Hitler's U-Boat Lair: The Secret Nazi Underwater Superstructures | Timeline

From 1939 to 1945, the Atlantic Ocean was the scene of the most important battle of the Second World War. A duel to the death between the submarines of the Third Reich and the Allied Navy led by the British. The British Navy was considered at the time as the most powerful in Its size was the combined size of the two next largest navies, which was France and Germany. To try to defeat the English, the Nazis built gigantic bases on the French Atlantic coast to shelter the German submersibles. These superstructures almost turned the most important naval battle of the war to the Germans' advantage. Faced with these fortresses, the British develop a radically different strategy based on espionage and the decryption of communications of the German Navy. It is from one of the most secret places of the Second World War, hidden in the basements of Liverpool, that they will lead the Battle of the Atlantic. It was a battle of intelligence, it was a battle of courage, and it was a battle of keeping going through dreadful conditions out in the North Atlantic. Through these strategic locations, you will discover the incredible duel between the German Empire and the British Empire. A duel that was decisive in the course of the Battle of the Atlantic. The French ports of Brest, Lorient, Saint-Nazaire, La Rochelle, and Bordeaux are home to the largest buildings built by the Nazis outside German territory. Authentic fortress castles on the Atlantic, they still embody today the madness of a Reich that already saw itself as master of Europe. Remaining in its original state since 1945, the base of Saint-Nazaire still contains numerous vestiges. The two historians, Luke and Mark Brouwer, are the only ones who know all its secrets. Here were hundreds of workers and technicians. All this infrastructure makes it possible to repair, refuel, and rearm German submersibles in a short time. Their mission is to hunt down and destroy the maximum of enemy ships crossing the Atlantic. Lorient is the largest of these bases. You can protect 13 submarines at the same time here. We can see the floating door that will allow us to block the water and dry the submarine. To understand the origin of these indestructible bunkers, we must go back to September 1st, 1939. That day, a German battleship fired the first shots of the Second World War. Great Britain goes to war two days later on the order of its prime minister. This country is at war with Germany. For the Fuhrer and his generals, the looming confrontation is coming too soon. The Commander-in-Chief High Admiral Raeder and Admiral Donitz, chief of the submarine fleet, will have to deal with it. Karl Donitz refuses to voice any pessimism. This war is his moment. For the past five years, this underwater specialist has been training a whole generation of submarines in the Baltic Sea. His young sailors are now ready to die for him and Nazi Germany. Sure of himself, upon entering the war, he galvanizes them. We know our enemy. We have the right weapons and the command that can face him. The war will be long, but we will win if everyone does his job. However, he had only 57 submarines out of the 300 that he believed would allow him to win the war against the British fleet. It's not much, but he'll be relentless in his attacks. On September 3rd, 1939, he decided to hit the British first. Their first victim will be the British liner Athenia. Heading to New York, it carries 1,400 civilians. 128 people will perish in the sinking. The others will be rescued at the last moment the next morning. Karl Dönitz kicks off a huge chess game against the English to control the sea lanes. Its purpose is to stifle the economy of the British Isles by isolating them from the rest of the world. This is the beginning of the Battle of the Atlantic. As Churchill said, everything in the Second World War depended on the outcome of the Battle of the Atlantic. 70% of Britain's food came through onto the sea routes. To starve England, Dönitz pushes his commanders to torpedo a maximum of merchant ships. He instructs them to have no pity. Do not spare anyone. Take care only of your submersible and push for victory as fast as possible. We must destroy the enemy. Nothing else matters. To undermine the morale of the British and galvanize his troops, Dönitz needs a stunning blow. One of his submarines discreetly managed to penetrate the British Navy's rear base and sank one of the Royal Navy's most powerful battleships. 