The D/F Controversy

Discussions about the history of the ship, technical details, etc.

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The D/F Controversy

Post by wadinga » Tue Feb 20, 2018 7:30 pm

Hello All,

Recently my ability to understand geometry and mathematics has been impugned somewhat, and although I am impervious to such opinions, I thought I would try and explain my current understanding about something that has puzzled me for a while. It is a long winded explanation and I would welcome comments from those who will bear with me.

Reading Patrick Beesley's book Very Special Intelligence, about the work of Bletchley Park and the radio interception Y stations during WW II, I was considering again the apparent failure to plot accurately the bearings for Lutjens long winded transmission which should have allowed earlier interception by Tovey. I also noticed that Wellings' claims that the same same bearings were successfully plotted in Rodney. How could this be?

Even Rhys-Jones in The Loss of the Bismarck writes a whole chapter and yet does not really pin things down. Tovey's navigator, who has been accused of making a tyro's error, apparently suffered no censure and had a successful career through the rest of the war. Yet the error resulted in KG V steaming in the wrong direction for hours and nearly let Bismarck get away.

The standard marine chart has a lat/long grid at right angles to one another, the meridians all pointing to true north. This is the Mercator chart. However since on the globe meridians all converge at the pole, this is not represented and the effect is more pronounced at higher latitudes. In fact the grid pattern remains and has the effect of distorting distance between points away from the equator.

Ships (and aircraft) travelling long distances choose the Great Circle route which represents the shortest distance ie a straight line over the curved surface of the globe, but this crosses meridians at different angles along its length and so the vehicle is actually steering a continuously varying heading. In practical terms the course to steer consists of a number of straight elements on a series of headings approximating to the curved shape as represented on a Mercator projection chart.

For long ocean passages ships will carry a Gnomonic projection chart, which has a single straight meridian, located around the middle of likely routes, but all other meridians end up with curvature, the effect becoming more extreme at the east and west extremities. Having the straight meridian in mid Atlantic, when the straight line is drawn from say Land's End in Cornwall to New York harbour, course to steer can be derived, with some difficulty, given the curved meridians at the extremities, but as the meridians in mid Atlantic become more straight, the course is easier to derive. The navigator would likely transfer these meridian crossing angles to a Mercator chart, and derive the local courses for his series of straight elements.

Another thing travelling the great Circle route are radio waves as transmitted by Bismarck and so the bearings picked up by interception stations on the UK coast, mostly located for WW I purposes at this time, and thus the East coast, were measured and sent to the Operations Information Centre at the Admiralty London. Beesly implies, but does not actually say, that special Gnomonic charts created for the longitudes (meridians) of the interception stations were then used to plot the bearings out into the Atlantic. Even then the intersection was of a number of lines very nearly parallel to one another with a ellipse of error very wide in longitude and somewhat narrower in latitude. Stations in Iceland and Gibraltar did not pick up the signal so could not improve the geometry. The experienced team at OIC concluded a position and compared with Bismarck's previous location, before Wake-Walker had lost contact, showed she was heading for France.

Having spent some time on deriving this elongated position, the bearings alone, apparently at Admiral Tovey's insistence, were sent to him but also intercepted and at least in Rodney's case independently plotted. What could Captain Frank Lloyd Tovey's Master of the Fleet ie Chief Navigator do with these bearings?

It is clear he did not have gnomonic charts with a central straight meridian for the interception stations. These would be very specialist items. He very likely would have an ocean passage gnomonic chart with a central meridian located in the middle of the Atlantic. However on such a chart the distortion over on the East Coast of the UK would have meant there were curved meridians and somewhere between them were the intercept stations whose local north would be difficult to derive accurately. An error of less than a degree would swing the line many miles either north or south out in the Atlantic.

However radio navigation by bearings of shore transmitters was a well understood exercise, used for many, many years, albeit for usually much shorter ranges and a description of the half-convergency correction technique is included in the Basic RN navigation manual. The allows the navigator to compute an angular correction to the bearing so he can plot a corrected bearing as a straight line on a conventional Mercator chart. With several of these he will get an intersection of varying quality which will have his location within it. It is likely Lloyd used this technique and yet came up with an answer which sent Tovey off in the wrong direction for hours. He has been castigated by some writers and yet how could the technique fail if he carried it out competently?

Well, the Admiralty Manual of navigation says it can be used up to a hundred miles from the transmitter and this example was much more than this, so this is one factor, but also the technique assumes you have a reasonable estimate of position (EP) to input in the first place. In the normal course of navigation one has this as an estimated position from dead reckoning sun sights etc. In the case of the Bismarck where Lloyd was attempting to use the technique in reverse, he didn't have any idea where Bismarck was. The EP is an important parameter in the equation because effectively it draws the curvature of the Great Circle as if on a Mercator chart and then computes the angle of the chord joining the two ends. One end is the known location of the receiving station ashore, but the other end is the location out in the ocean. If this outer end is not constrained in longitude/latitude the bearing of the derived chord could vary considerably.

