British v German rangefinders

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paul.mercer
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British v German rangefinders

Postby paul.mercer » Mon Jun 20, 2011 8:52 pm

Gentlemen,
Please excuse me if I am talking rubbish, but I get the impression that during WW1 & WW2 the German rangefinders were quicker to find and keep the range but were more susceptible to damage than the British ones, wereas the British, although slower, were perhaps better at keeping the range even afte sustaining hits. This seemed to be the case in the Hood/PoW v Bismarck battle and also the Rodney/KGv v Bismarck battle although I know KGv& Rodney did not get hit.
What is the opinion of you experts - were the German rangeinders better but more delicate?

dunmunro
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Re: British v German rangefinders

Postby dunmunro » Tue Jun 21, 2011 8:55 am

paul.mercer wrote:Gentlemen,
Please excuse me if I am talking rubbish, but I get the impression that during WW1 & WW2 the German rangefinders were quicker to find and keep the range but were more susceptible to damage than the British ones, wereas the British, although slower, were perhaps better at keeping the range even afte sustaining hits. This seemed to be the case in the Hood/PoW v Bismarck battle and also the Rodney/KGv v Bismarck battle although I know KGv& Rodney did not get hit.
What is the opinion of you experts - were the German rangeinders better but more delicate?


The problem with that is that Bismarck and KGV had radar ranging systems, and it likely that Bismarck was using radar ranging at Denmark Straits. Hood was likely using radar as well, but PoW's radar systems failed. KGV used radar very effectively against Bismarck. I doubt there was much difference in RF performance between the major navys in WW2.

Byron Angel
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Re: British v German rangefinders

Postby Byron Angel » Wed Jun 22, 2011 2:31 am

paul.mercer wrote:Gentlemen,
Please excuse me if I am talking rubbish, but I get the impression that during WW1 & WW2 the German rangefinders were quicker to find and keep the range but were more susceptible to damage than the British ones, wereas the British, although slower, were perhaps better at keeping the range even after sustaining hits. This seemed to be the case in the Hood/PoW v Bismarck battle and also the Rodney/KGv v Bismarck battle although I know KGv& Rodney did not get hit.
What is the opinion of you experts - were the German rangeinders better but more delicate?



..... I will confine my remarks to a comparison of WW1 British and German range-finders. With the exception of the British 15in gun dreadnoughts, which mounted much longer base length 15-ft Barr & Stroud range-finders, German range finders were hands down superior to the 9-ft Barr & Stroud coincidence range-finders fitted to the balance of the Grand Fleet's capital ships of WW1

The Zeiss 3-meter stereoscopic range-finder itself was not affected by vibration effects produced by ship's machinery operating at high speed or distortion of its tube due to uneven solar heating; it had superior light gathering properties due to better quality optical glass and more intelligently selected magnification levels; it did not need a distinct and clearly visible vertical element upon which to take a range-cut and could in fact range on indistinct elements such as smoke clouds; it was better in conditions of poor visibility, as were often encountered in battle, and, in conditions of dim light, it could often measure ranges when the British Barr & Stroud 9-ft coincidence range-finder was unable to do so; it was more comfortable for its operator to use; it also kept its adjustment better and was easier and faster to calibrate.

In addition, the German range-finding SYSTEM, based upon the "Mittlungsapparat" real-time electro-mechanical range-averaging device, IMHO elevated this superiority to a decisive level. Approximately six range-finder positions were electrically linked to an electro-mechanical data assimilator which simultaneously received and processed range readings from all six positions on a continuous rolling basis, averaged them on the fly, and automatically input a continuously updated averaged range value into the fire control computer. Whereas the precision of any measurement is broadly equal to the square root of the number of measurements, this system produced results perhaps 2.5x more accurate than a reading from an individual range-finder. My reading has turned up comments to the effect that the IGN found this range-finding system satisfactory out to about 20,000 meters.

The British system involved the input of a single range-finder mounted in the control top and the process for incorporating range-finder readings into the FC process was largely manual at this time.

What Germany had developed was "a range-finder control" based gunnery ysystem - a method of FC based upon and controlled by inputs of multiple range-finders - which had also been conceived by the British shortly before WW1 but never actually engineered and fitted to its ships in a workable way.

..... which is one of the reasons I take issue with the argument that the IGN's fire control system in WW1 was somehow "more primitive" than that of the GF. Different? Yes. Less sophisticated? By no means.

For what it's worth.

B

dunmunro
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Re: British v German rangefinders

Postby dunmunro » Wed Jun 22, 2011 9:09 am

Here's a brief summary of RN trials between the B&S and Zeiss RFs:


Rangefinders in Light Cruisers and Torpedo Boat Destroyers.- All rangefinders in Light Cruisers and Torpedo Boat Destroyers suffer from vibration at high speed to such an extent that the results obtained are practically useless.
Trials are being carried out with various types of mountings in ships of the 1st L.C.S., which included an “Argo” mounting which compared unfavourably with the Barr and Stroud type of mountings. (G.5007/21/)
Comparative trials were carried out with a 3 metre German Stereoscopic Rangefinder and a 9 ft. Barr and Stroud Coincidence Rangefinder mounted in the destroyers “Verity’ and “Whitshed” and the general conclusions arrived at were:-
For initial ranges at ranges of 10,000 and above the coincidence rangefinder is superior.
Under ordinary conditions and steering up to 25 knots there is little to choose between the two types.
At Full Speed the stereoscopic gave the best results, which was partly attributable to the heavier weight of this rangefinder and mounting (especially the mounting), which was 2,144 lb. compared with 1,005 lb.
Interference from funnel gases, the coincidence gave the best results.
Smoke Screen stereoscopic alone could range on the screen. Not much difference in ranging through smoke.
During Firing stereoscopic gave the best results.
Low visibility, stereoscopic gave the best results.
Ranging on a Searchlight. No particular difference.
Ranging on a ship illuminated by searchlight, stereoscopic gave the best results.
Further trials will be carried out from “Winchester” and special attention will be given to obtain the causes and reduction of vibration. (G.0902/20.)

http://www.admirals.org.uk/records/adm/ ... 86-251.pdf


Summing Up. - The "Verity-Whitshed" trial and trials in the Fleet have shown that the coincidence rangefinder is superior;

a) When the visibility is good.
b)When taking "snap" ranges.
c)When taking initial ranges.
d) Under ordinary conditions and steaming up to 25 knots there is little to choose and inferior:
(i) At full speed.
(ii) Low visibility
(iii) Ranging on smoke screen.

