Original subtitles

November 1943.

In the quiet countryside of France,

an unassuming chalk quarry comes alive with activity.

In the wake of an enemy invasion,

Allied reconnaissance watches closely as

the landscape is slowly transformed to serve

the needs of the Third Reich.

Here, on the outskirts of a small village,

a monumental construction project is underway.

One harrowing leap poised

to shape the outcome of the Second World War.

This is a strange construction,

and it's located as close as you can get in Western Europe

to British soil, in Pas-de-Calais, France.

Given the Nazis' proximity to Britain,

it was crucial to keep their plans hidden from enemy aircraft.

Code name - Bauvorhaben 21.

Under constant threat of air raids,

a prisoner workforce feverishly toils

to complete construct.

Before long, a colossal concrete shell emerges from the earth,

a symbol of Hitler's unyielding pursuit of victory

even as the tide of war begins to turn against him.

This dome is a menacing sight from the air.

By Allied estimates, it is 70 metres in diameter.

There is thousands and thousands of tonnes of concrete here.

What was it shielding? And why was it bomb proof?

Nothing around it gives them any kind of clue of what

the hell this thing is.

This imposing stone dome hovers over

a hidden Nazi complex,

shrouding a deadly secret that could alter the course of history.

What was it protecting?

Was it some kind of a biological weapons facility?

Is it self-contained? Are there weapons in there?

Who built it? What's it for?

And what does it mean for the war effort?

The quiet communes of northern France harbour a dark,

decades-old design.

A complex web of concrete that stretches across

the Pas-de-Calais region.

From defensive block houses to an annexed chateau,

concealed rail lines to a subterranean stronghold.

The Nazis erect a labyrinth of stone fortifications

meant to protect a devastating scheme.

There are many remnants of

a massive Nazi undertaking in this region today,

and the scale and diversity of the structures here reveals

a region that must have been very important to the Nazis.

Picture if you're the Allies,

you need to figure out what these are for,

what danger they represent for you,

and how they can be breached.

This is ominous, this is threatening.

And deciphering what these structures are for is

a project that will take years of hard work.

Rising from the battle-scarred hills of Wizernes

is the centrepiece of this Nazi network.

An immense circular slab of concrete known today as La Coupole.

My first thought as

a structural engineer is, how did they do that?

This is thousands of tonnes of concrete emerging from

the green hillsides of France.

This is an imposing structure,

and it gives you a feeling of unease.

A creation from the minds of the Reich's leading engineers,

this aged bunker is built during Nazi occupation,

cleverly camouflaged into the rugged plate of

an old chalk mine.

Beneath this earthen guise,

a thick, reinforced lid protects tall hallways carved into

the stone hillside.

But where they lead remains

a daunting question throughout much of the war.

Where does this go? Is it self-contained?

Are there weapons in there? What's it for?

And what does it mean for the war effort?

Why situate this massive dome

and whatever it's hiding

so close to the Atlantic in the Pas-de-Calais,

only 30km away from the British coast?

La Coupole lingers near the narrowest stretch of

the English Channel, a mere stone's throw from

the watery divide that once separated

Hitler from his greatest foe.

Three years before breaking ground,

a Nazi invasion sets the stage

for this grand design to take shape.

Although the Second World War begins in September 1939

with Hitler's invasion of Poland,

the war doesn't actually come to Britain

and France until the following summer.

On May 10th, 1940,

the Western Front erupts as Hitler's panzers rush into

the Netherlands, Belgium, Luxembourg,

and France.

Six weeks of a vicious campaign ensues,

resulting in approximately 2.4 million casualties,

the majority of which are sustained by the French.

One by one, these European nations fall to the Reich.

Weakened and overwhelmed,

France is the last to surrender,

signing an armistice that

effectively abdicates part of their nation to Nazi control.

With France capitulating,

Britain now stands alone against Nazi Germany.

The Nazis move swiftly into their newly acquired territory,

spanning much of northern France.

As British leaders pull their forces from the continent,

Hitler turns his gaze to the English Channel,

preparing his troops for Operation Sea Lion,

the incoming invasion of Britain.

Yet, as more promising victories lure them to the Eastern Front,

the Atlantic coast instead becomes a vast bulwark

to safeguard his growing empire.

Stretching over 6000km from the tip of Norway to the Spanish border,

the Nazis unfurl a vast barricade along the seaboard -

the great Atlantic Wall.

