Original subtitles

A colossal wall of concrete, perilously wedged

between mountains...

Something so impressive in the landscape to be built

is a real engineering feat.

..Five epic circular structures

mysteriously deserted.

Everything is curved.

There's no place you can go and not be seen.

An American escape route from nuclear armageddon.

You can almost envision terrorised people trying to avoid

a nuclear explosion in a large metropolitan area.

And an unsung hero of world war ii.

The fact is it's got far more historical significance

than you could ever imagine.

Once they were some of the most advanced structures

and facilities on the planet...

At the cutting edge of design and construction.

Today, they stand abandoned, contaminated,

and sometimes deadly.

But who built them and how?

And why were they abandoned?

In northern Italy,

in the mountainous province of belluno,

just 60 miles from venice is a monumental feat of engineering.

Towering above the town of longarone,

an 870 foot wall of concrete spans the tree-covered cliffs

on either side of this narrow gorge.

All of a sudden, you'd come to an opening

with this big concrete wall in front of you.

It's an astonishingly impressive piece of engineering.

Even by modern standards,

it's still one of the highest in the world.

627 feet wide at its summit,

the structure narrows to just 89 feet at its base.

Here the wall is an immense 72 feet thick.

Constructed using 1.3 billion cubic feet of concrete,

this fortress is not holding back water...

But rather 9 billion cubic feet of sedimentary rock and debris.

Standing at its base, gazing up at it,

you would be overwhelmed at its size.

You would be dwarfed.

But why did engineers build this giant structure

in such a precarious location?

And why was it then abandoned?

Italy, at the end of world war ii,

was a nation in tatters,

living under the occupation of foreign armies.

The industrial heartland in the northeast was vital

to the recovery of its flagging economy.

But the region's factories were chronically short of power.

In the 1950s, when Italy was just coming

off the back of the second world war,

its economy was in a state of devastation.

Rising from the ashes, the nation embarked

on a massive program of industrialisation

backed by the us who saw Italy

as a valuable bulwark against the threat of communism

from the east.

The program was driven by hydroelectricity,

drawing on natural resources, they harnessed the power of water

flowing from the Italian alps.

An abundance of rivers, melting snow,

and high rainfall provided perfect conditions.

Hydroelectric power is incredibly attractive

in a mountainous region because if you can

have a tight valley and you can trap water high up,

you've suddenly got the ability for that water to move downhill

very quickly and generate free electricity.

In the shadow of the mighty mount toc,

engineers identified the deep and narrow vajont valley

as an ideal location to store water...

Huge amounts of water

that could be used as part of a vast hydroelectric plan.

The gorge itself was a particularly attractive site

because of the sheer height-ness of the gorge

and the amount of the volume of water that you'd be able

to get for such a small cutting off of the valley.

You can more or less throw a stone from one side to the other.

At the core of this hydroelectric network

was this...

The vajont dam!

A curved dam is a very classical way

of structuring a dam to make it strong

and resist the fluid forces of the reservoir behind it.

It was designed to hold a 3-mile long reservoir.

When you have a huge amount of water pushing up against a dam

and the dam is in the shape of an arch

and it's made from materials that are really good in compression,

then what it means is that the arch is really strong,

you don't need as much material to resist that massive force,

and it stays stable.

And the clever thing is that it channels all of that force

into the cliff faces either side of it.

Employing over 400 labourers from the local area,

work started in 1957.

The dam was the centrepiece of an ambitious hydroelectric network

that spanned the region.

Engineers hoped it would hold

over 6 billion cubic feet of water

and feed 4 power stations

via 37 miles of water delivery tunnels,

bringing much needed energy to the cities of northern Italy.

For three years, workers laboured

until the dam's distinctive curvature

was finally in place.

For something that big, something so impressive

in the landscape to be built

at that time is a real engineering feat.

The filling of the reservoir basin was underway in February 1960.

The moment of truth had arrived.

