British Fire-control and time of flight

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Byron Angel
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Re: British Fire-control and time of flight

Postby Byron Angel » Thu Nov 07, 2013 4:45 am

Comparison of British versus German optical range-finding in WW1 is a complicated exercise that requires examination not only the respective range-finding devices themselves, but the overall range-finding systems of the two navies. Overall, IMO, the IGN fielded a materially superior system.

It's late here at the moment and I have work tomorrow. If anyone is interested in more detail I'll be happy to expand on the issue over the weekend.

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garder
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Re: British Fire-control and time of flight

Postby garder » Thu Nov 07, 2013 1:47 pm

See:
http://www.admirals.org.uk/records/adm/ ... 86-259.pdf , P.125 (P.49).


That document tells us very little, if anything, about the capabilities of the German rangefinder system during the war.

Firstly, though the stereoscopic range takers at the trial are described as having two years’ experience with stereoscopic rangefinders, that doesn’t mean that they were as proficient as German rang takers, trained at the Gunnery School in Sonderburg, which (at the time of Jutland) had 8 years of institutional knowledge in the use of the stereoscopic rangefinder. And whose range taker courses flunked a large part of the participants each year.

The proficient use of a stereoscopic rangefinders takes more skill that the use of a coincident rangefinder. As we can´t know if the range takers in the test were trained to the same standard as war-time German range takers, we can´t on the basis of that test safely conclude that there were no significant difference in precision between German and British rangefinders during the war.

Also that test tells us nothing about the German rangefinder systems capacity for producing data under realistic combat condition.

Thirdly it ignores the German approach towards range finding in general. The Germans knew that the mean rangefinder range, based on several range cuts, would be a lot more precise than any single rangefinder measurement. That was the motivation behind the development of the Mittlungsapparat, which gave the Germans an advantage over the British in range finding.

Optical RFs couldn't take enough ranges/minute with sufficient accuracy to build up a good range plot in the time required


This just shows that one must be careful in concluding anything on the German rangefinder system on the basis of that test. Because the Germans at Jutland were able to calculate range-rate on the basis of rang cuts.
Both von Hass and Mahrholz states that they during the approach of the two battlecruiser forces noted down the time and mean rangefinder range at that moment (in practice the same data collecting as the British Rangeplot) and calculated the range-rate from this data. This calculated range-rate was then compared with the one found on the EU/SV-Anzieger (in practice the same as the British Cross-cut, although only for range-rate). It is in this regard significant that both Lützow and Von der Tann used a range-rate of -400 m/min. during the approach, which was very close to the actual range-rate. Later (c.1917) the German Gangmittler gave an accurate range-rate in 1-4 min. based on ragefinder data. If this Gangmittler was ever tested under battle conditions is not known.

Were not the Germans rather more successful in this respect? In part this might have been due their choice of stereo rather than co-incidence type range finders. The former possessed some advantage under certain poor visibility conditions and the longer base length was advantageous.


I am certain that the German rangefinder system was much more capable to supply rangefinder data to the fire control system at Jutland that the british. For example Von Hase states that his rangefinders rarely measured more than 300 m. different from each other, while during the approach Von der Tanns rangefinders was all within 100 m. of each other.

The reason for this superiority is an open question. I do not think the base length had much to do with it. The German rangefinders base length was only 26 cm longer than the British. Not enough in my opinion to make any difference. Other possible explanations are:

Better trained German range takers. I think it is safe to conclude that the Germans had better trained range takers than the British.

A better integrated rangefinder system in the fire control system. The RW gave the barring to the target to the rangefinder which made it much easier/faster to start ranging on a target.

Weather conditions favored stereoscopic over coincident rangefinders.

Vibrations didn´t effect Stereoscopic RF as much as coincident RF.

German rangefinder readings were sent electro-mechanical to the fire control station, whereas British rangefinder data was transmited by phone or voicepipe (except for the Argo rangefinder), making for a faster and less error prone transferal of data. I think this is correct but I am not sure how The British turret rangefinders transmited there data. Does anyone know?

The Mittlungsapperat was a fast and precise way of calculating the mean rangefinder range, whereas the rangeplot was not.

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Re: British Fire-control and time of flight

Postby tommy303 » Thu Nov 07, 2013 11:50 pm

I do not think the base length had much to do with it.


Increasing the base length of a rangefinder has effect of reducing the amount of error inherent in optical range finding, thus even the only slightly longer based German rangefinders had a lesser inherent error than their shorter based British cousins--all other things being equal.

Better trained German range takers. I think it is safe to conclude that the Germans had better trained range takers than the British.


Beyond their initial training as rangetakers, during which time they had to pass a very stringent course and testing, they were tested for proficiency on an almost daily basis. I recall that once one was used to the Basisgeraet, it was not really a difficult instrument to use.

