On the night of 13/14 October 1939, Kapitänleutnant Gunther Prien's U-boat penetrated the Royal Navy's primary base, Scapa Flow and sank the battleship Royal Oak. He returned to Germany to instant fame. He was awarded the Knight's Cross of the Iron Cross, personally by Adolf Hitler, the first sailor of the U-boat service and only the second member of the Kriegsmarine to receive this award. Prien received the nickname Der Stier von Scapa Flow ("The Bull of Scapa Flow"); the emblem of a snorting bull was painted on the conning tower of U-47 and soon became the emblem of the entire 7th U-boat Flotilla.