(Reference C.B. 1594, Section I, para III.)

37

The series of trials under report show that, in addition, with the modified structure (i.e., less vibration) the stereo has lost its superiority at high speeds, and further that on difficult objects, provided the coincidence rangefinder is able to get any ranges at all, the stereo is worse as regards accuracy and consistency, and only scores through obtaining more ranges per minute. On several occasions in low visibility with ill-defined object, the stereo was able to range when the coincidence could not, but on comparing the ranges obtained with the true ranges they were found to be very much in error, and in practice would have been useless and misleading.

Reviewing all the above, it is considered that the 9 ft. coincidence rangefinder is the most suitable for use in destroyers but that the mounting should be an improvement on the M.12.

Stereoscopic rangefinders have the further practical disqualification that the selection and training of rangetakers for them is more difficult than for coincidence rangefinders.

http://www.admirals.org.uk/records/adm/ ... 86-259.pdf


A 3m RF = 9.8 ft.
Vibration was not much of an issue on BBs and much less on a BC than a DD, and when either was used on a BB, much of the advantage of the superior Zeiss mount would disappear.
The Dreyer table was able to plot multiple RF inputs and the operators could produce a mean range with little difficulty.

Byron Angel
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Re: British v German rangefinders

Postby Byron Angel » Wed Jun 22, 2011 12:29 pm

..... I recomend that anyone interested in the question of the relative merits and efficiencies of British versus German WW1 range-finders closely read the Cumberland Trials report included in Progress in Naval Gunnery 1921, then compare their conclusions with those of the authors as regards the utility of the evaluated instruments under battle conditions. Keep in mind as well that no German or German-trained operators, suitably qualified for Zeiss instruments, participated in the trial experiments, while a team of Barr & Stroud specialists was prominent throughout the event. Also keep in mind that the testing process was conducted entirely on land.

My further comments as follow, keeping in mind that they largely relate to WW1 North Sea campaign -
[ 1 ] The effect of vibration at high speed upon range-taking was indeed a problem on British capital ships, especially the BCs, as evidenced by contemporary service commentary.
[ 2 ] The input of turret range-finder readings into the Dreyer table was done, but (a) verbal data transmission over the ship's comms was too slow; (b) manual plotting and interpretation of the data on the scrolling paper FC plot was a much slower and less efficient method than the "Mittlungapparat" system. That is the reason for the post-Jutland push to automate the input of range-finder data into the FC process. By and large, the lack of useful range-finder data with respect to the gunnery process was a repeated theme in post-Jutland wash-ups and analyses, with comments such as "the gun served as its own range-finder" or "it was at this time that we managed to get a few useful range-finder readings" being common themes. The Pollen FC system, fitted in some British ships, had an automated data feed IIRC, but relied upon a single gyro-stabilized RF to supply linked range + bearing data couplets.
[ 3 ] While it is true that competent operation of a stereoscopic range-finder required individuals with good innate stereoscopic vision and consequently had a smaller pool of suitable candidates upon which to draw, and while it is also true that the training is more difficult than for coincidence range-finders, no evidence yet suggests that the IGN ever faced any difficulties in filling its operator requirements (nor did this perceived personnel issue apparently deter the USN from fitting its fleet with stereoscopic range-finders during WW2).

B

delcyros
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Re: British v German rangefinders

Postby delcyros » Wed Jun 22, 2011 1:16 pm

Thanks Byron for these comments.

I may add that the 3m stereoscopic rangefinders were sometimes replaced in the repair and docking process following the battle of Jutland. After the battle, all of the 3m and 4m (KÖNIG class only) instruments in the fore and aft GCT positions were changed. Usually, the 3m instruments were changed with 4m Zeiss rangefinders. In all of the 12in (except the whole HELGOLAND class) and 15in armed ships 5m Zeiss instruments were refitted. There were a number of additional 1.5 and 2m Zeiss rangefinder instruments in the NASSAUs and HELGOLANDs which were carried additionally to the 3m instruments of the fore and aft GCT in lower "controll positions" scattered over the sides. There is some evidence that in 1918 most of the battlecruisers carried at least one 8m instrument (there are photos of VON DER TANN carrying an 8m instrument at her aft GCT) and it has been claimed that BADEN and BAYERN carried them in 1918 but this cannot be confirmed.
Turret rangefinders were 6m Zeiss instruments for the 28.3cm and 30.5cm ships and 8.2m Zeiss instruments for BADEN and BAYERN.

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Re: British v German rangefinders

Postby dunmunro » Wed Jun 22, 2011 8:15 pm

Byron Angel wrote:..... I recomend that anyone interested in the question of the relative merits and efficiencies of British versus German WW1 range-finders closely read the Cumberland Trials report included in Progress in Naval Gunnery 1921, then compare their conclusions with those of the authors as regards the utility of the evaluated instruments under battle conditions. Keep in mind as well that no German or German-trained operators, suitably qualified for Zeiss instruments, participated in the trial experiments, while a team of Barr & Stroud specialists was prominent throughout the event. Also keep in mind that the testing process was conducted entirely on land.

My further comments as follow, keeping in mind that they largely relate to WW1 North Sea campaign -
[ 1 ] The effect of vibration at high speed upon range-taking was indeed a problem on British capital ships, especially the BCs, as evidenced by contemporary service commentary.
[ 2 ] The input of turret range-finder readings into the Dreyer table was done, but (a) verbal data transmission over the ship's comms was too slow; (b) manual plotting and interpretation of the data on the scrolling paper FC plot was a much slower and less efficient method than the "Mittlungapparat" system. That is the reason for the post-Jutland push to automate the input of range-finder data into the FC process. By and large, the lack of useful range-finder data with respect to the gunnery process was a repeated theme in post-Jutland wash-ups and analyses, with comments such as "the gun served as its own range-finder" or "it was at this time that we managed to get a few useful range-finder readings" being common themes. The Pollen FC system, fitted in some British ships, had an automated data feed IIRC, but relied upon a single gyro-stabilized RF to supply linked range + bearing data couplets.
[ 3 ] While it is true that competent operation of a stereoscopic range-finder required individuals with good innate stereoscopic vision and consequently had a smaller pool of suitable candidates upon which to draw, and while it is also true that the training is more difficult than for coincidence range-finders, no evidence yet suggests that the IGN ever faced any difficulties in filling its operator requirements (nor did this perceived personnel issue apparently deter the USN from fitting its fleet with stereoscopic range-finders during WW2).