Assuming that there's going to be a counterattack,

Hitler builds this enormous line of fortifications,

bunkers, pillboxes, barbed wire, barricades,

minefields and it becomes known as the Atlantic Wall.

This is the greatest protection

because whatever attack is going to come from either England

or the United States,

either it's going to be in the form of air power,

or it will be in the form of a naval fleet.

To complete his impregnable wall,

Hitler orders the roll-out of thousands of defensive structures,

including five Sonderbauten

scattered across the Pas-de-Calais region.

"Sonderbauten" means special constructions or special buildings.

They would have "sonderprojekt", special project.

But what is that special project?

You don't know and you're not supposed to know.

Fortifying the sprawling coastline

of occupied Europe demands both engineering prowess

and a vast army of labourers.

One bunker complex would take hundreds

to thousands of people to build.

That's just one bunker complex,

let alone you're now trying to protect this entire coast.

The person power involved in that is astronomical.

Hitler entrusts this undertaking to Organisation Todt,

the only entity in Germany capable of marshalling

the hands and expertise for such an ambitious task.

It's a massive organisation with enormous power given

to them to do basically anything they want for

the engineering defence of Nazi Germany.

Staff from Organisation Todts Festung 27 Division are dispatched

to Pas-de-Calais to plan and supervise

the fortifications in France.

Seeking a location both close to the coast yet somewhat concealed

from Allied surveys, they establish their headquarters in

the commune of Hallines, taking over a 19th-century chateau

that had been seized during the Nazi assault.

Chateau Dambricourt was owned by the Dambricourt family,

and they were a wealthy local family.

They made their money in paper making,

and they owned a lot of properties throughout this region.

The chateau is chosen because of its location.

It's situated on a very large lot that is camouflaged

by quite dense vegetation.

It's also within relative proximity to a railway station,

and so it also allows for the transportation of people

and materials, in and out.

Chateau Dambricourt becomes

a hive of highly confidential coordination.

The new occupants expand the surrounding roads

for military personnel

and build a protective Blockhaus equipped with

a series of foxholes that protrude from the building's roof.

Nazi Blockhauses are an above-ground fortification

used by the Germans and their allies during the war.

Hitler orders the construction of thousands of Blockhauses across

the Atlantic Wall alone.

These Blockhauses are made of reinforced concrete

and have ports for machine guns, along with observational decks.

Tobruks were installed on the roof of this Blockhaus.

Shelters with an opening at the top

where one soldier could stand upright

with his head and shoulders exposed usually with a machine gun.

The castle estate's once pristine lawns are levelled

to make way for 600 square metres of office space,

housing the top architects and designers of the organisation.

One of the first tasks on their agenda,

a special construction project in an old chalk quarry.

Summer, 1943.

Just four kilometres from Chateau Dambricourt,

Allied pilots spot a frenzy of activity as labourers rush

to install rail lines in the stark white basin of

a hollowed chalk mine.

These steel arteries snake their way from

the quarry's subterranean depths to

the main railway that cuts through Calais.

Allies really have to rely on aerial reconnaissance

because, of course, this is occupied territory.

You're getting photographic evidence at best,

so you can only make logical inferences based on

what it is that you're seeing.

And observation only goes so far.

Plumes of dust billow into the sky as

the top workforce dig their shovels into the chalky earth.

A seemingly significant undertaking has begun.

The Allies know that something is happening here.

From the sky, it looks like an ant colony

with all of these workers doing something,

but they hesitate about blowing it up.

Sending out bombers

to attack something is using precious resources,

but also putting men's lives at risk.

And they are aware that the workforce that is being used

to build this is French labourers.

Killing a bunch of French civilians is not

going to be something that the Allies are going to

want to do unnecessarily.

They also aren't sure if anything really nefarious is going on here,

because the Nazis have this tendency to set out decoys.

So they start creating these sites where they make it look like

something important is happening, but they use it

to divert attention from where they're actually doing something.

Is this a decoy, or is this something that is

going to surprise us in a very bad way?

Allied intelligence had already been alerted to

a seemingly more dangerous threat lurking just 15km northwest in

the commune of Watten.

Hidden beneath the dense tree cover of the Eperlecques Forest,

the Nazis' prisoner workforce had arrived en masse

to excavate trenches for another covert Sonderbauten.

