Original subtitles

- [Narrator] In 1977, Peter Johnson, a geomorphologist,

stumbles upon the remains of something strange

and manmade in the remote region of Labrador, Canada.

- This is in an extremely remote,

almost arctic part of Labrador.

- [Narrator] Canisters and antennas are strewn

among the rocks.

One canister is labeled Canada Meteor Service.

- It's not something ancient.

It's something modern that doesn't make

any sense to be there.

- [Narrator] Although he suspects

it's a Canadian meteorological installation,

Peter Johnson has no idea what secret he has uncovered.

- This place is hundreds of kilometers away

from any settlement.

And this geomorphologist must have been left thinking,

"What on earth are these objects?

What are they doing here, and how did they get here?"

- If Germany could establish a base on Newfoundland,

imagine what they could do to North America.

[intense dramatic music]

[graphics thudding]

[graphics crumbling]

[guns firing]

- [Narrator] In May of 1940, Germany invades France,

Belgium, Luxembourg, and the Netherlands.

In June, the Nazis invade and capture Paris,

and days later, France signs an armistice.

- As Great Britain now suddenly is isolated

from the continent, especially by 1940,

after June 1940, France falls.

Belgium, Holland, the Netherlands are, you know,

occupied by the Germans, the entire coast.

Really, Britain is the only one left standing.

- [Narrator] Pursued by Nazi forces,

the British evacuate from Saint-Nazaire,

leaving behind one of the largest port cities

in northern France along the Atlantic coastline.

- Saint-Nazaire played an important part early in the war

during the defeat of France.

When British forces were fighting in France

alongside the French forces,

they eventually had to retreat in what's called

the Miracle of Dunkirk.

And what people don't always realize is that

Saint-Nazaire was another location by which British

and French forces were rescued from the continent.

With its important place on the Bay of Biscay,

it had always been an important port facility

or dry dock facility where ships could be

repaired and rebuilt.

- [Narrator] With the surrender of France

to the German forces,

the port quickly becomes a hive of activity.

- What on earth was going on here?

[knuckles rapping]

- [Narrator] Many residents are evicted from their homes,

and those who remain in the now occupied city

witness activity near the Loire.

Traffic in the harbor increases,

and Nazi officials arrive to assess the space.

- Northern France for

the Nazis during the Second World War was strategic,

both in terms of any kind of offensive drive

into Great Britain,

it would've been launched from that area,

and certainly in terms of defensive strategy, as well.

- [Narrator] Within a year,

a massive building project will commence.

- The secrecy surrounding this project

was so important to the Nazis.

- [Narrator] Although the Germans utilized

their ground and air forces with extreme efficiency

in the early years of the war, increasingly,

the Atlantic Theater becomes an important venue.

In 1939, the war enters the Atlantic

and becomes a major battlefield

between the Allies and the Nazis.

- The stakes couldn't have been higher for the Allies.

How were they going to defend themselves?

- They realized that looming behind Allied forces

on continental Europe is a pipeline of support,

as North America sends firepower,

supplies and troops to help push back the Nazis.

Disrupting Allied shipping routes becomes top priority.

- They were dependent on food,

but also dependent on the troops

and the machinery and the weapons of war

that were produced in North America.

And for those tanks and those soldiers to get to Britain,

they had to travel across the Atlantic Ocean.

- [Narrator] During the early months of the war,

access to waterways is given to the Kriegsmarine.

In 1939, the Kriegsmarine,

unable to challenge the British and French navies

for the commandment of the sea,

focused on commerce raiding.

Many German warships, including their U-boats,

were already at sea when war was declared

in September of 1939,

and they immediately began attacking

British and French shipping.

- It shows you how important it was

that the Germans were able to go after

the supply lines to the Empire,

and that never stopped.

From the beginning of the war to the end of the war,

the Germans saw that as a vital importance.