B


The Fort Cumberland trials noted that the Stereo operators had 3 years of training and practice. The conclusions of the Fort Cumberland trials closely match those of the USA's NDRC, referenced below. B&S was closely involved in the trials, but B&S were quite capable of building stereo instruments and would have been happy to do so but their main interest was in examining the excellent engineering of the Zeiss RF . The Fort Cumberland trials makes note of the fact that coincidence (CI) is theoretically more accurate, and the USA's NDRC came to the same conclusion. The only optical ranges obtained by USS Washington during her engagement with Kirishima came from her 'A' turret mounted CI RF:
http://www.usswashington.com/washingtonguadalcanal.pdf
see pages 9 and 19.

B&S patented many aspects of CI RFs and this made it difficult for Zeiss and Baush and Lomb to match B&S CI RFs in accuracy and efficiency without paying royalties. There is some evidence to suggest that this spurred both firms into stereo development. The USN made greatly inflated claims for 5"/38 AA kills:
http://www.sfu.ca/~dmunro/images/USN_AA ... ims_42.pdf
and stereo RF efficiency, especially in the AA mode, but neither claim stands up to scrutiny. The USA was overclaiming AA kills by a factor of 5 to 1 in 1942 which doubtless influenced some WW2 RN officers into believing that stereo (and the Mk37 GFC System) was better, but the NDRC did not find stereo be more accurate, again as predicted by Fort Cumberland, 20 years earlier.

1) Doubtless vibration was an issue on some capital ships at some speeds, as it was on USN BBs during WW2 but it would have been, typically, much less than on a DD, especially on turret mounted RFs, where the heavy turret damped vibrations and evened out temperatures.

2) range transmission from the RFs to the TS was through step by step transmitters and was nearly instantaneous to the TS, where it was plotted on the Dreyer Table. Optical RFs can only obtain several cuts/minute so even a 1/2 dozen RFs inputs only results in 12 - 24 individual ranges/minute and the Dreyer Table range plotter had no problems with that. See:
http://www.dreadnoughtproject.org/tech/ ... trolTable/
http://www.dreadnoughtproject.org/tfs/i ... eyer_Table

There are a number of factors which mitigate against optical RFs obtaining useful data, repeatedly in a timely manner, which is why radar was so welcomed by all WW2 navies. Using the guns as a rangefinder is actually quite useful and again was SOP in all navies.

3) The USN expended very large sums of money to build, select, train, and establish a stereo training infrastructure, yet testing by the USA's NDRC did not find stereo to be more accurate:
http://en.wikipedia.org/wiki/Coincidenc ... ngefinders
and this agreed with the RN's conclusions that stereo RFs were simply not worth the extra expense involved.

Byron Angel
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Re: British v German rangefinders

Postby Byron Angel » Sat Jun 25, 2011 6:46 am

Apologies for the tardy reply, but work has been bearish this week.

By way of preface, let it be said that I have no desire to promote any acrimony or disagreeable debate on this topic. What follows is simply the fruit of my studies and some considered opinions I have derived therefrom.

My previous remarks were focused upon the British versus German range-finding situation as it existed during the North Sea campaign of WW1. It was not an argument for or against any particular type of range-finder design, although it cannot be denied that the stereoscopic range finding principle confer certain unique advantage under actual battle conditions - especially with respect to the ability to range upon indistinct or dynamically amorphous images. The other advantages of the Zeiss 3m stereoscopic range-finder over the 9ft Barr & Stroud range-finder, as described in my previous post, can be atrributed to better German design decision relating to technology unrelated to the range-finding function per se - better image clarity through the use of superior quality optical glass, better light gathering light as a function of more judicious selection of magnification options, better resistance to vibration effects as a result of a much heavier and suspended range-finder mount, better resistance to heat distortion of the range-finder tube through use of a specialty metal with low expansion factor versus temperature, better operator ergonomics, and better system of electro-mechanical integration of multiple range-finders into the fire control system. One of the other important points here is that the coincidence range-finder, relying as it does upon the matching of a horizontally split image of a vertical element to make a range determination, requires a clearly and cleanly visible vertical element upon which to range. Contemporary opinion in the Granf Fleet had it that the 9ft B&S was useful up to 16,000 yards >>>provided that visibility conditions were clear<<<. Under the considerably less clement visibility conditions prevalent in the North Sea, useful ranges were considered to be up to about 12,000 yards.

As regards the Fort Cumberland trials - With respect to the operators selected to operate the Zeiss range-finders under examination, my point was that none of them were trained under the German system or German wartime training standards. Nor do we know whether the devices were properly maintained or calibrated. In specific, two leading seamen were mentioned. The operators of the B&S devices were, on the other hand, quite familiar with the operation, maintenance, and calibration methods related to their device, had the benefit of a B&S technical team standing by. To my mind, the ultimate balance of the testing process remains an open issue. Again I urge interested readers to peruse the Fort Cumberland test results themselves - it is at the very least fascinating reading.

As regards the comment ' "The only optical ranges obtained by USS Washington during her engagement with Kirishima came from her 'A' turret mounted CI RF" needs to be put into context. The range taken by this turret mounted coincidence range-finder was only 10,500 yards in night time visibility of approximately 12 sea miles after setting of the moon. The principal 26.5 ft stereoscopic range-finder mounted in the main director was probably not taking ranges because it was busy providing the necessary precision bearing information for the radar FC solution. The fact that it was providing this bearing data suggests that the target vessel KIRISHIMA was visible to it as well. Although I do not want to get into a debate about the perceived superiority of one optical range-finder technology over another, the selection of the USN to fit stereoscopic range-finders as the principal optical range finding devices for its most modern battleships must carry some weight.

