On the night of 13/14 October 1939, the German commander of U-boat U-47, Günther Prien, steered past the sunken block ships and chains which inadequately protected the British naval base at Scapa Flow in the Orkney Islands. The U-Boat sank the old British World War I battleship HMS Royal Oak and then escaped into the North Sea. The loss of the Royal Oak was insignificant in naval terms though over 800 men perished with her, however this was a bitter blow to British moral.