Mk3 and Type 284 radar

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Brad Fischer
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Re: Excellent posts from very knowledgeable posters

Post by Brad Fischer » Sun Nov 04, 2007 1:58 pm

Tiornu wrote:How does a scartometer differ from a rangefinder?
I’m not sure. Who used them besides the Italians? Russians perhaps?

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Re: Excellent posts from very knowledgeable posters

Post by Tiornu » Sun Nov 04, 2007 5:07 pm

Yes, those were the only two navies I know of who used them.

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Post by RF » Thu Nov 08, 2007 1:30 pm

In the generally clear conditions of the Med. would the Italians be at any great disadvantage with this system?

In the engagement in July 1940 between HMAS Sydney and two Italian light cruisers the Sydney was able to target one cruiser and sink it with gunfire, whereas the Italians evidently had problems with ranging as with a theoretical two to one superiority the only damage they caused were shrapnel hits on Sydneys' funnel (as shown in the famous photo of crew members lounging in the holes!). Or would the difficulty with sighting a target dead astern be the real problem here?
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Just Read the Warship Int article again- Oh thaat Brad Fisch

Post by wadinga » Thu Nov 08, 2007 5:48 pm

Thanks Brad & Dave,

I don't whether you are familiar with The Gunnery Pocket Book at http://hnsa.org/doc/br224/index.htm but this 1945 edition includes radar usage as well as optical rangefinding and spotting.

Although it appears to be fully up to date, the optical spotting function is very definitely seperate to rangefinding, which may reflect the practicalities of coincident v stereo rangefinders.

The primitive Under, Over or Straddle indicators described might have been superceded by more complex verbal descriptions from several optical and radar observers.

What does seem clear is that by 1945 radar has become the primary source of information for both functions. I am still trying to home in on the relative performance of the two techniques, as I think Brad's examples suggest at least the Mk 3 was no better at 20,000yds than optical rangefinding with an 8m Iowa rangefinder but that a Yamato 15m was twice as good, +/- 155yds v +/- 85 yds. Is this real?

I find myself astonished that optical rangefinding could be that good. Presumeably there was calibration carried out against surveyed targets to confirm this? Surely this performance dropped off very rapidly under service conditions?

Back to the article and its predecessor to glean more vital info.

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Post by tommy303 » Thu Nov 08, 2007 6:45 pm

I find myself astonished that optical rangefinding could be that good. Presumeably there was calibration carried out against surveyed targets to confirm this? Surely this performance dropped off very rapidly under service conditions?
Stereo rangefinders were checked and calibrated at regular intervals. Under ideal conditions the amount of error is, as Brad has said, a combination of human error and a degree of error unavoidable with the instrument itself, as no optical instrument is completely flawless. The amount of error on the part of the operator can increase over time, which is why a rangetaker's eyesight was checked frequently and he was required to practice and be scored on a regular basis. In short term, changes can occur as well. The amount of error increases with stress, lack of sleep, and fatigue. In the latter case, eye fatigue can play a part in very long actions and an operator might experience gradual increase in error on his part the longer he is at the rangefinder.

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Post by Dave Saxton » Fri Nov 09, 2007 2:59 am

Optical range finding could be very good indeed. As the primary means of obtaining range data before the advent of radar, tremedous effort and funds, were expended over a period of decades, to make this type of equipment as capable and as accurate as it could possibly be. For example, the optical equipment of most could utilize special filters to extend it's effective range and to improve it's resolution in adverse conditions.

One special advantage of some or most radar equipment (trying to be careful not to lump general characteristics of all FC radars together) was that the range accuracy and the range resolution was independant of the actual range.

It's quite true that among those navies that had obtained experience with radar directed gunnery, that radar had become, or was becoming, the primary means of obtaining targeting data. For example, some in the German Navy were expessing concern by early 1944, that proficiency in the use of more traditional methods may not be maintained to a high level, because radar direction of weapon systems had become so prevasive, and so primary. One understandable concern was, what if the radar system(s) broke down (a very real possibility), or otherwise could not be fully utilized, and they were forced to fall back once again on optical, or other techniques?