As I understand it, the Barr & Stroud patent of coincidence range-finding technology did deter other optical device manufacturers from commercializing competitive products of similar design, including Zeiss. However, that does not necessarily make the argument that a range-finder based upon the stereoscopic principle was a forced second-best choice. The German navy's enthusiastic adoption of the Whitehead ( "Schwarzkopf" auf deutsch = Blackhead ) automobile torpedo suggests that it had no compunctions about adopting outside technologies when it was perceived as sensible, so it is equally possible that it opted for stereo on it perceived technological merits. I need to go back into my books on this to try to pin down exact details.

1) Doubtless vibration was an issue on some capital ships at some speeds, as it was on USN BBs during WW2 but it would have been, typically, much less than on a DD, especially on turret mounted RFs, where the heavy turret damped vibrations and evened out temperatures.

2) range transmission from the RFs to the TS was through step by step transmitters and was nearly instantaneous to the TS, where it was plotted on the Dreyer Table. Optical RFs can only obtain several cuts/minute so even a 1/2 dozen RFs inputs only results in 12 - 24 individual ranges/minute and the Dreyer Table range plotter had no problems with that. See:
http://www.dreadnoughtproject.org/tech/ ... trolTable/
http://www.dreadnoughtproject.org/tfs/i ... eyer_Table


Point ( 1 ) is doubtless correct, but the problem lay in the fact that the turret-mounted range-finders were ancillary devices principally supplied as support the fire of the parent turret when in local or individual control. These turret range-finders did not enjoy direct electro-mechanical data feed to the FC system and any readings they were able to make had to be passed by means other than electro-mechanical (voice tube, telephone) and then manually entered into the FC plot. Point ( 2 ) is correct to a certain degree and I apologize for my earlier mis-statement - it is true that specific range-finders aboard Grand Fleet capital ships were able to automatically transmit their range readings to the FC system via electro-mechanical connection. However, as I have read, these were only the top-mounted range-finders fitted to Pollen Argo gyro-stabilized range-finder mountings and situated in the tops and only forty five such mountings were built during the war. I remain firm in my statement that the RN never successfully fielded a workable multi-range-finder fire control method during WW1 (see Brooks, Burt, etc on this point).

There are a number of factors which mitigate against optical RFs obtaining useful data, repeatedly in a timely manner, which is why radar was so welcomed by all WW2 navies. Using the guns as a rangefinder is actually quite useful and again was SOP in all navies.


I fully agree.

3) The USN expended very large sums of money to build, select, train, and establish a stereo training infrastructure, yet testing by the USA's NDRC did not find stereo to be more accurate:
http://en.wikipedia.org/wiki/Coincidenc ... ngefinders

and this agreed with the RN's conclusions that stereo RFs were simply not worth the extra expense involved.


..... Below is the NDRC excerpt quoted in the above Wikipedia article. There may be more compelling evidence provided in the full report, but, based upon the Wiki excerpt alone, I find the argument inconclusive on the following grounds - slow moving naval targets were tracked at ranges up to 12,000 yards and no other range taking tests exceeded 14,500 yards. Such ranges were well within the limits of high precision for all three RF types.

"COINCIDENCE AND STEREOSCOPIC RANGE FINDERS
The first of these reports is concerned with the comparative test of coincidence and stereoscopic range finders. (353) In these tests the American stereoscopic Height Finder Ml was operated against the British coincidence type Range Finders FQ 25 and UB 7, in ranging on fixed ground targets, moving naval targets and moving aerial targets. The coincidence and stereoscopic methods utilize the same basic principles of geometrical optics for the determination of the distance to a target. The two methods differ radically, however, in the nature of the criterion presented for human judgement. These British instruments were of the split field coincident type. American crews were being trained at Fort Monroe to operate the coincidence instruments but this plan was dropped when six British seamen, who were experienced range takers, were made available for the tests. Until recently the British Services had tended strongly to the coincidence type of instrument while the American Services had adopted the stereoscopic principle for long-base instruments at least. The decisions of both the British and American Services apparently grow out of different interpretations of the experience of the Battle of Jutland in World War I and are of no concern in this place.

Tests were run in November and December 1941 using the British seamen on the British instrument and experienced American observers on the Standard M1. Bad weather conditions and various experimental difficulties and mishaps made it impossible to obtain a really satisfactory quantity of data before the tests hall to be terminated. Fixed target reading were made on targets from 2,700 to 14,500 yards. Only five aerial courses could be recorded and these were all level flight courses, at altitudes of 3,000 to 4000 yards and slant range between 4,000 and 12,000 yards Continuous contact was used. Nine courses were obtained on slow moving naval targets at ranges from 4,000 to 12,000 yards. In these latter courses continuous and broken contact were used at different times.

It was found, throughout the tests, that the performances of the various instruments were more nearly alike when measured in external units (Reciprocal range) than when measured in terms of error at the observer's eye, in spite of marked differences in physical dimensions of the instruments. The American MI has a base length of 4.5 yards and used 12 power; FQ 25 with a 6 yard base used 28 power and UB 7, a portable instrument, has 25 power and 3-yard base. The coincidence instruments did not use internal adjusters but were calibrated on targets of known range. In other words. the net performance of the different instruments were essentially comparable although the instruments exhibited varying degrees of efficiency in performance relative to the size. On aerial courses precision errors of the four instruments were about alike when measured in reciprocal-range units. In UOE[4], the FQ 25 had comparatively poor precision, while the UB 7, for three of the five aerial courses, had very small precision errors. The number of aerial courses was too small to yield much information about consistency of observations from one course to the next.