- [Narrator] On September 21, 1939,

US President Franklin D. Roosevelt replaced

the Neutrality Act of 1937 with cash and carry,

a provision in the Neutrality Act that Congress had added,

permitting the sale of arms to European warring parties

as long as they crossed the Atlantic on their own ships

and paid for them at once in cash.

- Roosevelt ideologically is dedicated to somehow

supplying the British effort.

Firstly, this is a hold out,

and he's gotta get that through Congress,

and it is difficult.

- We're talking about transport ships carrying

thousands of men, but also oil, gas, iron ore,

textiles, food stuffs.

Those are big, slow ships.

They travel in huge numbers together.

Those convoys principally launch from Canada,

from places like Halifax,

and their jaunts over the Atlantic is perilous.

As a matter of fact, many of them never came home.

We often forget that,

how many ships went down in the process.

- The United States moved gradually from a system

of not selling weapons,

to selling weapons to the United Kingdom,

to ultimately entering into a system called Lend-Lease,

where the United States was lending weapons

to the United Kingdom,

who would then pay back the United States after the war.

- And Roosevelt knows that Great Britain

is this last bastion

of freedom, essentially.

This isn't about democracy.

Screw democracy. We're just talking liberty.

- And so the Atlantic was this pathway through which

the combined might of North American industry

could send aircraft, tanks, cannons, bullets,

and shells to those forces in the United Kingdom

waging the Second World War.

- [Narrator] And it isn't long before U-boats

joined warships in targeting Allied convoys

during the early days of the war.

- U-boat was essential to interrupting

all this naval traffic.

- [Narrator] And as U-boats target and take out

Allied shipping lanes, performing countless sneak attacks,

the Allied cruising vessels and military struggle

to keep the Nazis at bay.

- Between July and October 1940,

almost one and a half million tons of cargo

was sent to the ocean floor by these invisible predators.

- [Narrator] And with the Germans battering their fleets,

the Allies have their work cut out for them.

- The Allies were terrified of the threat

posed by the U-boats because they just didn't have

an effective means of defending themselves against them.

- [Narrator] The Royal Navy, in response,

introduced convoy systems

and formed anti-submarine hunting groups

based on aircraft carriers to patrol shipping lines.

They had anti-submarine weapons, but nothing comparable.

- These U-boats would kind of pick off

the weak in the convoy.

There would be destroyer escorts that would attempt

to sink the U-boats, but of course,

escorts are also vulnerable to a torpedo.

- [Narrator] But despite the Royal Navy's efforts

to stop the attacks on their fleet,

the U-boats continue to wreak havoc in the Atlantic.

- In that age of, again, non-satellite,

unsophisticated electronic detection systems,

it could hide very easily,

although acoustically you hear it.

But still, not the way you can target a U-boat today.

- [Narrator] In the early days of World War II,

U-boats team up on taking down shipping boats,

gaining incredible success in the ongoing

Battle of the Atlantic.

There is simply no end to the terror beneath the water.

- U-boat crews spent weeks and weeks, sometimes,

you know, before they would resupply, re-up.

- [Narrator] From July of 1940 into October,

282 Allied ships are sunk off the northwest approach

to Ireland, and by March of 1941,

shipping convoys are sailing with escorts

along with aircraft support overhead.

- The U-boat was the one weapon that could really sever

the lifeline of Allied forces,

and it was crucial to find a way to defeat it.

This is what made the U-boat menace so threatening,

because if the Nazis could cut off this route,

this Atlantic route by which convoys of troops,

men and food were reaching the United Kingdom,

they could strangle the UK and force it out of the war.

- German U-boats successfully targeted

more than 1300 Allied vessels.

- [Narrator] But this wasn't the first time

they had been used in war.

[explosion booming] [intense dramatic music]

As the battle of the Atlantic rages on,

Germany's U-boat fleet manages to more than double

the number of Allied warship hits.

- German engineers had had almost

a hundred years' experience working with submersibles,

dating right back to the very first submersible,

something called the Brandtaucher in 1850.