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Re: Just Read the Warship Int article again- Oh thaat Brad F

Post by Brad Fischer » Tue Nov 13, 2007 9:03 pm

wadinga wrote: What does seem clear is that by 1945 radar has become the primary source of information for both functions. I am still trying to home in on the relative performance of the two techniques, as I think Brad's examples suggest at least the Mk 3 was no better at 20,000yds than optical rangefinding with an 8m Iowa rangefinder but that a Yamato 15m was twice as good, +/- 155yds v +/- 85 yds. Is this real?
I apologize for the belated reply. Those rangefinder numbers represent theoretical calculations and representative of a good, well trained operator who has plenty of experience. The figures I gave for the 26.5’ Mk 48 in the Mk 38 directors is likely to be quite accurate since it’s based on actual fleet experience. The Yamato figures are more theoretical because there is very little information on Japanese rangefinder design. Several big questions such as are they stabilized, do they have light enhancing coatings, glare filters etc come to mind.

Another question about the Yamato class in general revolves around the various rangefinder stations and whether they had stereo or coincidence units. There is a lot of circumstantial evidence that turret positions may have been coincidence units but there is little information. Only the fwd MB director is known to have one stereoscopic unit.

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Rangefinders v Radar

Post by wadinga » Thu Nov 15, 2007 1:25 pm

Brad,
Thanks for your response. I followed http://www.eugeneleeslover.com/USNAVY/CHAPTER-16-F.html
to an excellent description of the fundamentally different (to coincidence) technique of stereoscopic rangefinders. This article http://www.navweaps.com/index_tech/tech-078.htm
apparently confirms that the theoretical performance of a given baseline rangefinder is apparently an extrapolation of an individual human's ability to differentiate between distances multiplied up by having an "eye to eye" distance of 8 or 15m (ie a very big head) plus the optical magnification of the system.
This ability is as you and Tommy have suggested, a complex psychological and fine eye muscle control skill which needed to be honed, created fatigue and might require the operator to be replaced at frequent intervals, especially in the stress of action.

The section http://www.eugeneleeslover.com/USNAVY/CHAPTER-20-C.html describes a late war US Gun Directors Mark 34, and incidentally mentions the oscillation of the radar antenna to improve target bearing resolution. Notably it calls the optical rangefinder operator a spotter.
Two men operate the rangefinder-the spotter, who sights on the target and positions the wander marks, and the rangereader, who reads the range.
However if the spotter switches between measuring the range to the target, and positioning his wandermark on his estimate of where he thinks the MPI of the current salvo is, the rangereader will have to know which he is doing, and when sending to the transmitting room- differentiate. Also there does not seem to be a mechanism for sending right/left error of the MPI from this system.
The listing of outputs does not mention the range element of the MPI error.

http://www.eugeneleeslover.com/USNAVY/CHAPTER-20-G.html gives an excellent description of using Mk 13 radar for spotting and saysfor a target at 30,000 yards, the norma ... 45 yards,. I am still trying to find the Warship International ref from maybe 15 years ago in which a former Iowa gunnery man said their Topspot 1 rangefinder was +/- 1000 yds at 30,000 yds.

The laddering salvo technique or bracket and halving spotting techniques described in http://www.eugeneleeslover.com/USNAVY/CHAPTER-18-C.html basically says we may have no confidence in our measured target ranges or our ability to direct spot where the MPI is relative to the target so will lob shells at the enemy, maybe with an artificially elongated spread, and see where they land and act accordingly. It seems IMHO the range of jobs described for the spotter would be very difficult to do from the eyepiece of the rangefinder, so surely somebody else is doing this. As described in the Gunnery Book 1945 for Royal Navy practice.

This is what I am trying to get a handle on:- real measured performance of stereo and coincidence rangefinders at various ranges. All comments appreciated.