The OIC had the Gnomonic charts, with the correct central meridian to plot accurately. Lloyd was making do with Mercator charts and had to guess a reasonably accurate position for Bismarck before he could get bearing corrections to apply at all. Maybe he assumed Bismarck was heading for Norway and put an EP into his calculations based on that. Maybe Rodney's navigator, Gatacre input a more realistic EP for Bismarck into his calculations and came up with corrections to the transmitted bearings which allowed a position to be plotted on their Mercator that was closer to OIC's estimate.

If only the Admiralty had overridden Tovey's ridiculous stipulation and sent the derived position as well as the bearings, there would have been error trapping and Lloyd would have suspected there was something wrong. If only the men at sea had trusted OIC's expertise and just trusted a location sent to them. If only it had been envisaged that this might happen and the necessary gnomonic charts with east coast straight meridian had been sent to Lloyd in case they were required.

Thus Lloyd, although sometimes pilloried by those who don't understand the problem, had done nothing wrong. He had done the best he could with the information he had. If Tovey had truly insisted that he wanted no worked out position sent, then he was foolish. However far worse were the decisions of the Admiralty not to send a worked out solution anyway and worse still not to comment for hours when Tovey's transmitted solution differed so much from their own. A hugely valuable intelligence advantage was thrown away for the lack of a little preparation and thought.

It parallels the situation before Jutland when Room 40 told Jellicoe the High Seas Fleet was coming out, so sending the Grand Fleet out to do battle, but subsequently the naval liaison officer assured the Admiral that Scheer's flagship was still in the Jade, because he was unaware of an important fact and never asked the right question. When Scheer went to sea he exchanged call-signs with the Shore Base, so Jellicoe didn't realise his opponent had actually sailed and didn't concentrate with Beatty as early as he might.

Thanks for bearing (joke) with me on this navigational conundrum, if you have.

All the best

wadinga
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Re: The D/F Controversy

Post by wadinga » Thu Jul 26, 2018 11:50 am

Hello Bill Jurens,

In the hope that you are still keeping tabs on this forum, could you peruse my post on the D/F controversy and the difficulty of plotting the supplied bearings and see if it makes cartographical sense? One of the real mysteries of the Bismarck operation is the British failure to exploit Gabby Gunter's lengthy transmission and if there were any kind of "Cover-Up" it would be the failure to effectively use this intelligence and that it was brushed under the carpet.


Of course any other parties who want to contribute are most welcome.


All the best

wadinga
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Re: The D/F Controversy

Post by Herr Nilsson » Thu Jul 26, 2018 12:10 pm

@ wadinga

I wonder whether a correction like the half-covergency solution has also to be considered not only in terms of D/F, but also optical bearings.
Regards

Marc

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Re: The D/F Controversy

Post by wadinga » Thu Jul 26, 2018 7:27 pm

Hello Herr Nilsson,

If you could see far enough it would, but your line of sight would have to bend around following the curvature of the Earth, so as to cross different meridians at different angles. Even with the coldwater mirages extending visibility as experienced at Denmark Straits, it would not be significant with distances involved.

I have read nothing which indicates the plus or minus accuracy of these bearings from the UK on Bismarck. As I understand it, the shore stations used large, fixed, spatially spread-out arrays of aerials to derive the bearings. According to Beesly neither Iceland nor Gibraltar could get bearings. He says Captain Jock Clayton the Deputy Director Operational Intelligence Centre (OIC) told Denning and Kemp who were specialist D/F plotters that Tovey had specifically requested bearings only. So only bearings were sent. :stubborn:

Beesly suggests specialists like Kemp and Denning required months of practice to achieve successful plotting, and of course they had special gnomonic charts. Probably Tovey's ignorance of what was required, led to him assuming Lloyd could reproduce what specialists could, just as well, only with no training and no specialist charts.

There is a note (of surprise maybe) in the awards committee comments that Lloyd was left out of the list of navigators who got awards after the action. However the following year Lloyd got a gong and later in the War, a command.

OIC had noted the switch of operational control to Gruppe West in France and a Bletchley decrypt of the easier German Air Force message for the anxious relative in Athens confirming Bismarck headed for France reached OIC at 18:30. OIC had been convinced of this since about 10:30 but the Admiralty had been sending contradictory messages to Tovey and Darymple-Hamilton.

