British Fire-control and time of flight

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British Fire-control and time of flight

Post by garder » Tue Oct 29, 2013 5:29 pm

Hello

I have a question that I hope someone can help me with.

How did the British fire control system handle the time-of-flight of the grenade?

Time of flight is probably the most important reason why gun range and clock range differ. But how did the British introduce time of flight into their system. Was it by means of the Dreyer Calculator? Reading on how the calculator worked would suggest this, but since the BCF didn´t use their Dreyer Calculators at Jutland, leaves me to think there was some other way of correcting clock range for time of flight. Surely the entire BCF couldn´t just have ignored time of flight, could they?

Could the correction have been read off a Range table and put directly on the Spotting Corrector?

Or was the correction put on the mean rangefinder range, before it was entered into the Range Clock? Which would have meant that Clock range, wasn´t really Clock range at all.

I hope my qustion is clearly understood and that someone can help me.

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Re: British Fire-control and time of flight

Post by tommy303 » Tue Oct 29, 2013 7:45 pm

If one were not using the Dreyer table, one would use the Dumaresq calculator to obtain range rate or rate of change and gun order deflection from a built in range drum. The Vickers Range clock would be fed with range estimates from range finders, enemy course and speed estimates, own course and speed, and rate of change from the Dumaresq to produce actual gun range taking into account time of flight. The range clock thus solved the problem of calculating the necessary elevation, while the Dumaresq solved the deflection problem. By using a method called cross cutting, the Dumaresq could also be used to check the accuracy of the range clock's enemy course and speed input.

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Re: British Fire-control and time of flight

Post by tommy303 » Tue Oct 29, 2013 11:44 pm

I should add, that the German EU/SV Anzieger was a similar instrument to the Dumaresq and fulfilled the same function, although being of a different design. It is useful to look at the range clock, after being set for initial range from rangefinders and with range rate from the Dumaresq or EU/SV Anzieger, as a predictor of where the target would be in real time at the end of shell time of flight. Deflection orders for setting the director sights for lead would come from the Dumaresq, while range prediction would come from the range clock.

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Re: British Fire-control and time of flight

Post by Byron Angel » Wed Oct 30, 2013 11:47 am

..... IIRC, the ballistic component of the gun (drift. ToF) was incorporated into the calculation of the Dreyer Table by means of a specially ground cam. However, I need to unearth the source on that for confirmation. It is also worth noting that, given the period under discussion, the difference between "rangefinder range" and "gun range" in the prescribed broadside to broadside mode of engagement would have been small and, in practical terms, probably accounted for within the spotting process (as was "error of the day" back then). Only in the case of very large target inclinations would the range differential have become pronounced.

When discussing WW1 naval gunnery, a very great deal of attention is paid to the intricacies and capabilities of the mechanical FC computers of the day. However, (and strictly my opinion) far too little attention has been paid to the difficulties in obtaining accurate target data for input into these marvelous calculating devices. Target range is an obvious issue, but target inclination was also a terribly important component of the FC solution and its measurement proved to be a difficult problem indeed until the introduction of radar FC.

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Re: British Fire-control and time of flight

Post by Dave Saxton » Wed Oct 30, 2013 2:57 pm

Byron Angel wrote:..... When discussing WW1 naval gunnery, a very great deal of attention is paid to the intricacies and capabilities of the mechanical FC computers of the day. However, (and strictly my opinion) far too little attention has been paid to the difficulties in obtaining accurate target data for input into these marvelous calculating devices. Target range is an obvious issue, but target inclination was also a terribly important component of the FC solution and its measurement proved to be a difficult problem indeed until the introduction of radar FC.

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I agree the problem wasn’t as much with the computers as it was with the accuracy of the data feed into them.

We tend to think that radar had problems with accurate bearing more than range as a general rule. American literature explains that the typical range accuracy of optics was 1% of the range. The typical accuracy of almost all radar is 0.1% of the range. So radar is about ten times more accurate than optical range finders. The British placed high value on electronic range measurement as first priority. Accurate bearing measurement with radar using lobe switching came only by 1942, because unless the target could not be seen at all they could use optics for bearing. The Americans preferred to combine radar range with optical bearing if possible according to their gunnery manuals as well. British Type 284M radar had a typical range accuracy of 120 yards. (The L24 Range Panel could measure the time base to an accuracy of 25 yards but there were variations in the exact time that the pulser fired the pulse.) Still 100 meters was more accurate than typical of the optical rangefinders used by the British, especially as the range increased.

