Two Historical Firing Methods (Hit What You Are Aiming At Without AOB or Speed)

[derstosstrupp]

Hi All,

Thought I would bring this back to the forum's attention. I posted this awhile back in the SH3 forum, but as it relates to historical U-boat firing procedures, SH5 fans deserve to know about them as well!

Note the following refers to SH3 mods etc, but the methods do not change as a result.

As a user of Vecko's outstanding TWOS megamod with TDW's excellent additions, I can say that, if the folks here find these methods useful, it would be great to see them added as reference sheets in similar fashion to the Target Assessment help charts for in-game reference.

And, to admin, given the historic nature of these methods (procedures from the 1930 Torpedo-Schiessvorschrift), could I request this become stickied to preserve it, if the folks here find it useful (folks, please chime in!)?

Introducing two firing/data acquisition methods which, after repeated tests using the torpedo tutorial in the academy, have proven to be successful and are 100% historically accurate, which ought to make other fellow “targeting realism” die-hards grin. I am using NYGM with Hitman’s GUI.
These methods are:

1. Ausdampfverfahren - (constant bearing to target)
a. Advantages/Requirements:
i. requires no estimate of target AOB or speed prior to firing
ii. requires only maintaining a constant bearing (collision course) and knowledge of own speed
iii. requires range estimate to correct for parallax prior to shot, but can be roughly estimated
iv. can use to derive target speed with solid knowledge of AOB
b. Disadvantages:
i. not optimal when target AOB is small when on collision course due to small target presented for the torpedo
ii. less accurate than plotting during the overhaul maneuver, and is thus best used when encountering the target forward of the beam (say at 45 deg AOB or so)
iii. should not be used for night surface attacks, as Hundekurve (dog’s course, keeping bow to target) should be followed to minimize sub silhouette.

2. Auswanderungsverfahren - (change in bearing of target over 1 minute)
a. Advantages/Requirements:
i. requires no estimate of target AOB or speed prior to firing
ii. requires one rough range estimate, own speed, and the bearing change of target over 1 minute
iii. requires final range estimate to correct for parallax prior to shot, but can be roughly estimated
iv. can be used at long distances during the overhaul maneuver to obtain rough speed with a rough idea of target AOB without slowing and thus losing time in overhauling
v. can be used to derive actual target speed with solid knowledge of AOB
vi. allows more freedom of maneuver than Ausdampfverfahren as no requirement to keep a constant target bearing, and thus can be used for night surface attacks
b. Disadvantages:
i. Less accurate than the Ausdampfverfahren and plotting during the overhaul maneuver, and is thus best used when encountering the target forward of the beam (say at 45 deg AOB or so)
ii. not optimal when target AOB is small due to small target presented for the torpedo and need for appreciable bearing change

Of course, the results of either method are only valid if the target maintains course and speed. For both methods, a scientific calculator with trig functions (otherwise known as your WO standing near you working the slide rules) is also necessary.

I will preface this by saying that by no means are these original ideas; these methods are historical and come from the Torpedo-Schießvorschrift (torpedo firing provisions) from 1930. I credit my knowledge of these methods to the gentleman who put together this site:

http://www.tvre.org/en/acquiring-torpedo-firing-data

This site outlines the ins and outs of the real-life Torpedo-Vorhaltrechner (German TDC) as well as other ancillary information and is a must-read for all who haven’t yet. The page linked above details the methods of acquiring firing data and includes the methods I will be demonstrating below. Thus, I am merely compiling these methods below in a thread for ease of reference and implementation into SH3.

I will discuss each method in a separate post to follow. :salute:

[derstosstrupp]

Step 1:
Gain position forward of enemy’s beam. Submerge once a position sufficiently forward of the target’s beam has been achieved. Otherwise, at larger AOBs, a constant bearing may not be possible due to the low underwater speed of the sub. Not too far forward, however, that the target presents too sharp of an AOB – your eels will then have little surface area of the target to impact.