The location of the Blockhaus d'Eperlecques

is strategically significant.

It's located in the Eperlecques Forest,

very close to a river.

It's also near electrical grid lines

and a Luftwaffe airfield,

and that provides crucial access to air.

Soon, rising 18 metres from the Earth,

a German Blockhaus is born,

forged from thousands of tonnes of reinforced concrete.

For the Allies, its sheer mass is dwarfed

only by the enigma it conceals.

By 1943,

the Germans are now beginning to get pushed back.

The German army is expelled out of Africa.

The Russians are pushing the army out of the Soviet Union now,

and things are getting a little desperate.

The question becomes,

is this construction part of Hitler's attempts to regain

the upper hand?

Hitler is relying on wonder weapons.

And the question is,

is what are German scientists working on?

What wonder weapon might they be producing?

From the war's outset,

Hitler had proudly promised

a secret super weapon of apocalyptic power.

Although initially dismissed as nothing more than

a propaganda ploy, by 1943,

Allied intelligence gathers convincing evidence of

a German missile programme at work.

The Germans recognised that

the only thing that they have left to be able

to develop is a weapon that can actually pass through

the air defence and naval defences that the British have.

So it has to be something that

they can launch from far away to be able to make

a direct hit on Great Britain.

As Hitler's suspicious blueprints materialise right under

Britain's nose, the Allies spring into action with

the precautionary Operation Crossbow.

On August 27, 1943,

an American fleet of 185 Boeing bombers unleashes

a devastating air strike on the Watten Blockhaus,

bringing construction to an abrupt halt.

A British civil engineer, Sir Malcolm McAlpine,

advised the Royal Air Force

to bomb this Blockhaus when it was most vulnerable,

while the concrete was still setting.

By bombing that when it's wet,

you are destroying the formwork,

you're bringing them back to square one.

This strategic attack renders the site unusable,

leaving nothing but a maze of mangled rebar

and shattered concrete behind.

Hitler, forced to recalculate his scheme,

turns to his trusty architect, Albert Speer,

and the chief engineer of Organisation Todt,

Franz Xaver Dorsch.

Dorsch recommends that the chalk pit be used as

the new site for this secret operation.

The Nazis' original plan was for the chalk quarry

to serve as a simple storage facility for the Blockhaus,

but now it's going to become the centre of the operation.

The irony is that

the decoy ends up actually being the real threat.

However, the standard Blockhaus design will not suffice.

To deter enemy interest and protect their plan from carnage,

the Nazis will have to take their mission underground.

November 1943.

The sleepy storage centre in Wizernes is abruptly transformed

as more than 1,000 workers descend into the pit

under the scrutinous eye of Franz Dorsch.

The bold plan to convert the quarry into

a lucrative Nazi base commences under the code name

Bauvorhaben 21.

This ambitious task will require one million tonnes of concrete

to create an expansive network of tunnels,

operational facilities,

and storage rooms forged deep beneath the hills.

They'd already invested large amounts of time

and labour into the Watten facility,

and now they're about to do it all over again.

Hitler was determined to bring this project to fruition,

and he was not going to be dissuaded, even by major setbacks.

Most critically, Bauvorhaben 21 will be bomb proof,

and Dorsch enlists engineer Werner Flos to implement

an ingenious method of making this possible.

Utilising a technique known as "verbunkerung", Flos relies on

the structure of the natural chalk hills to fashion

a protective hood atop the soon-to-be subterranean site,

a massive reinforced concrete dome weighing 55,000 tonnes.

The verbunkerung method

of construction revolutionised bunker architecture.

On the hilltop,

the Nazis constructed this enormous mound of earth that would act like

a mould on which the roof would be set.

They then poured concrete and more concrete

and more concrete until

the shell was an astonishing five metres thick.

That is a huge chunk of concrete.

Five metres thick is about the height of

a standing giraffe.

You don't build a five-metre-thick roof

unless you are protecting something important.

Once that massive concrete in the roof has then cured,

they can then start excavating the earth from

the hillside below without the threat of being bombed from above.

Even by today's standards,

this IS a remarkable piece of engineering

and the fact that it was created whilst there was

a war on, in many senses, makes it even more impressive.

The concrete slab spans an impressive 71 metres across,

with ample space beneath to carve through the hills.