The Germans during WWII and during the 1930s were more concerned with accuracy of their radar's range measurement than they were of its bearing measurement. When specifications were issued to GEMA during 1936 as to how accurate the radar needed to be for firecontrol purposes: they were giving a range accuracy of 50 meters and bearing accuracy of 0.20 degrees. The prototype Seetakt had already demonstrated a bearing accuracy of 0.10 degree during a demonstration in Sept 1935. When the first production radar set was being installed on the panzerschiffs during 1937 they asked to leave out lobe switching for the time being, forcing a dependence upon optical bearing however.

It would seem that they were happy with the range accuracy and could use it in combination with optical bearing data. However the documents do not confirm this. The documents consistently point out that the Kriegsmarine was unhappy with the range accuracy of their radars which prior to 1940 was typically 100 meters, which was stated to be inferior to their optics, so the German optics attained a different standard of accuracy than 1% of the range. Was this purely theoretical?

While re-capping the journey toward what was considered acceptable radar accuracy, the Research and Testing Command stated: that considering the vital importance of radar directed gunnery it is inexplicable that the range accuracy had taken so long to be improved. They had just explained that with the early model sets the fine ranging indicator had to be zoomed out so that at least 600 meters of time base was presented. This could cause the range accuracy to suffer. However, with the late model fine ranging system they could have it zoomed in as tight as 300 meters of time base presented, making range accuracies of 25 meters available.

Bearing accuracy of 1 or 2 mils was available from lobe switching and phased array or mechanical scanning radars during WWII. This was more accurate than optics if we take the German requirement of 0.20* as a guide to what optical directors typically attained, or was required.

The problem of bearing accuracies of radar didn’t come from the radars themselves but to the mechanical tolerances of their mountings in most cases.
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Re: British Fire-control and time of flight

Post by garder » Wed Oct 30, 2013 7:04 pm

Thanks for taking the time to respond to my question.
one would use the Dumaresq calculator to obtain range rate or rate of change and gun order deflection from a built in range drum. The Vickers Range clock would be fed with range estimates from range finders, enemy course and speed estimates, own course and speed, and rate of change from the Dumaresq to produce actual gun range taking into account time of flight. The range clock thus solved the problem of calculating the necessary elevation, while the Dumaresq solved the deflection problem.
I´m sorry but I don´t think this is correct. The Dumaresq gave two outputs, range rate and speed across (or Dumaresq deflection). The speed across had to be corrected for range, via reference to a range table, to become gun deflection.

In this detail the Dumaresq and the German EU/SV-Anziger differed. The EU/SV-Anzieger gave a gun deflection (SV, or Seitenverbesserung) without the need for reference to a range table.

But back on topic. While you of course are correct that time-of-flight was a component of the gun deflection found by the Dumaresq, this only accounted for the time-of-flights influence on lateral movement of the enemy ship while the grenade was in the air. Not it´s influence on gun range, or in other words, the difference in range from own and enemy ship during time-of-flight.

The only value taken from the Dumaresq and put on the Range clock was Range rate, which wasn´t affected by time-of-flight. The Range clock thus gave the Clock range, not Gun range (or the necessary elevation).

At the risk of answering my own question I think I might have found the answer while writing this post.

John Brooks writes in his book: Dreadnought Gunnery and the Battle of Jutland page. 162: Before opening fire, the spotting dial (on the Spotting Corrector) was set with the ballistic range correction obtained from the Dreyer Range Corrector (Calculator). These ballistic range corrections from the Calculator included time-of-flight (see here http://www.dreadnoughtproject.org/tfs/i ... Calculator).
Even though as I stated in my first post Beattys Battlecruisers didn´t use the Calculator at Jutland, it would have been fairly easy to look up the required time-of-flight correction for the current range/range-rate in the Range table and manually put it on the Spotting Corrector. I think this must have been how they did it. Does this sound plausible?

To Byron: I think you are thinking of the Deflection Totaliser, which corrected the Gun deflection for wind, drift and spotting.