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Re: British Fire-control and time of flight

Postby dunmunro » Fri Nov 08, 2013 2:25 am

Series IV

Method and Procedure of Carrying Out the Trials

The trial lasted about five months, commencing in June, 1922, and finishing in November, 1922. In all, some 700 runs were carried out, representing about 30,000 observations...

4. Rangefinder Operators. - The operators taking part in this trial were the same as in Series I, II, and II, with the exception of P.O. Barrett, who did not participate in Series I. They were:
Coincidence.

P.O. Wearn, Qual. RT. I. ..
P.O. Barrett " "

Stereoscopic

L.S. Webb, R.T. II
L.S. Kibblewhite, RT.II.
Qualified stereo operators of about three years' experience.
From the above mentioned document.


So that represents about 7500 recorded observations for each RF (two stereo, two CI) and this was just one of 4 different trials.

But to get back to using an RF to generate range-rates, remember that the typical RF at Jutland was either a 3m stereo or a 9ft CI, and neither of these will be useful to generate a range rate at a typical range of say 16000 yds, where even the measured accuracy and consistency of 25 and 30ft stereo and CI RF was insufficient. It is possible that at some unrealistic, close range, an RF might be useable to generate range rates, but not at the ranges that the RN and SMS BCs and BBs were engaging at.

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Re: British Fire-control and time of flight

Postby Byron Angel » Fri Nov 08, 2013 3:44 am

Range rate data were precisely what the IGN derived from their system of multiple range-finders electro-mechanically feeding a stream of range data via the Mittlungsapparat/Gangmittler devices, whose outputs were then applied to the fire control computation. Post WW1 analysis of the German FC system by USN ONI described it as "rangefinder control". British thinking on the subject in WW1 led them as well in the same direction, but they did not succeed in developing the suitable technology. The key here is that, other things being equal (which they were not), the precision of measurement varies according to the square root of the number of measurements. The German system was capable of producing (and processing) materially more range measurements per unit of time than the British system under action conditions.

My opinion.


Note - According to Brooks, range data from British turret range-finders were transmitted by electro-mechanical typewriter which put the range reading on a counter located in the T/S. The data was then manually taken from the counter and plotted on the table.


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garder
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Re: British Fire-control and time of flight

Postby garder » Fri Nov 08, 2013 11:29 am

So that represents about 7500 recorded observations for each RF (two stereo, two CI) and this was just one of 4 different trials.


The number of recorded observations is a moot point. The design of the test is such, that we can learn nothing of the capability of the German wartime rangefinder system from it. If you don´t agree I would like to know what you think that test can tell us about the German rangfinder system?

remember that the typical RF at Jutland was either a 3m stereo or a 9ft CI, and neither of these will be useful to generate a range rate at a typical range of say 16000 yds, where even the measured accuracy and consistency of 25 and 30ft stereo and CI RF was insufficient. It is possible that at some unrealistic, close range, an RF might be useable to generate range rates, but not at the ranges that the RN and SMS BCs and BBs were engaging at.


Contemporary eyewitness accounts from German Artillery officers states clearly that the Germans were able to generate an accurate range rate at 15.000 + m. under battle conditions based on rangefinder data. And as I stated above this is why that American test doesn’t really tell us anything about the German rangefinder systems capabilities because actual combat experience contradicts the findings of the test.

Thanks Byron, I will check Brooks again.

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Re: British Fire-control and time of flight

Postby dunmunro » Fri Nov 08, 2013 10:10 pm

Byron Angel wrote:Range rate data were precisely what the IGN derived from their system of multiple range-finders electro-mechanically feeding a stream of range data via the Mittlungsapparat/Gangmittler devices, whose outputs were then applied to the fire control computation. Post WW1 analysis of the German FC system by USN ONI described it as "rangefinder control". British thinking on the subject in WW1 led them as well in the same direction, but they did not succeed in developing the suitable technology. The key here is that, other things being equal (which they were not), the precision of measurement varies according to the square root of the number of measurements. The German system was capable of producing (and processing) materially more range measurements per unit of time than the British system under action conditions.

My opinion.


Note - According to Brooks, range data from British turret range-finders were transmitted by electro-mechanical typewriter which put the range reading on a counter located in the T/S. The data was then manually taken from the counter and plotted on the table.


B


The RN tests show us how many accurate ranges/minute might be obtained from an RF; the tests have absolutely nothing to do with integrating that data into a fire control computer, but it is clear that the number of ranges/minute and the accuracy of a 3m RF at ~15000 yds will not allow for an accurate range rate to be developed, even with no delay in processing the ranges obtained.

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Re: British Fire-control and time of flight

Postby dunmunro » Fri Nov 08, 2013 10:36 pm

garder wrote:

Contemporary eyewitness accounts from German Artillery officers states clearly that the Germans were able to generate an accurate range rate at 15.000 + m. under battle conditions based on rangefinder data. And as I stated above this is why that American test doesn’t really tell us anything about the German rangefinder systems capabilities because actual combat experience contradicts the findings of the test.