For the naval target courses, one American instrument was not operating. Precision errors of the other three instruments there similar to those on aerial height courses. In reciprocal range units the three instruments had comparable precision. In UOE the FQ 25 was worse and the UB 7 was better than the American M1. Consistency error of the UB 7 was smaller than that of the M1, even when measured in reciprocal range units, while the FQ 25 was similar in consistency to the Ml, again in reciprocals units. On ground targets the same general situation holds. Consistency errors of the four instruments over the 9-day period were the same when measured in reciprocal-range units. Again the UB 7 was better than the stereoscopic instruments in UOE and the FQ 25 was worse. Consistency over the 9 days was not perceptibly worse than daily consistency for any of the instruments. In other words, the readings over the 9 days did not scatter in total more than did readings for a typical day. An analysis or these results leads to the following conclusions. (1) Performance of the coincidence and stereoscopic instruments was about the same when range errors were measured in yards (2) The UB 7 however, with a virtual base length smaller than that of the American stereoscopic instruments was more efficient than the stereoscopic height finders in terms of performance for its size, while the large coincidence instrument, the FQ 25. was less efficient in this sense. This situation held for all types of targets— fixed ground, naval, and aerial. (3) The UB 7 is somewhat better than the American instrument in consistency on naval targets, even when measured in external units.

This report is attached. as supporting data, to a Report to the Services issued by the Fire Control Division of NDRC (20)This points out that the tests indicate no important difference in the precision obtainable from the two types of instrument— coincidence and stereoscopic They do indicate, however, that the difference in performance between large and small instruments is by no means as great as would be anticipated from simple geometrical Optics The report concludes with the belief that stereoscopic and coincidence acuities are about equal. Under favourable conditions existing instruments of the two types perform about equally well, and the choice between them for any given purpose must be based on matters of convenience related to the particular conditions under which they are to be used."


B

dunmunro
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Re: British v German rangefinders

Postby dunmunro » Sat Jun 25, 2011 10:15 am

The USA's NDRC looked at Stereo and CI, and did not find an advantage for stereo. The US 13.5 ft M1 Stereo performed equally with a 18ft CI (FQ-25) and not as well as a 9ft CI (UB-7). The UB-7 was a fairly modern CI design and IIRC, the FQ-25 was an older instrument.

The Fort Cumberland trials came to the same conclusion as the NDRC; both types had pluses and minuses but that stereo had no overall advantage. The logic of the situation is then inexorable, namely that if the two systems are nearly identical, then CI wins because it is much cheaper and easier to implement, especially because it does not require the stringent testing, selection and training required by stereo.

One of the patents that B&S held was on the strip field CI RF:

Image
Image
and this (along with inverted field CI) allowed CI RFs to range efficiently on aircraft and other targets where a vertical line might be hard to find, and it obviously worked well.

In WW1 it is true that only a few Dreyer and Argo tables were setup to automatically plot RF ranges into the table. However, all Dreyer tables were setup to manually plot RF ranges from multiple sources, either through a bulkhead step by step receiver or by phones, which were then entered as pencilled or typed marks on the plot. It was then easy for the table operators to assess the mean range and to reject outlier values.

Ft Cumberland did not find the Stereo units to be more accurate under average conditions. - This has to be emphasized!
Stereo had some advantages under adverse conditions, especially on light ships, but in reality this was of little consequence because small ships, especially destroyers had very little in the way of centralized FC anyways, and it was not until destroyer DCTs were developed, along with the AFCC that RF's became truely useful on light ships. On larger ships, the poorer engineering of B&S RFs was not such a disadvantage, as these results show:

Rangefinders in Light Cruisers and Torpedo Boat Destroyers.- All rangefinders in Light Cruisers and Torpedo Boat Destroyers suffer from vibration at high speed to such an extent that the results obtained are practically useless.
Trials are being carried out with various types of mountings in ships of the 1st L.C.S., which included an “Argo” mounting which compared unfavourably with the Barr and Stroud type of mountings. (G.5007/21/)
Comparative trials were carried out with a 3 metre German Stereoscopic Rangefinder and a 9 ft. Barr and Stroud Coincidence Rangefinder mounted in the destroyers “Verity’ and “Whitshed” and the general conclusions arrived at were:-
For initial ranges at ranges of 10,000 and above the coincidence rangefinder is superior.
Under ordinary conditions and steering up to 25 knots there is little to choose between the two types.
At Full Speed the stereoscopic gave the best results, which was partly attributable to the heavier weight of this rangefinder and mounting (especially the mounting), which was 2,144 lb. compared with 1,005 lb.
Interference from funnel gases, the coincidence gave the best results.
Smoke Screen stereoscopic alone could range on the screen. Not much difference in ranging through smoke.
During Firing stereoscopic gave the best results.
Low visibility, stereoscopic gave the best results.
[i]Ranging on a Searchlight. No particular difference.

Ranging on a ship illuminated by searchlight, stereoscopic gave the best[/i]
P.10, http://www.admirals.org.uk/records/adm/ ... 86-251.pdf

Again, no decisive superiority for one design or the other, and as always, if they are equal in performance, CI wins because it is easier and cheaper to operate.

As a rule, and the USN was no exception, navies do not like employing technologies that require royalty payments to foreign powers. If they can buy or acquire the technology outright they will, but licensing foreign designs was always a political and economic minefield and likely to be strongly opposed by influential segments of society.

As regards the comment ' "The only optical ranges obtained by USS Washington during her engagement with Kirishima came from her 'A' turret mounted CI RF" needs to be put into context.


The RF operators in Washington had no other duties except to take ranges, but why might they have not used stereo ranges?

The Ft Cumberland trials give us a clue:



The results of the coincidence type are more reliable. because they are less affected by the personal element than the stereo readings. This personal factor engenders an attitude of suspicion towards the latter, and where the two types are at variance it is very unlikely than any reliance would be placed on the stereoscopic ranges...

The series of trials under report show that, in addition, with the modified structure (i.e., less vibration) the stereo has lost its superiority at high speeds, and farther that on difficult objects. provided the coincidence rangefinder is able to get any ranges at all, the stereo is worse as regards accuracy and consistency, and only scores through obtaining more ranges per minute. On several occasions in low visibility with ill-defined object, the stereo was able to range when the coincidence could not. but on comparing the ranges obtained with the true ranges they were found to be very much in error, and in practice would have been useless and misleading.
Speaking generally, there is little to choose between the two types of rangefinder, provided the operators observing are equally skilled in rangetaking.

