Constant Bearing Method, with TDC
 

Hello fellow captains,

I have newly subscribed, but have been eavesdropping as stowaway for a while now. I am actually an old hand in playing Silent Hunter. I have enjoyed them all: SH1, SH2, SH3 and SH4... Stock game in SH4, no mods yet.

I want to share the most accurate method for shooting torpedoes in SH4, American submarine, which I have come across so far. It is a constant bearing method which employs the TDC. Whenever I use it, and do everything right, I get sure hits, even with long-distance shots up to 4000 meters. I have also found it to work well for convoy surprise attacks. Last time I encountered a convoy, I got all 3 front row ships with my 6 bow torpedoes, they all sank...

Ok, here we go... I have included screenshots for clarification.

First thing to do when acquiring a new ship contact: Determining course and speed. I won't go into details here on how to do it, there are many well-documented methods plus it's easy when map contact updates are set to "on", but it has to be done with a high degree of accuracy for the constant bearing method to work out well.
Draw the enemy course line on the navigation map.

Second step: Choose your firing spot, somewhere near the target course line, wherever you like best. Go there, and stop the sub completely. We will stay here until after firing.

Third step: Choose the line of bearing for your attack. This is the constant bearing line which we will aim along later. Draw the constant bearing line on the nav map using the ruler. You get the distance from your sub to the target when it will be at the aiming point. This is not a critical measurement.

http://astro.nightsky.at/Download/ConstantBearing_1.jpg

3000m - is he kidding....? (I am playing with metric units here.)

Fourth step: Use the protractor tool to get the exact AoB.

http://astro.nightsky.at/Download/ConstantBearing_2.jpg

64 degrees starboard.

Fifth step: Now we need the angle between our heading and the constant bearing line for setting the periscope. Easy when you have a 360° Bearing Plotter, just read the scale on the constant bearing line. In the stock game, I don't have it, so I measure the absolute angle of the constant bearing line with the protractor tool.

http://astro.nightsky.at/Download/ConstantBearing_3.jpg

113 degrees, add 180 for left (western) side -> 293 degrees.

OK, now let's input all the data into the TDC. The Position Keeper remains off, we set up for a static solution. Don't forget to confirm each step by pressing the red "Send to TDC" button with the white triangle on it:

Target speed...

http://astro.nightsky.at/Download/ConstantBearing_4.jpg

Angle on Bow... (not easy to input exactly!)

http://astro.nightsky.at/Download/ConstantBearing_5.jpg

Target range... Read it on the PK

http://astro.nightsky.at/Download/ConstantBearing_6.jpg

OK, now set the periscope to the preselected constant bearing. I repeatedly press the "set heading to view" button for that. We won't turn because we don't move, but the chief executive will read you the absolute bearing you are looking at currently. I repeatedly try until it matches the absolute value of my constant bearing line - 293° in my case. Press the red triangle button on the TDC again to confirm it.

http://astro.nightsky.at/Download/ConstantBearing_7.jpg

(Note that the PK will now display the data you did enter - for example the AoB.)

Don't touch the periscope after you have done this! Its vertical line is now our well-aimed firing reticle. We will wait until the juiciest parts of the enemy ship cross it, and fire exactly then!

For now, let's wait submerged at periscope depth, periscope lowered, well hidden and silent until the enemy is where we want him - no need to expose the periscope until just before firing... We are playing now a big, silent hole in the water, but a hole with a well-aimed high-precision gun...

Now is a good time to open the torpedo tubes, go to silent running (without moving), and ring the bell for battle stations.

The nav map with its sound bearing lines is a good indicator when to raise the scope for the firing procedure.

http://astro.nightsky.at/Download/ConstantBearing_8.jpg

Up scope! Let the target steam into the firing reticle. Fire at will. I usually shoot two torpedoes, one into the foreship, one aft. Three torpedoes will do nicely for larger targets.

http://astro.nightsky.at/Download/ConstantBearing_9.jpg

Oh, a small Engine-Aft - I didn't look earlier, set it all up using radar data only...

http://astro.nightsky.at/Download/Co...Bearing_11.jpg

Both running straight and true. I love those Mk23's...

http://astro.nightsky.at/Download/Co...Bearing_12.jpg

Really? At 3000 meters...? :yep:

Additional comment: For a convoy attack, I use the same procedure, and set up for an average distance. Using an AoB between 60° and 80° (depending on target speed), I can fire at two or three ships which are aligned in a row, furthest first, nearest last, to time the torpedo impacts near-simultaneous. Let them run into the firing reticle, one ship after another, they are all traveling at the same course and speed - unless previously alerted, which is when they go into wild zigs...