OIC information was so tight that Pound was on the "need to know list" but not Alexander. When the latter got into the secure office one day and started asking awkward questions, the staff clammed up untiil he left, extremely cross. That is the difference between First Sea Lord and First Lord.

All the best

wadinga
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Re: The D/F Controversy

Post by Bill Jurens » Thu Jul 26, 2018 9:12 pm

It would be difficult for me to try to reconstruct the source of the error in chart plotting without having at hand full numerical information regarding exactly what was sent to the British ships at sea. I don't have that.

Presumably British practices in interpreting such signals is (or, strictly speaking was) fairly similar to those used in the USN. Using British or American practices, and given the information actually supplied from ashore, it might well be possible to step through the processes actually employed on the receiving ships and thus deduce in more detail exactly what sort of error was made, and from whence it sprang.

I am surprised to learn that those afloat appear to have requested that only bearings be sent, as it would have probably been more efficient (and safer) to send reduced positions for Bismarck based upon D/F readings instead. In other words, the work necessary to fully reduce the D/F bearings to a position for Bismarck would probably have been better done by relatively well-rested personnel who had access to all of the information available, rather than depending upon some navigator working in poor light, at sea, who probably hadn't slept well in 30 hours or so.

The error may have revolved around reciprocal bearings. It was common during this period for ships to fix (or at least attempt to fix) their locations be D/Fing shore stations which would send out high-powered signals at certain previously specified frequencies and times. The problem is that the problem of locating oneself is different when one is the recipient of the signals vs one who is reporting a D/F position. Most navigators would have been very familiar with plotting one's own position via D/F bearings on shore stations, but the actual process involved is somewhat different when the D/F station is, in effect, reporting to you instead. One might reasonably assume, for example, that a station reporting your position as bearing (say) 123 degrees true would mean that you are therefore on a reciprocal bearing to the transmitting station, i.e. if his bearing to you is 123 degrees, then your bearing to him must be 303 degrees, but for calculation purposes -- especially when performing corrections -- this is not really the case.

In any case, the first step in attempting to unravel this particular part of the issue would be to obtain the signals actually sent from shore to positions at sea, and, of course, the precise positions of the shore stations so reporting.

If that can be obtained, then the methods (probably) used to reduce the D/F information into positions can probably be reconstructed, provided one can now properly decipher and employ the methodology used, which by current standards is, to say the least, somewhat arcane.

Someone asked if the positional errors due to DF observations would apply to optical observations as well. As noted earlier, probably not. These sorts of problems fall into the category of what is known in land and aerial navigation as 'spherical excess', i.e. as a triangle on the surface of the earth becomes bigger and bigger, the sum of the internal angles tends also to increase beyond 180 degrees. On very large triangles, this does indeed represent a problem; for example given lines from 0 degrees longitude and 90 degrees longitude down the the equator, the sum of the interior angles of the 'triangle' so created would be 270 degrees, instead of 180 degrees as expected.

Generally, spherical excess, i.e. the error involved in assuming a flat rather than a spherical earth can be considered essentially negligible if the distances involved are under thirty miles or so. For twenty kilometers, the spherical excess tends to be around 1 arc second, which is very small indeed, and well beyond the accuracy of normal bearing measurements at sea, which tend to be rounded to the nearest full degree.

Bill Jurens.

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Re: The D/F Controversy

Post by wadinga » Sat Jul 28, 2018 9:28 am

Hello Bill Jurens,

And any others who are interested. :D

Since the activities and capabilities of the intercept stations were highly secret, unfortunately I think the chances of getting all the information you suggest are pretty slim. Even the signals logs leave out the streams of numbers necessary to do what you suggest.

However even if techniques are arcane we can hopefully achieve some understanding. Can you confirm for a gnomonic chart the meridians converge "off the chart" somewhere to the north in our hemisphere? Hence unlike a Mercator where you can use parallel rules to transfer a bearing from a compass rose to the location you want, on a gnomonic chart the printed meridians show true north, but for a desired location between them, like the Scarborough master D/F station, the direction of true north is something between the nearest meridian to the east and nearest to the west.

Denning and Kemp, as D/F specialists may have had gnomonic charts with specially printed meridians passing through the various D/F station locations enabling them to simply use a protractor to mark off the bearing at each individual station against a true north meridian printed for that station. These lines passed out into the Atlantic, but because only UK stations were available, say from the Shetland Isles down to Cornwall the lines drawn were closer to parallel, and a location based on their intersections required interpretation, experience and skill. If the Iceland and Gibraltar stations had extended the north-south baseline by many hundreds or perhaps thousands of miles the geometry of the intersections would have been better.