- [Narrator] Designed by Bavarian inventor Wilhelm Bauer,

the Brandtaucher was designed to end

the Danish naval blockade.

- Hitler had anticipated the importance of the U-boat.

He had worked hard to make sure that Germany

was constructing these in the 1930s,

even breaking some international rules to do so.

- [Narrator] The Minister of the Marine allowed him

to construct a model that was demonstrated in Kiel Harbor.

It performed adequately and was followed up

with a full model, although slightly scaled down.

On February 1, 1851 in Kiel Harbor,

the Brandtaucher sank.

The crew escaped, but due to it having no ballasts,

water pooled in the bottom of the submarine under the floor.

The Brandtaucher was followed by the Forel,

the first fully-functioning German-built submarine

built by the Friedrich Krupp Germaniawerft yard

in Kiel, which had an internal ballast and tanks.

New models were created, the SM U-1, U-2,

and eventually the U-19, built for the Imperial German Navy,

which conducted raids all throughout World War I.

- So if you compare that to the Allies

at the beginning of the war, at least,

the Nazis had a significant advantage

when it came to submarine warfare.

- [Narrator] Although submersibles give the Germans

an edge during World War I,

they are forced to surrender their fleet

on October 24 of 1918 under the armistice

of the Treaty of Versailles.

Those in home waters were taken to Harwich.

Vessels were studied, scrapped, or given to other navies.

The Treaty of Versailles was signed at

the Paris Peace Conference in 1919,

and restricted total tonnage of the German service fleet

and independent tonnage of slips,

and forbade construction of submarines.

- The Treaty of Versailles that had ended

the First World War governed just what arms

Germany was allowed to build.

And Hitler explicitly worked around the Versailles Treaty

to ensure that Germany was building U-boats.

- [Narrator] Hitler negotiates to start building

them up again and overall rebuffs the Treaty of Versailles.

- So by the time the Second World War begins,

the Germans are ready for undersea warfare,

and they're only going to keep building more

and developing better U-boats throughout the war.

- [Narrator] But no more than would put him on parody

with the United Kingdom.

For years, he's been concealing the building of vessels

or explaining them away as research.

Now, Hitler is ready to re-arm.

- Early U-boats typically had a range

of 4,300 nautical miles

and a capacity to carry up to 14 torpedoes.

By the end of the war,

those numbers had increased significantly.

- [Narrator] The Type VII U-boat had a range

of 8,500 nautical miles, active sonar,

diesel engines with electric motors,

and the capacity for 14 torpedoes.

- A Type IX U-boat, for example,

could travel almost 13 and a half thousand nautical miles

and could carry up to 22 torpedoes.

- [Narrator] The G7e, an electric torpedo,

had 20 different versions, and depending on the warhead,

could contain a charge of 250 to 280 kilograms

of a mixture of dipicrylamine and TNT.

They were powered by a 60 to 72-kilowatt electric motor

with lead acid batteries.

The Type IX U-boat was also equipped

with an anti-aircraft deck gun and two periscopes.

- The U-boat posed the single biggest threat

to the Allied war effort.

- [Narrator] With new U-boats being sent to the coast

to an impenetrable hiding place for them to dock to refuel,

the U-boat menace is one that is hard to stop.

- If the United Kingdom could not receive food,

let alone troops and war material required

to attack conquered Europe, the war could be lost.

- [Narrator] The importance of getting supplies,

weapons and machinery to the UK and Europe is crucial.

- It was massive.

It was strategically probably the most important

battle of all.

It's the one we kind of don't realize,

I guess because it was happening underwater,

literally, submarine warfare.

- [Narrator] With Nazi sunken dangers stalking the convoy,

German U-boat technology and hunting tactics make it

particularly difficult to target U-boats from the surface.

- They use communication, of course,

radio and secret codes like the Enigma machine

to communicate with one another once they've identified

a suitable target.

So they will conceivably go after any military ship.

