Scapa Flow anchorage of the Royal Navy, in the Orkney Isles, was considered by naval experts as one of the most secure havens for naval ships in the world. Its location at the extreme north of the British Isles made it an impossible target for enemy surface warships, submarines, and aircraft. To make things more difficult for any potential attacker, the entrance to Scapa Flow was protected by sunken "block" ships and by natural tidal currents that made navigation through the narrow channel known as Kirk Sound hazardous, at best.
    On 13 October 1939, the Royal Navy battleship HMS Royal Oak was lying at anchor in Scapa Flow. She was one of ten old battleships retained by the Royal Navy after the Washington Treaty. These battleships comprised the bulk of the Royal Navy battle line in 1939. The Royal Oak belonged to the R-class battleships which also included Royal Sovereign, Ramillies, Revenge, and Resolution. In the early hours of 14 October 1939, the battleship Royal Oak became the first Battleship to be lost in the Second World War. A German U-boat, U-47, under the Command of Günther Prien, managed to penetrate Scapa Flow and achieve the impossible. Kapitänleutnant Prien was able to conduct a skilful attack and put three torpedoes into her side. In little more than 13 minutes, HMS Royal Oak, after a magazine explosion, rolled over and sank with heavy loss of life.
    The Royal Oak history goes back to World War I. She was built at Devonport in 1914-1916. She was nearly 600 ft. long with a maximum width of 100 ft. She was armed with eight 15-inch guns contained in four turrets, and a secondary armament of six- and four-inch guns for anti-aircraft protection and four torpedo tubes. The battleship was well armored with 13 inches of steel that extended five ft. below her water line. She was capable of a 22-knot speed powered by 40,000 HP oil-fueled engines. A crew of nearly 1200 men was needed to handle her. The battleship also saw action at the battle of Jutland in 1916.
    The captain of U-47, Kapitänleutnant Günther Prien, was one of the best submarine officers in the German Navy. Prien was born on 16 January 1908 and joined the German Merchant Navy in the summer of 1923. He transferred to the German Reichsmarine (the Navy) in 1933 and served on board the light cruiser Konigsberg before entering the U-boat service in 1935. At the end of his training, he was assigned First Officer of the Watch to U-26. The talented Prien rose steadily in the ranks until he was given command of the new Type VIIB submarine, U-47, when she was commissioned on 17 December 1938, and was promoted to the rank of Kapitänleutnant on 1 February 1939.
    Prien’s submarine, the U-47, was one of the oceangoing Type VIIB boats with which Commodore Karl Dönitz, Commander of U-boats in the German Navy, planned to cut the life line to Britain within the scant budget granted him by Berlin. U-47 displaced 750 tons. She also had a range of 6,500 miles which was enough to allow her to reach the mid-Atlantic. She could hit 17 knots on the surface, seven underwater, and she could dive to more than 350 ft. underwater. She packed four 21-inch torpedo tubes forward and one aft, and carried 14 torpedoes. An 88mm gun on the foredeck and a 20mm antiaircraft gun behind the conning tower completed the armament of U-47.
    Commodore Karl Dönitz was an old submarine veteran from the First World War, when U-boats had very nearly starved England to death. He believed that a force of 300 subs would finish the job this time. Döenitz began the war with just 57 boats, only about half of which were the open- water Types VII and IX. He had planned to deploy them in "wolf packs" of six to nine boats each, but it was all he could do to keep that many at sea at any time. But where could a German submarine, operating alone, strike fear into the heart of the Royal Navy and cause repercussions all out of proportion to the actual effect? Scapa Flow was the answer! If a U-boat could get into the anchorage and sink a few capital ships, the damage to the Royal Navy’s pride would be enormous.
    At 0116 hours on 14 October 1939, the German submarine U-47 under the command of Prien navigated through the narrow channel and fired a spread of three torpedoes at HMS Royal Oak and the British seaplane tender HMS Pegasus lying at anchor in the harbor of Scapa Flow. A few minutes later U-47 turned around and fired a stern torpedo at 0121 hours. Prien misidentified the seaplane tender as the battlecruiser HMS Repulse and claimed a hit, but a torpedo apparently hit the starboard anchor chain of the battleship and did not damage the ships. After reloading the front tubes, the U-boat fired a second spread of three torpedoes that hit HMS Royal Oak on the starboard side and caused a magazine to blow up. The battleship rolled over and sank in a little more than 13 minutes. The ship complement was 1208 officers and men. 833 of them were killed, leaving 375 survivors.