Happy shooting! ;)

Pretty impressive first post there. Welcome to the forums. :up:

I just tried your method, works very well. Pretty nifty trick using the heading to view while stationary. It does raise a question. Did real periscopes have the ability to know what direction (heading) they were looking in? It would seem so, as it would not have required anything difficult, just a compass on the scope. Otherwise, some might say "that a cheat", just curious.

Well, you know your heading by looking at the compass. You know the angle you want 293 degrees, so if you look at the picture where the 293 is circled that is about 22 degrees, look at the compass, it is NW, add 293 degrees plus 22 degrees, and you get NW. Or take your heading of NW subtract 22 degrees and get the 293 you want. So, I don't see it as cheating since you can calculate where the periscope is pointing just by knowing the heading of your sub.
I haven't tryed it, but if it works, great!! The only drawback I can see is if there are any DDs in the area and they are pinging, you don't want to sit in one spot. So you would need a Plan B.;)

Peabody

yup, when i was really little, and i was making play attacks on passing ships in Groton @ the nautilus museum, I could almost sense what bearing i was looking in, just by the instant i started looking thru the scope, what direction i was facing...my stepdad used to call out bearings when I called "bearing...mark!"
its too bad im almost too old for that :rotfl:

EDIT: beautiful work, Rocks'n'Shoals, I shall try that next time the Scorp puts out

If I'm not mistaken, the TBT and scope had a button that could update the heading.

How are you changing that value on the PK for range?

One deal-killer for me in your technique is your very first step: stop the boat. In real life you couldn't do that. Even on the surface, stopping loses all directional control of the sub. Under water it is even worse, as all depth-keeping and directional control are lost. Your entire technique relies on defects in the game physics model. Other than that, it's bulletproof!:up:

You know, there is no reason you have to stop your sub. Just throttle down to about a knot or a half a knot to begin with. Turn on the PK as you enter your parameters and use the present AoB of the target for this part. Calculate the AoB in your way for your intended shoot bearing for later. This will actually allow you use the attack screen to check your inputs of speed and target course for accuracy as the target cruises down the line. When the target is 5 or 10 degrees before the shoot bearing, turn off the PK, enter the AoB for the shoot bearing, sight on that bearing, press send range/bearing and just wait a few seconds for the target to pass through the crosshairs, shooting as juicy parts are in the sights. Your resulting dozen yards or so of range error won't mean a thing (range cancels out of any constant bearing attack anyway and is only important for correcting parallax errors with increasing gyro angles on the torpedoes).

NOW you have a realistic shooting technique!

Nisgeis is now going to jump on the thread with his method of vector analysis to do the whole shebang in seconds and you could shoot at full throttle if you wanted to. THEN you can throw the whole TDC overboard, as all it is is ballast!

True.
But there is an easy solution to that, if you want to play that realistic: A little time prior to shooting, ring up very slow speed for directional control. Correct your setup just before shooting. Target speed won't change, and range is not critical except when you are very close to your target. But you may have to to update the AoB and your periscope bearing. It helps if you move in the direction of the bearing line, then you probably won't have to update the AoB.

Thanks, RR ;)

I have tried that, and have not been satisfied with the accuracy I got, except if I actually stopped the time and entered an exact solution. But that would be unrealistic as well, wouldn't it?
But maybe I can work out a method along those lines which satisfies my ambition for long-distance killer shots ;)

Actually I find the TDC a very good and accurate tool, that is if you know what it does and how to use it correctly. Of course you could compute your solution with a separate calculator or plot a graphical solution on a sheet of paper, but why should I do so, if I have the calculator on board?

It is updated by pressing the red triangle button on the stadimeter input of the TDC. If you are not satisfied with the value shown, correct the stadimeter, and press the button again.

That last advice is right on. I manually correct ranges all the time. Just make sure the target is in the crosshairs when you press the button because range and bearing are updated together!

Rocks'n'Shoals, this thing goes in the [REL] Video Tutorals: TDC + PK advanced thread, with your permission of course. Your instructions are very precise, you don't leave out any steps and you communicate very clearly. It deserves to be in a sticky thread, not buried for all time in the anonymous archives.:up:

Thanks RR, I am of course happy to give that permission.