833 British sailors were killed. For Dönitz, it's the best victory. Against all odds, the beginning of the war benefited the submersibles. The Fuhrer is now convinced that the underwater weapon is his key weapon in his attempt to bring the British to their knees. The invasion of France on May 10, 1940 gave Dönitz an unexpected opportunity to capture what his submarines needed to defy the English. Home ports on the Atlantic seaboard, not far from the British coast. While the German motorized detachments rush to take control of the main French ports, the English army is pushed back onto the beaches of Dunkirk and it re-embarks. The British are now the last adversaries in the way of the Nazis, who are already considering an invasion of the United Kingdom. On June 22, 1940, the day of the signing of the Franco-German armistice, the Third Reich is in control of France's Atlantic coast. The next day, Admiral Dönitz inspects the Bretton ports of Brest, Lorient, and Saint-Nazaire. He chooses Lorient to become the first operational port for U-boats in France. The peninsula of Carolin is an ideal location to install a large base in the future. Captain Julius Lemp, responsible for the destruction of the liner Athenia, proudly poses for propaganda photographers to show that he is the first German submarine to arrive in a French port. Shortly, the whole second flotilla comes to claim its quarters in Lorient. Admiral Dönitz takes over three middle-class houses on the peninsula of Carnaval, making this his command post. From the location in the Villa Carolin, just in front of the peninsula of Carolin, he can observe the comings and goings of his submarines in the harbor. He personalizes the space by installing in the small bar a Kriegsmarine clock and a coffee table. On the table are tiles with the emblems of submarines that pass through Lorient. He also launches the construction of a command bunker attached to the Villa Carolin. He will settle his staff there. In September 1940, he chooses Brest and Saint-Nazaire as two new ports. They will allow him to accommodate even more submarines. He gives clear orders to his commanders who arrive at the French coast. An immense coastal arc is now at our disposal. It is an incomparable advantage for the war effort against merchant ships. This is our chance. It must be seized as soon as possible. I will not tolerate weakness. Attack without letting go. Do not give an inch. What we take, we keep. Advance through attack. His faithful commanders will follow his instructions to the letter. Thanks to their new bases, their hunting ground has expanded considerably. The numerous prey will be easy victims. Discover the past with exclusive history documentaries and ad-free podcasts presented by world-renowned historians, all from History Hit. Watch them on your smart TV or on the go with your mobile device. Download the app now to explore everything from the wonders of ancient Pompeii and the mystery of the princes in the tower to the life of Anne Boleyn and D-Day. Sign up via the link in the description. The biggest danger of the Battle of the Atlantic was really from 1941 to 1942. This is when the biggest losses were experienced in the mid-Atlantic, which the Germans called their happy hunting ground, where convoys had no protection because quite often their escort ships had moved away and there was no aircraft protection for them either. For the Allies, the losses are colossal. During this first year of war, 1,060 boats are sunk. More than half of them by U-boat torpedoes. At the front of the submarines, the pennants show the tonnage of the sunken ships, which accumulates as fast as the number of the ornaments. Admiral Dunitz generally rewards his men when they get these results. Iron Cross and Chevalier maintain the legend of the men who are willing to die for their leader. Otto Kretschmer will set the ultimate record by torpedoing 56 ships of the Allied forces. The effectiveness of the Kriegsmarine Aces encourages Hitler to build more and more submersibles. In the German arsenals, the pace is hellish. A submarine is launched every three days. Admiral Dunitz will soon be able to count on an additional 200 U-boats. The new priority is to establish them on the Atlantic coast in fortified bases, well equipped to protect, repair, and especially rearm them. For this gigantic operation, the great builder of the Reich, Fritz Tant, is enlisted. This early companion of the Fuhrer rises to Minister of Armament of the Reich. He directs a huge organization of public works that develops the aura of the Nazi regime on a massive scale. His leadership since 1934 has contributed to the building of 3,000 kilometers of German motorways and the 600 kilometers of fortifications between Germany and France. The TOT paramilitary organization, which employs the best German engineers, bears his name. The Reich's labor department can mobilize a large workforce in minimum time, even on megaprojects. The architects of the compulsory labor service, called the STO, imagine an imposing aesthetic design. They model the project after the fortifications that prevented the total destruction of German submersibles during the First World War. The Bruges base will serve