Step 2:
Achieve a collision course to target by either adjusting own speed or turning to or away so that the target bearing does not change.

Step 3:
Ideally, maintain this constant bearing for a period of 10-15 minutes, preferably the 10-15 minutes up to firing. 10-15 minutes allows you be sure you are truly on a collision course, however in practice you could get by with much less, perhaps 3-4 minutes. Use this time to set up your eels for firing (depth, pistol, outer doors etc).

Step 4:
Set up TDC for the shot.
1. With scope pointed at the target (collision bearing you’ve been hopefully maintaining), set AOB in TDC to 90 starboard or port based on the direction of the target’s bow.
2. Compute speed for the TDC as follows:
a. Own speed x sin(target bearing) = target speed to input into TDC. Remember, this is degrees from the bow, so if she’s constant at bearing of 330, the target bearing for this formula is 30!
3. Immediately prior to firing, obtain a range estimate and input into the TDC. Now toggle TDC to auto. This is a must to correct for parallax, or the error caused by the fact that you are not shooting torpedoes out of the lens of your periscope, unless of course the gyro angle is within 10 degrees or so of your bow, in which case parallax error is moot. Use whatever your GUI offers. I use Hitman’s top-notch GUI and thus only estimate using the scope reticles. This is more than sufficient. Just know that errors due to inaccurate range will be more pronounced the closer you are and the larger the gyro angle. Alternatively, you could start a turn toward the target once you obtain the gyro angle for the shot and pull the trigger once your bow crosses the zero gyro angle bearing, thus eliminating the need for the torpedo to turn and the need for a range estimate, but I have found this a bit unwieldy in practice.

Step 5:
Once at a good firing range, fire!

Nary was a mark or line or angle drawn on the map throughout this whole process. No information was needed from the rec manual either, although a rough knowledge of the target’s mast height is needed for a range estimate if at large gyro angles.

Below is a video demonstration of this method:
https://www.youtube.com/watch?v=Pc42omH5iio

[derstosstrupp]

A note to modders/tech-savvy folks: The tvre.org site I linked above in the first post has an example of the slide rule for this method (see part about Auswanderungsverfahren “B”, toward bottom of page). It is relatively self-explanatory how this slide rule is used once you understand the guts of the calculation. Makman had mentioned in a post I’d seen about the desire to implement this slide rule in-game. I second that!

Step 1:
Gain position forward of enemy’s beam. Submerge once a position sufficiently forward of the target’s beam has been achieved. Otherwise, at larger AOBs, approach may not be possible due to the low underwater speed of the sub. Not too far forward, however, that the target presents too sharp of an AOB – your eels will then have little surface area of the target to impact.

Step 2:
Once you’ve nearly closed to firing distance, jot down your own speed (Ve), estimate range to target (E) and note the target’s bearing (b1). Start stopwatch. Do not alter own speed! The rest of this method only takes a couple minutes before firing, and so keep that in mind with respect to “nearly closed to firing distance”.

Step 3:
Once exactly one minute has passed, stop the stopwatch and note the new target bearing (b2). Do not move scope from this bearing until you fire for the rest of the method!

Step 4:
With scope pointed at (b2), set AOB in TDC to 90 starboard or port based on the direction of the target’s bow.

You now have 4 pieces of information noted: own speed (Ve), first bearing (b1), range at first bearing (E) in hectometers (this is important – take your range and divide by 100 and use this figure in the calculations), and second bearing (b2). Remember, this is degrees from the bow, so if she’s at bearing of 330, (b2) for this formula is 30! The change in bearing (b2-b1) we will call (w). Time to crunch numbers (in other words, time for your trusty WO to start spinning those slide rules, and thus pause is fine until you become proficient). Items in parentheses above are used to denote items in the formulas below.

