On 14 October 1939, under the command of Günther Prien, U-47 penetrated Scapa Flow and sank the World War I – era battleship HMS Royal Oak anchored in Scapa Bay.
After firing its first torpedo, the submarine turned to make its escape; but, upon realising that there was no immediate threat from surface vessels, it returned to make another attack. The second torpedo blew a 30-foot (9 m) hole in the Royal Oak, which flooded and quickly capsized.
Of the 1,400-man crew, 833 were lost. The wreck is now a protected war grave.
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