Here's some food for thought: Provided your observations on the target's course and speed are correct and you're firing with a gyro angle of zero using the constant bearing method, range doesn't matter. That naturally means that it doesn't matter if your boat is stopped or moving either.

It doesn't matter how fast the target is going, what its course is or at what bearing it is, a zero gyro-angle constant bearing shot will always hit regardless of the range, provided that it is actually possible to hit the target at all. Here's short illustration:

Here we have a torpedo track angle of 45 degrees, just as in one of RR's tutorials. Our Mk18 torpedo has just exited the tube, going straight forwards at 29 knots as a good Mk18 with a gyro angle of zero should. The target we're aiming at is the middle one, and the two others are to show you the effect of miscalculating the range, badly. Distance to the "firing bearing"-node is written there, ~4400 meters. The red circle with "x" in the middle is the intercept point for a 29-knot torpedo for those targets.

http://staufa.sytes.net/files/sh4/pics/45degrees.jpg

Same situation, torpedo track angle is 90 degrees.
http://staufa.sytes.net/files/sh4/pics/90degrees.jpg

Yet again, with a torpedo track angle of 120 degrees.
http://staufa.sytes.net/files/sh4/pics/120degrees.jpg

As you can see all the targets sit on the same bearing line when the torpedo is fired, and regardless of the target they sit on the same bearing line when the torpedo hits. Naturally the firing bearing varies depending on the situation, but if you are able to calcuate it accurately for each target you can forget about range. :up:

Shooting on sound & radar data only
 

With the constant bearing method, you don't have to use the 'scope to shoot. You can also shoot on the map only, using sound bearing lines and/or radar positions (if you are at radar depth). Just wait until the ship passes your constant bearing line on the nav map. Bear in mind that sound bearings originate from the screws, which are located at the stern of the ships...

A sea story to go with that: Recently I encountered a small task force consisting of three destroyers, running 12 knots. Heavy rain, visibility about 600 meters. I set up for constant bearing, for a range just over 1000 meters, and stayed at radar depth to detect them steaming to the firing spot - both with sound and radar. Got the first one amidships (I think, never actually saw him). It sank immediately, one torpedo is enough to crack up those small tin cans...

Too bad his colleagues were of the elite kind. Can't imagine what they had against me... :doh:

I fired at the second one when it crossed the constant bearing line, but it turned on me, so the torpedo couldn't hit. I immediately went deep, below a thermocline, and crept silently along at just over 1 knot to get away, changing course now and then to confuse them... No chance. They seemed to know exactly where I was, circling above me, and dropping DCs right on top of me. After hours, and after sustaining an increasing amount of damage, they backed off a little. I tried to go to periscope depth for a possible shot... BAD mistake, they where back right on top of me in no time, and bombarded me again, this time for critical damage. Good tactics on their part. :o

Getting desperate, I surfaced and tried to run for it, flank speed. But they are expert gunners, you know... I got one with the deck gun, but the other sank me. Ouch! :damn:

So, learn the lesson, and avoid task forces consisting of destroyers only... It might be their "task" to sink unsuspecting subs like you. They are just waiting for you to shoot at them - you will be lucky if you escape alive, certainly not undamaged. Great addition to the stock game, keeps the tension up...

Well, that is a good approximation for far-away targets, but not exactly true, because there is a thing called "torpedo ballistics". Torpedoes do not instantly accelerate to full speed. Instead, they start with a slower ejection speed, and reach full speed only after a few seconds in their run. So you actually have to calculate with a corrected torpedo speed, which is dependent on distance: Lower for nearby target, higher for far-away targets. The TDC does that for you, if you enter the range correctly.

A zero-gyro shot aimed correctly for a far-away target will miss a bit astern, if the target is suddenly very close and moving fast.

I figured that out after reading your instructions again. I have to say, it worked just great. However, and no fault of your own.....to friggin duds:down: Darn BuOrd...fix the torpedoes!!!! Anyway, RR is correct, the sub will either sink or submerge when propulsion is not present. I do not remember. GWX was able to implement that for SH3. Cool feature. Might be a good idea to drum up a mod to do this in SH4:hmm: This will then overcome the only critical point RR presented. So, at the very least, your sub would have to maintan 1 kt and that should not screw up your shot at that speed.