When you're filling the dam up with water,

there's a lot of weight, a lot of pressure

that's being exerted on sides of the valleys.

But at the same time, you're bringing water

into areas where it's not normally there all of the time.

So, those two factors clearly changed the way

the landscape was reacting.

For nine months, the dam held its water level

at almost 600 feet,

part of a hydroelectric industry

that provided around 85% of the countries power.

However, a 6,000-foot crack

soon appeared across the slope of mount toc.

And it was followed on 4 November, 1960, by a massive landslide.

24 million cubic feet of rock slid into the reservoir

just under 2,000 feet from the dam wall.

The water level drastically increased

and it's threatened to breach the crest of the dam.

Providing you keep enough space

in the level of the reservoir

and this slow rock mass moves into it,

it would not necessarily be a problem, they can control it.

Engineers lowered the water level,

easing pressure on the surrounding cliffs

and decided to employ a fundamental principal of physics

to control any further land movement.

So, if you imagine taking a metal spoon

and then you bend it back and forth a number of times,

eventually that spoon is going to snap.

So, by raising and lowering the level of the water

in the reservoir, they changed the pressure

exerted on the soil.

Using the water level in a dam to control the surrounding land mass

is a risky operation.

It makes it virtually impossible to predict

how fast the landslide might react.

But for three years, the technique appeared to pay off.

The dam successfully supplied water to four power stations,

producing much needed hydroelectricity for the cities

of northern Italy.

In April, 1963, with the landslide seemingly

under control, engineers filled the reservoir

behind the dam to capacity

at 2,345 feet above sea level.

The lesson that civil engineers

are reminded of time

and again is to be acutely aware of the natural surroundings

and the geology in which you are building your structure

because, if you don't take heed of those lessons,

the price you pay could be devastating.

Disaster soon struck.

At 10:39pm on 9 October, 1963,

over 9 billion cubic feet

of rock broke away from mount toc.

Hurtling down at 68 miles an hour, the destructive debris smashed

into the reservoir below.

It wasn't just the mass of earth that slid away

into the reservoir, it was the ferocious speed

at which it came.

45 seconds for effectively half of the mountainside

to drop into the water.

It cascades into the water and causes big waves.

Now, if you imagine a bath, you've got a wall on one side

of the bath and you've got a lip the other side,

you jump into that bath,

you're gonna cause waves in two directions.

One will hit the wall and bounce back,

that's exactly what happened in one part of the valley.

The other's going to actually go over the rim.

It is literally like an airborne Tsunami.

Over 800 million cubic feet of water

became a massive wave,

a wave 820 feet high with the village of longarone

directly in its path.

A massive amount of water forced down

such a tight gorge, it displaced all of that air

and it was almost like a shockwave of air

hit the village directly before the water did

and started destroying some of the buildings.

And then next minute, a wall of water hits you.

It's got rocks in it. It's got trees in it.

It is like liquid sandpaper and it just wipes the village clean.

Barely four minutes after the landslide began,

most of the town was obliterated by the subsequent wall of water.

It's one of the worst natural disasters in European history.

Nearly 2,000 people lost their lives.

The tragic irony of this story

is that whilst the villages below the dam

were completely destroyed by the onrush of water,

the dam itself remained completely intact.

I guess that's testament really to the quality of the design

and build of the dam.

It was just a dam built in the wrong place.

Ultimately, the reservoir was filled with debris

and this spelt the end for the great vajont dam.

It was then abandoned.

Today, the vajont dam stands isolated in the rocky landscape,

scattered with hints of its tragic past.

It forms a permanent reminder of humanity's underestimation

of the forces of nature.

From an engineering perspective,

the vajont dam should have become

one of the most impressive dams in history.

Instead, it's become one of the most infamous.

It's an unfortunate tragedy.

But from tragedy, we learn about how the landscape can react

and, hopefully, we can mitigate against such tragedies

in the future.