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Post by tommy303 » Fri Nov 16, 2007 12:34 am

Hi Wadinga,
However if the spotter switches between measuring the range to the target, and positioning his wandermark on his estimate of where he thinks the MPI of the current salvo is, the rangereader will have to know which he is doing, and when sending to the transmitting room- differentiate. Also there does not seem to be a mechanism for sending right/left error of the MPI from this system.
I am not too sure about the US approach to spotting, but in the German practice, the rangefinder was kept with the Wandermark on target at all times (and thus continued to give range readings) and spotting fall of shot was done with the lateral and vertical lines of diamond markers in the reticle pattern. Each diamond represented an increment of vertical or lateral distance, usually something like 200m increments in range and 50m increments in lateral distance. So if the spotter sees the the farthest and closest splashes as having a spread of say 200m and the right and left splashes as having a spread of 100m, he can easily give a rough estimate of the MPI without taking his Wandermark off the target. The spotter can thus give a verbal estimate to the controlling Artillerieoffizier of the necessary correction for up or down and right or left without interrupting the flow of range data.


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Post by Serg » Fri Nov 16, 2007 1:14 pm

Hi,
Warship International ref from maybe 15 years ago in which a former Iowa gunnery man said their Topspot 1 rangefinder was +/- 1000 yds at 30,000 yds.
You must find Warship International 1986, No4 and look on p334. According to gunner data,
at 30.000 yds Mk52 (46 ft) give 136.6 and Mk48 (26.5 ft) 237.1 yds, in so-called units of error. However, unclearly what represents "unit of error" in statistic values. Is it mean deviation, probable error or something else?
Similar data on comparable 8m japanese coincidence RF was in Lacroix's brick. But Japanes used double and triple rangefinders in one box. I.e in the case of simultaneous their work on one target a mistake will be less then with single one.
It seems IMHO the range of jobs described for the spotter would be very difficult to do from the eyepiece of the rangefinder, so surely somebody else is doing this.
I agree. In the russian practice the command rangefinder station (american and british analogs is Spot or DCT, if I saving correction) usually had 2-3 single rangefinders, one of them give range on target, another on splashes and third could execute either of two tasks. With the exception of italian rangefinder which had built-in scartometer and could measure deviation of salvo directly. However the single imported model with scartometer which used by navy before and during war was an OG3 - Galileo 3m stereo rangefinder, installed on some destroyer leaders. Also I have read that as a last resort possible to use the single stereoscopic rangefinder. However unclearly how effective such method in practice. In case of maximum magnitude the field of view quite limited (~ 1 degree for 8m RF operator!) and some salvos simply will be drop out of sight.

BTW, such question. Mr.Skelly (who was in Iowas's fire control team) asserted that "at 26.000 yards and beyond establishing fall of shot MPI error in relation to target is difficult to impossible as to magnitude - it becomes a matter of sensing longs and shorts..." I.e up to 26.000 yds a possible direct method using? Is it connected with the splash base beyond the horizon or there is something else in mind?

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Post by tommy303 » Fri Nov 16, 2007 4:35 pm

Hallo Serg,


BTW, such question. Mr.Skelly (who was in Iowas's fire control team) asserted that "at 26.000 yards and beyond establishing fall of shot MPI error in relation to target is difficult to impossible as to magnitude - it becomes a matter of sensing longs and shorts..." I.e up to 26.000 yds a possible direct method using? Is it connected with the splash base beyond the horizon or there is something else in mind?
Assessing longs and shorts, as well as right and left limits of the fall of shot pattern is difficult at longer ranges. As you and Mr Skelly surmise, it is easier when the entitre splash from base to top can be seen. When the splash bases are hidden by the horizon one has less time to make an estimate before the water column collapses. as range increases more and more of the splashes will be hidden and less and less time is available for the the spotter to make his estimate. I think this is what Herr Skelly is implying when he says it becomes a matter of sensing longs and shorts.

