target on the map. Stop the stopwatch. Speed up to maximum to try to regain some lost ground, or slow down to previous speed setting. (It is not vital that you regain lost ground, if we have got this far you will probably be able to intercept the target and you would ultimately like it if the target is a little in front of you when you make visible contact)

If target changes course

If you have a stable track and the target suddenly changes relative bearing, then the target has changed course. It may not be possible to catch up with the target, but if you still have plenty of range and it is not moving too fast then you may be able to keep up with the target. Bear in mind that most course changes are of 30 degrees.

Preparing for attack

Now mark true courses for the different possible AOB’s on the map, with the courses passing through the measured range. There will be an area in which you expect the target to appear. Mark in a point on your course at which range to target is 3000m and again at 2000m. Also note the angles at which you will intercept the target track. You should plan ahead for the firing course, and the final AOB solutions, you will adopt once you have made visual contact. Any mental preparation you can make in advance will save you valuable time once visual contact has been made.

If you already know the range of visibility, mark the point on your track at which you expect the target will become visible.

These precautions are necessary because you do not want to miss the first possible observation, especially if visibility is very poor.

Make regular scope observations. Once visual contact is made, look to see if its apparent range and AOB falls within your predicted area. If so, prepare for attack. If you have passed the nearest predicted track and the target has not yet appeared, reset your calculations assuming the target will appear around the next predicted track.

Attack Phase
In situations of poor visibility or severe sea conditions, your firing solution is going to be weak. In order to minimize the error there are three things that should be considered essential.

Firstly, you want a gyro angle as near to 000 as possible, in order to eliminate errors due to torpedo tube parallax (the difference between the angle to the target from the front of the submarine and the angle to the target from the periscope in the middle of the submarine). This error becomes significant when range solutions are weak.

Secondly, you want to be firing on the optimum torpedo track to hit the target. It is not 90 degrees from the target’s bow. For a fast running torpedo it is about 100 degrees on the bow for a merchant and about 110 degrees on the bow for a warship at medium speed. See the Submarine Torpedo Fire Control Manual (http://hnsa.org/doc/attack/ ) for further information.

To obtain this optimum firing course using the SACF, assuming it is already set up accurately to represent the sub’s and the target’s courses, move the periscope marker to the 100 or 110 degree point on the appropriate side of the target’s bow. Read off the correct firing course on the true course wheel on the opposite side of the scope.

Thirdly, just as in real life, you must use spreads. Single shots are not sufficient. I prefer to make my spreads manually as I then have more control over the angle and time between shots. For a two shot spread, aim the first to near the stern and the second a few seconds later to near the bow. If you use a third one, send it down the middle.

Extended Example
We are cruising at 3kts on silent mode at 25m depth about 50km north of Scapa Flow on heading 275 degrees.

Contact


“Contact. Warship. Closing. Medium Speed. Bearing 005. Long range”

Set course bearing 275 on SACF. Set periscope to 005 on SACF and read off true bearing to target, 281. Mark this bearing on the map.

As the target is close to directly ahead of the sub it soon gives a new relative bearing of 006 without my having to maneuver. This means the target will show its starboard side and pass to my north.

Begin approach

By now target is at relative bearing 008. Read off from periscope view on SACF the 90 degree approach course (normal approach course), which is 015. Turn to 015 and speed up to 6kts. Reset submarine’s true course on SACF.Reset Periscope view on SACF to the now presented target relative bearing – 272 degrees.

The relative bearing to target appears stable after a few seconds, so I start the stopwatch. After 2 mins the relative bearing still hasn’t changed, therefore I consider us to be on a collision course.

Estimate AOB

Assuming the target is cruising at a typical speed of 12-15kts, I use the AOB table to get possible AOB’s of 30 for 12kts, 27 for 13 kts, 25 for 14 kts and 24 for 15kts. Using the SACF I obtain target true courses of 075, 078, 080 and 082 degrees. I mark these on the map as a reference.

Estimate Range

I reset stopwatch and set speed to 3kts, and note the exact bearing to target, 272 degrees.

Once the speed reaches 3kts, start the stopwatch.

On the SACF rangefinder, set speed to 3kts, AOB to 25 and read off predicted range for stable 270 degree relative bearing, which is 7kts.

The bearing moves forward 3 degrees to 275 at exactly 4 mins and 50seconds. Set speed to 7kts to regain some lost ground, but this is not urgent, as ultimately I do not wish to collide.

Estimated target speed is, say 14 knots, and 14-7 gives 7. Put the arm of the range finder on the 7 knot mark. Keeping the arm steady, rotate the degree wheel until the 3 degrees marker on the degree wheel matches the time of 4 mins and 50 secs. Read off the range in line with the estimated AOB of 25 degrees. 9000 yds.