as a matrix for all U-bunkers to be built on French territory. A special construction technique will allow the Germans to advance the work of the five bases at a pace that defies the imagination. A huge dike is first built to dry the site, which allows workers to work in dry conditions. The next step is the manufacture of the metal skeleton of the bunker. To assure its resistance, the mesh understructure is very dense. An iron rod every 10 centimeters. The skeleton is then boxed, and a specially treated concrete is poured inside to further reinforce it. Cranes position a giant metal frame on the supporting walls. The roof structure is formed. It will then be sealed and completely cemented over. At the end of the construction phase, the dikes are destroyed, and the water rushes into the cells, making the space ready to accommodate the precious submarines. This construction principle is quite incredible. The dimensions and volumes of this gigantic concrete will be the same on the five bases. Thousands of workers come from the whole of Europe for these high-paying jobs. Their wages are aligned with those of German workers. Sometimes, they prefer to work on the site of the Atlantic Wall to avoid being sent by the STO, the mandatory labor service, to Germany. At the time, the Germans had quite important social insurance and bonus systems, bonus for remoteness, bonus for celibacy, bonus for the risk of bombing, etc. And they apply these same conditions to French workers, in fact. We met a lot of former workers who told us that at the age of 15, they earned as much as a French teacher To add to this voluntary workforce, the Vichy authorities provide the TOT organization with cheap labor. There are people coming from North Africa working alongside Spanish Republicans who were imprisoned in France after fighting Franco. These second-class workers are exploited at the base yards. Several thousand people will participate in these building projects. Later, hundreds of technicians set them up to operate independently. With the plate marked CEMENT on the side, we see the bell here at the back. For the salary. And all of this is part of a large electric board. Which was powered, in fact, which allowed electricity to be distributed in the different workshops of the base. Incredible, look at the markings, MOTOR 1, MOTOR 2. It was the room of the transformers to transform the energy that arrived at a very high voltage. We see here that we could go from one voltage to another, from 220 to 380. Because there were also French devices that worked, German devices. We see the arrival of the cables. They could then connect with their devices directly to work on submarines. So what do we discover? A profile of Winston Churchill, the British Prime Minister at the time. And who was number one enemy for the submarines. To prevent the construction of German bunkers, in April 1941, he launched the Royal Air Force in an attack on the Germans' constructions on the French coast. But the Crete Marines' air defenses are well organized and efficient. Unable to slow down the completion of the Germans' shipyards, the British adopt another strategy. In Liverpool, the largest English port, the Royal Navy installs a new command post. From here, they will organize all the combat strategy against the submarines and protect their convoys. We are underneath what was known as Derby House, in Exchange Flag Square behind the Town Hall. This is possibly one of the most important buildings of the Second World War for the Allies. We're currently under street level in what's known as the Map Room or the Operations Room. This building was a combined headquarters between the Navy and the Air Force. So the Navy obviously were managing and controlling all the shipping, but the Air Force was really, really important because aircraft are extremely good at detecting and bombing U-boats effectively. The building took about 300 people. 80% of those staff were women, many of whom were very young, around the ages of 17, 18, 19. Many of the men who worked here were reserve officers and over the age of 40. Because if you were younger than that, you would be at the fighting front. It was here that one of the most important decisions for the conduct of the Battle of the Atlantic was made. The temporary abandonment of the bombings of the underwater bases on the French coasts. Those U-boat bases were, they're still there. They were built with roofs, I don't know how thick. You know, they were almost impregnable. So again, where do you get most bang for your buck, as we say? You know, it's better to try and focus your resources on sinking U-boats in the North Atlantic and bombing civilian targets in Germany than trying to bomb something that is impregnable. As a result, the Germans complete the construction of their Sennheiser base almost unhindered. The first three cells were built in just three months. June 30, 1941. Admiral Dönitz inaugurates the base with great pomp. And Fritz Todt gives him the original plans as a symbol of this feat. Cell No. 5, which the first submarine entered, is today the best preserved of all of them on the French bases. It's the one where we can observe the greatest number of traces left by the German crews. You can see the wheel arches that remained in place. There are two wheel arches there. The numbers with the box. The C-5, marked at the time. You even have the wooden passage on the top of the alveolus. This is really the last one that remains of all the bases. There's not a lot of people coming in. No, you can't have access here. Let's go. The crucial element that makes these war machines go is obviously diesel. So bases also serve as service stations. Once filled, the submersibles can travel thousands of kilometers. What's amazing is that with a single tank here in Saint-Nazaire, they could still reach the coasts of the United States from here. This is what Dönitz will plan to do in January 1942, by organizing Operation Symbol. Following America's entry into the war a month earlier, the Admiral decided to attack the east coast of the United States. U-boats departing from the French bases cross the Atlantic in 15 days and torpedo all ships they encounter. Within a month, 25 Allied ships are sunk. This is a new success for the German submarines and their leader. Admiral Dönitz took the opportunity to inform all the German staff. In this American coastal zone, our enemy does not expect our attacks. We must use this advantage to the maximum. Every time the Americans lose a tanker, it's an immediate setback to their construction program. I believe that the competition between their factories and our submarines is not a lost cause. For their part, British intelligence warns Churchill of an immense danger threatening them. The Tirpitz, the largest battleship in the German Navy, is preparing to join the packs of U-boats in the Atlantic. To prevent it from ravaging the Atlantic, Churchill has only one solution. Organize a commando raid on Saint-Nazaire, the only French port with a dry dock big enough to accommodate it. The 350-meter-long Joubert Lock is the only basin large enough to dry dock the giant battleship. This attack will be the first major operation of the British commandos on the occupied French coasts. On the night of March 28, 1942, 611 British soldiers attack by sea the port of Saint-Nazaire, defended by 4,000 Nazi soldiers. When the German commandos land, they come under fire from the Germans positioned on the roof of the base. 170 men are killed, 200 others are taken prisoner. But their mission will succeed thanks to a ship loaded with explosives. The next day, the Germans discover the destroyer HMS Campbeltown caught in the mouth of the Joubert Lock. In 1942, construction of the U-bunkers of La Rochelle and Bordeaux is still underway. 98 U-boats. An incredible organization is being set up which allows attack missions to be carried out continuously in the Atlantic. For Admiral Dunnett, it's a golden time. It is with pride that he welcomes Japanese allies into his largest base in Lorient. The Japanese will send three Japanese submarines here, which will arrive on the French coast. There are two in Lorient, one in Brest. They are cargo submarines, because they have huge hulls that allow them to transport raw materials that are essential to the German industry, opium, quinine, rubber. And in exchange, they fill their hulls with torpedoes, aircraft engines, and all that goes back to Japan. There is also a diplomatic meeting between allies led by powerful Admiral Raeder. German news stories tell of a welcoming interaction of exchanges between Japanese submariners and Germans about culture and sports. This illustrates that they have become brothers in arms. Faced with the power of the German forces on land as well as on sea, Churchill is worried. He knows that the aftermath of the war depends on the military control of the North Atlantic, especially because at the time the priority of the Allies is to supply the Red Army that is struggling against the Wehrmacht's offensive. Huge convoys loaded with weapons, fuel, and food are leaving the United States for the Soviet Union. They are closely watched by British escorts that are charged with protecting them from underwater attacks. Admiral Dunitz understood that he absolutely had to win this battle. He will deploy all his forces to stop these convoys and to use to his advantage an area dubbed the Atlantic Hole. A large area of several thousand square kilometers in the middle of the North Atlantic. Here, Allied convoys cannot expect any help from aviation. This is where Dunitz positions his submarines to await them. When a U-boat spots a ship, it picks it up and warns the Admiral's headquarters by radio. The headquarters then directs the other U-boats in the location of the convoy to intercept it. This sudden convergence of submarines in the manner of a pack of wolves panics the Allies. These group attacks devastate the Allies and become Dunitz's hallmark. But this formidable tactic has a weak point, which will eventually cause the loss of Nazi submarines. It uses a lot of radio communications from one place. A place today forgotten. Indeed, the U-boats operating in all the oceans must receive messages. They must be told where the convoys have been spotted. They must be able to regroup. These messages are sent to them through giant antennas behind them. There are 10 huge pylons, 180 meters high, with 12 kilometers of cables that will send messages to the U-boats on all the oceans. From here, the submarines can receive messages From his headquarters in Kernevel, Karl Dunitz encrypts his orders. Confident in their Enigma machine, the Germans deem their coded messages as indecipherable. At Bas Lund, the communications are amplified to be sent to the entire fleet in operation. But this information from the Kriegsmarine is very much monitored. The British intercept it with radio receivers installed on their shores. It's their attempt to thwart the strategy of the Germans. All the messages seized are then sent to the English countryside at Bletchley Park. It is in this pastoral atmosphere that the decoding teams of the ULTRA project work under the utmost secrecy to decode Enigma. Alan Turing, a 29-year-old math genius, achieves this by June 1941. Bletchley Park did the work in being able to break the Enigma cipher. The most important thing about it is the Germans never knew that the Allies had broken the Enigma code. So they didn't know we were reading their messages over and over again. They actually thought we must have some special secret weapon in the North Atlantic because we knew what they were about to do. But they were so confident in the Enigma code that they couldn't believe it had been broken. From then on, the Allies will be one step ahead of their opponent's game. To protect the convoys, the British Intelligence Service also cross-checks its information with another very important source, the networks of the French resistance, like that of La Rochelle. In Lorient, one man will be particularly effective in this intelligence war. The maritime engineer Jacques Doscuff belongs to the Alliance network. He hides his game so well that he becomes deputy director of Carrowman's arsenal. Endowed with an extraordinary memory, Doscuff memorizes all the comings and goings of the German submarines in the Bay of Lorient. This information he recites by heart to his contact with the Alliance network, which is then transmitted to the British command. His skill and cover make him one of the greatest spies of the Second World War. He will be one of the last Breton resistance fighters to be unmasked and to be executed shortly before the end of the war. In early 1943, all the combined Allied efforts begin to pay off. The Germans have seen a large part of their surface fleet and all their great battleships disappear. Hitler decides to sack Admiral Haeder, who has lost all credit in his eyes. Karl Donitz replaces him at the head of the Kriegsmarine and leaves France definitively. To mark his consecration, the new Grand Admiral organizes a large naval parade, a demonstration of strength which aims to impress his opponents, but especially to re-engage his men. We have to win. Considerations about the state of the fleet are of no interest. War at sea is submarine warfare. Everything else must support this primary objective. But Donitz's submarines are no longer in a strong position. For several weeks, the losses on the German side have been increasing. In Liverpool, the command center of the British Navy also has a new leader who will become, for Karl Donitz, the most formidable opponent, Admiral Max Horten. Max Horten was somewhat of a character. He had been a submariner during the First World War in 1914. Legend has it that he saw his battle with Karl Donitz as being like a personal golf match with him, where each stroke was a tactic and a move against your opponent. And they were sort of mirroring each other over that distance of what they were all trying to do. To take advantage, Admiral Horten will use the Allies' progress in the field of detection. Surface radar and sonar installed on ships are becoming more efficient. They can spot and destroy submarines before the subs attack. New models of long-range aircraft now provide aerial coverage of shipping routes. Ruthlessly, they hunt down German submersibles. In May 1943, Donitz lost 41 submarines, half his combat strength. 27,000 tons of bombs are dropped on the bases and their surroundings. The civilian population is forced to evacuate the cities. Hundreds are killed. Shipyard workshops are destroyed, but the basics continue to work. The roofs, composed of three layers of concrete, resist Allied bombing. An incredible bidding is taking place. To deaden the shock of these giant bombs, German engineers design a system called Fangrost. This forms the first protective layer of the roof. It is composed of parallel beams placed over corridors, which are called explosion or burst chambers. Upon impact of a bomb explosion, the beam breaks and crumbles, raining down the powder, but without breaking down the lower layers of the roof. The Fangrost cover technology was started on all the bases, but not one project was completed anywhere. In Senna's air, it covers only one-third of the roof. It is, however, thanks to this system that the bases are reputed to be indestructible. Numerous setbacks by the end of May 1943 force Admiral Dönitz to announce to the Führer that he was temporarily withdrawing his submarines from the North Atlantic. Convoy attacks are being phased out. Nazi Germany is retreating everywhere, on all fronts. On June 6, 1944, Operation Overlord was unleashed. The Allies land on the beaches of Normandy and smash the Atlantic wall. Their goal is to quickly take control of a large French port to establish a beachhead capable of supplying their troops. The United States military chooses the most westerly port of the French coast, Brest. On July 27, 1944, began a fierce battle around the submarine base that serves as a shelter for German troops. Brest is flattened. After a month and a half of fierce fighting, the U.S. forces win. But the battle brings heavy losses. In Lorient, Saint-Nazaire and La Rochelle, nearly 120,000 German soldiers are besieged. Underwater bases become impregnable fortresses, symbols of the ultimate German resistance. Hitler even orders that these pockets of the Atlantic be defended until the last man. This is an anti-tank gun, 47mm. It's a Czech gun, a Skoda gun. You can see the armored mask and the gun was here. It protected all the rear access to the base. You can still see this pocket, which was used by the soldiers to pre-regulate their shots. And this little cartridge is still totally phosphorescent. The phosphorescent paint dates from 75 years ago, Some of the personnel of the submarine bases will join the combat units. The workshops are adapted so that tanks and land armaments can be built there. The German soldiers who are holed up in these bunkers will hold on until the end of the war. Lorient and Saint-Nazaire will be liberated two days after the surrender, on May 8, 1945. Once again, the walls of Lorient and Saint-Nazaire and the walls of these bases testify to history. We're crossing the Alveole, number 5 of the Saint-Nazaire base, and we see a beautiful Lorraine cross with the V of victory. And we know which unit it is. It's the 4th Marine Rifle Regiment, which took the base here on May 11, 1945, which painted this Lorraine cross here. These strange vehicles were built clandestinely by the men of the resistance. General de Gaulle will make the Breton ports the symbol of reconstruction. The bases that had been under German Marines as abandoned structures will now be invested by the French Navy. The few captured German submersibles will be put back into service under the French flag. Despite the Nazi debacle, mythic Admiral Karl Donitz will remain loyal to the Reich until Hitler's suicide. In the meantime, the Fuhrer makes him his successor. He will take his place at the head of Germany before being stopped by the Allies at Flensburg on May 23, 1945. A few months later at the Nuremberg trial, he is found in the box of the accused with many of the surviving Nazi dignitaries. Accused of crimes against humanity and war crimes because he ordered his submarines not to rescue the castaways of the torpedoed ships. He will escape the rope, but will serve 10 years in prison. He dies in a village in northern Germany in 1980. 5,000 people, including many veterans of the Navy, will attend his funeral. But Winston Churchill, the great winner of the Battle of the Atlantic, probably best explained in his memoirs the danger that Donitz, his submarines, and his bunkers represented. The only thing that really worried me during the Second World War was the danger presented by the German submarines. The submarine bases of the French coastline are the last vestiges of Nazi Germany's desire to dominate the Atlantic. Like the Third Reich's dream of lasting forever, the bases do still seem indestructible today. Yet the reinforced concrete of which they are constructed is heading towards its own demise. Day after day, drop by drop, their metal core is rusting away. The Battle of the Atlantic, the longest campaign of the Second World War, cost the lives of 45,000 Allied sailors and 30,000 German submariners. 85% of the men who served under Karl Donitz died in action.