- [Narrator] While the Allies continue to look

for signs of the hidden menace on the water,

on land British code breakers do their part,

working to crack the Kriegsmarine U-boat communications.

- The German codes during the Battle of the Atlantic

are ciphered using a special machine

called the Enigma machine,

which was thought to make their communications unbreakable.

- [Narrator] In that same year,

after Enigma machines and code books are captured,

Bletchley Park breaks the Enigma code.

On May 8, 1941, German submarine U-110

is rammed by the HMS Bulldog.

The crew evacuated, but the U-boat doesn't sink immediately.

Allies are able to seize an Enigma machine

and its operating instructions,

giving code breakers access to German communications,

an edge the Allies desperately needed

if they were to take control in the Battle of the Atlantic.

[explosion booming]

As the Battle of the Atlantic rages on,

the Allies gained control of a U-boat,

giving them access to secret Nazi communications.

- When they were able to break the U-boat codes,

they were able to find out where these U-boats were.

This would allow them either to move

to destroy these U-boats,

or even better to route the convoys on a different path

to avoid the wolf packs.

- [Narrator] The Nazis would have to come up

with new tactics and technologies to win

the now intensified Battle of the Atlantic.

- The Germans, for their part,

realized that their codes were broken,

and they added an extra rotor,

an extra complication to their Enigma machine,

which made their codes even more difficult to break.

- [Narrator] Having secured their ability

to safely communicate once again with the fleet,

the U-boats would continue to wreak havoc on the Atlantic.

- They were truly, truly built to cause damage.

There was nothing benign about a U-boat.

Their mission was to be secretive,

to be unseen and to destroy.

On September 3rd,

the day that Britain declared war on Germany,

there was a civilian ship that had left England

sailing to Canada, and it was called the SS Athena.

And these were people that were fleeing Britain.

That very day, actually, it was in the evening,

it was sunk by a German U-boat,

and over 100 people perished.

- They were really at the mercy of these U-boats.

- [Narrator] By 1941, the Nazis had gained superior access

to the waterways of the Atlantic by conquering

many countries such as the Czech Republic,

Slovakia, France, Belgium,

Greece, and many more.

The U-boat threat feels like one that can't be contained,

but to keep pressure on the convoys,

the U-boats have to be kept up.

The fleet requires constant fuel, supplies,

and safe harbors to dock between missions.

- Over the course of their occupation of France,

almost immediately they begin this massive construction

of what becomes a massive city of concrete.

[flames roaring]

- [Narrator] While the Battle of the Atlantic rages on,

Saint-Nazaire is eyed as an early U-boat base.

- Saint-Nazaire is a particularly important location

for the Germans once, of course, they occupy France,

because it ultimately ends up being

their only Atlantic base where they have

a dry dock facility,

which means that they can affect repairs.

- [Narrator] So what is it about Saint-Nazaire

that made it so important for the Nazis?

- Saint-Nazaire is also located on the coast of Brittany.

That makes the range of U-boat operations

across the breadth of the Atlantic the logical place

that they would be based,

so it's a hub in many respects.

- Germany being landlocked, you needed access to the seas.

That was going to be a critical thing for this war.

That played into the design for sure.

They weren't gonna build a facility

that could easily be damaged.

They needed to make something that was quite robust,

would be able to manage any sort of attack,

and work and function for them,

because this was a critical thing to access

the seas and bring war that way.

- In December 1940, a group of elite German engineers

arrive at Saint-Nazaire on the French east coast

with plans to construct an enormous concrete structure.

- It became incredibly important for the Nazis

as a site to house and repair the U-boats

that were fighting the Battle of the Atlantic.

When the Nazis finally took over Saint-Nazaire,

they found already existing dry dock facilities,

but what they built there dwarfed anything

that had come before.

- There needs to be a particular depth of water

for it to be able to traverse to.

It needs to have adequate space to draw from.

And then you also have to get that U-boat

up to the surface and then service it.