The results of the coincidence type are more reliable. because they are less affected by the personal element than the stereo readings. This personal factor engenders an attitude of suspicion towards the latter, and where the two types are at variance it is very unlikely than any reliance would be placed on the stereoscopic ranges.

http://www.admirals.org.uk/records/adm/ ... 86-259.pdf


I'm sorry if this reply is a bit scattered, but the key points are that Ft Cumberland, conducted by professional RN officers and the NDRC RF trials came to exactly the same conclusions:

NDRC: The report concludes with the belief that stereoscopic and coincidence acuities are about equal. Under favourable conditions existing instruments of the two types perform about equally well, and the choice between them for any given purpose must be based on matters of convenience related to the particular conditions under which they are to be used."

Ft Cumberland: Speaking generally, there is little to choose between the two types of rangefinder, provided the operators observing are equally skilled in rangetaking.

but Ft Cumberland goes on to state:
Exhaustive comparative trials have been carried out between stereoscopic and coincidence rangefinders and although the German stereo has the very important advantage of being unaffected by variations in temperature, it is not as good an all round rangefinder for Naval Service as the Barr & Stroud coincidence rangefinder.

The disparity between the two would appear more marked were the provision of more stereoscopic rangefinders to be made, as there can be little doubt that it would not be possible to maintain the efficiency of the operators at the high standard attained by those at Fort Cumberland. Even when highly-skilled operators are available it is only under circumstances that are not likely to arise that the stereo is superior to the coincidence. and it is considered that the complication and expense of training and maintaining the two types of operators would not be justified at any rate as far as low-angle work is concerned. For anti-aircraft work the stereo may prove superior, but this is not considered likely, and will in any case be investigated in Series V now in progress.


I did a quick calculation, that in midwar, the RN had about 300 sloops and DDs (one RF)in commission, about 80 (~ 5 RFs, some duplex) cruisers, depot ships and AMCs, and about 25 (~6 RFs, many duplex) capital ships, and that the RN would need about 3 trained RF operators per RF. So for the DDs that equals ~1000, and 1200 for the cruisers and about another 1000 for the capital ships, or about ~3000 altogether. Only 3 to 5% of the population have sufficient stereo acuity to be RF operators, and only a subset of these will have the mental aptitude to serve. Selection and training requires a large infrastructure and at the end of the day, the results are no better than CI, which is far cheaper to operate and the selection pool is very large, virtually anyone can fill in in a pinch and RF operators will have the time to qualify for other naval trades. It is easy to see why the RN turned down stereo RFs.

It is essential to read the Report of Division 7, NDRC, Rangefinders and Tracking, to get a real feel for the enourmous (and ultimately largely wasted) effort that the USA and USN put into stereo RF development, selection and training...and the final product was no advance over CI.

Byron Angel
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Re: British v German rangefinders

Postby Byron Angel » Sat Jun 25, 2011 3:49 pm

I re-iterate that I do not want to become enmeshed in a stereoscopic versus coincidence range-finder debate. I am posting the following item solely to make a point about placing too much reliance upon a single document to support any argument. In this case, the sentiments of the RN toward stereoscopic range-finders had apparently materially changed by mid-WW2.

I will, however, take the liberty of pointing out the closing remarks regarding maintenance of skills of stereoscopic rangetakers as it may perhaps relate to the efficiency levels of the British personnel selected to operate both the Zeiss and B&S stereoscopic instruments at the Fort Cumberland trials.

- - -

Excerpted from Progress in Naval Gunnery 1942-1943, page 18 –

Chapter IV

STEREOSCOPIC RANGEFINDERS

85. As is well known almost all foreign navies have adopted the stereoscopic principle for all or some of their rangefinders, whereas we have always usedthe coincidence type only.
During the past year this policy has again been reviewed, largely because of the extreme difficulty of obtaining a “cut” on the modern aircraft which, from many aspects, presents only a horizontal line on which to range. This time was, moreover, an excellent one at which to give further consideration to the subject since we had access to a large amount of data collected by the U.S. authorities, as well as the benefit of the experience of some of our other allies.

86. As a result of this study certain conclusions were reached, which were briefly:-
(a) That the stereoscopic rangefinder is a definite requirement for A.A. purposes, especially at long ranges.

(b) That the stereoscopic rangefinder is at least equal to the coincidence type by day for L.A. purposes under all conditions an is probably superior in heavy weather or bad visibility.

(c) That the difficulties of selecting personnel suitable for further training have in the past been over-estimated and that the experience of the U.S. and other navies indicates that training should not present any serious difficulties.

(d) That there is no definite evidence of the extent to which stress of battle may cause temporary loss of stereo-vision as has sometimes been alleged.

87. Resulting from these conclusions it was approved to adopt a policy whereby 50 per cent of rangefinders in all positions should be stereoscopic, except at close-range weapons and in ships with only one rangefinder. To implement this policy some instruments are being obtained from the U.S.A. and two British firms have been given contracts to produce stereos to American designs. Instruments from these sources will begin to go to sea early in 1945.

88. Meanwhile Excellent have been investigating the training of stereo rangetakers and have found, as expected, that there are no particular difficulties and that a reasonable standard of accuracy can be produced in an eight weeks’ course. Thereafter there is no rapid improvement, but constant practice will enable a man to improve slowly. The vital importance of daily practice has been clearly demonstrated and as short a period as a week without practice is found considerably to reduce the efficiency of a rangetaker. It will therefore be essential to arrange that all stereo rangetakers take a daily series of cuts both in ships and in depots. Another point of interest that has been discovered by Excellent is that a man trained as a coincidence rangetaker will not make a good stereo rangetaker. Steps are now being taken to set up stereo sections at each gunnery school so that the training of rangetakers can be started.


B

dunmunro
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Re: British v German rangefinders

Postby dunmunro » Sat Jun 25, 2011 6:06 pm

Byron Angel wrote:I re-iterate that I do not want to become enmeshed in a stereoscopic versus coincidence range-finder debate. I am posting the following item solely to make a point about placing too much reliance upon a single document to support any argument. In this case, the sentiments of the RN toward stereoscopic range-finders had apparently materially changed by mid-WW2.

I will, however, take the liberty of pointing out the closing remarks regarding maintenance of skills of stereoscopic rangetakers as it may perhaps relate to the efficiency levels of the British personnel selected to operate both the Zeiss and B&S stereoscopic instruments at the Fort Cumberland trials.