.


The above was an RN test.

The problem with combat reports is that the gun is also being used as an RF, through the use of spotting corrections.

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Re: British Fire-control and time of flight

Postby garder » Sat Nov 09, 2013 2:30 pm

The above was an RN test.
The problem with combat reports is that the gun is also being used as an RF, through the use of spotting corrections.


From von Hase Kiel and Jutland page 132: “the Bg. Officer will report the change of range per minute calculated from the difference of the range-finder readings”.

From Mahrholz page 54: “Während der Flugzeit liest ich mir den E.U. nach Messung geben, der genau mit dem des Anzeigers übereinstimmte

The Germans calculated the range-rate based on mean rangefinder readings on the Mittlungsapparat. Spotting corrections was put on the Aufsatz-telegraph and had no connection with the Mittlungsapparat. The calculated range-rate was clearly calculated on the basis of rangefinder data. Spotting corrections had absolutely nothing what so ever to do with this process.

At the risk of repeating myself for a third time: Contemporary eyewitness accounts from German Artillery officers states clearly that the Germans were able to generate an accurate range rate at 15.000 + m. under battle conditions based on rangefinder data (and only rangefinder data). And as I stated above this is why that British (don´t know why I thought it was an American) test doesn’t really tell us anything about the German rangefinder systems capabilities because actual combat experience contradicts the findings of the test.

The RN tests show us how many accurate ranges/minute might be obtained from an RF; the tests have absolutely nothing to do with integrating that data into a fire control computer, but it is clear that the number of ranges/minute and the accuracy of a 3m RF at ~15000 yds will not allow for an accurate range rate to be developed


Correct, the test have absolutely nothing to do with integrating that data into a fire control computer and that is why that test tells us nothing of the German rangefinder system, because integrating RF data into a computer was exactly what the Germans did. The Mittlungsapparat gave the mean rangefinder range on the basis of 5-7 rangefinders. So while you might be right in asserting that one 3 m. RF will not produce data enough to calculate a range-rate that is completely irrelevant in an evaluation of the German rangefinder system, because that was not how the German RF system worked.

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Re: British Fire-control and time of flight

Postby Byron Angel » Sat Nov 09, 2013 3:05 pm

The Cumberland tests were also performed from land under peace-time conditions, i.e. - no vibration problems, no smoke problems, no spray problems.

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Thorsten Wahl
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Re: British Fire-control and time of flight

Postby Thorsten Wahl » Sat Nov 09, 2013 8:57 pm

see the attachments
Attachments
Emessung Deutschland 1 HJ 1937Hires.jpg
(114.39 KiB) Not downloaded yet
E-mess-Uebung gegen vermessenes Ziel.jpg
(245.6 KiB) Not downloaded yet
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!

Byron Angel
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Re: British Fire-control and time of flight

Postby Byron Angel » Sun Nov 10, 2013 6:22 pm

Hi Thorsten,

I'm having a bit of trouble deciphering your attached documents. Can you clarify what they represent?


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Thorsten Wahl
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Re: British Fire-control and time of flight

Postby Thorsten Wahl » Sun Nov 10, 2013 8:48 pm

first chart of "E mess Übung gegen vermewssenes Ziel" shows the performance of all optical range keepers compared to the true distance
(black line) own ship<-> target ship during a "Ortungsübung"
the second chart shows how fast changes are detected in the approach speed.
It takes about 1 minute on average to detect a change of course of the target.

Emessung Deutschland shows the individual performance of a sailor (St. Matr, Meier) with different rangekeepers 10 U = 10m RuM
6 U = 6m RuM and so on
page 85
average result from 2.II. using 10 m RuM at distances of 23,5 km - 20,0 km
absolute accuracy +38m
relative accuracy 18m
average 29 m
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!

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Re: British Fire-control and time of flight

Postby garder » Sun Nov 10, 2013 9:00 pm

Interesting. Thanks for posting it.

Just to be clear. A 6M RuM is a rangefinder with a 6 m. basis, correct?

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Re: British Fire-control and time of flight

Postby dunmunro » Sun Nov 10, 2013 9:37 pm

Thorsten Wahl wrote:first chart of "E mess Übung gegen vermewssenes Ziel" shows the performance of all optical range keepers compared to the true distance
(black line) own ship<-> target ship during a "Ortungsübung"
the second chart shows how fast changes are detected in the approach speed.
It takes about 1 minute on average to detect a change of course of the target.

Emessung Deutschland shows the individual performance of a sailor (St. Matr, Meier) with different rangekeepers 10 U = 10m RuM
6 U = 6m RuM and so on
page 85
average result from 2.II. using 10 m RuM at distances of 23,5 km - 20,0 km
absolute accuracy +38m
relative accuracy 18m
average 29 m


Perhaps you can explain result 29.II at 48300m?

thanks.


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