And you have to be able to access all sides of it, as well.

So from a structural point of view, we need a big space.

- [Narrator] Two months later,

building begins under the watchful eye

of a Nazi engineer named Probst.

- Then you need machines to operate.

You need cranes, you need people,

you need platforms, you need tools,

you need machinery that's going to service this boat.

So there's a ton of activity inside of this space.

- [Narrator] It takes four months to build

the first three pens, and an additional 11 by June 1942.

- The entire structure covers an area

of 39,000 square meters.

It's 300 meters long and 18 meters high.

Almost half of that height, though,

is taken up by the roof, which is eight meters thick,

and it's built up through different layers of concrete,

granite and steel-reinforced concrete.

And this building is built to protect.

- [Narrator] Here, crews can refuel, rest,

dine with others, have their U-boat serviced,

and be protected from aerial attack.

- The Germans built a series of U-boat pens.

These are protected areas where U-boats could be repaired,

but could also replenish and restaff themselves

when out of the battle.

In addition to the docking stations for U-boats,

Saint-Nazaire represented a large facility.

It had dozens, 92 dormitories, a whole series of offices.

It was an important node in the German's ability

to wage the Battle of the Atlantic.

- [Narrator] But at Saint-Nazaire,

danger lurks over the Kriegsmarine.

- Repeated attempts to attack Saint-Nazaire

and to eliminate the U-boat base there in particular

are pretty useless.

They make some damages and they destroy part of it,

but they're not able to get to the hub of the base,

and therefore the Germans are able to prey upon

all ships in the Atlantic,

which is the lifeline for the British, in particular,

in surviving the war.

- The roof or the top layer of the U-boat pens

at Saint-Nazaire was over eight meters thick,

made up of concrete with reinforced steel and other stone

designed to make the U-boats totally protected

from Allied bombers.

- [Narrator] As the Kriegsmarine entrenches itself

along the coast, docks become a target for Allied bombings.

Is this the only hope for incapacitating the U-boat threat?

- Over the course of the Nazi occupation of France,

they continued to fortify and build up

the facilities at Saint-Nazaire,

and they actually built a series of locks,

which was a defensive system that made it

very difficult to approach the U-boat pens from the water

without the proper authorization.

- [Narrator] With refueling stations,

maintenance and crew replenishment all happening

under one roof in Saint-Nazaire,

the prospect of incapacitating Saint-Nazaire

by bomb becomes obsolete.

The U-boat and warship menace is now operating

completely unchecked.

Having control of these waterways enabled them

to provide fuel and other supplies needed

for the U-boat pens.

The infrastructure that they created for the upkeep

of their U-boat fleet was staggering.

- The fact that the U-boats were successful

in sinking so much Allied tonnage

or so many Allied ships crossing the Atlantic

raised real fears that the Allies would lose the war

during the Battle of the Atlantic.

- They were hunting.

They were looking for these Allied ships,

whether they were tourism, whether they were military,

whether they were merchant marines.

They were targeting anything that shouldn't be

in the waters that they didn't recognize

as being one of their own.

And so they, that they were on the hunt, if you will.

They were looking for ships to take out,

and they didn't really care about how big

or how small these ships were.

- [Narrator] As the Allies scrambled to keep up

while monitoring U-boats, the fate of the war is at stake.

- We often forget that

biggest, longest battle fought in the Second World War

was the Battle of Atlantic.

This was, this went for years,

and this essentially

was the battle to keep supplies coming.

- [Narrator] With new fortified U-boat pens

being erected along the shores of continental Europe,

the U-boats docked in Saint-Nazaire

would be embarking on a new mission,

one in particular that would see a U-boat

go to an extremely remote and strange place.

This is the coast of Labrador.

Harsh, remote, and far from Europe.

Why would the Nazis send a lone U-boat to remote Canada?

- Weather and information about weather

played a remarkably important role in planning operations

in the Second World War.

- [Narrator] Controlling the skies came down

to new technology,

one that could accurately predict the weather.