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Post by tommy303 » Fri Nov 16, 2007 5:27 pm

In the russian practice the command rangefinder station (american and british analogs is Spot or DCT, if I saving correction) usually had 2-3 single rangefinders, one of them give range on target, another on splashes and third could execute either of two tasks. With the exception of italian rangefinder which had built-in scartometer and could measure deviation of salvo directly.
In Germany too, the main spot estimate was done by the control officer at the director. His optics were a similar to a modern stereo panoramic sight. The fire control station in the foretop and forward control station also had a binocular panoramic sight used as a spotting glass, so the whole spotting proceedure was a matter of teamwork with estimates from three sources being used to evaluate fall of shot.

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Spotting

Post by wadinga » Sat Nov 17, 2007 11:22 am

Serg: Thankyou for doing what I should have done myself and locating the source. I have that letter and article in front of me and am working through them. Like you I do not understand what "units of error" are, but to get to .1 yds at 30,000 must surely be a mathematically derived theoretical. The article says radar and optical could match at 44,000 yds to within 100yds, Mr Skelly's letter says 500-1000, (which is what I remembered (kind of :oops: ).

Unlike you I have no idea what a Scartometer is, and Google comes up with nothing. Can you enlighten me?

Skelly says 26,000 yds is the limit for direct spotting, the USN manual suggests 18,000, Height of observer is obviously important but how often does one get a clear, sharp horizon?

Tommy, as always, very informative. Although the simulated rangefinder view in the USN article does not give the reticule effect to my stereo vision I think I have it now. The Wandermark can be moved in and out to coincide with the image of the target and the reticule marks appear at different distances in front of and behind this so as to aid MPI determination.

However your posts above on overall control of spotting are a little contradictory. (I'm sure you won't take offence!) The last says the control officer and other dedicated optical sights do it, whereas your earlier post shows the rangefinder has the reticle to apparently quantify it better. Do you think this reflects that under operational conditions of smoke, vibration, spray etc the ability of the reticule to allow direct spotting fails at relatively shorter ranges and the German and probably US systems fall back on the low resolution Short, Over and Straddle system backed up with a Mk 1 eyeball guess at how far short/over etc? The British system, rightly or wrongly, seems to take this view from the start. It doesn't use the more sophisticated stereo rangefinder, buts sticks with coincidence, and doesn't go to high mounted 8 or 10 or 15m rangefinders, but uses what can conveniently be installed in the Director Control Tower.

The Is Bismarck the Best? thread is heading toward this discussion but of course we know Tina Turner is the Best.

All the Best
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Post by tommy303 » Sun Nov 18, 2007 11:16 pm

Hi Wadinga,

Yes that is precisely how it worked. The operator turned his handwheel clockwise or anti-clockwise moving the entire retical pattern in and out. His job was to place the Wandermark so that it appeared to be at the same range as the target and keep it there. When the Wandermark was properly on target, the other, successive lines of marks or diamonds would appear to be short of and beyond the target at regular intervals. When the operator had the range, he pressed a foot pedal which sent the range reading to the range plot in the transmitting station.

An earlier form of Stereo rangefinder, the E-Geraet, had no moving parts such as the rotary prism of the later ones. Instead the operator saw a series of range posts and numbers which appeared to start close up and receed into the distance. He would also see the target in sharp 3D focus. Most of the range posts and numbers would appear to be out of focus, but one would appear clearer than all the rest----and this was the one that gave the range to the target.