Out in the Atlantic, Lloyd had no such advantages. The half-convergency technique, as I understand it- feel free to correct me- anyone, uses the known position of the base station, the D/F bearing of its transmissions as measured aboard the ship, and the current estimated position of the ship to effectively "draw" the arc on a Mercator chart and derive the chord joining the two ends. The bearing of this chord can be drawn on the Mercator chart as a reciprocal bearing originating from the base station location and extending into the area where the ship must be. Carrying out the process on multiple base stations gives a series of drawn bearings, the "centre of effort" of which is the best guess for the ship's location. It seems to me that using the technique in reverse to solve for a ship in unknown location, if the estimated position is seriously in error it will degrade the accuracy of the derived bearings.

This could explain why Gatacre the navigator in Rodney appears more successful , or luckier using the same received information. He may have guessed a better estimated position to input. However as the idiotic battle chart argument fails to understand, a position like Gatacre derived is only a best guess "at that moment" and his accuracy could only be confirmed in retrospect. You have pointed this out clearly, that only when an external reference is available can the validity of multiple possible answers be checked retrospectively. Lloyd's different position was only less valid than Gatacre's when Bismarck's movements were subsequently identified.

The idiotic battle chart argument continues to look at "X marks the position" points placed on a chart and believes this can be derived from a single D/F bearing, rather than just being a best guess, possibly inaccurate by miles.

Lloyd may initially have been blamed by those to whom the Navigator's Art was incomprehensible territory, and although the "cock-up" of failing to use the D/F advantage is underplayed in the reports (is that the same as a cover-up) eventually it would appear it was understood the fault was not his and he received rewards. If it was anybody's fault it was Tovey's. His obstinate refusal to have the shoreside specialists' estimate sent to him was ridiculous. Beesly points out it would have sent in the format of a position with a circle of error in miles, say a 100 mile radius of that position. If he wanted to play at having his people second guess the specialists he could. However the serious procedural error was Pound/Phillips' in allowing the Commander to exercise this ridiculous prejudice and even more incomprehensible not immediately questioning why his transmitted estimate was so different to their own.

This is the Real Cover-Up of the Bismarck Chase.

Please feel to shoot me down if my understanding is incorrect, and all comments welcome.

All the best

wadinga
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Re: The D/F Controversy

Post by Antonio Bonomi » Sat Jul 28, 2018 12:48 pm

Hello everybody,

I am not much interested right now on determining a warship position from a ground D/F radio station, ... so I let you discuss about it and his tolerances and correction factors to be applied when the sea miles are in the range of some hundreds if not thousands.

But what I read above being declared by a person instead is of my interest because as usual is trying to disqualify somebody competent work based on correct assumptions with the only intent to leave the knowledge of those arguments as they are, ... nothing to be changed and the novel he loves so much will hopefully survive in the future as the only possible solution.

Sorry, you have already lost this hope, ... you better realize it.

When the D/F measurement is taken from a ship to ship in the same quadrant and the range is only a couple of dozen of sea miles, ... less than 50 sea miles, ... than the correction factors are close to zero and well within the tolerances one can accept.

When the 2 ship course and speed is known, ... when there is a common reference mark in between ( the enemy ships ) and they are both visually referring to it, ... and the geographical position of the enemy is well known, ... with minimum tolerances, ... than the D/F bearing between the 2 units is more than enough to define both their relative to each other and their geographical position.

But as far as I can read and I have verified myself thru those years this process is too complicated for the capabilities of the writer above.

Bye Antonio
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Re: The D/F Controversy

Post by HMSVF » Sat Jul 28, 2018 4:30 pm

wadinga wrote:
Tue Feb 20, 2018 7:30 pm
Hello All,

Recently my ability to understand geometry and mathematics has been impugned somewhat, and although I am impervious to such opinions, I thought I would try and explain my current understanding about something that has puzzled me for a while. It is a long winded explanation and I would welcome comments from those who will bear with me.

Reading Patrick Beesley's book Very Special Intelligence, about the work of Bletchley Park and the radio interception Y stations during WW II, I was considering again the apparent failure to plot accurately the bearings for Lutjens long winded transmission which should have allowed earlier interception by Tovey. I also noticed that Wellings' claims that the same same bearings were successfully plotted in Rodney. How could this be?

Even Rhys-Jones in The Loss of the Bismarck writes a whole chapter and yet does not really pin things down. Tovey's navigator, who has been accused of making a tyro's error, apparently suffered no censure and had a successful career through the rest of the war. Yet the error resulted in KG V steaming in the wrong direction for hours and nearly let Bismarck get away.