- The Nazis must have intended for this site

to be an incredibly crucial part of their war machine.

- [Narrator] In 1940, the Germans were sending out

weather ships for three to five weeks at a time,

using Enigma machines and radio technology

to transmit weather data back to Nazi military strategists.

- It was especially important when it came to deciding

when and where aircraft could fly,

and also when and where U-boats

and other naval vessels could operate.

- [Narrator] But many of these ships

were vulnerable to attack,

traveling into areas where the Allies held territory.

As a solution, they began plans to set up

covert weather stations.

- A land-based weather station,

a series of sensors and transmitters

that could pass information about weather

back to the Germans.

- [Narrator] On October 22, 1943,

U-boat 537 arrives at Martin Bay, Newfoundland.

- The Germans used an extremely long-range U-boat,

a U-boat that could travel over 25,000 kilometers,

to send a small team of men to Martin Bay

in Newfoundland, Labrador, on the North American coast.

- [Narrator] The location is a barren and isolated outpost,

almost 550 kilometers north of any human settlement.

From here, the Germans plan to transmit

crucial weather data.

- Not many people realize what the Nazis

were up to when they landed in Newfoundland.

And not many people realized that they even

had landed in Newfoundland

and that what their agenda was

in terms of covert operation.

- [Narrator] They drop anchor and send a scouting party

ashore to find the best location

for a secretive piece of technology,

one that could give the Nazis an advantage

over the ever-pressing Allied forces.

[guns firing] [plane roaring]

Miles from any population on a barren piece

of Newfoundland tundra,

the Nazis are preparing to change the course of the war.

- If Germany could establish a base on Newfoundland,

imagine what they could do to North America.

To have that kind of base,

a grounding, if you will,

right on the shores of North America.

So Newfoundland was a great target.

- [Narrator] The crew leaves the boat

after more than a month at sea,

having departed Kiel, Germany on September 18, 1943.

After a brief stopover in Bergen, Norway,

the boat proceeded to the North Atlantic,

led by Captain Peter Schrewe.

Also aboard is scientist Dr. Kurt Sommermeyer.

When the crew aboard the U-537 lands ashore,

they are dragging a covert weather station,

a series of canisters and antennae that will transmit

crucial weather data to help Nazi brass

plan military operations by land, air, and sea.

It is a Siemens manufactured Wetter-Funkgeraät,

a covert weather station featuring

a 150-watt, 150 FK transmitter powered by

10 nickel cadmium and dry cell high voltage batteries.

- A lot of countries were trying to understand

and, you know, predict weather for a really key reason,

which is that it makes your war effort that much easier

if you know when to go, when to launch an attack,

how to launch it.

So meteorological weather-based technology

became important in the course of the war.

- [Narrator] After the successful deployment

of battery canisters and sensitive meteorological equipment,

the U-boat raise anchor and returns to

an anti-shipping U-boat patrol located off of Newfoundland.

- Even today, I think very few people realized

that the Nazis managed to even reach North America,

let alone set up any kind of military installation.

- The whole idea there was, of course,

to anticipate weather with particularly convoys in mind

in this case, right?

Understanding when and where they may be launched

and how you could try to anticipate that.

- [Narrator] The station, uncovered in 1977 by a geologist,

also provides proof of a harrowing fact.

- Having found a weather station

that happened on the side of the Atlantic, unknown,

actually says that, you know, there was a footprint.

- [Narrator] That the Nazis were far closer

to America than anyone realized.

- By '42 people on Coney Island could see ships burning.

Submarines were operating up the St. Lawrence River

and sinking a lot of tonnage.

- [Narrator] Unable to answer the U-boat presence

in the seas, the Allies planned their most daring raid

to take out the U-boat threat.

- Saint-Nazaire, however, was so heavily fortified

that it couldn't be easily bombed into submission.

A naval attack was out of the question.