I haven´t thought of the possibility of them correcting for time-of-flight only via spotting. That is of course a possibility. But the Germans did correct for time-of-flight and also for “error of the day” down to even correcting for how many shots each individual gun barrel had fired in its life. Via the Dreyer Range Calculator the British also could correct for “error of the day”, so I find it unlikely that they would ignore such a relative important factor as time-of-flight (important compared with for example temperature).

Regarding your other point I agree wholeheartedly. No computer is better than the data being feed into it. If one examines the British experiences at Dogger Bank and Jutland it is for me clear that the rangefinders (and rangefinder system) failed to supply anywhere near enough accurate ranges to the Range plot for it to calculate a range-rate.
In my opinion the Dreyer table failed to calculate a range-rate and a bearing rate (which was used to calculate a gun deflection via the deflection drums). This left the British to fall back on the Range clock, Dumaresq and spotting. In effect the same system they had before the introduction of the Dreyer table.

Because of these points I really don´t understand the universal positive view of the British fire-control system compared with the German system in the existing literature (Brooks, Sumida, Campbell, Friedman and Padfield).

If anyone disagrees I would love to hear your opinion and discuss it.

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Re: British Fire-control and time of flight

Post by tommy303 » Wed Oct 30, 2013 8:32 pm

The speed across had to be corrected for range, via reference to a range table, to become gun deflection.
According to the Handbook on Minor Fire Control Instruments, the Dumaresq instruments in fire control positions incorporated a deflection drum to give gun deflection without having to consult a table; this automatically allowed for times of flight and rotational drift.
I think you are thinking of the Deflection Totaliser, which corrected the Gun deflection for wind, drift and spotting.
If I recall the Deflection Totaliser was not introduced until ca.1917 Prior to that time, the correction for wind drift had to be input manually from readings taken from a wind Dumaresq.
Even though as I stated in my first post Beattys Battlecruisers didn´t use the Calculator at Jutland, it would have been fairly easy to look up the required time-of-flight correction for the current range/range-rate in the Range table and manually put it on the Spotting Corrector. I think this must have been how they did it. Does this sound plausible?
One started the range clock with the initial range from range finders, then, once the range rate was determined by the Dumaresq, that value was added by turning a knob or handle to set the rate dial; spotting corrections could be added by other knobs or handles as the clock ran without disturbing its operation. As the clock ran, it would therefore be giving the actual gun ranges on the range dial which was passed to the gunners.
In my opinion the Dreyer table failed to calculate a range-rate and a bearing rate (which was used to calculate a gun deflection via the deflection drums). This left the British to fall back on the Range clock, Dumaresq and spotting. In effect the same system they had before the introduction of the Dreyer table.
There were certainly problems in the early Dreyer tables, but these were overcome in successive models up to and including the last one which was installed in Hood. The German system ca1916 was much simpler, but lacked flexibility and needed quick reaction times and a high degree of training. As a general trend, they began to automate more and more by the introduction of more complex systems, although something akin to the British fire control table was not forth coming until post war. The main problem with the Dreyer, which was a work in progress throughout its operational life, was it represented a dead end developmentally. This is why the British went to the post war AFCT which was much more automated and flexible. The big advantage of the Dreyer was its graphic range plot and this accounted for a gradual tendency for gunnery to improve the longer an action lasted. The opposite tended to be true of the German system ca1916. In good visibility it worked well enough, but as fatigue set in or visibility deteriorated, so too did German gunnery. This is why the Germans spent so much time post Jutland to try and improve their system, particularly after getting details of that being used in the Russian Navy (based on Argo and Pollen systems).

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Re: British Fire-control and time of flight

Post by Byron Angel » Thu Oct 31, 2013 12:19 am

Very interesting discussion. You are making me scramble back into Brook's DG@BJ, which I have not read in a while.

By "error of the day" I was referring to meteorological conditions - particularly with respect to specific wind conditions in the upper reaches of the trajectory arc - which were essentially not measurable by the firing ship. While I do not deny the possibility that the IGN had developed certain guidelines for making anticipatory adjustments to aim based upon what WAS measurable (in fact I would be surprised had the IGN not done so), there is at least one example - Mahrholz's handling of Von der Tann's initial main battery fire at Jutland - where his concern for the uncertainty of the exact nature of the error of the day influenced his selection of distance interval between the salvoes in the initial ladder fired at Indefatigable.