Nearly 5,500 miles away on the Cuban island,

Isla de la juventud or isle of youth

sprawls a group of peculiar structures.

Laid out like five spots on a die, these circular giants

are a 174 feet in diameter

and tower over a 4 million square foot open plane.

If you were flying over the island

and you looked down

and saw these five yellow circular buildings,

you would think,

"what, is this some sort of industrial beehive?

Is it a power plant?

No, it's not really shaped like a conventional power plant.

What is it?"

The four outer buildings, each 98 feet high,

consists of six levels, yet inside there are no floors,

only a colossal empty space.

Light pierces the dank grim interior

through 465 rectangular openings.

Had a pretty sinister reputation

amongst the local residents and the conditions inside

were just atrocious.

The most bizarre feature is a short lighthouse

like tower standing in the centre of each building.

When you walk inside, you're instantly

struck by the fact

that there are no straight corridors,

everything is curved.

You are constantly in view from somewhere else.

There's no place where you can go and not be seen.

And that was all by design.

What happened in these strange hollowed out structures

on this remote island?

And why was this site abandoned?

In the 1920s, Cuba was experiencing

a period of economic development

set against a backdrop of political corruption.

Cuban president Gerardo machado

had ordered a major construction program

to modernise the nation.

He was also determined to stay in power at all costs...

And maintain ultimate control over his political opponents,

not only physically but psychologically.

To help him achieve this, the dictator turned

to this extraordinary island complex,

presidio modelo, Cuba's model prison.

It was created and conceived by a Cuban dictator

who drew upon an 18th century

social reformer whole ethos

was that behaviour could be modified via surveillance.

The brainchild of English philosopher

and prison reformer Jeremy Bentham,

it was part of his panopticon theory.

It was a design intended to rehabilitate prisoners.

Surveillance was conducted from an observation tower

at the centre of the structure.

And this was key to the building's design.

You have a central observation tower.

And then you have a circular structure

that surrounds that tower, which is where all the cells are.

And the idea is that all the prisoners in their cells

are not really sure whether the guards are looking

at them or looking at their neighbour downstairs

and so they have to be on their best behaviour all the time.

That design inside the prison

certainly feels quite menacing to me.

That central tower with guards who theoretically

then can be observing what's going on

in all of those prison cells at any time.

I mean, it certainly feels quite 'big brother',

something you might have read in George orwell's '1984'.

Construction began in 1926 using inmate labour.

As each building was completed, it was populated.

President machado's motive was one of control rather than reform.

But as well as creating fear and paranoia amongst the prisoners,

the structures also had an engineering benefit.

This philosophy of prisoner observation

actually lead to a very interesting structural advantage,

and this advantage is the fact that having a circular wall

going all the way round

meant that there was an inherent stiffness

in the structure that meant

you don't need to put intermediate floors in

to keep the structure stable.

By the 1930s, presidio modelo was fully operational,

with each building containing 465 cells,

the complex was designed to house less than 3,000 inmates.

Every cell faced inwards,

pointing towards the central guard tower

and most incredibly, there were no cell doors.

The architecture itself was designed to control

the behaviour of those imprisoned.

Gualdemar llevaron was a guard here

and kept watch over the prisoners.

(Speaks foreign language)

Unseen by the captives

who never knew if and when they were being watch,

guards entered the observation tower through a 98 foot long

underground tunnel.

Hidden from view, the guards could keep an eye

on the prisoners through narrow slits

in the top of the tower.

You're constantly being watched,

not only by the prison guards from the central tower

but other prisoners whose cell was only a few feet from yours.

There's no privacy whatsoever.

And it must have generated a whole lot of paranoia.

The large open space

within each building made surveillance easy

and the result was the inmates increasingly

policed themselves.

Even at meal times, within the central dining hall,

there was no respite from the constant silence

or watchful gaze of the guards.

You would think that leaving your cell

where you're constantly under surveillance

and going for a meal would be a nice experience of chatting

with your fellow cellmates.

