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    Re: Relative bearings
    From: David Pike
    Date: 2015 Apr 17, 02:28 -0700

    Geffrey Butt wrote. I have a radar manual from 1986 which refers to Royal Navy practice of referring to radar relative bearings as 'red' or 'green'.

    Wrt the film “Sink the Bismarck” and The Battle of the Demark Straight the bearings don’t quite fit in.  At 0535/36 when visual contact was first made with the German ships, Bismarck was at a relative bearing of about 090-100Rel to the British.  At 0537, Hood and Prince of Wales turned 40° port to reduce the range, so Bismarck would have born about 060Rel.  At 0552 Hood and PoW turned a further 20° to port, to reduce range faster, because of Hoods known vulnerability to long range shells, so Bismarck would have been at about 040Rel as spoken in the film.  However, the German ships would have been in view for about 15 minutes by then (1).  Red and Green bearings appear to have been used in radar reports context to indicate “aspect”.  In other words, where your vessel appears on the bow of the observed vessel, red being on the observed vessel’s port side and green on its starboard side (2).  As Hood was always on Bismarck’s port side, a radar plot report should have said something like Red90.  This would have been useful, because it would indicate that Bismarck was able to engage with both foreword and rear main armament. In the film the sighting is relayed as something sounding like. “Bridge …… Slap Bang Green 40” https://www.youtube.com/watch?v=J93GPUh-ta0 14 seconds in.  If anyone can interpret what the words “Slap Bang” actually were, we might know if this was a visual sighting or a report of a radar plot.  Dave

    (1)   http://en.wikipedia.org/wiki/Battle_of_the_Denmark_Strait#/media/File:090101_PoW_track_chart.jpg

    (2)   Use of Radar at Sea.  The Institute of Navigation.  Hollis and Carter 1952.  Ch 9 p134


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