Scapa Flow lies barely seven degrees below the Arctic Circle, in the cold, windswept Orkney Islands at the northern tip of Scotland. Measuring 10 kilometres wide by 8 kilometres long with an average depth of 30 metres, this natural anchorage is bounded to the north by the mainland, to the east by the islands of Burray and South Ronaldsay, and to the west by the island of Hoy. In 1904, Scapa Flow was chosen as the home base for the British Grand Fleet, allowing the Royal Navy and German Imperial Navy to glower at each other across the North Sea. It was from here that the Grand Fleet sailed to the historic 1916 Battle of Jutland, and to here that the German High Seas Fleet sailed to surrender in 1918. In the years leading up to the Second World War, Scapa Flow was thought to be impregnable, and came to symbolize the supposed invincibility of the Royal Navy itself. But in the early morning hours of October 14, 1939, a lone German U-boat succeeded in doing the impossible, penetrating the harbour’s defences, sinking a 30,000-ton battleship, and slipping away undetected. It was one of the most daring feats of the war, and one which shattered the Royal Navy’s illusion of invulnerability. This is the incredible story of the U-47 and Captain Günther Prien, “The Bull of Scapa Flow.”

Though best remembered for its campaign of unrestricted submarine warfare against Allied merchant shipping, the German U-boat arm was, in the early days of the War, a very different animal, operating by very different rules. In September 1939 the fleet stood at barely 56 boats, only half of which were larger ocean-going types. And while U-boat crews were the most capable and well-trained submariners in the world, they were still bound by the so-called “Cruiser” or “Prize Rules,” which required them to stop merchant vessels and allow their crews to escape before sinking or sailing them home as prizes. Warships, on the other hand, were fair game, and barely two weeks into the war the U-boat arm scored its first major victory when U-29 torpedoed and sank the 19,000-ton aircraft carrier HMS Courageous off the course of Ireland.

But Admiral Karl Dönitz, head of the U-boat arm, had bigger plans. With a fleet of 500 U-boats – and the Hitler’s blessing to unleash them on Allied merchant shipping – Dönitz believed he could sever Britain’s vital supply lines from North America and starve the island nation into submission. Convinced he could win the war single-handedly for Germany, he begged Hitler to approve the construction of more submarines. But U-boats did not fit Hitler’s vision of a mighty German fleet, and the Führer dithered. Dönitz thus decided to plan a daring mission that would demonstrate the utility of U-boats once and for all. And it did not take him long to choose the target: Scapa Flow.

To the German Navy, Scapa Flow held important symbolic importance. Following the Armistice of 1918, the Imperial High Seas Fleet was ordered to sail to the British anchorage and surrender itself. The ships and their crews remained interned in Scapa Flow for seven months, until on June 21, 1919, on the orders of Rear-Admiral Ludwig von Reuter, the crews scuttled their ships in a final act of defiance. The Scuttling of the High Seas Fleet was romanticized in Nazi propaganda, portrayed as an atoning act which rid the Navy of the shame associated with the 1918 Kiel Mutiny that triggered the German socialist revolution and the abdication of Kaiser Wilhelm II. For Dönitz, striking at the heart of the Royal Navy’s innermost sanctum was the perfect means of avenging this national humiliation.

But it would not be easy. Two U-boats had already tried to infiltrate Scapa Flow: U-18 in November 1914 and UB-116 in October 1918. Both were spotted and destroyed by British forces. In the wake of these attempts, the British had tightened security, increasing patrols, erecting antisubmarine booms and nets across the harbour entrances, and sinking blockships in the smaller channels. Yet aerial photographs taken by the Luftwaffe revealed that Scapa Flow was no longer as impregnable as it seemed. Thanks to a combination of complacency and interwar budget cuts, the base’s defences had fallen into disrepair. Antisubmarine patrols were infrequent, antiaircraft defences woefully inadequate, and many of the blockships had disintegrated and collapsed, leaving several smaller channels open to infiltration. One in particular, Kirk Sound, was around 50 feet wide – just wide enough for a single U-boat to slip through. And Dönitz knew just the man to command it: 31-year-old Captain-Lieutenant Günther Prien.

Described by American war correspondent William Shirer as“clean-cut, cocky, a fanatical Nazi, and obviously capable,” Prien was the epitome of the daring new breed of commanders that had made the U-boat arm the most elite and respected service in the German armed forces. Born on January 16, 1908 in Osterfeld, Prussia, Prien joined the German Merchant Marine at the age of 15, serving aboard the passenger liner Hamburg and earning his Sea Master’s certificate in 1932. Unable to find a commercial job due to the Great Depression, in 1933 Prien joined the German Navy, serving aboard the light cruiser Königsberg before transferring to the U-boat service in 1935. Prien’s first posting was as Watch Officer aboard U-26, assigned to patrol the Spanish coast during the Spanish Civil War. Prien rose steadily through the ranks, finally being commissioned as Captain-Lieutenant on February 1, 1939 and given command of the new Type VIIC U-boat, U-47.

The Second World War began while U-47 was out on its first war patrol, and Prien wasted no time making a name for himself. On September 5, 1939 – two days after Britain declared war on Germany – Prien stopped and sank the British freighter Bosnia, transferring her crew to a neutral Norwegian ship.

