In 1939, a Nazi Submarine Slipped into One of Britain's Biggest Bases and Sunk a Battleship

In 1939, a Nazi Submarine Slipped into One of Britain's Biggest Bases and Sunk a Battleship

The 1939 sinking of the HMS Royal Oak at Scapa Flow by U-47 caused grave concern within the British Admiralty and changes in the Anchorage.

In October 1939, illuminated by the northern lights, the German submarine U-47 threaded its way through sunken barriers and slipped into the British anchorage at Scapa Flow, a 125.3-square-mile natural port off the northern coast of Scotland, in the Orkney Islands.

Penetrating the anchorage had long been an unrealized German dream, one that U-boats had attempted twice in World War I; both times they had failed. One U-boat had been rammed and run aground and the second destroyed with all hands.

But now, at last, a German submarine slid quietly across its surface.

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U-47 and its 31-year-old captain, Günther Prien, moved across the anchorage from the east where they had entered and then turned toward the north, searching for targets. Prien was surprised at how few British ships were in the area.


He had expected hundreds and was unaware that Sir Charles Forbes, commander in chief of the British Home Fleet, had become concerned by German aircraft recently spotted in the area and had ordered most of the fleet to disperse.

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Finally, a lookout on U-47’s bridge spotted a small cluster of ships including the 1914 battleship Royal Oak silhouetted against the northern lights.

Unknown to Prien and the crew of U-47, the 29,000-ton Royal Oak had just returned to Scapa Flow after a battering from storms in the North Atlantic. Some of her smaller caliber guns had been rendered inoperable by flooding and many of her life rafts had been seriously damaged. Because of her condition, Forbes had decided to keep the Royal Oak in Scapa Flow to provide added antiaircraft fire if needed.

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In the darkness, U-47 slid toward the big ship.

The Royal Oak, like Scapa Flow itself, was a veteran of World War I, but by the outbreak of World War II, the 25-year-old ship was no longer considered fit for modern combat.  She had been launched in 1914, had seen battle in 1916 at Jutland, and had later served as part of Britain’s Atlantic, Home, and Mediterranean Fleets.

At the end of World War I, Royal Oak had also served as escort to several German vessels that had surrendered and were interned at Scapa Flow, which had been used by ships since prehistory.

In 1904, in response to the German naval action, British naval planners had decided a northern base was needed to control access to the North Sea. Scapa Flow was chosen, and the area was reinforced with minefields, artillery, and concrete barriers.

Primarily because of its distance from German airfields, Scapa Flow was again selected as a main British naval base when World War II broke out. By then, however, the defenses built earlier and during World War I had fallen into disrepair and new “block ships” were sunk in an attempt to block the Flow’s three entrances. Navigable channels remained, however.

German Commander of Submarines Commodore Karl Dönitz, who had commanded a submarine in World War I and who had developed the German Rudeltaktik (“wolf pack”) submarine attack tactic while a British POW, decided early in the outbreak of hostilities to attack the Flow.

Such an attack, he realized, could, if successful, force the British Home Fleet out of Scapa Flow, thus lessening the British hold on the area and allowing greater German  access to the North Atlantic and the convoys that sailed there with supplies for the United Kingdom.

Such an attack would also be seen as an act of vengeance for the ships of the German High Seas Fleet that had surrendered at the end of World War I and—like those escorted by the Royal Oak—had then scuttled themselves in Scapa Flow.

In addition, Dönitz believed, the propaganda value of the attack and its effect on British morale were inestimable. In a single attack, Germany could bring the war to Britain and show the British that even their home waters were not safe from German aggression.

Dönitz was aided in his planning by aerial reconnaissance photographs taken by German aeronautics pioneer Siegfried Knemeyer, who received an Iron Cross for the mission that supplied the photos. (Knemeyer’s flight may have been the aircraft that had moved Forbes to scatter the fleet.) Dönitz also handpicked U-boat Kapitänleutnant Günther Prien as commander of the actual attack.

Prien was a loyal member of the Nazi Party and had in fact been called “the most Nazified U-boat captain.”  He had been at sea in the Merchant Marine and the German Navy since he turned 21 and, by the end of the war, would be credited with sinking or seriously damaging 40 Allied ships. At the time of the Scapa Flow mission, however, he had been in command of U-boats for less than a year. The Scapa Flow attack was only his second patrol of the war.