Now we have to convert yards to meters, 9000 yards – 90 = 8100 meters

Now we plot the estimated courses at the correct range.

I also draw a line of sight bearing indicating when the 2000 m range to target is coming up.

I note that my track angle on the target is close to the optimum of 110 degrees, so I do not need to change my course to get a better firing position, and so can begin to program the TDC assuming I contact the target on the earlier course.

At about 2000m from the target I make visual contact. It is very heavy weather and accurate range, or even type recognition, is impossible. However, range and AOB appear to fall within my estimated range.

At about 1000m I can see that the target is too far to be on the nearest estimated track, so I assume it is on the next track. I shift the AOB wheel on the TDC 4 degrees. I identify target as V&W destroyer.

I am in firing position, and have only a 350 degree gyro angle, I make a final observation, realize range is about 500 m further than estimated; giving a total 1500m range, but my position is optimal, so my figures should work and I must make a decision now.

I send range to TDC.

At 358 gyro I send tube 1 at the stern of the target, 4 secs later at 001 gyro I send tube 2 at the bow.

Boom! First torp hits forward of the center. Second torp skips past the bow but the damage is done. The destroyer knifes straight down to the bottom. It was a C-class destroyer.


Acknowledgements

Thanks to Captain Krunch for his research and excellent vision in building the first SACF replica. Thanks to the admin of hnsa.org for coming up with the declassified submarine doctrine manuals. I am a changed man now!

[Hitman]

Wow that's a great job

Really useful for those of us using the MK3

Would you consider doing a pdf version? I can host it at my filefront account if you are not interested in opening one.

EDITED: Forgot to add: I did not just the reverse side of the MK3 but also a german wiz wheel that has in its rear side the same funcionality as the US MK3, but with a metres scale. If you want a wiz-wheel for SH3 you can build that one and you no longer will need to convert anything from yards to meters! Do a search in this very same forum or go to my filefront page and download the templates: http://hosted.filefront.com/HitmanPacificAc

[joegrundman]

Thank you. I'm glad you like it .

I'm just downloading PDF creator now. The pdf one will include diagrams to clarify it.

I forgot to note that for people without a SACF (you really should know better), you can approximate this method by simply setting your intercept course to bring the target to 90 or 270 degrees relative to you and assuming that long range = 9000m in fair weather.

[joegrundman]

Hi Hitman

I have made the pdf with some crude illustrations. Are you still interested in hosting it? If so, how do I send it to you?

by the way, i love the german is-was. Awesome work. I look forward to you hosting your Aspect ration whiz wheel too

joe

[Hitman]

Sure! You got PM from me

[jmr]

Is this available for download now?

[joegrundman]

If you can't find it yet, PM me your email address and I'll send it to you

[jmr]

Sent, and thanks again.

[Maraz]

Very interesting, I hope the PDF guide can be soon available. Maybe with some hints when using Hitman's German whizwheel.

Thanks
Maraz

[Hitman]

Catching up with my e-mail today I got the tutorial and uploaded it to my FileFront account, you can get it here:

http://files.filefront.com/UsingtheM.../fileinfo.html

Happy Hunting all, and thanks again Joe for the great tutorial

[joegrundman]

This tutorial has been updated with labelled diagrams as well as appendices describing some other uses for the SACF to help calculate convoy width and aspect ratio.

You can get it from my filefront in my sig, and hitman, if you are interested would you like the updated version?

[Hitman]

Well since you already opened a Filefront account I think I no longer need to host it, as you would obviously prefer the control of your own work, so I will delete mine if you want. (Of course I will download the updated file and keep it ) Or if you want two hosts, then also just tell me. I'll do whatever suits you better

[joegrundman]

OK, just removed an error in the convoy width appendix.

Hitman, well, i really don't mind if you host it. I am happy for this to be seen by anyone who might find it useful and the fact is that people are more likely to come across it in your filefront link than in mine, but equally i appreciate that you don't want to be hassled by me every time i make some trivial amendment to it.

You know what I think would be a good idea?

A stickied thread linking to all the various strategy and tactics articles written by the community, with a very short review for each one. I'm only recently here and have come across some great stuff and can only wonder at the other marvellous stuff that has been lost to the depths of the forum, never to be seen again except through a lucky search result or someone's comment.

[jmr]

Is the corrected version uploaded somewhere?

[joegrundman]

Yes, you can get it from my filefront account in my sig.

It's still not the final version. I'm working on an improved method for preparing your attack in conditions of very low visibilty without ever having to stop.

It'll still be based on having final visual confirmation before firing however. Gotta check it ain't a neutral after all