Step 5:
Compute speed for TDC.
1. (Ve) x sin(b2) = (Vk). This represents the speed to input to the TDC IF WE WERE ON A COLLISION COURSE. We are not – the bearing is changing and thus we need to apply a correction:
2. (E) x 3.2967 x sin(w) = (d). Remember to convert your range (E) to hectometers by dividing by 100! The 3.2967 factor is to correct from metric to nautical miles since the correction (d) is in knots.
3. (Vk) +/- (d) = speed to input into TDC. If sub and target bows going in the same direction and the bearing change showed the target pulling ahead, you will ADD correction (d) to (Vk). SUBTRACT if sub and target bows are going the opposite directions, or if you are gaining on target (bows in same direction).

Step 6:
Obtain a final range estimate and input into the TDC (easily estimable since you got (E) already, just use judgment as to what the firing range would now be a minute or so later). After inputting, you should still be on (b2). This is a must to correct for parallax, or the error caused by the fact that you are not shooting torpedoes out of the lens of your periscope, unless of course the gyro angle is within 10 degrees or so of your bow, in which case parallax error is moot. Use whatever your GUI offers. I use Hitman’s top-notch GUI and thus only estimate using the scope reticles. This is more than sufficient. Just know that errors due to inaccurate range will be more pronounced the closer you are and the larger the gyro angle. Alternatively, you could start a turn toward the target once you obtain the gyro angle for the shot and pull the trigger once your bow crosses the zero gyro angle bearing, thus eliminating the need for the torpedo to turn and the need for a range estimate, but I have found this a bit unwieldy in practice.

Step 7:
While still on (b2), toggle TDC to auto, reacquire target and fire! You’re already at a good firing range. That is a benefit of this method – it is very quick once you get the hang of the calcs, all done immediately prior to firing.

There are also other handy uses for the Auswanderungsverfahren method, such as at long distances during the overhaul maneuver to obtain rough speed with a rough idea of target AOB without slowing and thus losing time in overhauling. In time, and if interest is shown by the community, I will post.

Below is a video demonstration of this method:
https://www.youtube.com/watch?v=pylYxlBkgfk

Enjoy and gute Jagd!

[vdr1981]

Thank you very much for this thread! :up:
Maybe Sjizzle could indeed add your instructions to his charts, that would be very useful for sure...:yep:

EDIT:
Scripted tutorial mission based on these instructions would also be great...:yep:

[siege00]

I'm planning on trying it out between patrols. Downloaded a free iPhone slide rule to increase the realism. lol. Great stuff, and the value of being able to fire confidently while in constant transit has immeasurable benefit without having to drop into the map or put my nose on the target. :up:

[derstosstrupp]

Thank you very much for this thread! :up:
Maybe Sjizzle could indeed add your instructions to his charts, that would be very useful for sure...:yep:

EDIT:
Scripted tutorial mission based on these instructions would also be great...:yep:

That would be outstanding! By the way, TWOS brought me back to SH5.... I thank you sir!

[derstosstrupp]

OK I've had an epiphany. The speed to input for the above methods can be easily computed using the rear side of the attack disk (click in the middle of the front side to flip it over) included in TDW's UI within TWOS.

For the first method (Ausdampfverfahren), get speed for TDC by aligning own speed (middle numbers within middle ring) with 90 deg mark on outer ring (right at the top). The speed that intersects the outer ring at the collision bearing is the speed to input.

For the second method (Auswanderungsverfahren), same procedure as above, but to this result you must add/subtract correction (d) as we know. To compute this correction, align range at 1st bearing (E) with 90 deg on outer ring. Then align 1-00 on the "Zeit" disk (or longer if we waited more than a minute) with the change in bearing (w) on outer ring. Read speed correction at the red index line. Should be noted that you need at least 6 deg of bearing change to use the disk. Therefore wait as long as you need to get that change; just be sure to note the exact time you waited and align it with the bearing change on the outer ring.

No need to take eyes off the game with this method. Please share your thoughts/success!

