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."
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