The standard marine chart has a lat/long grid at right angles to one another, the meridians all pointing to true north. This is the Mercator chart. However since on the globe meridians all converge at the pole, this is not represented and the effect is more pronounced at higher latitudes. In fact the grid pattern remains and has the effect of distorting distance between points away from the equator.

Ships (and aircraft) travelling long distances choose the Great Circle route which represents the shortest distance ie a straight line over the curved surface of the globe, but this crosses meridians at different angles along its length and so the vehicle is actually steering a continuously varying heading. In practical terms the course to steer consists of a number of straight elements on a series of headings approximating to the curved shape as represented on a Mercator projection chart.

For long ocean passages ships will carry a Gnomonic projection chart, which has a single straight meridian, located around the middle of likely routes, but all other meridians end up with curvature, the effect becoming more extreme at the east and west extremities. Having the straight meridian in mid Atlantic, when the straight line is drawn from say Land's End in Cornwall to New York harbour, course to steer can be derived, with some difficulty, given the curved meridians at the extremities, but as the meridians in mid Atlantic become more straight, the course is easier to derive. The navigator would likely transfer these meridian crossing angles to a Mercator chart, and derive the local courses for his series of straight elements.

Another thing travelling the great Circle route are radio waves as transmitted by Bismarck and so the bearings picked up by interception stations on the UK coast, mostly located for WW I purposes at this time, and thus the East coast, were measured and sent to the Operations Information Centre at the Admiralty London. Beesly implies, but does not actually say, that special Gnomonic charts created for the longitudes (meridians) of the interception stations were then used to plot the bearings out into the Atlantic. Even then the intersection was of a number of lines very nearly parallel to one another with a ellipse of error very wide in longitude and somewhat narrower in latitude. Stations in Iceland and Gibraltar did not pick up the signal so could not improve the geometry. The experienced team at OIC concluded a position and compared with Bismarck's previous location, before Wake-Walker had lost contact, showed she was heading for France.

Having spent some time on deriving this elongated position, the bearings alone, apparently at Admiral Tovey's insistence, were sent to him but also intercepted and at least in Rodney's case independently plotted. What could Captain Frank Lloyd Tovey's Master of the Fleet ie Chief Navigator do with these bearings?

It is clear he did not have gnomonic charts with a central straight meridian for the interception stations. These would be very specialist items. He very likely would have an ocean passage gnomonic chart with a central meridian located in the middle of the Atlantic. However on such a chart the distortion over on the East Coast of the UK would have meant there were curved meridians and somewhere between them were the intercept stations whose local north would be difficult to derive accurately. An error of less than a degree would swing the line many miles either north or south out in the Atlantic.

However radio navigation by bearings of shore transmitters was a well understood exercise, used for many, many years, albeit for usually much shorter ranges and a description of the half-convergency correction technique is included in the Basic RN navigation manual. The allows the navigator to compute an angular correction to the bearing so he can plot a corrected bearing as a straight line on a conventional Mercator chart. With several of these he will get an intersection of varying quality which will have his location within it. It is likely Lloyd used this technique and yet came up with an answer which sent Tovey off in the wrong direction for hours. He has been castigated by some writers and yet how could the technique fail if he carried it out competently?

Well, the Admiralty Manual of navigation says it can be used up to a hundred miles from the transmitter and this example was much more than this, so this is one factor, but also the technique assumes you have a reasonable estimate of position (EP) to input in the first place. In the normal course of navigation one has this as an estimated position from dead reckoning sun sights etc. In the case of the Bismarck where Lloyd was attempting to use the technique in reverse, he didn't have any idea where Bismarck was. The EP is an important parameter in the equation because effectively it draws the curvature of the Great Circle as if on a Mercator chart and then computes the angle of the chord joining the two ends. One end is the known location of the receiving station ashore, but the other end is the location out in the ocean. If this outer end is not constrained in longitude/latitude the bearing of the derived chord could vary considerably.

The OIC had the Gnomonic charts, with the correct central meridian to plot accurately. Lloyd was making do with Mercator charts and had to guess a reasonably accurate position for Bismarck before he could get bearing corrections to apply at all. Maybe he assumed Bismarck was heading for Norway and put an EP into his calculations based on that. Maybe Rodney's navigator, Gatacre input a more realistic EP for Bismarck into his calculations and came up with corrections to the transmitted bearings which allowed a position to be plotted on their Mercator that was closer to OIC's estimate.

If only the Admiralty had overridden Tovey's ridiculous stipulation and sent the derived position as well as the bearings, there would have been error trapping and Lloyd would have suspected there was something wrong. If only the men at sea had trusted OIC's expertise and just trusted a location sent to them. If only it had been envisaged that this might happen and the necessary gnomonic charts with east coast straight meridian had been sent to Lloyd in case they were required.