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Re: British Fire-control and time of flight

Post by Byron Angel » Thu Oct 31, 2013 12:59 am

Tommy,

[ 1 ] On what grounds do you make your assessment of the Dreyer fire control table as a developmental dead-end? My impression of the post-WW1 AFCT system was that, although borrowing certain features from the Pollan/Argo system, it was still very much a Dreyer table.

[ 2 ] Tommy303 wrote - "The big advantage of the Dreyer was its graphic range plot and this accounted for a gradual tendency for gunnery to improve the longer an action lasted. The opposite tended to be true of the German system ca1916. In good visibility it worked well enough, but as fatigue set in or visibility deteriorated, so too did German gunnery."
>>>>> I disagree with this statement. The GFG&TM assessed plotting-based gunnery as having been rendered largely ineffective by the German tactics of evasive maneuvering. I cannot see any concrete example of British fire improving over time - it was certainly not the case with the BC actions; the good shooting of 5BS can as easily be put down to steadily declining ranges as to anything else; the engagements of the battle lines were of too short duration to support such an argument. As for German BC gunnery at Jutland, I cannot see any apparent deleterious effects of fatigue in the shooting of Derfflinger or Lutzow when they engaged Invincible late in the battle or in their efforts against Defence and Warrior. As for the effects of poor visibility on shooting at Jutland, the British were hardly immune. German FC was indeed different in approach from that of the British, but, based upon battle results and the discretely cloaked but nevertheless evident British praise for German performance it can hardly as "inferior".

Strictly my opinion of course.

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Re: British Fire-control and time of flight

Post by garder » Thu Oct 31, 2013 2:52 pm

According to the Handbook on Minor Fire Control Instruments, the Dumaresq instruments in fire control positions incorporated a deflection drum to give gun deflection without having to consult a table; this automatically allowed for times of flight and rotational drift.
Thank you, I did not know that. I found this online: http://www.maritime.org/doc/br1534/inde ... late01.jpg. Was that the source you were referring to?
One started the range clock with the initial range from range finders, then, once the range rate was determined by the Dumaresq, that value was added by turning a knob or handle to set the rate dial; spotting corrections could be added by other knobs or handles as the clock ran without disturbing its operation. As the clock ran, it would therefore be giving the actual gun ranges on the range dial which was passed to the gunners.
I think I see the confusion. I have totally misunderstood what you were talking about. I thought you were describing the Range clock on the Dreyer table. But now I see you meant the original Vickers Range clock. My bad, sorry.
The big advantage of the Dreyer was its graphic range plot and this accounted for a gradual tendency for gunnery to improve the longer an action lasted.
I don´t agree that the range plot was the Dreyer tables biggest advantage; I actually see it as the tables biggest disappointment. In the report from the Dreyer Table committee I 1919 (ADM 186/241) they state: “Experience has shown… that it will very seldom, if ever, be possible to obtain the rate of change of range from rangefinders” and “The measurement of rate of change of rate…by the Range plot is frequently misleading and is not recommended”.

For me this clearly shows that the Rangefinder plot failed in its primary duty, to allow a calculation of range-rate based on Rangefinder readings. It was instead demoted to serve as a means to visually mean the different Rangefinder readings. A job the German Mittlungsapparatus did faster and more accurate. Range-rate was instead found via the Dumaresq, just like before the introduction of the Dreyer. That the Dreyer had difficulties calculating the range-rate is supported by this statement from an American naval officer, after having talked to the British naval fire control expert CDR Down: “In the Battle of Jutland, they (the British) simply set the rate at zero, because they had no idea what it really was” (Christopher Wright: Questions on the effectiveness of US navy Battleship Gunnery, Warship International vol. 41, 2006 page 93).

Also any improvement in British gunnery over time at Jutland can more plausible be explained by decreasing ranges and better visibility for the British ships later in the battle. Similarly any decline in German gunnery at Jutland (the only real case to investigate) can be explained by decreasing visibility and damage to German turrets which diminished the volume of German fire.