Not at all.

You went to a building that was called

the hall of the 3,000 silences,

and it was aptly named

because you weren't allowed to speak.

Imagine how oppressive that would be.

You're being watched all day in your cell,

and now you're having a meal and you can't even speak.

Ironically, its cutting edge design originally conceived

to rehabilitate convicts earned the prison a reputation

for horror

and the prison relied on more than watchful guards

to keep inmates under control.

There are all sorts of legends about the prison,

including the fact that there were crocodiles

in the ponds and lakes

on the perimeter of the prison itself.

(Speaks foreign language)

President machado was unable to hold on to power.

But the prison continued for 27 years

and saw multiple regime changes.

But then in 1953, its most notorious inmate

entered its doors.

The communist revolutionary fidel Castro served two years here

for attempting to overthrow

the ruthless dictator fulgencio Batista.

By his side was his brother, Raul.

Though themselves treated humanely as political prisoners,

fidel Castro witnessed firsthand the psychological success

of the jail's design and realised the potential

for control and paranoia.

It was knowledge and experience he went on to exploit

when he overthrew Batista in 1959 to become leader of Cuba.

When he comes into power, he doesn't, you know,

destroy the place, he doesn't knock it down.

No!

He then sends his political opponents there.

I think that's quite rich.

For eight years, Castro used presidio modelo

to Bury his enemies.

But these political prisoners posed serious threats to security.

One dramatic plan hatched during the CIA-backed

bay of pigs invasion in 1961 involved destroying the prison

using the underground guard tunnels.

There was actually a plan to blow up

these structures using that tunnel

by actually packing it in with explosives.

And thinking about the sheer size and scale of these structures,

the fact that they had this inherent stiffness because of its shape,

I think it would have been quite difficult to actually bring

that structure down.

Dynamite couldn't destroy presidio modelo but Castro could.

The prison had a capacity for 3,000 inmates,

but he packed it with double that number.

Something that was originally designed

to house up to 3,000 prisoners was now housing anything

from 6,000 to 8,000 prisoners.

Riots were commonplace, fights, unsanitary conditions,

and the place was just hellish.

This measure of overpopulation backfired.

Cramped, dirty, and overcrowded, it encouraged growing resistance

from the inmates and was increasingly

seen by Castro as a security risk.

Cuba's model prison closed its doors in 1967

and Castro's enemies were dispersed to other prisons.

It just stops to function.

And it's a little bit dilapidated anyways,

but the political climate had changed

and it no longer had a purpose to serve.

The unique design and function of the prison

made the buildings virtually impossible to re-purpose.

After 41 years of oppression and paranoia, they were abandoned.

The gigantic circular cell blocks of presidio modelo

are now decaying shells and stark reminders

of Cuba's political turmoil.

While Raul Castro, in early 2018,

remains president of Cuba,

the hospital building honours its most famous inmate,

his brother, fidel.

But these structures also represent the closest

anyone has come to turning Jeremy Bentham's

panopticon concept into a reality.

Today, the prison is a museum.

It's a school.

It's a research centre.

And that's about right.

Because what it really was, historically, I think we look

back at it as an innovative attempt at social reform.

It was all about surveillance,

and actually, it was quite ahead of its time.

Over 2,000 miles away, across the Gulf of Mexico,

a barren landscape hides an enigmatic enterprise.

High above Los Angeles is a closed off road,

winding 900 feet up in the San Gabriel mountains.

It leads to a mysterious masonry arch over 20 feet high,

driven into its slopes.

But what is this an entrance for?

And where does it lead?

When you first see these entrances opening up

on the sides of the mountain, you can't fathom

why the effort was gone to to build these huge big tunnels.

For me, you'd expect to see some kind of railway or a road

or something coming out of it, but none of that's there.

In fact, it becomes quite mysterious.

A tiny light at the end of the dark tunnel suggests

this structure runs directly through the mountain.