[siege00]

Nice! You're doing the same formula on the Attack Disk's slide rule instead of the calculator. I've been using it to lower my map work for visual contacts and intercepts, but have just started truly using it and understanding it as a slide rule. Very cool!

[Sjizzle]

Thank you very much for this thread! :up:
Maybe Sjizzle could indeed add your instructions to his charts, that would be very useful for sure...:yep:


do u mean something like this ?????

and i still have more charts :D

http://www.mediafire.com/convkey/c906/7uqt8f0qnl5088ezg.jpg

http://www.mediafire.com/convkey/5d7b/ee9f3lt8t3vftrvzg.jpg

http://www.mediafire.com/convkey/d89e/2xw8jazehp51y22zg.jpg

http://www.mediafire.com/convkey/7802/hnfdwwdhb8ldaplzg.jpg

http://www.mediafire.com/convkey/3fa0/klbtz1n638fhtu2zg.jpg

[siege00]

Plate XIV is the process that I've been using with the attack disk, based on one of the Angriffsscheibe Handbuch methods. It uses the same formula as plate XIV. The method that Destross wrote about below eliminates the denominator from the formula (for the first method at least - sin(AoB). Don't know if it considers the sin(AoB) negligible as it approaches 1 @ 90°. I love the maths, but don't know how formula from the plate would work and formula from Ausdampfverfahren.

I haven't started looking at the 2nd method (Auswanderungsverfahren) yet. :D

Do you have charts for those Sjizzle?

[derstosstrupp]

Plate XIV is the process that I've been using with the attack disk, based on one of the Angriffsscheibe Handbuch methods. It uses the same formula as plate XIV. The method that Destross wrote about below eliminates the denominator from the formula (for the first method at least - sin(AoB). Don't know if it considers the sin(AoB) negligible as it approaches 1 @ 90°. I love the maths, but don't know how formula from the plate would work and formula from Ausdampfverfahren.

I haven't started looking at the 2nd method (Auswanderungsverfahren) yet. :D

Do you have charts for those Sjizzle?

Oh the 2nd method is where the real fun is! I've found the 2nd method to be much more useful in practice as it allows for more freedom of movement/less rigidity prior to firing.

Once you get good at spinning that slide wheel the calc for speed is so quick it almost feels as easy as plinking tin cans with a BB gun.

You are correct - these methods used a proxy AOB of 90 for simplicity's sake and take advantage of the fact that sin(90)=1.

Sjizzle, your charts are amazing! I make use of them frequently. Hopefully we're not close to the limit of 50!

[siege00]

Oh the 2nd method is where the real fun is! I've found the 2nd method to be much more useful in practice as it allows for more freedom of movement/less rigidity prior to firing.

Once you get good at spinning that slide wheel the calc for speed is so quick it almost feels as easy as plinking tin cans with a BB gun.

You are correct - these methods used a proxy AOB of 90 for simplicity's sake and take advantage of the fact that sin(90)=1.

Sjizzle, your charts are amazing! I make use of them frequently. Hopefully we're not close to the limit of 50!

Awesome Derstosstrupp... I'll be giving method 2 a try very soon! :D

[palmic]

Wow the first method is completely adorable.
I tried to learn it in exact way (by complete solution of the law of sines), but this your thread made me realize how it works WITHOUT AoB of the ship!

It counts only with proxy 90 AoB to simplify it and it still works because he do it in both ways - he pretends the ship is at 90 AoB and he counts the speed in that way.
And because of this, he inverts the effect of target real AoB in opposite logic, so this way REAL target AoB is actually corrected by real different target speed.
(in another words - his solution is exactly correct at any target's AoB in optic of torpedo closing to target)

Awesome thread man, thank you! :salute:

[palmic]

... There are also other handy uses for the Auswanderungsverfahren method, such as at long distances during the overhaul maneuver to obtain rough speed with a rough idea of target AOB without slowing and thus losing time in overhauling. In time, and if interest is shown by the community, I will post. ...