Thus Lloyd, although sometimes pilloried by those who don't understand the problem, had done nothing wrong. He had done the best he could with the information he had. If Tovey had truly insisted that he wanted no worked out position sent, then he was foolish. However far worse were the decisions of the Admiralty not to send a worked out solution anyway and worse still not to comment for hours when Tovey's transmitted solution differed so much from their own. A hugely valuable intelligence advantage was thrown away for the lack of a little preparation and thought.

It parallels the situation before Jutland when Room 40 told Jellicoe the High Seas Fleet was coming out, so sending the Grand Fleet out to do battle, but subsequently the naval liaison officer assured the Admiral that Scheer's flagship was still in the Jade, because he was unaware of an important fact and never asked the right question. When Scheer went to sea he exchanged call-signs with the Shore Base, so Jellicoe didn't realise his opponent had actually sailed and didn't concentrate with Beatty as early as he might.

Thanks for bearing (joke) with me on this navigational conundrum, if you have.

All the best

wadinga
As a mere minion, ignoramous ,sheep (please feel free to add to the list) I will ask an obvious...

If I am reading you right, you are talking about the episode when KGV and Rodney effectively sail off in the wrong direction?

If this is the case what I don't understand is this...

Wouldn't Tovey's gut feeling have been that he would be heading towards France (if he knew that Bismarck was leaking oil)? Same with HMS Rodney. At some point didn't the commanders of either ship think 'wait a minute, somebody has dropped a clanger' when they were plotting out Bismarcks course?



Best Wishes


HMSVF (avid learner!)

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Re: The D/F Controversy

Post by wadinga » Sat Jul 28, 2018 6:08 pm

Hello HMSVF,

We all have blank spots in our knowledge, and my understanding is that this forum exists to share information and help fill them in.

In fact it would appear there fairly equal reasons for heading either back to Norway or on to France. Since Scharnhorst and Gneisenau were being pinned in Brest by the RAF, maybe a tactical return, "retreat" to Norway and via safe inshore waters to the repair facilities of Germany was more attractive. Everybody now knows Lutjens would push on, but only with hindsight.

Yes indeed Tovey, having got the D/F bearings from shore stations assumed Lutjens was heading north and having made a decision, sailed his force to intercept, and thus in the wrong direction for many hours. As I mentioned there are many guesstimates about the positions and intentions of remote units, friendly and otherwise made, and one only knows which was the right one later.

This thread http://www.kbismarck.org/forum/viewtopic.php?f=1&t=8249 shows that there was an unwarranted criticism of Dalrymple -Hamilton's (Rodney) thought processes for independent interception, made by VCNS Tom Phillips, but overidden by Pound. Half the problem was that it was not made clear to Rodney's captain by Phillips or Edwards in Whitehall, whether he should use his own initiative, or obey the Admiralty or C-in-C Tovey. What there doesn't seem much (any) evidence of is investigating why the only evidence Tovey had to rely on, was actually wrong. There is also no evidence that the several procedural errors were identified, like not sending a worked out solution, whether the at-sea officer wanted it or not, and not reacting for hours when his solution based on the same data was radically different to that made by the experts onshore.

Hindsight is the thing one must avoid. There were two at-sea solutions worked out from the same data. Whether Gatacre in Rodney or Lloyd in KG V were right, could not be determined until later. Comparing results was not feasible because radio silence must be maintained as much as possible.

Tovey records his appreciation for intelligence received from the Admiralty in his report. He does not say "because I was obstinate, that intelligence sent us off in the wrong direction, and nearly let Bismarck get away" or "why didn't you tell us you had a different result". Phillips tries to blame Dalrymple-Hamilton instead of admitting it was his own department's fault. I have been shouted down several times but the Admiralty in London was trying to handle two major operations simultaneously Crete and Bismarck. Maybe that is why they were contradictory and slow to react. However, somewhere along the line the lessons were drawn.

As I understand it, the aerial arrays used by shore stations like Scarborough allowed much higher accuracy in bearing determination than the small aerials which were all that could be accommodated aboard ship. However as has been observed, the ranges from east coast UK were huge, so small errors in azimuth would move the bearing line a long way out in the Eastern Atlantic. D/F became more important when the geometry for tracking U-boats was improved, when multiple LOPs lines of position could be generated.

Single Line of Position D/F shortcomings from moving locations trying to fix other moving locations do not concern us here.

All the best

wadinga
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Re: The D/F Controversy

Post by Antonio Bonomi » Sun Jul 29, 2018 6:58 pm

Hello everybody,

very good, ... because the D/F radio bearing from a close at sea position between warships, ... is comparable to a visual bearing as far as precision and tolerances.