    Following the attack on the Royal Oak, Prien escaped the Flow unmolested, as most of the Royal Navy thought a submarine attack was unlikely and that Royal Oak had been damaged by internal explosions. It was not until a diver went down that same day and found a torpedo propeller that the truth sank in.
    The sinking of the Royal Oak was a tremendous blow to the Royal Navy. The war had just begun and the Germans had sunk one of its finest battleships. When Prien returned to Germany, he was given a hero’s welcome. Prien was awarded the Knight’s Cross of the Iron Cross, the first sailor of the U-boat service and the second member of the German Navy to receive this award. Prien also went on to become one of the most famous U-boat “aces” of the war, with U-47 sinking an amazing 30 merchant ships totaling 162,769 gross register tons (GRT) and damaging eight merchant ships totaling 62,751 GRT. In 1940, a grateful Germany awarded Prien Oak Leaves to his Knight’s Cross.
    Germany claimed the sinking of HMS Royal Oak only after it was announced on the BBC. As for Günther Prien and his crew, they became instant folk heroes. They were exploited by Minister of Propaganda, Dr. Joseph P. Goebbels to extract the maximum glory from their deed. A few months later, Prien's autobiography, Mein Weg Nach Scapa Flow, was published and sold an astonishing 750,000 copies.
    Even before his arrival in Wilshelmhaven on the morning of October 17, the entire nation of Germany was already celebrating the remarkable exploits of U-47 and its commander. As a commemorative, the First Watch officer Endrass painted the outline of a charging bull on the conning tower of the boat. It was to become Prien’s personal insignia and later, the official insignia of the Wegener Flotilla. As U-47 sailed into harbor, crews of the battlecruiser Scharnhorst cheered and saluted the returning of the “Bull of Scapa Flow.”
    The crew of U-47 was met at the dock by two admirals - Dönitz and Raeder - who presented Prien with the Iron Cross First Class and to all other crew members, the Iron Cross Second Class. But Hitler himself was ecstatic and was anxious to meet the Reich’s new hero. That afternoon the entire crew of U-47 was flown to Berlin in Hitler’s personal airplane, where they were paraded in a motorcade through the streets of Berlin. Thousands turned out, cheering and lining the streets, whipped into a frenzy of enthusiasm. A brass band, guard of honor, flowers, candies, lunch with Hitler, press conference, speeches, and even more speeches. Prien and his crew were treated like celebrities. It was the greatest and the most grandiose celebration of a naval victory in Germany, or any country in the world, and such a celebration was never equaled then, or now in the history of modern submarine warfare.
    As a result of the raid, Grand Admiral Raeder promoted Dönitz to Rear Admiral. Having gained Hitler’s attention, Dönitz seized the opportunity to press upon his Führer for higher U-boat construction priorities – to which der Führer grudgingly agreed. Almost simultaneously, Hitler eased the political restraints governing U-boats. All enemy ships, including passenger liners, could be torpedoed on sight. For all purposes, by November 17, 1939, the official policy against British and French shipping was unrestricted submarine warfare.
    For the British, the attack ended the careers of several naval figures. Winston Churchill, First Lord of the Admiralty, escaped only because he was just recently appointed. After the U-47 attack, Scapa Flow’s defenses were further strengthened with additional "block" ships sunk, completely sealing off the channel. Additional barriers and booms were further constructed over the next few months, so that what the Admiralty deemed as a tragedy would never happen again. Meanwhile, until Scapa Flow could be made secure again, the British Home Fleet dispersed to other anchorages. As planned, Dönitz had already mined the most likely refuges. Mines damaged the battleship Nelson and cruiser Belfast and another four vessels were sunk.
    Despite the tragedy, Winston Churchill described it as a "remarkable exploit of professional skill.” Like the USS Arizona at Pearl Harbor, the Royal Oak remains to this day, a 30,000 ton war grave.