Orignal flag from the wellknown battlecruiser H.M.S. Hood, which was sunk by a direct hit of the German Battleship Bismarck on the 24th of may 1941 in the battle of the Denmark strait. This particular flag is of an naval special flag signal type which means "screen flag" as can be seen in the "Seaman's pocket book" published in June 1943 (encircled in the picture below)

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This flag comes from the David Boyd collection. Below you can see a copy of the original documents from D.Boyd.