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Re: Spotting

Post by Serg » Mon Nov 19, 2007 2:36 pm

Hi all,
thank for answers.
Firstly, I was incorrect above about gunner, not Skelly but Skelley more correctly. Secondly, sorry for delay, I have internet only on my work and sometime it difficult to find the free time.
Thankyou for doing what I should have done myself and locating the source. I have that letter and article in front of me and am working through them. Like you I do not understand what "units of error" are, but to get to .1 yds at 30,000 must surely be a mathematically derived theoretical. The article says radar and optical could match at 44,000 yds to within 100yds, Mr Skelly's letter says 500-1000, (which is what I remembered (kind of :oops: ).
Oh, don't mention it. There are only few efficient articles about fire control and they almost get by heart.:-)
1000+ yds quite possible if the our matter concerns the probable error, for example. Then by analogy with gun dispersion with the 0.9999+ probability the maximum possible error at 30.000 for 26.5 ft rangefinder is 237.1x10=2371 or +/-1185.5 yds. As I understand according to Mr.Fischer possible to estimate the practical error as theoretical error multiplying by 1.5 (according to old russian reference even by 3, but it is very old book, 1929 year) i.e. maximum error up to +/-1778 yds.
Unlike you I have no idea what a Scartometer is, and Google comes up with nothing. Can you enlighten me?
I do not know really. I only have some of the common knowledge, not in so more details as yours or Tommy. As one book says this is complementary optical system, built-in to the rangefinder. The OG-3 mentioned above can to measure the deviation for salvos landed within interval +/- 15 cabels with it help, i.e. this is about +/- 3000 yds relative to target.

I reread the memoirs of the former Novorossiisk artilleryman, "Chas X dlia linkora Novorossiisk"/X-hour for battleship Novorossiisk by Bor-Biriukov. There was two powerful rangefinders on the italian KDP (command rangefinder station, actually, 7.2m stereo and coincidence instruments plus director sight and two separate sights for stabilisation, it is from another source). One of them a "scartometer" consisted of two rangefinders packaged in the single case, one of them work on the target, another on splashes (it seems scartometer simply is a duplex rangefinder, but there are many mistakes in memoirs and it is necessary to consider words of the veteran critically).
The general scheme was as follow: two rangefinders give range to the target and one to the bursts or splashes. Averaged readings come to device where control officer can read salvo deviation and add own correction. So, I can summarize that "italian" spotting procedure in general also not differed from the common method.

Naturally, there were some differences. For example there was an unique device a so-called "salvo spreader ". The broadside automatically divided by spreader into three groups - the long, middle and short, all groups landed near target simultaneously with a given range interval and assisted control officer. In the russian fleet similar devices were not present.
I not sure, there were analogues of this device on other fleets of the world? I read about double salvos but not once about triples.

That intrestingly, he also wrote that the gunners which was transfered from the BB Arkhangel'sk on the Novorossiisk estimates italian FC as excellent and tenfold better than british. But initially FC devices and aim was disbalanced and even curious incidents happened. During first firing trials instead of sled a 320mm salvo landed near tug. The scared tug's skipper has lopped rope and make off. It was difficult to constrain him to drag the sled especially because of absence practical solid projectiles! Eventually the error was fixed after trouble-shooting.
Skelly says 26,000 yds is the limit for direct spotting, the USN manual suggests 18,000, Height of observer is obviously important but how often does one get a clear, sharp horizon?
I hope that Mr.Fischer will clarify this.
When the splash bases are hidden by the horizon one has less time to make an estimate before the water column collapses. as range increases more and more of the splashes will be hidden and less and less time is available for the the spotter to make his estimate.
Seems you are right. Another question that the splash itself has unstable form while for correct focusing is required clearly expressed stable border. Unclearly how rangefinder operator concentrated own attention when necessary to make a "cut". The point of aim the splash base or possible higher, i.e. if the splash slightly hidden behind the horizon?
In Germany too, the main spot estimate was done by the control officer at the director. His optics were a similar to a modern stereo panoramic sight. The fire control station in the foretop and forward control station also had a binocular panoramic sight used as a spotting glass, so the whole spotting proceedure was a matter of teamwork with estimates from three sources being used to evaluate fall of shot.
Something like slightly improved ww1 technique if take into no account the control position height and stabilization. I read memoirs by Herr Haaze, IIRC, he used for spotting the stereoscopic telescope in the upper part of the conning tower which simultaneously operate as director sight. Germans never used rangefinder exclusively for salvo ranging?
Yes, there usually were director sights on all command rangefinder stations (KDP) starting with new DDs (excluding Marat). The control officer place was near director sight "column".
regards,
sergei

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