Ida, Katharina, and Sophia,

some of the facility's codenamed tunnels,

are planned to stretch up to 90 metres through the earth,

seamlessly integrating

the previous lead railway through the compound.

The one vulnerability of the chalk pit, however,

is that it is completely exposed.

How do they avoid

the same fate as the Blockhaus d'Eperlecques?

To disguise the construction of their concrete cocoon,

and any equipment or materials that could tip the Allies off,

Todt officials devise an intricate camouflage to cover

the building site.

They had to build their own camouflage by hand.

They're building a net of ropey material and tying fake

and real vegetation to it to make it look real,

and they've got to cover a 71 metre dome.

Just the camouflaging is a huge project.

This site is like a nesting doll of secrecy.

You have a camouflage net that protects a concrete dome,

which in turn conceals a covert facility.

Meanwhile, security tightens at the nearby Chateau Dambricourt,

where a similar veil of netting is placed atop

the grounds housing Werner Flos

and the Festung 27 Engineering Division.

Were they creating another...

..underground bunker that would house members of

the Organisation Todt to protect them

in case the chateau was attacked?

Once the Germans begin to move everything underground,

this really now begins to signal to the Allies

that there's something significant about to be happening there.

Just a few hundred metres from the chateau,

a complex of tunnels is being planned underfoot.

Armed with jackhammers

and over two million individual bricks,

the Todt workforce begins chiselling their way into the earth.

Once completed, a 60-step descent will lead officials into

a three-metre-high passageway.

This tunnel system will open onto two parallel halls,

separated by a 30 metre gap,

that branch off into six galleries of office space

for high ranking staff.

Here, the work on their valuable Sonderbauten will be able

to proceed entirely out of sight.

The initial sight for this new weapon system,

the Allies bomb that.

The Germans now learn that exterior sights are not necessarily

going to be the safest way to go.

So everything is moved underground for both security and safety.

By 1944, Allied intelligence begins to paint a disturbing picture.

Photo reconnaissance and undercover reports amass sightings

and blueprints of never-before-seen missiles that are being developed

and tested by the Reich.

Pursuing their initial suspicions of Hitler's intentions in France,

Operation Crossbow intensifies bombings across Pas-de-Calais.

This site was built just 15km away from another location that had been

destroyed by Allied bombs.

So why keep building in this area that's so susceptible

to Allied bombing raids?

Pas-de-Calais is the closest part of France to Britain.

This is an incredibly menacing structure.

But what role does it play in the Nazi arsenal?

In the early months of 1944,

construction at the quarry is halted hundreds of times by

the ominous blare of air raid warnings.

Yet, despite its vulnerable and seemingly easy to target location,

the site remains remarkably unscathed.

All the elements to raise suspicion are there.

The British are making the calculation.

Are we 100% that this kind of rocket capability is ready

to be used by the Germans?

Because if it were to be ready to be used by the Germans,

why haven't they used it already?

Do you see what I'm saying? So, in a way,

they're calling Germany's bluff.

With the dome completed,

most of the workforce moves underground,

leaving the quarry above to appear deceptively quiet.

Little more than a pit of shrubbery and stone.

However, on March 4th, 1944,

a British Spitfire captures photographs of

a vast concrete mixing operation beneath the site's camouflage veil.

This is the Allies' smoking gun.

It proves that there is far more happening here than meets the eye.

March 11th.

34 B-24 Liberators pierced the clouds above Pas-de-Calais

and begin their descent on the quarry.

Though obstructed by thick, overcast skies,

ground-based radio transmissions guide the pilots to their target.

Suddenly, the village erupts

as 248 half-tonne bombs rained down from the sky.

BOMB WHISTLES THROUGH THE AIR

Even with direct hits on the dome, nothing happens.

It's just bouncing off the concrete.

And especially because this has this kind of curvature on it.

Often they don't even detonate.

They just bounce off and then they detonate after the hit.

In order to add additional protections,

they built this element called a shatter wall

that was two-metre thick, reinforced concrete wall

that ran the circumference of the dome.

And this would help absorb any forces from bombing.

It was essentially sacrificial.

It could be destroyed,

and it would not have impacted

the structural integrity of the main dome itself.

As the sheer tenacity of the German dome comes into focus,

the Allies escalate their efforts,

launching seven additional air raids.