Once this is clear, … I can leave you this thread argument I am currently not interested about.


Bye Antonio
In order to honor a soldier, we have to tell the truth about what happened over there. The whole, hard, cold truth. And until we do that, we dishonor her and every soldier who died, who gave their life for their country. ( Courage Under Fire )

pgollin
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Re: The D/F Controversy

Post by pgollin » Mon Jul 30, 2018 1:00 pm

.

Warning : "Gossip" and ignorance ahead.

I once talked to Alan Raven about this, and he had looked into it. He SEEMED to say that the KGV did not have the (at sea) Gnomonic (sp ?) charts required to properly plot the likely position of the Bismarck. He said that such charts were available, but had not been shipped in the KGV.

As such the plotting would have been a very difficult task - but that the officer doing the work "should" have known the problems. Why Tovey went along with all that he did not know. "Accurate" plotting would have been possible but would have required many, many hours of geometrical calculations. IF Tovey had requested the position from the Admiralty, instead of the bearings, they would have had suitable charts to do the job quickly.

He may include this in his book due out next year, I have no idea.

.

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Re: The D/F Controversy

Post by wadinga » Mon Jul 30, 2018 4:50 pm

Hello P Gollin,

As I said above:

"Denning and Kemp, as D/F specialists may have had gnomonic charts with specially printed meridians passing through the various D/F station locations enabling them to simply use a protractor to mark off the bearing at each individual station against a true north meridian printed for that station. These lines passed out into the Atlantic, but because only UK stations were available, say from the Shetland Isles down to Cornwall the lines drawn were closer to parallel, and a location based on their intersections required interpretation, experience and skill. If the Iceland and Gibraltar stations had extended the north-south baseline by many hundreds or perhaps thousands of miles the geometry of the intersections would have been better."
IF Tovey had requested the position from the Admiralty, instead of the bearings, they would have had suitable charts to do the job quickly.
With a position to plot rather than uncorrected Great Circle bearings received, Lloyd could have done this on their ordinary Mercator chart in KG V.

Lloyd's guess where Bismarck was, the estimated position used in the Half-convergency equation, was probaby wrong, and may have badly slewed his results. Apparently, according to the 1938 Admiralty Manual of Navigation, you can use the plotted position derived from the corrected bearings to refine the process when repeated. How long Lloyd could take when Tovey was desperate for an answer remains to be seen. As we have discussed he only knew he was wrong much later.

Bill's point that the correction applied is different depending on whether the ship is measuring angles from the shore station transmissions or whether through prior arrangement the shore stations monitor the ship's transmission and send the bearing from different locations back to her, is another matter which should have been familiar to the senior navigator Lloyd.

The opportunity for Lloyd to make either simple errors or damaging assumptions only existed because of Tovey's insistence on raw data only, and no worked out solution. The shore station bearings could have included the corrections to be applied to each bearing so Lloyd could have plotted them as a simple drawing exercise on his Mercator chart. Maybe it wasn't only Tovey exhibiting "bloody mindedness". Maybe the OIC attitude was, "Well if he doesn't respect our expertise, he can do it all himself". It would be nice to think such pettiness didn't occur in the face of the need to co-operate against the Nazis, but of course it did. It is interesting to hear Alan Raven will visit the subject next year. A very much-respected writer.

All the best

wadinga
"There seems to be something wrong with our bloody ships today!"

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Re: The D/F Controversy

Post by pgollin » Thu Aug 02, 2018 9:13 pm

The following was posted by Alan Raven on another board. He obviously visits here, but doesn't post. He requested that I post it (it is here in its entirety - I also posted it on the idiot thread) ;

The Bismarck D/F Story for P Gollin

Re the exchanges on the Bismarck site,

As I went through official Admiralty files looking for many things on many subjects, I came across a question and answer letter to and from Admiral Tovey in 1946, when he was C in C Nore shortly before his retirement. This was an attempt to tie up loose ends on the Bismarck affair, and to assist in the preparation of the second official account that was published in 1952.
After reading the file it became obvious that Tovey was satisfied with Leach and Wake Walker's performance. It was also obvious that he felt the matter was closed, and had NO wish to discuss it any more.

In a quite different file, (from memory, an HW), I found the explanation as to why Tovey had searched in the wrong sector after Wake-Walker had lost contact with the Bismarck; The chief navigating officer on Tovey's flagship had not been informed as to the correct number of H/F D/F shore stations taking bearings on Bismarck's transmissions. It was the standard practice at the time to send the bearings and then to leave the plotting of the fixes to the on-board officer. KGV's officer had only five H/F D/F stations listed, whereas the actual number taking bearings was seven. All of these stations were located in the UK.

