Original subtitles

NARRATOR: During World War II, a vast complex of secret bunkers

was constructed under the streets of London.

This world now lost to time was once an important refuge

from the nightly onslaught of Nazi air raids.

The subterranean labyrinth kept the British government

led by Prime Minister Winston Churchill

c through the darkest days of the war.

It's the most dangerous place in the world,

it's the most dramatic place in the world.

And at the center of it all is Churchill, who actually

is himself in the firing line.

NARRATOR: This secret network also sheltered American General

Dwight Eisenhower, but very little else has ever

been revealed to the public.

This is an immense effort that never before had been set up

in the history of wartime.

And it's done while most people above never realized

what is happening.

NARRATOR: Now we had underground and bring this Lost World back

to life.

We will use cutting edge computer graphic technology

to peel back the layers and reveal a hidden city.

Deep below the sidewalk, we will expose wartime secrets

we were never meant to know.

C is one of the world's most densely populated cities.

And yet few people have any idea that a secret world lies

beneath her streets.

Built during World War II shelter Winston Churchill

and Dwight Eisenhower, this underground government complex

actually had its origins in an earlier conflict.

During the First World War, Zeppelins and Gotha bombers

attacked London in large quantities

and dropped bombs on civilian targets.

This was a shocking occurrence, and it gave Britain

a kind of pervasive fear of what aerial bombardment could

do to them.

NARRATOR: For the British, the rise of Nazi Germany

brought all these fears back.

During the 1920s Churchill had thought that the no war was

going to be possible, but when Hitler came to power

he saw the increasing possibility of war.

He recognized the beast in Germany. he, he,

he had a very acute understanding

of what Hitler could do.

And in particular, he recognized the threat that the Luftwaffe

would pose to Britain.

NARRATOR: Hitler's aggressive foreign policy

led to paranoia in London.

The British believed a new war would

lead to the dropping of bombs and poison gas on their city.

London needed bomb proof and gas tight shelters.

But building such structures was an unknown science.

Civil engineers and architects were recruited

to help with air raid planning.

At the outset of the war, anyone

trying to design or build a bomb resistant structure

was really getting into very unfamiliar territory.

One fundamental question really was whether to shelter

underground or overground, and it's interesting

that in Germany at the time they produced designs for some very

large heavily fortified above ground shelters.

NARRATOR: But British engineers influenced

by the trench experience of World War I develop

their own ideas, they would build below ground.

Those ideas and developments from them

are beautifully illustrated in a set of cartoons

that were put together by over inflate engineer at that time.

NARRATOR: Starting with an open trench,

the defenses got progressively deeper and more elaborate.

Solid walls and reinforced roofs proved capable of protecting

people in large numbers, but not everybody

wanted to go below ground.

Churchill disliked the idea of hiding underground.

He always had done in the First World War, he despised it.

He regarded it as a sort of form of cowardice,

and he would think of bunkers as sort of funk holes not

what he wanted to do.

And the first of these funk holes

that were suggested to him was a place code named Paddock.

NARRATOR: Paddock was the brainchild of Norman Hollis,

secretary of the Committee on imperial defense.

In 1938 he was asked to find the government a suitable bomb

and gas proof bunker.

After scouring basements, tunnels, and disused subway

stations all over London, he settled

on a cluster of buildings in the suburbs

four miles from parliament.

This was the post office research station.

It was the perfect mask for a top secret government

installation.

To this day, it remains largely ignored by the public.

None of the existing buildings was large enough or suitable

for reinforcement.

So in February 1939, Hollis ordered the construction

of a 50 room emergency bunker.

Excavation went 40 feet down, then the bunkers

were built on two levels.

The foundations, walls, and ceilings

were all made from reinforced concrete.

c The building was covered and then hidden

with the construction of innocuous civilian buildings.

Paddock was one of the great secrets of the war.

Lost under suburban homes and gardens,

it was eventually discovered by amateur detectives.

We can now enter the shelters some 60 years

after the government ordered it sealed.