The German fire control system was much better at integrating the different elements of the system into one. The Richtungweisser is often described as a simpler version of the Director. But it was much more than that. It gave the captain of the ship the ability electromechanically to send the bearing values of the target, to the fire control officer. And allowed the control officer to send the targets bearing values to every gun, spotter, rangefinder and searchlight on the ship. This gave the Germans the means too much faster fire on a suddenly emerging target (fx. coming out of a fog bank). This was an ability the British really could have used at Jutland (as shown by their haste to upgrade their ships with Evershed bearing receivers after the battle).

Also for wht its worth, the Germans was very satisfied with their Fire control after Jutland, even going so far as to give the Iron Cross to the chief of fire control development at Siemens & Halske. But notwithstanding this, you are right that the German, as the British, spend a lot of effort post-Jutland developing and upgrading fire-control equipment. The main focus seems to be to put Fire control stations on tripod mast, and ship rangefinders of longer base length. Both in response to increased firing ranges.

One last comment regarding the “simple” German fire control equipment. From at least 1917 the Germans, via the Gangmittler, had the capacity to automatically calculate range-rate from Rangefinder readings. This let them find the range-rate in between1-4 minutes, depending on range. Something the British in 1919, as shown in the quote above, thought was impossible.

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Re: British Fire-control and time of flight

Post by tommy303 » Thu Oct 31, 2013 11:58 pm

The German fire control system was much better at integrating the different elements of the system into one. The Richtungweisser is often described as a simpler version of the Director. But it was much more than that. It gave the captain of the ship the ability electromechanically to send the bearing values of the target, to the fire control officer. And allowed the control officer to send the targets bearing values to every gun, spotter, rangefinder and searchlight on the ship. This gave the Germans the means too much faster fire on a suddenly emerging target (fx. coming out of a fog bank). This was an ability the British really could have used at Jutland (as shown by their haste to upgrade their ships with Evershed bearing receivers after the battle).
The only problem with the Rw was, besides its optics being not up to standard in some instances, in its initial form as a director pointer, was the guns were not automatically fired from it. While it kept the guns on the proper target, the gun layers were still responsible for firing at the sound of the fire gong when they felt they had the target at the proper point in the ship's roll. There were times, when the Rw operator could see the target because of his higher elevation above the water and the gun layers in the turrets could not. This was eventually overcome by the introduction of Julius von Petravic's automatic roll tracking and firing gyro mechanism called the Abfeuerungsgeraet which took the burden off of the gun layers. At Jutland, only Luetzow had them in three of her four turrets and they failed during the battle due to shock of firing, but after improvements, they became standard equipment throughout the fleet. This marks a trend in German developments away director fire control as used by the British towards a central fire control system; the central fire control system, however did not appear until after the war.
Also for wht its worth, the Germans was very satisfied with their Fire control after Jutland, even going so far as to give the Iron Cross to the chief of fire control development at Siemens & Halske. But notwithstanding this, you are right that the German, as the British, spend a lot of effort post-Jutland developing and upgrading fire-control equipment. The main focus seems to be to put Fire control stations on tripod mast, and ship rangefinders of longer base length. Both in response to increased firing ranges.
Yes, and there was an increased effort made to protect vital communications lines from the spotting tops to the gunnery control towers as the battle had shown the existing arrangements to be too easily cut by splinters.

As to the Dreyer table having problems calculating the range rate, a good deal of that was due to the too narrow based range finders in British service and the poor visibility during the battle which made it difficult to obtain reliable range readings in the first place. This meant it took longer for the British to acquire the target than the German system which utilized longer based range finders and a better salvo ranging system (bracket salvos vs single shot brackets). The other was the Dreyer table could not keep up with radical maneuvers of ones own ship without having to be reset as it needed a constant rate. This was only partially corrected in the late marks which took the development of the Dreyer system pretty much as far as it could go. As more emphisis was placed on continuous aim, the Dreyer was eventually superseded by the more capable AFCT. It is interesting to note, that American officers visiting Hood in the 1920s, when shown her MkV dreyer table, thought it to be quaint compared to their own rangekeepers.

