Scapa Flow, a natural harbour in the Orkney Islands off the northeast coast of Scotland, was the base of the Home Fleet. In October 1939, a daring attack by a German U-Boat successfully sunk HMS Royal Oak at anchor, killing 834 men. The U-47 had stealthily entered Scapa Flow through the eastern side, utilizing the high tide and the gaps in the existing blockships from World War I. This attack prompted the building of the Churchill Defences, with the work carried out by Italian prisoners of war. Four causeways made from concrete blocks linked the islands from the mainland down to South Ronaldsay, creating strong barriers and effective defences. The Churchill Defences were officially opened on 12 May 1945, four days after the end of World War II in Europe.
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