These are bombs that had successfully destroyed plenty

of other structures,

and yet this one has remained intact.

The harder the target is to destroy,

the more worried the Allies become about it.

This thing is made indestructible. What is it?

What are they doing there?

When the Allies discover that their bombs aren't penetrating the dome,

they start bombing the roads and the rail lines

going into the location in an effort to choke out any kind of activity.

Despite these setbacks,

work at the quarry presses on at a heightened pace,

with the workforce expanded to meet Hitler's intended deadline.

The Allies respond with innovative bombing techniques

and new pathfinding technologies.

Yet, the dome withstands each attempted assault.

To shatter this concrete behemoth,

they're going to need a heavier bomb.

The Royal Air Force decides it's time to deploy

a newly developed device, the Tallboy,

a vessel of destruction otherwise known as an earthquake bomb.

The Tallboy was first deployed in the summer of 1944,

and it was enormous.

At six tonnes,

it was 12 times the size of the typical medium capacity bomb.

These are known as earthquake bombs

because upon impact they were designed

to create an earthquake-type shock,

undermining the foundations of any building.

On June 24th,

the Royal Air Force's Dambusters squadron puts the formidable device

to the test with a fleet of 16 modified Lancaster planes.

They assemble into formation above Wizernes.

In a matter of minutes,

15 menacing Tallboys plummet towards the quarry.

The impact inflicts significant damage on the ancillary structures,

roads and rail lines,

but the dome itself is remarkably unshaken.

Undeterred, the squadron returns one month later,

unleashing a dozen more earth-shattering explosions

in what will be the decisive Blitz.

The air raid in July finally delivers

a meaningful breakthrough.

Whilst the bombs don't directly penetrate

the dome itself.

They compromise its integrity by destabilising

the supporting structure.

They totally destroyed

the infrastructure underneath the dome.

The air raid seals off the site's tunnels

and causes part of the hillside to collapse.

16 major air raids carried out by hundreds of planes,

drop a staggering total of over 3,000 tonnes

of explosives on the site.

Ultimately, the mighty Tallboy finally brings

Bauvorhaben 21 to its end.

It shakes up Hitler's confidence in his wonder weapons

and his architects.

It signals that nothing is indestructible.

We'll get to you eventually.

The fall of the dome is just one domino in a cascade of loss

for the Nazis.

Around 350km down the French coastline,

the tide of defeat had already washed ashore.

On June 6th, 1944, over 150,000 Allied troops

landed on the beaches of Normandy

in the largest amphibious invasion in history.

Ushering in a wave of liberation, they surged towards Pas-de-Calais,

slowly reclaiming Hitler's occupied France.

Hitler believes that the most likely landing spot for

the Allies is at Pas-de-Calais.

The Allies realised that, that is the area

that the Germans expect them,

and that is where most of the defences of

the Atlantic Wall are built.

So the Allies choose another location in Normandy.

As the Allied forces close in,

the once impenetrable dome stands exposed and vulnerable,

its secrets ripe for the taking.

By September, the site comes under British control

and the concrete curtain is finally drawn back.

An unexpected benefit of the dome not being destroyed is that when

the allies arrive after D-Day,

they're able to infiltrate the site

and gather information about what the Germans were up to

and what kind of technology they were developing under the dome.

September 5th, 1944.

At the request of Operation Crossbow officials,

British engineers enter the deserted quarry

for the first intimate glimpse of its monstrous Nazi bunker.

Clambering through the rubble, they inch closer to

the inner workings of Hitler's elusive operation

and unearth a secret far more extensive than ever imagined.

As the Allies advanced into territory held by the Nazis,

they encounter a lot of weird stuff - strange structures,

and they're not sure what the purpose was,

but they know that Hitler had a secret weapons programme.

They have to ask themselves,

"Will we find evidence there of what the Nazis are working on?

"Will we find tools and intelligence that will allow us

"to counteract whatever secret weapon he's about to unleash on us?"

Adjacent to the massive domed roof,

they observe a concrete cube jutting from the hilltop.

A partially excavated ventilation shaft meant to service

the hidden complex below.

Though the two main entrances to the subterranean base

had been buried by British Tallboys,

an alternative access point is discovered via

the site's railway tunnel.

Codenamed Ida, this tunnel,

with a direct link to the main rail line through town,

leads to an unloading station for supplies and personnel.