And so the British had to develop a very ingenious

and bespoke attack to try and take Saint-Nazaire

out of commission.

- [Narrator] March 28, 1942.

Operation Chariot is launched.

Using covert memes to take out

one of the Kriegsmarine's most dangerous U-boat nests.

- They're gonna take a ship which is

largely unimportant now.

It's been battered and beaten

and isn't a frontline ship anymore, the Campbeltown,

and they're gonna load it with time-delayed explosives.

- [Narrator] But the mission comes with its share

of risks for all involved.

- I think all of the men going into it must have understood

this is a one-way ticket because this isn't a bridgehead.

It's not like the cavalry's coming over the hill.

This is a solo raid and you're trying to get out.

- This force, this British ship filled with explosives

and laden with commandos

approached Saint-Nazaire from the sea

and actually rammed its way in to Saint-Nazaire.

- And I think something like 600 commandos go on the ground.

They're extremely well-trained for the operation,

and their job is to blow up whatever they can,

basically, to cause maximum damage, try to take the town.

- The commandos entered the facilities

and engaged in a fight at this Nazi facility,

and the explosives on the ship were detonated.

The following explosion,

this enormous explosion destroyed

the dry dock facilities at Saint-Nazaire.

Many Nazis were killed by the attacking commandos

and a significant part of the facilities

were put out of commission.

- They have incredible success.

They're able to damage it quite substantially,

and they're able to blow a lot of stuff up,

and the British are able to have a very successful raid.

Success comes at a price,

because several hundred men are taken captured,

many die, and I think only 200 and some odd guys

actually come back,

so basically 1/3 are gone from this operation.

- The facility would continue to operate on the war,

but this was considered a successful commando raid

and one way of dealing with this

heavily reinforced U-boat pen.

- It's not outta commission because U-boats

are still able to run out of that,

as well as some surface fleet stuff,

but it's an important moment in World War II,

and it's also a propaganda value.

It it occurs in March 1942 when the war

isn't going so great for the British.

- [Narrator] Despite the facility's ability

to remain in operation even at a limited capacity,

thankfully for the Allies,

the tide in the war begins to change.

Hitler's strategy changes once he invades Russia.

Operation Barbarossa doesn't go as planned.

Hitler must divide his military might

between two fronts, and he's spreading himself too thin.

There is a drop in fuel supplies needed

to run Hitler's fleet of U-boats.

By 1945, the Wehrmacht are grounded,

and German tanks are running on fumes.

On October 30th of 1942,

U-boat 559 is seized, along with its code books,

and Bletchley Park is once again able to break the code.

With naval Enigma messages being read,

convoys could be routed clear of the Nazi wolf packs

waiting in the Atlantic.

- The Allies were very careful to ensure

that they never attacked a U-boat

solely on the basis of intercepted codes.

They always created another excuse

or another viable explanation for why

they were able to find and target a U-boat.

- [Narrator] This, combined with the success in breaking

the new Enigma codes in October of 1942,

sees a drop in the U-boats' efficiency.

- The Allied ability to read the Enigma codes

was more than top secret.

It was actually classified ultra secret,

and that's why we now call this ultra intelligence.

It was crucial that the Germans not know

when the Allies had broken various German Enigma codes.

And so the Allies went to a number of steps

to camouflage or protect the fact that they were able

to break the German ciphers.

- [Narrator] Allied ships lost to U-boats in 1943

dropped to 582.

In 1944, down to 243,

and just 98 lost in 1945.

By intercepting and cracking the Nazis' communications,

the U-boat threat in the Atlantic was less formidable,

and the Allies were now in a position

to change the course of the war.

Having gained the upper hand in the Atlantic

by cracking the latest Enigma code,

the Allies go on the offensive.

On June 6, 1944,

Eisenhower gives the go ahead for the largest

amphibious operation in history, Operation Overlord.

- Of course, the Germans don't know that's coming,

but the Allies have been preparing for the big assault.

- [Narrator] By daybreak, 18,000 Allied parachutists

were already on the ground.

13,000 aircraft mobilized to provide air cover.

By 6:30am, American troops came ashore at Omaha and Utah.

This was an enormous force

that was going to punch through

those fortifications at any cost.

- [Narrator] The British and Canadians captured

Gold, Juno, and Sword beaches.

Then Americans captured Utah.

By day's end, 155,000 Allied troops had stormed

the beaches and were able to push inland.

Within three months, the northern part of France

would be freed and the invasion force would be

preparing to enter Germany where they'd meet the Soviets.

Prior to the assault,

Hitler's armies had been in control

of most of mainland Europe.

Hitler had hoped to repel Allies from the coast

with counter attack.

Hitler had also believed the invasion was a faint

to distract from north of the Seine.

But what happened to the U-boat pens at Saint-Nazaire

after the Allies stormed the beaches of Normandy?

Why aren't they used to mount a counterattack?

- D-Day was such a massive convoy

that came across that very narrow channel.

Had they, you know, even deployed every U-boat they had,

it wouldn't have made a difference.

- [Narrator] Due to a disinformation campaign

mounted by the Allies to convince the Germans

of a second landing that would be happening after Normandy,

the Kriegsmarine decides not to risk

their dwindling naval forces on the Normandy landing.

The subs that could leave the dock

would have to do so on the surface,

risking getting targeted by the Allied fleet.

- The problem was in command and control,

and the problem was intelligence anticipating

where that invasion was actually going to take place.

- [Narrator] But one group of three German torpedo ships

risks slipping out of the docks to attack at Sword Beach,

sinking a Norwegian destroyer.

And that night, U-boats attempt to slip out

and disturb landings at Normandy, but were repulsed.

Two were sunk and four damaged.

The Allies had sub hunting planes that could detect

on the surface with radar at night.

Only U-boats with snorkels were viable,

and Germany only had 14 within range of the beaches.

For weeks, German U-boats were pinned in and navy limited.

Only eight Allied ships were lost to U-boats

off Normandy at a cost of 20 German U-boats.

The German force was simply too small

and two underpowered to take on the Allied fleet.

When Germany issues their surrender in 1945,

156 U-boats are turned over to the Allies,

of which 116 are scuttled as part of Operation Deadlines.

The Royal Navy tows the submarines

to three separate locations hundreds of miles

outside of Ireland and sinks them

to the bottom of the ocean,

putting them out of commission for good.

Today, only four U-boats remain intact from World War II,

relics of a time when U-Boats menaced the Allies

in the Atlantic and elsewhere.

- The Germans had great fun, as they called it, at sea.

And they really hampered the economics of the war,

at least up until the Americans joined,

and more importantly,

the British were able to crack

German military communications.

- [Narrator] Although the Allies and Soviets were able

to bomb and battle Germany to its knees,

the Nazi U-boat terror on the high seas

was an incredibly formidable threat.

- So much so that there were suggestions that even Churchill

was contemplating surrender or negotiation

given the tremendous losses that were occurring at sea.

And we are talking about, you know,

tens of thousands of boys and thousands of ships.

So those losses are really, really important

in the grand context of the war.

- [Narrator] In his memoirs, Winston Churchill remarks that

"the only thing that ever frightened me during the war

was the U-boat peril."

- Over the course of the Second World War,

it's almost impossible to fully acknowledge

the amount of death and destruction caused by the Nazis.

- [Narrator] What might have happened had Germany

not invaded Russia,

allowing them to keep the pressure on Western Europe

and the United Kingdom?

What might have happened had fuel supplies not dwindled

or if Bletchley Park could not crack the Enigma code twice?

What if the Germans had not been able to roll out

the new versions of the U-boat?

- Hitler wanted world domination.

They just wanted everything.

- [Narrator] With remnants of the U-boat threat

on North American shores,

the U-Boat brought the Nazis closer to home

than anyone ever realized.

[intense dramatic music]