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Thread: Effect of Window on H2S

  1. #11
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    Default Re: Effect of Window on H2S

    I have found the following:

    Possible Effect of Window on H2S

    “While these preparations were in train, Air Officer Commanding-in-Chief, Bomber Command raised the question of the possible effects on the performance of H.2.S. which might result from the use of Window and requested that action should be taken to determine the nature and extent of such effects.(1) Preliminary enquiries had led to the belief that the effect might be serious, not only while the strips were in the air but even after they had reached the ground, where it might possibly continue to give misleading echoes. Obviously if this proved correct, the successful use of H.2.S would be seriously prejudiced. This prediction was supported by Air Ministry who authorised the early conduct of trials to determine the effects of Window on H.2.S.(2) The result of these trials conducted by Headquarters Fighter Command was that there was no danger that Window used in the quantities required would interfere with the operation of H.2.S. (3)”

    (1) Bomber Command Letter B.C. S.26861/Air. 31 December 1942.
    (2) A.M. File C.S. 14198, Encl. 98A, 6 January 1943.
    (3) Fighter Command Letter F.C. S.31389/Sigs. J, 20 January 1943.

    All of the above references cited in AIR 41/13 Signals Volume VII Radio Counter-Measures, page 118. Interesting that the AOC Bomber Command had concerns similar to my own. There is no elaboration in this reference as to what trials were undertaken.

    Concerning the effect of A.I. operating under the same 10 centimetre wave length as H2S the following is notable:

    Postponement on the Use of Window

    “…Lord Cherwell advised the Chief of the Air Staff that in his view the experiments so far carried out to determine the effect of Window on British R.D.F. devices, particularly A.I. were insufficiently comprehensive. He was concerned that the serious results which might ensue if the enemy were to retaliate by using suitable Window against British R.D.F. had not been sufficiently appreciated. After discussion with…the Chief of the Air Staff ruled that the use of Window must be postponed until further experiments were completed. (1)
    “Trials to Determine the Effect of Window on British A.I.
    “A programme of experiments was prepared by Air Ministry and the Air Officer Commanding-in-Chief, Fighter command was made responsible for their conduct. (2) The test required a pursuit by fighter aircraft fitted with A.I. Mark IV, and with 10-cm A.I. through a Window-infected area to determine in what manner the A.I. was affected; also an A.I. pursuit of a bomber laying a protective Window trail while flying a steady course and while taking evasive action, the object being to determine whether the A.I. operator could follow the bomber during such manoeuvres and to note the effect of the window on his interception technique…

    “The results of these trials showed that the interference cause to A.I. Mark VII was very serious and that A.I. Mark IV was also affected, although not so seriously. (3) The Air Officer Commanding-in-Chief, Fighter Command, while appreciating that the Window would effectively reduce the efficiency of the enemy’s R.D.F. controlled guns and searchlight, and also his A.I. if in use operationally, was certain that the enemy would retaliate in kind as soon as he was in a position to do so. (4) This would mean that Royal Air Force night air defense R.D.F. devices would be affected adversely. He therefore recommended that the dropping of Window by Bomber Command should be prohibited.”


    All of the above referenced in AIR 41/13 Signals Volume VII Radio Counter-Measures, page 107.

    There were other trials conducted on the effects of A.I. Radar throughout May-August 1942, the results of which caused considerable concern to Fighter Command. These undoubtedly contributed to the delay in the operational use of Window. Summarizing these is beyond the original scope of this thread, and beyond my own research interests. However it would be interesting to see how this developed throughout the war as A.I. technology developed. To my knowledge, 100-Group Intruders only traveled with the bomber stream during the later stages of the war, so it seems for the most part their activities would have been unaffected by window.

    Jim
    Last edited by JDCAVE; 22nd September 2021 at 05:45.

  2. #12
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    Default Re: Effect of Window on H2S

    Indeed, but these are from before the widespread use of centimetric radars on the Allied side. As long as British radars were using similar wavelengths to German radars, then there can be little doubt that they would be affected. The introduction of the magnetron changed matters dramatically. H2S was a centimetric radar, as were the AI radars on the 100 Group Mosquitos and indeed the Air Defence of the UK ones by then.

    It is worth noting that the Germans did use Window (Duppel?) against UK defences. It is not however clear how (if at all) it affected their loss rates, which remained unacceptably high.

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    Default Re: Effect of Window on H2S

    Above, I mentioned that 100-Group Intruder Mosquitos began to provide close support to the bomber stream for the first time during the later months of the war. From the 100-Group ORB appendices for March 1945:

    "Operations [pages 1-2]

    5. A new plan for close escort of the bombers by the high-level Mosquitos, discussed in last month’s summary was put into operation in the early part of this month. A.I. Mark X can be used with success in close escort of the stream, if the patrols are flown above the bombers where the interference from Window and H2S is least. Most of the victories during the month have been obtained in the immediate vicinity of the bombers."


    AIR 25/784 https://discovery.nationalarchives.g...ails/r/C766517

    So while it seems there were operational work-arounds when it came to interference, from this record it seems the problem was not entirely rectified. Until reading this I was unaware of interference caused by H2S to the RAF A.I. systems, however they do operate on the same wavelength.

    Jim
    Last edited by JDCAVE; 23rd September 2021 at 00:01.

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    Default Re: Effect of Window on H2S

    An addendum to previous post:

    100-Group ORB appendices for February 1945

    "Operations

    5. During the month most of the supporting fighter patrols were flown well away from the bomber stream owing to the difficulty of operating A.I. in the midst of Window and bomber echoes. A number of sorties were, however, flown in the vicinity of the target areas during and after bombing and it is interesting to note that of the 11 claims by high level fighters 5 took place near the bomber target, and within a few minutes either way of bombing.

    6. An attempt will be made in future operations to provide a much closer escort of the bombers than has hitherto been tried. Mosquitos will be detailed to fly above, below and to the sides of the stream as well as to patrol the target areas during and after bombing. It is hoped that with experience the crews will become better able to operate among Window and bomber echoes."


    AIR 25/784 https://discovery.nationalarchives.g...ails/r/C766517

    Jim

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    Default Re: Effect of Window on H2S

    Quote Originally Posted by JDCAVE View Post
    [/I]The result of these trials conducted by Headquarters Fighter Command was that there was no danger that Window ... would interfere with the operation of H.2.S.” [/I]
    JIm,

    I think you've answered your own question here. Trials showed that Window did not interfere with H2S.

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