This was the U-boat arm’s first official victory of the war. While two days earlier U-30 had torpedoed the British liner Athenia off the coast of Ireland, this was condemned as a war crime and the German government denied responsibility until 1946. Prien quickly followed up his feat by sinking the freighters Rio Claro and Gartavon before being recalled home. Having sunk over 66,000 tons of shipping on his first patrol, Prien was awarded the Iron Cross Second Class and quickly became a favourite of Admiral Dönitz, who on October 1, 1939 summoned Prien to his office to present his plan for Special Operation P: the infiltration of Scapa Flow.

Prien was immediately enthusiastic, though he knew the mission would be a dangerous one. Not only were the channels into Scapa Flow extremely narrow, but tides in the area could generate treacherous 10-knot rip currents that could easily ground and damage his boat. The best chance of getting through would be at high tide on the 13th and 14th – barely two weeks away. In the end the potential targets proved too tempting for Prien to resist, for aerial reconnaissance had revealed a full lineup of capital ships moored along the northern shore. And so on October 8, Prien, First Officer Englebert Endrass, and the rest of U-47’s 42-man crew set sail from Wilhelmshaven, bound for Scapa Flow.

Though Prien had every confidence in his crew, he waited until he was well underway before revealing their destination, giving each man the option of leaving if he wished. Unsurprisingly, nobody was terribly tempted to disembark in the middle of the North Sea, and the crew stayed on as U-47 slowly made her way to the Orkneys. The journey took four days, with U-47 lying on the seafloor during the day and travelling only at night. Then, at 4PM on October 14, U-47 arrived just off the entrance to Scapa Flow. The weather on the crossing had been overcast and rainy, making navigation difficult, but judging from coastal navigation lights Prien determined he was only 2 kilometres from his intended position – a remarkable feat of navigation. As they waited on the seafloor for night to fall, the crew were treated to a feast of soup, veal, pork ribs, potatoes, and cabbage – or, as they called it, a “hangman’s dinner.” Finally, at 7PM, U-47 surfaced and began her mission.  But right away Prien sensed trouble. Though it was a moonless night, the aurora borealis danced brightly overhead, bathing his U-boat in light. For a moment Prien considered aborting the mission, but eventually decided to press on regardless. At 10 PM the Orkney Navigation lights came on, allowing Prien to fix his position and locate the proper channel to enter Scapa Flow. Nonetheless Prien nearly chose the wrong channel – between Lamb Holm and Burray Islands – before realizing his mistake and doubling back toward Kirk Sound. Then, while trying to negotiate the narrow channel, the swift current swung the U-boat’s stern into one of the blockships, causing her become fouled on an anchor chain. It was many tense minutes before the crew was able to free the boat. Gradually, however, the channel widened, the current slowed, and U-47 finally entered open water. At half past midnight, Prien wrote in his log: We Are in Scapa Flow.

Yet once again, something didn’t feel quite right. Prien had expected to find the harbour bustling with activity, but the scene before him was eerily quiet, with barely a ship in sight. Undeterred, Prien ordered U-47 forward, creeping towards the north anchorage where the Home Fleet was moored. Then, suddenly the U-boat was bathed in bright light as a truck on the shore turned on its headlights. The crew froze and looked on in horror, knowing they could be fired upon at any moment. But the truck quickly turned and disappeared into the night, and all was quiet once more.

It was not until 12:50 that Prien and First Officer Endrass finally spotted a pair of ships at anchor. The first was quickly identified as HMS Royal Oak, a 30,000-ton battleship and veteran of the Battle of Jutland. Endrass identified the second as the battlecruiser HMS Repulse, though it was in fact the ageing seaplane carrier HMS Pegasus. Though puzzled as to the rest of the fleet’s whereabouts, Prien could not pass up such plum targets, and at 12:55 he fired a spread of four torpedoes at Royal Oak. One torpedo struck home, blowing a fifty-foot hole amidships and shaking visiting Rear Admiral Henry Blagrove out of bed. Blagrove immediately ordered a thorough inspection of the ship, but as it was widely believed that Scapa Flow was impregnable, few crewmen could even conceive that they had been torpedoed. The blast  was chalked up to am minor explosion in a  paint locker, and Blagrove and the rest of the crew went back to bed.

Meanwhile, Prien looked on in confusion. Though he had heard the sound of the torpedo detonating, the scene before him was still eerily quiet, as if nothing had happened. Convinced that the torpedoes had malfunctioned – a common occurrence early in the war – Prien ordered U-47 about and launched his stern torpedo. This also missed, and in frustration Prien swung the boat back around and at 1:16 AM fired another salvo of three torpedoes. This time all three struck home, igniting Royal Oak’s powder magazines and causing the ship to erupt into a column of flame. As Prien later recalled:

“Flames shot skyward, blue…yellow…red, like huge birds, black shadows soared through the flames, fell hissing and splashing into the water…huge fragments of the mast and funnels.”