As you're standing there, you appreciate

what an impressive feat of engineering it is

and how difficult it would have been to have made.

The interesting thing is there's a lot more

to this story than meets the eye.

Why did someone go to the trouble of building

this immense tunnel only to seemingly down tools

and walk away?

Why was it abandoned?

In the 1950s, the cold war loomed large

over a paranoid america.

The nation feared not only an invasion

but nuclear attack from the Soviet union.

La's many aerospace facilities

and military bases made the city a prime target.

America's early warning systems could recognise potential

threats hours before impact.

But in that small window of time, how would the authorities

save the then population of nearly 2 million people?

The la authorities began to wonder how would we evacuate?

In the 1950s, there might have been 20 minutes

or half an hour's warning of an impending nuclear attack

on Los Angeles.

Any evacuation for the people of Los Angeles

had to be prepared in advance.

(Siren blares)

Man: In this troubled stage of the atomic age,

our very lives may depend on always being alert.

If the Soviets launched a nuclear strike on Los Angeles,

a credible escape plan would need to be set in place

for its citizens.

To get out of Los Angeles,

you've got to get through the hills and the mountains

and out the other side.

That means either twisting and turning through canyons

or tunnelling right on through.

So, a 25-mile shortcut was devised.

Designed to speed the city's residents

through the San Gabriel mountains via multiple tunnels to the safety

of the mojave desert...

This path to safety

was shoemaker canyon road,

better known as armageddon highway.

The armageddon highway would work in premise

that the entire population of Los Angeles

would get in their cars

and exit away from the city

and the eventual destruction that would happen.

This was part of the culture at the time,

this fear that the other guy has the technology

and can strike us and that we need to have

some kind of way to protect ourselves.

Once complete, these tunnels were designed to form a costly

but potentially vital evacuation route high above the city.

Given the cold war in the 1950s,

everyone was afraid of nuclear war and in that,

the response of the government was to drill a hole

through a mountain such that the population of Los Angeles

could escape given all out nuclear war.

One Soviet nuclear weapon air bursted over Los Angeles

could kill more people than were killed in Hiroshima,

Nagasaki combined.

(Loud explosion)

But carving a road through a mountain

of hard rock is difficult at the best of times.

And in the volatile region of the San Gabriel mountains,

with severe heat in the summer, avalanches in the winter,

and the continuous threat of landslides,

the challenge was all the more extreme.

Construction started in 1956.

To hold up in this harsh environment,

interlocking steel beams and moulded concrete

were needed to shore up critical stress points

of the 1,000 foot long tunnel.

You would have thought that a project of this importance

would have warranted professionals.

But what they got instead was a chain gang.

I mean, they literally asked the inmates of nearby prisons

to go up into the mountains, build a road.

Not only was their heart probably not into it,

but they didn't have the skill sets.

With unskilled workers struggling to cut through solid rock,

the two-Lane escape highway made agonisingly slow progress.

It was only completed in 1961, a full five years later.

The fact that they were prepared

to blast their way through these mountains

just shows that level of panic and urgency that was felt to give

the people of a major us city a means of escape

and a means to get to safety.

To be inside of it, you can almost envision

terrorised people trying to avoid a nuclear explosion

in a large metropolitan area.

The route to salvation had finally made progress

cutting through the mountains, but engineers realised

there was a fundamental flaw with their plan.

Predictably, progress on the road was slow

and that led to la authorities to say, "hang on.

Let's have a rethink."

"What we're really doing is creating a potential

very huge traffic jam in the future.

Do we really wanna do that?

It's going to be world war III just trying to get to that road."

Given Los Angeles's notoriously congested highways,

the premise that the armageddon highway

would have been able to safely transport the denizens

of Los Angeles to safety is basically ludicrous,

especially when viewed from a modern perspective

of gridlocked Los Angeles highways.

And with the advent of faster intercontinental ballistic missiles

giving even less warning,

escape from the Soviet nuclear fallout became impossible.