Of course there is interest, please publish it :up:

Danke shon! :salute:

BTW i've done some cheatsheet (https://drive.google.com/file/d/0B9Rj7Hxxu0DYbmxQdDRvaWVPZXM/view?usp=sharing) for myself to print to be able to calculate these solutions quickly for anyone who would like to have it..

[palmic]

Hi derstosstrupp:

I have one question about Ausdampfverfahren (Constant Bearing to Target)

At tvre.org i red the article you referred (awesome, thanks :) ) and found that this method is there described a little more simple.
It says they actually used (own heading - current target bearing) for target AoB and own speed for its speed. This way you dont need to calculate law of sine for 90 degrees AoB as you described.

Does your solution here have some advantage? For instance - you dont need to set accurate distance to TDC? Thanks :salute:

[siege00]

Here's a whole bunch of theorizing about why both methods would work.

I don't have all the maths behind it but from calculating and sketching these are my theories (not proofs).

1) Derstosstrupp's implementation of the (ausdampfverfahren) method works by simulating that the target is at a 90° angle on the bow. If you draw the triangle from yourself to where the target would be at 90° AoB, the torpedo path passes through where the target actually is so you've shortened the distance that the torpedo has to travel but still along the same path and intersecting the target's path in the process. If that's accurate then the torpedo run times projected by SH should be wrong since the target isn't actually making the triangle that the TDC thinks it is. It's being shorted.

2) With what the article says about how it was in practice, it's the same methodology but for an isoceles triangle instead of a right triangle. Entering that the target is running at the same speed sets a factor of the triangle. If ownship and target truly had the same speed then ownship and target should also have the same AoB (ie. forming an isoceles triangle), but since you're setting the target bearing as AoB, then the triangle is adjusted accordingly either shortening or elongating the shot.

Method 1 above uses the math directly while method 2 is a natural implementation of the math. Both still use the basic formula.

Does that make sense or did I just go too geeky? lol -- Again, I haven't proved it out on paper... just theory as to why both methods work.

[palmic]

Yes it makes sense completely, i cannot wait to try, thanks! :)

[derstosstrupp]

Hi derstosstrupp:

I have one question about Ausdampfverfahren (Constant Bearing to Target)

At tvre.org i red the article you referred (awesome, thanks :) ) and found that this method is there described a little more simple.
It says they actually used (own heading - current target bearing) for target AoB and own speed for its speed. This way you dont need to calculate law of sine for 90 degrees AoB as you described.

Does your solution here have some advantage? For instance - you dont need to set accurate distance to TDC? Thanks :salute:

Hi palmic,

You're right, the article doesn't expressly mention using 90 deg AOB for the Ausdampfverfahren method. It's really a matter of taste - you can either use the collision bearing as a proxy for AOB, which eliminates the need to compute "target speed" using sines (I.e. own speed x sin(target bearing)), or use 90 deg AOB, in which case the above formula would be necessary.

To answer your question about advantages: What may prove difficult with just using the bearing as AOB is the relative difficulty of entering the exact bearing into the AOB dial of the German TDC, as it only displays in 10s of degrees. 90 deg is easier to input exactly on the dial.

[palmic]

Awesome, thanks again :salute:

[palmic]

I am glad to tell you these works even in SH5 TWOS, right now i hit Cimarron tanker from his starboard by the second moving bearing method (the less accurate one) with critical hit. :salute:

Its awesome because with this you can hunt ships even if you was spotted (and they returned to some course then), or if you have not ideal position and even if you are slightly behind and submerged (and much slower than target because of that). :rock:

Scenario was:

I was spotted by aircraft near of Cimarron escorted by some corvette at April 1940 in south-west approaches area. I was informed about target about 3 days ago by radio from luftwafe, it was coming from somewhere about Liverpool.
I met them from south, but then aircraft suddenly spawned just near of me flying directly on me (bull**** - sorry, but i was very slow in about 10m wind waves, i was invisible for aircraft without radar, it could spot me by some flying around, but not before i hear it and just 10 minutes after emerging).