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Re: British Fire-control and time of flight

Post by Byron Angel » Fri Nov 01, 2013 9:55 am

..... I suspect that the underlying concepts of the German Richtungsweiser and British director differed - the German device being intended to function as a master device for overall control of fire, while the British director served as a master gunsight. It is true that the Rw did not control the actual discharge of the guns themselves, but one must ask why that was so. The inference I draw is that it was a matter of system design choice rather than any technical inability or lack of foresight. The gunnery officer operating the Rw had the task of controlling (or "directing") the overall fire of the guns, while the physical laying and firing of the guns was left to the gunlayers in the turrets. Within certain sea state limits, this system worked just fine, as the typically tight patterns of German salvoes attested. How it would have dealt with heavier seas is, however, another matter.

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Re: British Fire-control and time of flight

Post by garder » Tue Nov 05, 2013 7:43 pm

As to the Dreyer table having problems calculating the range rate, a good deal of that was due to the too narrow based range finders in British service and the poor visibility during the battle which made it difficult to obtain reliable range readings in the first place.
Regarding the narrow base of the rangefinders as cause of the range plots trouble with finding the Range-rate, the full quote that I posted earlier disagrees with this: “Experience has shown… that it will very seldom, if ever, be possible to obtain the rate of change of range from rangefinders. It is not considered that even the introduction of 30-ft. rangefinders will modify this conclusion
And the visibility wasn´t worse than what could be expected in the North Sea. For years the British knew that their future enemy would be the Germans and that the fight would be in the North Sea.
And that is my main problem with the description of the British fire-control system as more advanced than the German. The British might have developed an advanced analog computer, but they failed in developing a system to feed this computer with required data under realistic combat condition. That is not the sign of an “advanced” system; that should more precisely be described as a poorly developed fire-control system.
In short the problem with the British fire-control system wasn´t so much data processing as data collecting.

As to your coments on the RW I agree.

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Re: British Fire-control and time of flight

Post by tommy303 » Tue Nov 05, 2013 11:49 pm

The British might have developed an advanced analog computer, but they failed in developing a system to feed this computer with required data under realistic combat condition.
Precisely so. The RN had in the Dreyer an advanced mechanical computer, which put them a step ahead of the Germans who had the systems but not rolled into one central system. The Germans were moving towards that end, but by a different route which only came into fruition after the war with the post war Siemens-Halske/Hazemeyer developments. As I have stated before, the Dreyer was something of a mechanical dead end which could not easily be integrated with automatic inputs from various systems and spots--i.e., too much hand work was required. By 1919 it had gone as far as it could be taken design-wise, hence the British switch over to a newer more flexible system. Other systems such as the Barr & Stroud Table and Pollen's Argo had the potential lacking in the Dreyer. The Germans, in fact, were quite impressed with the Pollen Argo table used by the Russians and it influenced their post war designs for a central fire control computer as possibly did the Barr and Stroud table as well since one of the engineers on the Barr and Stroud team went to work for Hazemeyer in Holland, and controlling interest in Hazemeyer was held by Siemens-Halske.
Regarding the narrow base of the rangefinders as cause of the range plots trouble with finding the Range-rate, the full quote that I posted earlier disagrees with this: “Experience has shown… that it will very seldom, if ever, be possible to obtain the rate of change of range from rangefinders. It is not considered that even the introduction of 30-ft. rangefinders will modify this conclusion
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.

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Re: British Fire-control and time of flight

Post by dunmunro » Wed Nov 06, 2013 8:41 pm

tommy303 wrote:
Regarding the narrow base of the rangefinders as cause of the range plots trouble with finding the Range-rate, the full quote that I posted earlier disagrees with this: “Experience has shown… that it will very seldom, if ever, be possible to obtain the rate of change of range from rangefinders. It is not considered that even the introduction of 30-ft. rangefinders will modify this conclusion
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.
See:
http://www.admirals.org.uk/records/adm/ ... 86-259.pdf , P.125 (P.49).

Optical RFs couldn't take enough ranges/minute with sufficient accuracy to build up a good range plot in the time required, and the instruments tested included a 28ft Zeiss stereo and a 30ft B&S stereo and there was no appreciable difference between stereo and CI. It seems that most range rates were developed initially by estimates of enemy speed and course (inclination). Of course radar, with nearly continuous, accurate, ranging was able to develop good range rates and the KM was using radar from the beginning of WW2.

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