1941 was a period when the number of 'Y' and D/fing stations were rapidly increasing. By the end of the year, H/F D/F stations were operating in Iceland and the Maritimes. In May 1941, H/F D/F stations were operating from Gibraltar, Malta and Egypt, however ir appears from the various papers and official histories that none of Bismarck's signals were D/fd on by these three stations. This may have been because of the mountain ranges that ring the area.

As an aside, after going through a mountain of documents dated before, during and long after the Bismarck episode, I found nothing that remotely suggested a Courts Martial for ANY of the RN commanders. Not that this will mean anything to the two 'Gentlemen' from the Mediterranean with their unstated and hidden agenda.

The only note of criticism was that made of Captain Ellis; it was suggested that he should have kept his ship nearer to the Bismarck so as to maintain type 284 radar contact at all times. These remarks were tempered though by follow up statements that this was the very first occasion of shadowing by radar, also
, there being NO established procedure for same. Could you please put these notes up for me?

Thank you Phil.

.

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Re: The D/F Controversy

Post by Antonio Bonomi » Fri Aug 03, 2018 3:41 am

Hello everybody,

please provide " the guy " the May 31st, 1941 letter from Adm Tovey to Adm Pound and the 1961 letter from Adm Tovey to Stephen Roskill.

The 2 books published by Stephen Roskill will be a good read and will allow " the guy " to pursue the editor since he likes to take this type of legal initiatives as far as I remember.

Unfortunately it is too late for " the guy " to do a " peer review " on Stephen Roskill works, ... even if I doubt that Stephen Roskill would have ever taken that type of initiative in any serious account.

Wish him good luck on doing it.

Bye, Antonio
In order to honor a soldier, we have to tell the truth about what happened over there. The whole, hard, cold truth. And until we do that, we dishonor her and every soldier who died, who gave their life for their country. ( Courage Under Fire )

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Re: The D/F Controversy

Post by wadinga » Fri Aug 03, 2018 9:52 am

Hello P Gollin,

Thanks for this extremely valuable information on things that really happened during the Bismarck Chase. Please pass on appreciation to Mr Raven if you are in touch, and I hope he is picking up genuine new information like the May 31st letter and the others around 19th July . I am perplexed by:
It was the standard practice at the time to send the bearings and then to leave the plotting of the fixes to the on-board officer. KGV's officer had only five H/F D/F stations listed, whereas the actual number taking bearings was seven. All of these stations were located in the UK.
As Patrick Beesly is quite specific that the normal practice would have been to send a position with an error circle around it. I think maybe it reflects the much bigger errors which would result at the very long ranges out in the Atlantic in our case. If you were in the North Sea the ranges would be much shorter and maybe normal practice would be to give bearings only.

It has been suggested that Tovey's insistence on bearings only was so his navigator could create better geometry intersections by adding data from his own ships. If OIC had sent Mercator bearings ie with the corrections applied, Lloyd could have plotted these on his standard Mercator chart plus any other bearings he could get from other ships. Since the ranges on these latter would be short, the half-convergency errors would be negligible. However what he apparently ended up with, a set of bearings with no guarantee as to which stations they applied to is a hopeless cock-up. Especially since Lloyd still had to apply a half-convergency correction. With KG V attempting to maintain radio silence until a position was available, only then breaking it to set the hounds on the scent, Lloyd could not ask London for clarification.

This looks like is a serious case of very poor procedure at the Admiralty. There was no point in D/Fing targets out in the Atlantic if the Fleet Flagship could not use the data, or worse still, drew a misleading conclusion through lack of information. The error is compounded, when having received the faulty conclusion, Phillips/Edwards the latter did not spot and sound the alarm on the huge difference between what OIC had concluded and what Lloyd had at sea.

Another interesting point is that Gateacre, navigator in the Rodney, claims to have got a solution from the transmitted bearings that correlated well with what OIC had deduced. He can presumably only have found this correlation out some time later, but it would be a strange state of affairs if a ship proceeding to refit in the USA had more up to date information on D/F stations than the Home Fleet flagship. Phillips' unwarranted criticism of Dalrymple-Hamilton's course of action as "ill-judged" becomes a little sinister in the light of this D/F cock-up, and his own hand in it. D-H had better information than Tovey, but all was right in the end because Pound overruled Phillips.

With the expansion of the D/F chain described by Mr Raven, procedures for using the data accurately were obviously tightened up and evasive manouevres around U-boat patrol lines were a feature of the Battle of the Atlantic, tempered somewhat by B-Dienst success in reading British codes and countering the evasions.


All the best

wadinga
"There seems to be something wrong with our bloody ships today!"

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