- - -

Excerpted from Progress in Naval Gunnery 1942-1943, page 18 –

Chapter IV

STEREOSCOPIC RANGEFINDERS

85. As is well known almost all foreign navies have adopted the stereoscopic principle for all or some of their rangefinders, whereas we have always usedthe coincidence type only.
During the past year this policy has again been reviewed, largely because of the extreme difficulty of obtaining a “cut” on the modern aircraft which, from many aspects, presents only a horizontal line on which to range. This time was, moreover, an excellent one at which to give further consideration to the subject since we had access to a large amount of data collected by the U.S. authorities, as well as the benefit of the experience of some of our other allies.

86. As a result of this study certain conclusions were reached, which were briefly:-
(a) That the stereoscopic rangefinder is a definite requirement for A.A. purposes, especially at long ranges.

(b) That the stereoscopic rangefinder is at least equal to the coincidence type by day for L.A. purposes under all conditions an is probably superior in heavy weather or bad visibility.

(c) That the difficulties of selecting personnel suitable for further training have in the past been over-estimated and that the experience of the U.S. and other navies indicates that training should not present any serious difficulties.

(d) That there is no definite evidence of the extent to which stress of battle may cause temporary loss of stereo-vision as has sometimes been alleged.

87. Resulting from these conclusions it was approved to adopt a policy whereby 50 per cent of rangefinders in all positions should be stereoscopic, except at close-range weapons and in ships with only one rangefinder. To implement this policy some instruments are being obtained from the U.S.A. and two British firms have been given contracts to produce stereos to American designs. Instruments from these sources will begin to go to sea early in 1945.

88. Meanwhile Excellent have been investigating the training of stereo rangetakers and have found, as expected, that there are no particular difficulties and that a reasonable standard of accuracy can be produced in an eight weeks’ course. Thereafter there is no rapid improvement, but constant practice will enable a man to improve slowly. The vital importance of daily practice has been clearly demonstrated and as short a period as a week without practice is found considerably to reduce the efficiency of a rangetaker. It will therefore be essential to arrange that all stereo rangetakers take a daily series of cuts both in ships and in depots. Another point of interest that has been discovered by Excellent is that a man trained as a coincidence rangetaker will not make a good stereo rangetaker. Steps are now being taken to set up stereo sections at each gunnery school so that the training of rangetakers can be started.


B

Sigh, this is one of the most misunderstood areas of WW2 history and I have been investigating it for several years. The RN endured an unprecedented scale of air attack during the first 3 years of the war and many RN officers, including some highly influential persons, such as Stephen Roskill (later to be the RN's chief historian) became convinced that RN AA methods were completely wrong, and those of the USN (and everybody else except the RN) completely right and I suspect that Roskill may have actually written the above excerpt from P.N.G. The RN was in this sudden interest in stereo, heavily influenced by the apparent success of the USN in using stereo RFs for AA:
"In the official bags, combatant ship and merchantmen, an attempt has been made to list only those planes positively shot down. A reasonable estimate, allowing for duplication, of the total enemy aircraft that failed to make home port following an attack is larger by nearly 50 percent. It is estimated that the entire ship-mounted antiaircraft batteries have accounted for 650 airplanes during the first year of the war."
http://www.sfu.ca/~dmunro/images/USN_AA ... ims_42.pdf
where the poor RN with its apparently outdated methods and equipment only claimed:
Total kill claims; 740.
Total probable claims; 266.
Total damage claims; 448

for the entire period from Sept 1939 to Dec 31 1942. (stated later in the above document)
and this, IMHO, caused line officers to overrule the scientists. The USN claimed over 400 hundred AA kills in their first year of the war and hinted that their claims were on the low side, but for example, at Coral sea the USN claimed 49 kills, including 33 over Yorktown and Lexington...yet exhaustive research by historians such as Lundstrom shows that these claims were widely inflated, almost to the point of total fantasy, and Lundstrom concluded, for example that at Coral Sea only 3 of the 33 claims could be verified and only 9 of the 49 total (and 2 of these were probably made by Crace's RAN cruisers). The RN, OTOH, only made 22 AA kill claims during the Battle of Crete, for example, and studies by Shores and Cull show good agreement, with about 15 AA kills verified by post war study.

However, the USN 1942 5" and total AA claims were almost entirely bogus (the USN claimed to down one aircraft per 114 rnds of 5"/38 ammo) and the RN stereo policy appears to have been quietly dropped, and the 1945 edition of the Gunnery Pocket Book makes no mention of stereo RFs. By 1945, the USN quietly cut the 1942 claims almost in half in their late/post war AA summary:
http://www.ibiblio.org/hyperwar/USN/rep ... index.html
The situation in WW2 almost exactly mirrors that of WW1, where the apparently superior German gunnery was attributed to the use of stereo RFs and line officers agitated for,and succeeded in, the introduction of stereo RFs, but post war WW1 study exploded this myth in decisive fashion.

Anyone reading the entire above AA document and its 1942 predecessor would be most powerfully persuaded that USN AA gear was absolutely top of line...the only problem is that most of it was a complete fantasy and the document was worthless due to its complete lack of investigation as to the veracity of AA kill claims, or even the most rudimentary checks to prevent duplicate AA kill claims. The 1945 AA Summary states 60 5" and 246 total AA claims for 1942, when the real numbers are probably closer to 12 5" kills and 80-100 overall.

Again, the NDRC comparison did not show an advantage for Stereo over CI, and the RN never implemented the PNG Stereo recommendations.

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Re: British v German rangefinders

Postby Byron Angel » Sun Jun 26, 2011 5:26 am

I imagine that the RN's stereoscopic conversion program was more than likely simply halted due to the end of the war. In any case, I consider the AAA aspect to be extraneous to the matter I believe to actually be on the table, i.e. - the merits of British versus German range-finders within the context of naval surface gunnery. I have offered my opinion of the situation as it pertained in the North Sea in WW1. It is clear you have strong opinions of your own which run contrary to mine. That's fine. We will just have to agree to disagree and leave it at that.

