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.

[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:

[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:


Enjoy and gute Jagd!

[vdr1981]

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

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

[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.

[derstosstrupp]

Originally Posted by vdr1981

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

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

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]

Originally Posted by vdr1981

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

do u mean something like this ?????

and i still have more charts

[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.

Do you have charts for those Sjizzle?

[derstosstrupp]

Originally Posted by 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.

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]

Originally Posted by derstosstrupp

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!

[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!

[palmic]

Originally Posted by derstosstrupp

... 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

Danke shon!

BTW i've done some cheatsheet 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