La's evacuation plans through shoemaker canyon

were now useless.

When you really think about it,

that given the warning time, which is next to nil,

it's basically impossible to evacuate major urban areas.

Now, I think, by the late 1960s, they're thinking,

"whoa, this is just a whopping "waste of money.

It's just not worth it."

In 1969, 13 years after the project commenced,

the Los Angeles authorities finally called time on the escape route.

All that had been achieved of the 25 mile shortcut

through shoemaker canyon was a 4.5 mile road

and two tunnels that led to nowhere.

Today, the road and tunnels still stand on the slopes

of shoemaker canyon but are rarely visited.

They survive as a monument to cold war paranoia

and the real dangers felt

by the citizens of la half a century ago.

Today, the most striking remains

of the road are its tunnels.

And it makes you appreciate the fact that this is what

cold war paranoia forced us to do.

Thousands of miles across the Atlantic ocean,

on the south coast of england is the seaside village

of littlestone.

In the rough seas of the English channel,

a mysterious 200 foot long and 32 foot wide steel structure

lies partially submerged in its waters.

If you're one of the thousands of holidaymakers

playing on the beach at littlestone or even out

for an early morning walk, you'd quite happily dismiss it

as part of a sunken barge or something.

The fact is it's got far more historical significance

than you could ever imagine.

At low tide,

a large 6,000 tonne block of concrete is revealed.

Yet the object's humble appearance belies

its engineering and historic importance.

I can imagine that the engineers at the time

were a little bit worried that this was gonna be

a big risk to take.

But how did this simple-looking structure

play a key role

in one of the largest invasions in history?

Why is it here?

And why was it abandoned?

In 1944, a force of unprecedented scale was being mobilised

across southern england.

Millions of soldiers backed up by 12,000 aircraft and an armada

of 7,000 ships, all preparing for d day.

It was a phenomenal logistical undertaking.

And while the coastline was heavily defended by German forces,

the challenge was not simply landing this massive invasion force.

It becomes obvious to the British,

to the Americans that it's immensely difficult

to give an army the supplies it needs to keep on fighting

once you've thrown them onto a beach.

The allies developed a unique and ambitious plan to ensure

they could maintain the flow of supplies.

We, the allies, brought together technology

from the field of civil engineering, military engineer,

materials science to create something

that had not existed before, an entire harbour

that can 60 miles to where it's needed.

Codenamed operation mulberry, a critical element of these giant

floating harbours was the Phoenix caisson.

The Phoenix caisson is but a tiny element

of an incredibly complex but at the same time

brilliantly simple plan to take a self-assembling

floating harbour over to the beaches of normandy

for the d day landings.

These watertight structures were designed to provide

valuable protection for the artificial ports.

(Gun fires)

But with wartime steel shortages,

engineers turned to a more readily available material.

The idea of using floating concrete blocks

was actually nothing new.

Concrete vessels have been made since the late 1800s.

What was different was using them to create your own harbour

the size of any modern international ferry port.

Each concrete block was five storeys high,

intended to join together in a chain,

they would serve as a protective barrier

to the floating mulberry harbours.

The purpose of the Phoenix caissons

was to act as a breakwater as the outer limits of the harbour

within which you'd have much calmer waters to land the supplies,

the vehicles, and the troops required

on the beaches of normandy for the d day landing.

The caisson is made of a reinforced concrete shell,

but nine hollow compartments ensure its buoyancy.

Equipped with sea valves, each compartment

can be flooded again and the block sunk into position.

The Phoenix caisson itself rates quite high

in terms of the engineering ingenuity

involved in world war ii, right?

The engineers knew they had a job to do,

and they solved it very efficiently and very beautifully.

Construction began in late 1943, workers were tasked

with making 212 caissons with only 6 months to complete

this colossal task.

At 12 different coastal locations around britain,

45,000 labourers worked in complete secrecy.