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dunmunro
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Re: British v German rangefinders

Postby dunmunro » Sun Jun 26, 2011 9:41 am

Byron Angel wrote:I imagine that the RN's stereoscopic conversion program was more than likely simply halted due to the end of the war. In any case, I consider the AAA aspect to be extraneous to the matter I believe to actually be on the table, i.e. - the merits of British versus German range-finders within the context of naval surface gunnery. I have offered my opinion of the situation as it pertained in the North Sea in WW1. It is clear you have strong opinions of your own which run contrary to mine. That's fine. We will just have to agree to disagree and leave it at that.

B


I haven't found any references to actual RN use of stereo RFs on HM (other than HMS Delhi) ships during WW2. If you can find some, I'd be very interested. AFAIK, all RN ships using UK built FC systems used CI RFs throughout the entire war, including the latest classes of CLs and DDs using Mk VI DCTs, commissioned just as the war ended. If the RN planned on introducing Stereo RFs in large numbers, it is not evident in any histories that I have come across.

It is hard to separate RF design from the total FC system. I suspect that if the IGN had used 9ft B&S RFs, that their gunnery would not have suffered, simply because the RF was only one cog in their FC system, and they had designed their RF system to be highly redundant and to use multiple averaged ranges. The IGN also practised constantly and put great effort into realistic training. Yet when RN ships received similar training, as in Jellicoe's battleships, they achieved similar results.

yes, I do have strong opinions on this, which have been formed after extensive research, but I respect your opinions as well.

Cheers.

Byron Angel
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Re: British v German rangefinders

Postby Byron Angel » Sun Jun 26, 2011 4:12 pm

I haven't found any references to actual RN use of stereo RFs on HM (other than HMS Delhi) ships during WW2. If you can find some, I'd be very interested. AFAIK, all RN ships using UK built FC systems used CI RFs throughout the entire war, including the latest classes of CLs and DDs using Mk VI DCTs, commissioned just as the war ended. If the RN planned on introducing Stereo RFs in large numbers, it is not evident in any histories that I have come across.


..... I'm unable to help on that score, as my library is devoted principally to the naval aspects of WW1, the Age of Sail, and the night surface combats of 1942-1943 in the Solomons campaign.


It is hard to separate RF design from the total FC system.


..... At the end of the day, as I think I mentioned earlier, it is indeed the SYSTEMS that are really under scrutiny at Jutland. The physical range-finding instruments in use were simply components thereof, with the further sub-text being whether or to what degree any difference in performance/precision between the competing devices was attributable to the underlying technology (i.e. - coincidence versus stereoscopic) or to superiority in design and/or manufacturing quality.


I suspect that if the IGN had used 9ft B&S RFs, that their gunnery would not have suffered, simply because the RF was only one cog in their FC system, ...


..... As you are aware, I view the B&S 9ft RF - as fitted in the GF at Jutland in 1916 - as inferior to the Zeiss instrument in certain important technical areas. However, if we were discussing the B&S 15ft RF as fitted to 15in gunned capital ships of the GF, I would indeed concur with your assessment.


The IGN also practised constantly and put great effort into realistic training. Yet when RN ships received similar training, as in Jellicoe's battleships, they achieved similar results.


..... Everything I have read about the HSF points to a great emphasis upon gunnery training being carried out under realistic tactical conditions, i.e. - high speeds, imperfect visibility conditions, different sea and weather states, and varying/high range rates. My impression is that pre-war RN battle practices were rather too formal in nature - particularly in the sense that they were apparently always carried out in good weather and visibility conditions. I agree that the portion of the GF under Jellicoe's direct hand was well and efficiently drilled and extracted the absolute best results possible from the technology available to them. My opinion with respect to the gunnery training of the BCF under Beatty is rather less enthusiastic. Giving due allowance to the relative lack of gunnery training grounds available to the BCF, it is my opinion that their poor performance at Jutland was actually more the result of an eccentric and deficient gunnery doctrine unique to the BCF developed "in-house" during the period between Dogger Bank and Jutland. Explicit evidence of this is difficult to come by, as, to the best of my knowledge, no records whatever of any of the proceedings of the post-Dogger Bank BCF gunnery committees convened by Chatfield have yet come to light in the archives. However, there is a good amount of circumstantial evidence pointing in this direction. If anyone can provide or point to any BCF-related gunnery documents dating from this period of time between Dogger Bank and Jutland, I would be more than grateful and most appreciative.


yes, I do have strong opinions on this, which have been formed after extensive research, but I respect your opinions as well.


..... I appreciate your comment and reciprocate the sentiment. These sorts of topics deserve to be discussed in a collegial and decorous manner. This forum need not be an intellectual gladiatorial pit, which seems to occur from time to time.


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dunmunro
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Re: British v German rangefinders

Postby dunmunro » Sun Jun 26, 2011 10:18 pm

Some comments on selecting stereo RF operators, from the NDRC volume on Rangefinders, Chapter 13 (Selection of men)

The number of individuals eliminated during the Fort Eustis testing will be found in the monthly reports. A summary of the test with regard to validation and standardization up to July 1942 is given elsewhere. Between June 1, 1942 and May 31, 1943, of the 37,500 soldiers' records examined only 6,242 survived the earlier tests to be eligible for the the stereoscopic acuity test. Of these, only 1,474 succeeded in passing these tests as well.


The eighth report covers the period of September 1942. During this period 956 men were tested They were selected from an initial screening of 4,832 records. Of these, 155 or 16 per cent of those tested passed all tests. It should again be pointed out that only slightly more than 3 per cent of the men whose records were screened passed all of the tests and could be recommended for training as a stereoscopic observers.


In these reports will be found the selection costs for each sub-test in the battery, A single sample indicates the selection costs. The results are those of the men tested between June 10 and June 30, 1942. Approximately 4,500 Army records were studied and, after elimination because of GCT and MA test scores, height, or indication that the men did not want training as stereoscopic observers, 687 men were selected for examination at the Stereoscopic Testing Center. The table on the following page indicates the number selected and the causes of elimination. Total number of men tested: 687
Passed and recommended: 64


So in any sample of men, about 3% survive the initial selection process and about 1/2 of these survive the actual training, so only about 1.5% of the population will survive to serve. This is a much more selective process than for CI RF operators and it also tends to bias the performance of stereo RFs because of the more rigorous selection process. An equally severe selection process would probably produce more capable CI operators as well.


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