From here, seven kilometres of tunnels bridge out

to connect galleries, storerooms

and a 33-metre-high octagonal chamber directly beneath the dome.

Getting up close to this phenomenal structure must have been

a chilling experience.

The Nazis had excavated an immense network of tunnels

and chambers, clearly designed

to house something of incredible scale.

Armed with new observations and intelligence

gathered from local sources,

British engineer Colonel Terence Sanders is tasked

with compiling a definitive report.

Putting my engineering hat on would be

a fascinating exploration to try to deduce.

What was the purpose? What was it made for?

How was it made?

And you're trying to deduce that basically out of

a pile of rubble.

That's a tough project.

Gradually, Colonel Sanders

and his team assemble a chilling image of

a functional Wizernes base.

As ample storage rooms, workshops,

and towering passageways are sketched onto their map,

the report reveals a grim assembly line fitted to

the specification of a new vertically positioned projectile.

Hitler's rumoured wonder weapon, the deadly V-2 rocket.

The "V" in V-2 stands for "Vergeltungswaffe",

and this translates to vengeance weapon.

He brands them as vengeance weapons for what he felt was

the Allied bombing

of civilians in Germany.

The over 12.5 tonne missile stands 14 metres tall

and is built to deliver explosive payloads without

the need of a pilot,

an autonomous bullet capable of mass destruction.

This supersonic weapon has the potential

to revolutionise warfare, and the Fuhrer,

desperate to turn his fortune,

clings to the hopes that it will shatter Allied resolve.

As the Allies are coming to grips with the V-1,

the world's first cruise missile,

the Germans unleash a new weapon, the V-2,

the world's first ballistic missile.

The V-1 had a slow cruising speed.

Pilots were able to not only shoot the V-1 down,

but a pilot could fly at the same speed

and with the wing of their plane,

just tip it off target and the thing would crash.

It was very easily destroyed.

Hitler is looking for some kind of a last ditch magic weapon

that they can launch from far away,

and that could pass through the air defence

and naval defences to make a direct hit on Great Britain.

Designed by Nazi rocket scientist Wernher von Braun in utmost secrecy,

the V-2 entirely dwarfs its predecessor.

The missile is armed with an advanced guidance system

and utilises an innovative propellant system

to generate immense thrust.

This propulsion allows it to reach distant targets

nine times faster than the V-1 at speeds of over 5,000km/h.

The V-2 just came in silence until it detonates,

so you never knew it was coming.

We didn't have anti-ballistic missile technology at that time,

and so Britain certainly would have been vulnerable.

Not only was the dome well within range

to wreak havoc on as a V-2 launch site,

it also hosted testing and maintenance facilities.

Far more than a missile launchpad, the Wizernes Dome protects

an entire ecosystem of operations.

The V-2 rockets begin their journey through this fortress on

the Ida Railway, arriving from Germany,

where they are manufactured by slave labourers.

The missiles are then loaded onto trolleys

and transported to the heart of the dome,

the octagonal multistorey chamber,

where they are prepared for their deadly mission.

In here, the V-2 rockets would have been fuelled,

armed, and lifted into an upright position, ready for launch.

However, the potential of the V-2 relies on more than its range.

At the core of its revolutionary propulsion system is

a critical component, liquid oxygen.

The problem is the demand for liquid oxygen

to fuel V-2s far outstripped

the available supply of liquid oxygen that the Nazis had.

So they actually had plans to create

a manufacturing station right in this massive complex.

That would have transformed it into a self-sufficient V-2 hub.

The Wizernes complex is designed to be

a self-sufficient marvel of military engineering,

housing a hospital, staff barracks,

offices and generators.

A subterranean city dedicated to the V-2 programme.

Meanwhile, the remnants of the Watten Blockhaus were planned

to host a supplementary liquid oxygen factory,

while the nearby Roquetoire Substation would assist missiles

in their initial moments of flight.

About ten kilometres from the dome,

the Roquetoire blockhaus was built to house

a radio guidance system, for the V-2s.

That means that once functional,

this radio-beam technology could be deployed

to assist missiles with course correction in real time.

Just as the Allies had suspected, these Sonderbauten

or special construction projects scattered across Pas-de-Calais

were much more than isolated outposts.

Once fully primed for firing,

the V-2 rockets would be carefully guided down one of

the two main launch tracks, codenamed Gretchen and Gustav.

Leading westward to the quarry pit,

two hefty bombproof doors,

forged from 1.5-metre-thick steel plates would part

to reveal the outdoor launchpads.

This is where Colonel Sanders' team stumbles upon a strange discovery.

There were two tunnels that the engineers couldn't access.

The entrances had been destroyed.

However, they were able to determine that

the height of these tunnels was between 17 and 24 metres.

A five- to 7-storey-tall building could fit in that space vertically.

That's a really big tunnel.

They realised this was a much longer and deeper silo than you needed

for the V-2 weapon, and so there would have been a V-3,

a more powerful missile coming that would have been

an intercontinental ballistic missile, ICBM.

Further analysis of the quarry's location

finds the orientation of its launchpads to be

within a half a degree of the shortest aerial path to New York.

Britain is not the prize any more.

The prize is the United States of America.

That's the much more powerful enemy.

And the country that has been sitting protected by both

the Atlantic and the Pacific.

The prize is the United States.

It was going to be nicknamed the America Rocket.

The possibilities are frightening.

They now understood what that dome was about.

Though the Nazis' grand vision of unleashing

a daily barrage of dozens of missiles across

the English Channel is thwarted,

Britain does not escape unscathed.

Even as the Allied forces claim victory at the Wizernes Dome

and liberate the entirety of France, Hitler's V-2 programme persists in

the distant shadows of his crumbling Reich.

Learning from the shortcomings of a fixed launch site like La Coupole,

these V-2s are launched from mobile launchpads across Holland

and Germany.

They launched about 3,000 V-2 rockets over the course of the war.

They were responsible for the loss of nearly 9,000 lives,

both in Britain and in other Allied countries.

Yet, for all its human cost,

the V-2 campaign proves to be a futile endeavour.

The Furher's desperate bid to sow fear and chaos

among Allied populations fails to turn his fate.

Hitler isn't just looking for a final victory,

but it's also to do as much damage as he possibly can,

even if he is going to lose the war.

In a final frenzied act of defiance,

the last V-2 rocket screamed skyward just weeks before

the Reich's collapse, ending Nazi Germany's most ambitious

and costly armaments project.

A two billion Reichsmarks gamble that hastens

the downfall of the regime.

Hitler's motivations were demonstrating power,

and these massive undertakings took time away,

perhaps, from other things.

It is really quite a vast

and ambitious project that might have been part

of his downfall as well.

Though the Fuhrer's vengeance weapon ultimately fails,

the toll it takes is undoubtably profound.

The Todt Organisation is known for its enormous building projects,

and those building projects came with

an equally enormous human cost.

They were often carried out through the use of forced labour.

Prisoners of war, conscripted forced labourers,

and slave labourers from concentration camps.

Twice the number of people were killed who were working on the V-2,

than the V-2 killed of the enemy.

The Sanders team's final report, published in 1945,

deems the site perilously unstable due

to ongoing structural failures beneath the massive dome.

Recognising the potential dangers and possibility of future use,

British Prime Minister Winston Churchill orders

the complex to be partially demolished,

sealing its sinister legacy for years to come.

The cavernous halls of Bauvorhaben 21,

now known as La Coupole, stand dormant for decades.

Yet, the influence of this sprawling subterranean complex

soon reaches far beyond its stone walls,

becoming the prototype for modern underground missile silos

used in both military operations and space exploration.

The dome's innovative layout went on to influence

the blueprints for missile silos during the Cold War.

Ironically, the big winner from the V-2 rocket programme is

the United States and the Soviet Union,

because they will take that technology

and those German scientists,

and they will ultimately then develop

the rockets that are used to put the first humans into space.

While many of the Nazis' Sonderbauten sites

across northern France succumbed to decay, La Coupole finds new life.

In the 1980s, the Ida Tunnel is ceremoniously reopened to house

a historical exhibition.

The winding passages and chambers have since been transformed into

a comprehensive museum,

preserving the dark stories of its past.

A powerful reminder of the innovation

and devastation waged in a time of war.

The dome becomes a symbol of

the moral implications of engineering.

In war, we are forced to innovate.

It is a time of great engineering that advances our societies.

It challenges us to reflect on

the implications of scientific and technological advancement,

and the weight of responsibility that comes with that power.

Subtitles by Red Bee Media