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Thread: Change from mph to knots as units of wind speed

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    Default Change from mph to knots as units of wind speed

    I thought that the standard unit of wind speed used during WW2 was mph, but I've just found a note on page 116 of Middlebrook's "The Nuremberg raid, 10-11 March 1944" that reads as follows:

    " ..... aircraft and wind speeds will be quoted in ordinary miles per hour as this was the method used at the time although knots (nautical miles per hour) became standard soon afterwards."

    Seems a little strange such a change took place given the other stresses on aircrew, to say nothing of the necessary instrument changes, but please can anyone provide a definitive date for the change. Unfortunately he does not provide any reference for the statement.

    TIA
    Brian

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    Brian,

    Was the subject of discussion here in January 2005 (under 'Meteo codes'):

    http://www.rafcommands.com/cgi-bin/dcforum/dcboard.cgi?az=show_thread&om=6075&forum=DCForumID 6&archive=yes

    Errol

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    That's a relief, the thread was before my time.

    Thanks Errol; that sounds reasonable - changing after the war - but it doesn't quite gell with Middlebrook's statement. To be honest I can't see why he even made it since, as he states, the change occurred after the time-frame of the book.

    I had hoped from my met background I'd find a clue in the units used by the Met Office, but they complicate the matter even further. Until the end of 1943 upper winds were measured in Kilometres per hour, but that changed in 1944 to knots. However, it's clear from National Archives files relating to meteorology for Bomber Command that the forecasts were given in mph! (Don't ask me why - I was but a babe in arms at the time.)

    I can understand the logic of Coastal Command using knots since it was a maritime force and Bomber Command using Imperial units, but it does seem very odd and a possible source of error as aircrew transferred between Commands.

    Brian

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    A possible clue might be found in this file at Kew...

    BT 217/171 Use of terms knot and nautical mile for civil aircraft purposes 1945

    I haven't seen it, but it fits the time frame.

    Good luck,
    Bruce

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    Further to my earlier post Jim Cave has kindly sent some 6 Group documents for December 1944, and speeds are given in mph.

    Errol's link to the earlier (2005) discussion on the subject includes a post from Harry Newbould that Tee-Emm quotes the change from mph to knots as taking place in April/May 1945.

    Brian

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    Just in case someone asks the question again, and to put this thread to bed, Jim (JDCave) has found NA documents that show the change from mph to knots was introduced in April 1945.

    See http://lancaster-archive.com/forum/viewtopic.php?f=4&t=546.

    My grateful thanks to Jim for his hard work and persistence.

    Brian

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    I should add to this Brian, that I am having difficulty finding in the 6-Group records pertaining to navigation, any discussion beyond this comment. I do find it odd that there isn't any timetable or reason for the change, only that in April 1945, 419 and 428 Squadrons continued to use mph while other squadrons were using knots in their naviation. Evidently 419 and 428 had to convert to mph at briefing and back to knots when submitting records to Group. It seems odd to me but, as I said, I will continue to see if I can find other commentary on this subject in the 6-Group records.

    Jim

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    I have been digging into this still further and this issue remains cloudy: It's pretty clear that the transition to kts/h and mph was not uniform within bomber command, even between squadrons within a group. Caution is therefore important if people are trying to determine the location of crash sites, relative to turning points, or other interpretation, etc. Simlarly if units are not marked in historical documents, one cannot assume just what units were actually used by the crews. This would pertain to broadcast winds, A/S's and distances. I hope to provide more information in the future, but I have not yet found critical documents or orders pertaining to this important issue.

    Caveat Emptor!

    Jim

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    Since I started this thread I'd better finish it. I raised the matter with the RAF Museum and received the following in reply:

    Air Ministry Order A.365/45 dated 12 April 1945 states:

    "1. It has been decided to adopt the knot and nautical mile as the
    standard measurements of speed and distance throughout the Royal Air
    Force.

    2. These measurements are already in use in Coastal Command. They were
    adopted in Bomber Command from 1st April, 1945. Instructions for their
    adoption in other commands will be issued by the Air Ministry when
    circumstances make it convenient and practicable to do so."

    Presumably the circumstances relate to the availability of air speed
    indicators calibrated in knots. Pilot Officer Prune used to boast that
    "We were flying so low over the sea that our ASIs read knots..."

    From discussions on other forums it is apparent that although the official date of the change for Bomber Command was 1 April 1945 a number of squadrons continued using mph until such time as all aircraft were properly modified.

    Apologies to those who have read this elsewhere.

    Brian

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    Quote Originally Posted by Lyffe View Post
    Since I started this thread I'd better finish it. I raised the matter with the RAF Museum and received the following in reply:

    Air Ministry Order A.365/45 dated 12 April 1945 states:

    "1. It has been decided to adopt the knot and nautical mile as the
    standard measurements of speed and distance throughout the Royal Air
    Force.

    2. These measurements are already in use in Coastal Command. They were
    adopted in Bomber Command from 1st April, 1945. Instructions for their
    adoption in other commands will be issued by the Air Ministry when
    circumstances make it convenient and practicable to do so."

    Presumably the circumstances relate to the availability of air speed
    indicators calibrated in knots. Pilot Officer Prune used to boast that
    "We were flying so low over the sea that our ASIs read knots..."

    From discussions on other forums it is apparent that although the official date of the change for Bomber Command was 1 April 1945 a number of squadrons continued using mph until such time as all aircraft were properly modified.

    Apologies to those who have read this elsewhere.

    Brian
    And perhaps we should add that some squadrons were using knots prior to the official adoption date of 1 April 45.
    Regards
    Max
    Max Williams
    www.ordinarycrew.co.uk
    the story of Lancaster ME453

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