In total, this endeavour required

over 8 million cubic feet of concrete

and 31,000 tonnes of steel.

A lot of people would be out there fighting

the wars and so on, so you get the unskilled labour in

and you can actually train them up

quite quickly to fix steel,

to pour the concrete 'cause actually

the process of doing that

is not terribly technical or complicated.

While it was impossible to fully conceal a project

of this magnitude from the Germans, it was essential that Hitler

remain unsure of both when and where the invasion would come.

To help keep these preparations under wraps,

engineers used the caisson's design and function to great effect.

To keep the plans for the d day landings

a complete secret from the Germans,

once the Phoenix caissons had arrived at their assembly point

on the south coast, they were sunk to keep them

out of view below the water level.

The idea being then that you'd pump the water out

to float them up before being towed over to France.

In a mere 6 months, 212 Phoenix caissons

were successfully built and many sunk

in the English channel in preparation for d day.

Now, true to their name, they were to rise again

to play their part in the invasion of France.

Of course, there's always the chance

that once you've done the first sink,

it actually does what it's supposed to do and sticks into the ground

and then stays there nice and stable against the sea currents.

160,000 men crossed the channel on 6 June, 1944.

Within 24 hours, the beachheads were secured.

The allies now had to land enough arms

and supplies to equip an army that would liberate France

and ultimately Europe.

The Phoenix caissons were refloated

and sailed across the normandy beaches to create

the artificial ports that would make this epic feat possible.

The Phoenix caissons had a crew of six men.

I mean imagine that, being a crewman on board

a floating piece of concrete.

As they were towed along by tug boats on board,

there was a little accommodation hut,

a life raft in case anything went wrong,

but they also had anti-aircraft guns just in case they came under attack.

At a rate of 3 knots, it took 30 hours to float

146 of these giant concrete caissons to the beachheads,

codenamed Omaha and gold.

Sunk into position, they functioned as a 2 mile long breakwater

and outer wall of the artificial ports,

fulfilling their crucial role in operation mulberry.

The concrete boxes of the Phoenix caisson,

in and of themselves, are not terribly impressive

when described as a concrete box.

But the usage of that caisson in landing material,

men, and equipment on the beaches of France

was tremendously important.

The mulberry harbour made up an area of 500 acres

that was protected by a ring of Phoenix caissons.

Critically, they calmed the waters so boats

could safely dock at the floating piers

whether at high or low tide.

Having taken the Germans by surprise,

the Phoenix caissons evaded serious bombardment.

Designed to last only 90 days, the mulberry harbour

at gold beach was still going strong 10 months later.

With the help of the Phoenix caissons,

the allies were able to unload a staggering 2.5 million men,

0.5 vehicles, and 4 million tonnes of goods and supplies.

For the engineers involved, the mulberry harbours

were a phenomenal success.

The d day landings have been described

as one of the most monumental events in modern history.

The Phoenix caissons are a huge part of that.

Yet not all the caissons were successful.

Many didn't make it.

No matter how hard engineers tried,

the caisson beached here off the coast of littlestone

refused to budge and remained fully submerged.

The only problem was, in certain areas,

the seabed was extremely sticky and, try as they might,

the Phoenix caisson at littlestone

just couldn't be floated again.

Unable to rise from its watery grave off

the shore of england, it still lies abandoned.

These simple-looking

concrete blocks played a crucial role

in the allies successfully retaking France

and winning world war ii.

They are a monument to military ingenuity

and inspiration to future generations of civil engineers.

The story of the Phoenix caisson

at littlestone in a way is a story of failure.

It never made its way over to France.

But if you were able to get it off the seabed today and float it,

it would still be able to do the job it was designed to do.

And that's testimony to quality engineering

and a sound plan.

Now abandoned, they were once

on the cutting edge of human engineering.

Within these decaying structures are the echoes of history.

They speak of war and terror but also of exploration

and human endeavour.

Captioned by ai-media ai-media. TV