Royal Oak quickly heeled over and sank to the bottom of Scapa Flow, taking 835 of her crew with her – including Rear Admiral Blagrove. The harbour suddenly exploded with activity, and Prien took his cue to slip away:

“The bay awoke to feverish activity. Searchlights flashed and probed with their long white fingers…small swift lights low over the water, the lights of destroyers and U-boat chasers…. I could see no other worth-while target, only pursuers. At high speed I pass the southern blockship with nothing to spare. The helmsman does magnificently. High speed, ahead both, finally three-quarters speed and full ahead out…and at 2:15 we are once more outside.”

As it turned out, the dearth of targets inside Scapa Flow was the result of bad timing by the Kriegsmarine. Less than a week earlier, the battlecruisers Gneisenau and Köln had sailed out into the North Sea in an attempt to lure the Home Fleet within range of the Luftwaffe. The fleet duly sailed out in pursuit, with the older Royal Oak, unable to keep up with the rest of the other ships, remaining behind in Scapa Flow. When the chase was eventually abandoned, the fleet returned not to Scapa Flow but to alternate anchorages at Loch Ewe and Rosyth.

Nonetheless, Prien had pulled off one of the greatest naval coups of the war, and returned to Germany on October 17 to instant fame. Adolf Hitler sent his personal aircraft to fly the crew of U-47 to Berlin, where Admirals Karl Dönitz and Erich Räder presented them with Iron Crosses and Prien with the Knight’s Cross with Oak Leaves – the highest German military honour at the time. Prien became a national celebrity, known throughout Germany as “The Bull of Scapa Flow.” Prien painted a snorting bull on U-47’s conning tower, and this image soon became the emblem of the entire 7th U-boat Flotilla. According to First Officer Endrass, the image was chosen because:

“[Prien’s] frowning face and hunched shoulders [as we entered Scapa Flow] reminded me of a bull in a ring.”

In 1940, Prien released a book titled My Way to Scapa Flow, and in dozens of interviews and articles recounted his exploits in suitably propaganda-friendly fashion:

“We diddled our way through the guard line and were suddenly inside. Inside of Scapa Flow, the harbour of the English sea force. It was absolutely dead calm in there. The entire bay was alight because of a bright Northern Light. We then cruised the bay for approximately one and a half hours, chose our targets, fired our torpedoes. In the next moment there was a bang and the Royal Oak blew up. The view was indescribable. And we sneaked out in a similar fashion as we got in, close past the enemy guards, and they did not see us. You can imagine the excitement and happiness we all felt about the fact that we managed to fulfill our task and achieve such a huge victory for Germany.”

Meanwhile, back in Britain, Prien’s daring raid unleashed a political firestorm and shook the Royal Navy out of its pre-war complacency. Winston Churchill, then First Lord of the Admiralty, fired Sir William French, flag officer in charge of Shetland and Orkney, and ordered Scapa Flow’s defences overhauled.

Patrols were increased, new blockships, booms, and mines installed across the main entrances, larger antiaircraft batteries emplaced, and large causeways dubbed “Churchill Barriers” erected built the channels between the mainland and the islands of South Ronaldsay, Burray, Lamb Holm, and Glimps Holm. While these upgrades were being installed the Royal Navy was forced to use other anchorages, which the Germans promptly mined. This resulted in the battleship HMS Nelson and the cruiser HMS Belfast being damaged and four other vessels sunk – an unexpected side effect of Prien’s mission. It was not until March 1940 that the Home Fleet was able to return to Scapa Flow.

Prien himself would go from strength to strength, carrying out a total of 10 war patrols in which he sank 30 Allied ships totalling 200,000 tons, making him one of the top U-boat aces of the war. But in the end  his fame and legendary skill could not save him from the fate that befell nearly 70% of his fellow submariners. In the early morning hours of March 8, 1941, Prien was attacking the merchant convoy OB-293 off the coast of Ireland when he was spotted and fired upon by the British destroyers HMS Wolverine and HMS Verity. For the next five hours, the two destroyers kept U-47 locked in their sonar beams while relentlessly pounding her with depth charges. At 5:19 U-47 was forced to the surface, only to dive again and disappear in a massive explosion. Neither Prien nor his 45-man crew were ever seen again. Ten days later, two more top U-boat aces would be lost: Otto Kretschmer of the U-99 and Joachim Schepke of the U-100, captured and killed by Allied forces, respectively.

Due to his massive propaganda value, Günther Prien’s death was kept secret for nearly two months. However, now-Prime Minister Churchill officially announced U-47’s loss in Parliament while British propaganda broadcasts to Germany taunted listeners with the question “Where is Prien?” until finally, on May 23, the German government was forced to admit that the great U-boat ace had been lost. However, in order to soften the blow, the announcement was buried among figures of Allied shipping sunk that month by U-boats.

Despite the blow it struck to British naval prestige and morale, even Winston Churchill was forced to admit that Prien’s attack was:

“…a remarkable feat of professional skill and daring.”

And despite the fame and adulation his exploits brought him in Germany, to the end Prien remained level-headed and dedicated to his duty, writing:

“Success had singled me out. But what after all is success? A matter of luck, of providence? That which matters among men is to have the heart of a fighter and to lose one’s self in the cause he serves.”

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