So my target changed its course and it literally made circle clockwise.

Then i was catching him up from west, his course was about 185 degrees, just like my.
I changed my course to somewhat 125 to be for about 60 degrees angle on track.
Then i was just waiting and going full at 15.5 knots emerged.
His escort started firing on me from about 7km away, but it stayed before the tanker, to not letting him alone, so i just submerged and stayed in my way to shooting position.
After some 20 minutes, i was there - about 110 degrees AoB as you can see roughly by eye, about 6000m away as you can see at RAOBF (his mast height is 30m as you can see - 6km at RAOBF is 60 left - at 30 which is his mast height) (https://goo.gl/photos/5bVDtSXd9zhmebEo7).

Then i've just done Auswanderungsverfahren (Change in Bearing of Target Over 1 Minute), added all to TDC, moved periscope cross to him and fired one magnetic 2 meters under the keel just in the middle of bow and one with impact pistol on the front.. (the second image of link above).

The Eels was travelling to 6km, so i set it to medium speed (max distance 7.5km) and waited for about 3m time.

I play at full realism without external nor effect cameras, so i was just able to hear the torpedos and tanker in hydrophone, everything seemed accurate..

It was about 20% of time left to impact and suddelny it happend - Torpedo trefa!
(so he was just about 5500m away...)

the first magnetic torpedo exploded somewhere bellow him and broke him in the middle. Then we was just about to see beautiful fireworks of full Cimarron tanker (https://en.wikipedia.org/wiki/USS_Cimarron_(AO-22)) :rock:
Second one had ran around somewhere before him...
After short show, i was sneaking away before escort sprinting to my position....

This all was about 4hours operation in real life time, no special TC, i was maneuvering to his position, then closing up... so i enjoyed the hit a lot :salute:
UPDATE: And after lets say 10 minutes, listening sinking Cimarron, unplesant distraction (https://drive.google.com/file/d/0B9Rj7Hxxu0DYTXk1UmNvWUVaU3c/view?usp=sharing) came over me :)

[siege00]

I'm going to have to spend some time in sub school and practice all 3 methods. More tools for the toolbox. :salute:

[palmic]

I was thinking about how to use it immersively just on paper, or even in head and found easy helper for Auswanderungsverfahren.

When you calculate distance with bearing change into resulted speed modification where author of tutorial video is converting from metric system into speed (knots), just use 10 for every 300m of distance.

His distance was 1000m and he calculated in calculator result of 33.
By this hint 1000m is 300m * 3.3, so 3.3 * 10 as i said is the same :)

Sinus is 0.1 for every 6 angles from zero to about 30 then its a little different, you can print sin table from internet.
- sin(6) = 0.1, sin(12) = 0.2, sin(30) = 0.5.

In his example sin(10.5) = 0.18, so his example can be simply calculated in head like 33 * 2 / 10 minus some little portion -> 6.6 minus lets say 0.2 = 6.4.

Good enough for my TDC :03:

[palmic]

Hi palmic,

You're right, the article doesn't expressly mention using 90 deg AOB for the Ausdampfverfahren method. It's really a matter of taste - you can either use the collision bearing as a proxy for AOB, which eliminates the need to compute "target speed" using sines (I.e. own speed x sin(target bearing)), or use 90 deg AOB, in which case the above formula would be necessary.

To answer your question about advantages: What may prove difficult with just using the bearing as AOB is the relative difficulty of entering the exact bearing into the AOB dial of the German TDC, as it only displays in 10s of degrees. 90 deg is easier to input exactly on the dial.

You can use any AoB into TDC exactly, just set it to 90, lock and move periscope by (90 - your_wanted_AoB) degrees.

Its because of all triangle inner angles sums into 180.
So if you watch target moving 1 degree to the side, his AoB is changing also by 1 degree in virtual triangle solution. :salute: