Nazi-Megastructures - U-Boat Base

Michael Konnar

7/10/2025

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Transcript

00:01They're among the largest surviving structures of World War II.

00:05It's one of the biggest construction projects ever attempted anywhere in the world.

00:09A series of indestructible bomb-proof fortresses.

00:13I mean, that's the thickness of three stories of solid concrete.

00:18Built to protect one of Nazi Germany's deadliest weapons.

00:22The U-boat war was the only thing that frightened Churchill about the war.

00:26No!

00:27They were sapping Britain of its strength.

00:30This is the story of Hitler's Nazi U-boat pens.

00:34This system is unique. There's nothing like it anywhere along the Atlantic coastline.

00:39Order them to close immediately. The aces that called them home.

00:43They were running out of stores that would keep the crew fit and healthy and capable of actually fighting.

00:48Alarm! Aircraft are taking on the port bow!

00:51And an Allied campaign to smash them all.

00:54This is an absolutely incredible feature of defensive construction.

01:02The biggest construction projects of World War II.

01:06Ordered by Hitler to secure world domination.

01:10Now they survive as dark reminders of the Führer's fanatical military ambition.

01:15These are the secrets of the Nazi megastructures.

01:20The Atlantic Ocean.

01:33Torpedo 25 knots.

01:351940.

01:36U-boat captain Gunter Prien is on his seventh patrol, leading a wolf pack of Nazi submarines into battle.

01:50Range 500.

01:51Range 500.

01:52Range 500.

01:53Range 500.

01:54Their mission? To destroy Allied merchant ships carrying vital supplies to Britain.

02:11Keep it steady.

02:13The outcome of the war depends on whether these convoys get through.

02:19If the U-boats can stop them, then the Nazis could win.

02:26Fire!

02:27Fire!

02:28Fire!

02:29Fire!

02:30Fire!

02:31Fire!

02:32Fire!

02:33Fire!

02:34Fire!

02:35Fire!

02:36Fire!

02:37Fire!

02:38Sinking 730 Allied ships in the first two years of war, Prien and the wolf packs are a deadly unseen threat below the waves.

02:48And when they surface back at base, they turn from unseen to indestructible.

02:53Because home is one of the greatest fortresses ever built.

03:01The Nazi submarine base at Lorient was one of the most formidable defensive structures on the planet.

03:08Naval historian and author Dr. Glyn Pressel is exploring that base to uncover its incredible secrets.

03:15This whole site covers more than 50 acres.

03:19And at the time, it was incredibly ambitious.

03:21It was one of the biggest construction projects ever attempted anywhere in the world.

03:25Second only, perhaps, to the Hoover Dam in America.

03:28And I think it perfectly illustrates the ambitions of the Nazi regime to dominate both at land and at sea.

03:34The transformation of this peaceful French fishing port into a huge Nazi submarine base was the brainchild of one man.

03:49June the 22nd, 1940.

03:51Hitler's forces have rampaged through Europe.

03:53And now, the surrender of France completes Nazi domination of the continent.

04:05But 480 kilometers away, one German commander is focused on his own mission.

04:12Admiral Karl Dönitz is the commander of the German Navy's U-boat force.

04:19Convinced that U-boats can win the war in the west, he's personally searching the newly conquered French coast for somewhere to base his submarines.

04:29At this stage of the war, Britain was standing alone against Germany.

04:34And of course, Britain's weakness, its Achilles heel, was the fact that it needed to import raw materials for industrial production, food to feed its population.

04:43So cutting off shipping, blockading the whole of Britain would bring Britain to its knees.

04:48After the Germans defeated the French army and occupied France, they now controlled a coastline stretching all the way from Norway to the Bay of Biscay.

05:00Instead of having to sail all the way from bases in Germany, now Dönitz had bases in France.

05:10The bases in France gave the U-boats ready access, safer access to the Atlantic.

05:15With direct access to the ocean, Dönitz believes he has the chance to destroy Britain's naval supply lines.

05:24He quickly selects the best sites to locate his new bases.

05:31But the greatest of them all is Lorient, the Brittany fishing port which becomes his strategic command post.

05:38Dönitz wants to turn the port into an indestructible fortress so that he can protect his precious U-boats and keep them operational.

05:51The challenge is that unlike modern submarines, U-boats constantly need to return to base.

06:02Modern nuclear submarine can go on patrol for months at a time because of the nature of its nuclear technology.

06:08U-boats were very different.

06:10Using the combination of diesel engines, electric motors and batteries, they could only really go to sea for a matter of weeks.

06:16Ah, stop!

06:18Because as the fuel ran out, they would have to return to base.

06:21And these weren't very big crafts, so there was a limited amount of fresh water and food that they could store on board.

06:26So that was almost just as important, the fact that they were running out of the kind of stores that would keep the crew fit and healthy and capable of actually fighting.

06:33Once their stocks of food and torpedoes run out, U-boat captains like Gunther Prien must dock for fresh supplies.

06:43How did it go?

06:45Good. More torpedoes and I would have given you some more prices.

06:50Ah, you'll have your chance.

06:51By September 1940, Prien is already a hero in Germany, after sinking a British battleship at the start of the war.

07:02Now, Prien and his fellow commanders receive a further boost.

07:07The new base at Lorient opens for U-boat repairs.

07:09There's not a drop of fuel left. You were running on fumes. And we need a full complement of torpedoes, including aft.

07:18As well as being resupplied, each U-boat must be carefully inspected every time it returns from patrol.

07:26But how do you get something that weighs over one million kilograms out of the water?

07:31The first answer for the Nazis is to use Lorient's existing facilities.

07:40To properly protect Dönitz's precious U-boats, the base needs to evolve.

07:45So the Nazis engineered a second solution.

07:48The U-boats would be brought along these rails and into this building here.

07:5316 metres wide, with walls over one and a half metres thick.

08:00These two structures, built in just four months, are the first covered repair bunkers at Lorient.

08:12This is actually the original trolling that U-boats laid on.

08:17It's been modified to take the weight of larger boats by building these extra struts along the side.

08:21But it's basically the same equipment.

08:25And you can see just how important it was to be able to get at the hull, to make it accessible for all those really crucial repairs.

08:34What makes these buildings vital in the early days is the protection offered by their arch-like construction.

08:40From up here you can quite clearly see the distinctive shape of the bunker, with its curved roof and steep sloped walls.

08:53Built this way with the intention that any bombs dropped from the air would simply bounce off the sides.

08:57Without another name for it, the Germans began to call it a Dombunker, literally cathedral bunker in German.

09:07And it's easy to see why.

09:11Despite the fact that they are still in use today, the Dombunkers are a temporary fix.

09:15They're only big enough to hold smaller U-boats, and not the large vessels that Dönitz plans to build.

09:26Good. The plans for the bunker, please.

09:28What Dönitz dreams of is a base made up of gigantic submarine pens encased in indestructible concrete bunkers to protect and supply his fleet.

09:41Looks excellent, right?

09:43And to completely sever the link between Britain and America, he also needs hundreds more U-boats.

09:48But how many? Enough? Enough batteries?

09:53Enough batteries? Five? Six?

09:58Admiral Dönitz needed many more U-boats.

10:01He believed that if he had 300 U-boats, with a third of the force at sea at any one time,

10:08he would actually be able to cut off Britain from its overseas supplies.

10:11But at the start of the war, Germany, and specifically Admiral Dönitz, only had 22 ocean-going U-boats to fight his campaign against Britain.

10:22But Dönitz's belief that U-boats hold the key to winning the war is not shared by Hitler.

10:31The way Hitler understood naval power was as the battleship.

10:35Because these were prestige vessels. Vessels that projected the image of Nazi power abroad.

10:44This was a man who used to sketch images of battleships in his spare time.

10:49He thought naval power were big surface ships with big guns, not tiny U-boats under the surface.

10:56To change Hitler's mind, Dönitz is relying on U-boat commanders like Gunther Prien to prove that his submarines are war-winning weapons.

11:08And on the 19th of October, 1940, Prien does just that.

11:16No markings. Looks like a British supply ship.

11:21Alarm!

11:22Alarm!

11:23Alarm!

11:24Alarm!

11:25Alarm!

11:33Find...

11:34Fahr 12.

11:35Enemies B12.

11:36Lage.

11:3760.

11:38Angle on the bow, 60.

11:41Keep it steady.

11:45Torpedo 25 knots.

11:47Torpedo 25 knots.

11:57Torpedo 25 knots.

11:59Änderung 500.

12:03Entfernung 500.

12:06Jaw 8.

12:10Torpedo 25 knots.

12:11Entfernung 500.

12:12Tube one is ready.

12:16Stand by.

12:24Fire.

12:25Fire.

12:30Torpedo life.

12:31Torpedo running.

12:42In just 48 hours, Priyan and six other U-boats attacked two convoys, sinking 34 Allied ships.

13:05Well, these were exactly the sort of successes that Donuts needed.

13:10So all that tonnage that went to the bottom was a ship lost and resources lost.

13:16In other words, they were sapping Britain of its strength.

13:19But would these successes be enough to get Donuts what he wants?

13:27On the 25th of October, 1940, Donuts goes to see Hitler, determined to change his mind about U-boats.

13:35But we have a weapon capable of dealing Britain a mortal blow at her most vulnerable spot.

13:42The U-boat war, however, can only be successfully waged if we have sufficient numbers available.

13:48The minimum requisite total is 300 U-boats.

13:51300.

13:56Jawohl, mein Führer.

13:59You need 300 new U-boats.

14:03Jawohl, mein Führer.

14:04Now tell me about these concrete pens.

14:07I am assured there will be completely bomb-proof, my Führer.

14:18You'll have your U-boats.

14:21And the concrete pens.

14:23I'll see to it.

14:24You need take no further steps.

14:26Hitler could no longer ignore the success of U-boats.

14:33Not long after the meeting, he orders an increase in U-boat production.

14:40And construction of the indestructible base.

14:44A 200,000 square meter site is chosen on the Karaman Peninsula, opposite Donuts' HQ.

14:50The Karaman base, the collection of bunkers, represents around a million cubic meters in simple terms.

15:01The Karaman base is the most important construction by the Nazis in all the occupied countries.

15:12Work begins on the base with the first of two bunkers, K-1, in February 1941.

15:21Their construction will eventually consume a quarter of all the concrete used by the Nazis in France,

15:28at a cost of $2.6 billion in today's money.

15:34But the technical challenges are immense.

15:37So these buildings were built over 100 meters long and 100 meters wide and 18 meters high.

15:44It's just a huge amount of mass which your foundation needs to resist.

15:48To erect the pens as quickly as possible, the Nazis decide to build them on dry land.

15:56But there's a problem.

15:58Excavation of the foundations reveals that the soil is too unstable to take the weight of these massive structures.

16:04Engineers, I think, were quite worried about the building actually settling down and sinking into the ground.

16:11So they built the structure on pile foundations.

16:14Basically, long steel beams or poles inserted vertically, pounded vertically into the ground.

16:21And that gives you the ability to resist sinking of the building.

16:24With the foundations in place, boats, trucks and railway wagons bring 152 million kilograms of raw material into Lorient every month to feed the construction.

16:40On top of that, thousands of workers from all over the Nazi empire are drafted into Lorient to build the pens.

16:54Alongside them, a handful of skilled French engineers occupy senior positions.

16:59One of them, the deputy director of naval construction, is called Jacques Stoskov.

17:06I need the estimates from the steel chart for the tonnage.

17:13Stoskov was one of a number of highly skilled French engineers who worked here at the base.

17:17His main role was at the arsenal, the storage facility for torpedoes, which was a little way away from the pens themselves.

17:25I want you to provide this before the end of the month.

17:31So is that all, sir?

17:33No. Excuse me.

17:35What made Stoskov different was that he was from Alsace, the border region between France and Germany.

17:40That meant that he spoke excellent German.

17:43That made him particularly useful to the German hierarchy.

17:47When you all have the figures, let me have your reports.

17:56Gradually his responsibilities increased, and he supervised French workers all across the base.

18:01He wasn't particularly well-liked by his compatriots, partly because he was a rather serious character,

18:06but also because of his close associations with the Germans.

18:10But men like Stoskov were essential to the Germans in keeping the construction and the operation of this base on track.

18:19As construction progresses, U-boats continue to sail from Lorient.

18:24It rapidly becomes the most important base in France, known as the Base of Aces,

18:31as all the U-boat top guns dock here.

18:34Men like Gunter Prien.

18:39Having already sunk 27 Allied ships, at the end of February 1941, he sails out of Lorient on a new mission.

18:47Keep it steady!

19:03Hunting a convoy of 37 ships, Prien and three other U-boats attack.

19:08Fire!

19:09Fire!

19:10Los!

19:11But they're spotted by Allied destroyers, and forced to dive for safety.

19:27It's coming to us! Dive 90 meters!

19:30Stop!

19:31Stop!

19:32Stop!

19:33Stop!

19:35Stop!

19:36Stop!

19:37Prien's crew rush to the front of the U-boat to speed the Sub's dive.

19:39Stop!

19:40Stop!

19:41Stop!

19:42Stop!

19:44Stop!

19:46Stop!

19:48Stop!

19:49Remaining totally silent is vital

19:53as the destroyer's sonar listens for any noise from the U-boats.

20:06Once detected, the Allied escorts unleash hundreds of depth charges.

20:19No survivors?

20:39Priyan's death hits Durnitz hard.

20:45It confirms how vulnerable his subs are and how vital it is to complete the new pens.

20:53As construction steps up, so does the influence of Frenchman Jacques Stoscoff.

20:59He was a rather serious character, and his close associations with the Germans meant that he developed a reputation as a collaborator.

21:09On one occasion, he was responsible for organizing 250 Frenchmen to be sent to Germany to work.

21:19As the train left the station, some people in the crowd were heard to shout,

21:25Death to Stoscoff.

21:27Meanwhile, the submarine bunkers K-1 and K-2 continue rising at a phenomenal rate.

21:41By December 20, 1941, after just ten months' work, the pens are completed, and not a moment too soon.

21:49Just nine days earlier, Hitler had declared war on the United States.

21:57Despite facing two of the most powerful navies on Earth, Nazi U-boats continue causing havoc in the Atlantic,

22:03sinking 27 ships in December alone.

22:09The U-boats are using up their stocks of torpedoes almost as fast as they can replenish them.

22:15But Durnitz's new U-boat bunkers are ready, and the entrance towers over the harbor at L'Oreal.

22:23K-1 and K-2 were unique in that there was only one access point from the water.

22:29Once they'd entered the dock, the gates would have been closed and the water gradually pumped out.

22:39Beneath the water is a cradle sitting on a ten-degree ramp.

22:44The submarine settles in the cradle and is winched up the ramp towards the dock facilities.

22:54U-boats are then pulled out of the safety of K-1 and onto a transporter unit between the two pens.

23:06This is a post-war French submarine, but the unit itself is the original piece.

23:10It's absolutely enormous.

23:14It had 32 wheels running along various rails, left to right, and parallel with the pens themselves.

23:21That meant that the U-boat could be shunted into position next to whichever dock was ready to receive it.

23:28This system is unique. There's nothing like it anywhere along the Atlantic coastline.

23:34But it's also quite vulnerable.

23:36The U-boats are exposed out in the open air.

23:39But most importantly, the system itself is comparatively fragile.

23:44Just one bomb strike here would render the entire system completely useless.

23:50And any U-boats that were being repaired wouldn't be able to get back out to sea.

23:54And, of course, they wouldn't be able to receive any new U-boats coming in through K-1.

23:58The whole process takes around 90 minutes before the U-boats are safely under cover again.

24:11It's hard to describe just how enormous a space this is.

24:24And there were 13 of these all around the base in K-1 and K-2.

24:28It's so tall that an overhead crane could come over the submarine and remove the periscope completely.

24:38Pulling the entire 5-metre-long periscope out of the submarine is just one of a number of repairs and checks that must be done.

24:47In fact, almost half of all the repairs and refits that happened to U-boats on the French Atlantic coast were done here in Lorient.

24:55That's what made it so special and so critical to the German U-boat campaign.

25:01Lorient's transformation from fishing port to deadly U-boat base enables Admiral Dönitz to hit 500 Allied ships in 1941 and force Britain to the brink of defeat.

25:13The U-boat war was the only thing that frightened Churchill, as he later admitted in his memoirs, about the war, the possibility of Britain's resources being cut off at sea.

25:23And it prompted him to focus attention of the British Armed Forces and the Allies in general on winning the Bally Atlantic.

25:33He directed them to hunt the U-boats at sea and to strike them at their bases.

25:43Built to shelter the Nazi U-boat fleet from Allied bombs, Lorient is now British Prime Minister Winston Churchill's number one target.

26:00This leads the Nazi planners to fear that their concrete giants may not be tough enough to survive.

26:06So at Karaman II, the roof was roughly three and a half meters thick.

26:11I mean, that's even thicker than the walls of Fort Knox.

26:16Originally, I think they wanted something thicker than three and a half meters, but they were concerned at this location that the foundation wasn't strong enough to support it.

26:24And so the Lorient base has to evolve again. The Nazis begin building an even bigger pen, which they hope will be truly impregnable. K-3.

26:37The new pen requires stronger foundations. Built behind giant dams, which hold back the sea, they are forged from the bedrock itself.

26:50So the building work was much more difficult. There was considerably more construction done on Karaman III than on Karaman I and Karaman II.

27:02But they had a perfect structure, as in certain parts, the walls holding up the upper levels were up to 20 feet thick at the base,

27:09and the Germans could reinforce the upper level without destabilizing the building.

27:16Construction of K-3 moves at breathtaking speed, with concrete poured 24 hours a day to get the pens built before an Allied attack comes.

27:27But despite Churchill's decree, the skies remain empty.

27:31We are fortunate the British do not attack these pens from the air while they are under construction.

27:41Dönitz believes Lorient is safe.

27:48View 111, Captain Kleinschmidt.

27:52What he doesn't know is that the French resistance have a man on the inside.

27:57Jack Stosskopf.

28:02Jack Stosskopf was known as an active collaborator.

28:09But nothing could have been further from the truth.

28:12His increasing access to the U-boat pens meant that he could keep a daily watch over the comings and goings here.

28:18He had a formidable memory, almost photographic.

28:21And by identifying the emblems on the sides of the U-boats, he was able to build up a detailed picture of the daily operations here.

28:30He would meet in secret with the contact from the French resistance and pass on his information.

28:36Commandant.

28:37Commandant Lem departed at 0500 hours on the 20th of February.

28:44U-106, Captain Rush.

28:47Reciting it twice to make sure he had the details correct.

28:50U-103, Captain Schultz arrived at 2300 hours on the 24th of February.

28:58Three boats sunk.

29:00Three boats sunk.

29:05Again.

29:09Commandant Lem.

29:11He provides information on Wolfpack numbers and U-boat successes.

29:14Stoskov also passes on plans and technical information that might be used to defeat the U-boats.

29:27This information would then be sent back to the British.

29:31And in the Battle of the Atlantic, information could be a crucial weapon.

29:35But in his secret battle against Dönitz's fleet, Stoskov is risking everything.

29:56Through 1942, construction on the K3 bunker is consuming vast amounts of German resources.

30:02Hundreds of concrete mixers working day and night exhaust the available supply of sand.

30:09And so it's taken from the beaches.

30:13Notably sand for cement and reinforced concrete, this came from the seaside, the coast.

30:20So it contains salt and if you mix it with cement, it doesn't bond well.

30:25And as there was an extremely high iron content, this would accelerate the corrosion, making the building more fragile.

30:32So the Germans had all the sand washed in fresh water in these giant sieves.

30:43In a bid to build an indestructible submarine base, this attention to detail is crucial.

30:49Towards the end of 1942, the vast K3 bunker nears completion.

30:55It's a concrete fortress, with huge steel gates guarding the entrance to docks that can be drained of water in just a few hours.

31:03But the roof covering the complex is the Nazi engineers greatest achievement.

31:16So at Caravan 3, they weren't even satisfied with a three and a half meter thick roof.

31:20They wanted something thicker.

31:22And so they revised the design and what they came up with was, on top of the roof, build two precast beams in a triangular form to create an air gap of roughly half a meter.

31:34So on top of the air gap, they built another three and a half meter roof.

31:41So in total, you would end up with a roof of seven to seven and a half meters thickness.

31:46That's the thickness of two double-decker buses or of three stories almost of solid concrete just above the structure beneath.

31:55Dönitz has asked for an unsmashable layer, and it seems that the German engineers have delivered.

32:06In January 1943, the dams built to keep the sea out during construction are blown up, and the K3 pens finally open.

32:18But it's much more than just a military installation. For thousands of people, it becomes home.

32:28When you imagine that there were 15,000 people here, you realize that not only did the Germans need to bring in everything that the U-boats needed,

32:37but they also needed to bring in everything that the people needed, too.

32:39So this base was full of power stations, water purification units, storage facilities, extra railway tracks had to be built to bring in all of these supplies.

32:51And as the base developed, as its importance developed, more and more needed to be built here to sustain the workforce.

32:58This isn't so much a workshop as a small town.

33:01In the abandoned offices, storerooms and accommodation, some of which haven't changed since the war, you can still see flashes of the people who lived and worked here.

33:17All over the place, there are relics from the previous life of this room.

33:33But you can still make out some German writing here.

33:37After the war, the French would have taken down any Nazi insignia, painting over any German writing.

33:43You can still make out some of the original details.

33:51You can still see up here some of the original paintwork.

33:56At the time, they would have tried to make it as homely and as comfortable as possible.

34:00It's quite eerie. It's quite spooky.

34:06This is obviously a bed frame.

34:09So this would have been someone's bedroom as well as their workplace.

34:15And then just through this window that's been boarded up is the pen itself and all the work going on.

34:20So there's no escaping it.

34:22This would have been a 24-hour-a-day operation.

34:27And it needed to be because Lorient was absolutely vital to the U-boat campaign.

34:32They needed to get the work done quickly and efficiently and get the U-boats out back into the ocean.

34:38With servicing work going on round the clock, these chambers would have been hives of activity.

34:43But for the returning crews, Lorient offers more than just a base.

34:54It's a release.

34:58Since the start of the war, 155 U-boats have been lost, nearly half of them in the second part of 1942.

35:05But their sacrifices that year also result in a dramatic increase in Allied losses.

35:13Over 1,600 ships are sent to the bottom by these submariners.

35:18Amongst their number is U-954's new second watch officer, Peter Dönitz.

35:25Just 21 years old, the Admiral's son is part of a growing number of inexperienced U-boat crews brought in to replace those killed at sea.

35:41But Churchill is still determined to stop the U-boats putting to sea at all.

35:46British and American bombers launch raid after raid against the base.

36:00Contact the base.

36:02I want a detailed report of any damage as soon as possible.

36:07Yes, sir.

36:08Amidst the devastation, the U-boat pens still stand.

36:18Dönitz's determination to provide his fleet with the best possible protection has paid off.

36:24But the Allies are still determined to crack the pens.

36:27And so they construct the biggest bomb yet made.

36:32The Tallboy.

36:33The Tallboy is a special bomb.

36:35A bomb that weighed over five tons, carrying two tons of explosives.

36:40It was dropped at 6,000 meters.

36:42So by the time it reached the target, it would be traveling at the speed of sound,

36:46in the hope that it would penetrate the reinforced roofing of the U-boat pens.

36:52Eleven of these gigantic bombs are dropped on the city.

36:57Only one makes a direct hit on the pens.

36:59But with the Tallboy, one might be enough.

37:09In early 1943, the indestructible U-boat pens face their toughest ever test.

37:15Two and a half billion kilograms of thick reinforced concrete suffer a direct hit from an earthquake bomb designed to smash it.

37:23Well, this is absolutely incredible. This is where the Tallboy actually hit the bunker.

37:38But you can still see clearly where the original line of the roof would have been.

37:45And remember, that's three and a half meters of concrete that the bomb has penetrated straight through, literally obliterated.

37:51But you can also see the gap between the roofs, and then through that you can quite clearly see the second layer.

37:59And what's most impressive is that there's barely a scratch on that layer of roof.

38:03From underneath, for the people working in the bunker itself, it must have sounded quite horrendous.

38:10But crucially, they would have sustained no damage at all.

38:18Whichever way you look at it, this is an absolutely incredible feat of defensive construction.

38:22The base has proved indestructible, and Dönitz continues to personally direct the U-boat battles out at sea.

38:33Here are my orders. The Miser group are to proceed northwest at high speed.

38:41Understood? Good.

38:44The Allies realized that they will never defeat the U-boats in their indestructible base at Lorient.

38:52So they developed technology to go after them at sea instead.

38:56And it's Dönitz's own communications that give the Allies the chance they need.

39:02Allied intelligence were able to penetrate German high-level communications.

39:07Admiral Dönitz had to stay in constant communications with his U-boats to coordinate their attacks,

39:14and the U-boats had to communicate with each other.

39:16That gave the Allies a way of locating them and ultimately destroying them.

39:21The hunters are about to become the hunted.

39:25The Allies develop equipment to detect U-boat radio signals.

39:29And they break Dönitz's secret Enigma code, enabling them to read his messages to the U-boats.

39:35Oblivious to this, on May the 17th, 1943, Dönitz orders a wolf pack to attack a convoy of 37 ships sailing from Canada.

39:48Which boats are closest to the sector?

39:51U-544 and U-954, Admiral.

39:57Order them to close immediately.

39:59U-boat 954 is carrying Dönitz's son, Peter.

40:07The 21-year-old officer is eager to experience his first major action.

40:13Order, sir.

40:16A nice fat convoy heading for us.

40:19At least 14 heavy ships and a light screen of destroyers.

40:21From cracked Enigma messages, the British convoy commander knows exactly where the U-boats will be.

40:31The escort destroyers and bombers from Iceland spring their own trap.

40:35My God!

40:38Alarm!

40:39Aircraft attacking on the port bow!

41:15U-954, carrying Dönitz's son, is lost with all hands.

41:20The Allies' technological advantage proves the decisive blow in the battle for the Atlantic.

41:33243 U-boats are sunk in 1943.

41:37My U-boat men, you have fought like lions.

41:47We have been driven into a tight corner from which it is no longer possible to continue the war.

42:00Just five days after the loss of his son, Dönitz orders all his crews back to base and scales down operations.

42:10Dönitz's campaign had failed.

42:13The balance in the Bally Atlantic had shifted dramatically in favor of the Allies.

42:20The Allies had defeated the U-boat threat at sea, and in 1944-45, Hitler's armies were being pushed back on all fronts.

42:27Defeat was now inevitable.

42:31But at Lorient, one man won't live to see the end of the war.

42:36In 1944, Jacques Stoskopf vanished.

42:41He wasn't particularly missed here in Lorient.

42:43He still had a reputation as a collaborator.

42:47But in fact, his resistance cell had been broken, and his name given up.

42:52He was arrested by the Gestapo, and then taken to a concentration camp, where he was interrogated and tortured, and finally executed with a single shot.