This is the emergency cabinet war room.

This is where the government would have come from Whitehall

in the event of an attack on central London.

Here they should have been able to withstand a direct hit

from the largest high explosive bomb

that the Germans had available.

c We're going down to the first level of the bunker, about

15 feet.

After this point we're coming into an airlock,

one of the major worries was of a gas attack.

NARRATOR: The airlock worked because the air pressure

in the bunker was kept higher than the pressure

outside. c If someone entered the bunker from outside,

the airlock would be sealed and the high pressure would force

any gas back out.

The way would be clear for people

to enter the bunker safely.

Poison gas was a very serious factor in the government's

calculations, and they produced millions

upon millions of gas masks.

At the beginning of the war, about 85% of the population

could be seen in the streets with their gas masks.

It was such a real fear.

NARRATOR: Despite the enormity of this bunker,

it was built to house 200 people.

Paddock was constructed in complete secrecy.

Most work was done at night under camouflage netting.

c The vast quantities of spoil from the excavation

were allegedly removed in bread delivery vans,

and local people knew not to ask any questions.

No one wanted to be suspected as a spy.

Now we're moving into the inner sanctum of the bunker,

the basement where we are now could have been sacrificed.

But downstairs in the subbasement that's

where the government would have been,

that's where Churchill would have been.

There are three ways down and each of them

is protected by a heavy steel blast door.

c You turn the wheel and thick metal bars would have pushed

into these openings here.

So this would have been gas tight and blast proof.

As we go down the stairs, this is floor level.

And between this floor level here and the the subbasement

was five feet of reinforced concrete

to give added blast protection down in the sub basement.

NARRATOR: As the bunker was designed to operate in the most

extreme of wartime conditions, it had to be self-sufficient.

In case it was cut off from main supplies by an air raid

it had its own water tanks.

There was a generator capable of running everything

from the lighting, teleprinters and radio

equipment to the ventilation and filtration plant.

Paddock did not have a heating system.

c It was assumed that the warmth of 200 bodies

would have been sufficient to heat the sealed bunker.

The trade off would have been a humid and foul smelling

atmosphere.

However unpleasant, Paddock had a vital role

to play when war finally broke out in 1939.

c London braced itself for Hitler's bombs.

As soon as Britain was at war with Germany,

an air raid siren went off in London.

It was a false alarm as it happened,

but you've got an instant terror hence the wearing of gas masks,

hence the evacuation of people, hence

the moving of large quantities of the population into bunkers.

The bombers didn't come at first, but the fear of invasion

remained.

Should central London be evacuated,

Paddock would be at the heart of Britain's resistance

to the Nazis.

Right.

So we're coming into the map room here.

This is the military hub of the bunker.

This is where the war in Britain would have been run from.

The would have been maps on all these walls here.

And fluorescent light fittings angle the light

onto these walls where the maps were located.

we've got three offices, perhaps one for each of the services,

the admiralty, the Air Force, the army.

This is a vitally important room,

this is where the war could have been won or lost.

NARRATOR: In the end, the order to evacuate London

was never given.

Paddock remained on permanent standby.

Churchill did in fact, hold one cabinet meeting at Paddock.

But it was an impossible place to get at,

the cabinet got lost as they went there.

And he dismissed it as a piece of useless folly quite

unsuitable for his Majesty's government.

NARRATOR: Although it never fully served its purpose,

Paddock was important.

It helped engineers understand how to build bomb shelters

and it served as a prototype for many of Churchill's bunkers.

With Hitler's armies triumphant in Western Europe,

it was inevitable that he would direct his bombers at London.

What happened in one of these bunkers would save Britain.

Hidden deep in the corner of an Air Force base in London,

England is a top secret military bunker.

60 years ago it was the hub of Britain's air defense tasked

with stopping the most dangerous threat the country had faced

in 1,000 years.

By the summer of 1940, Hitler's armies

had smashed their way through Holland and Belgium

and had occupied Paris in France.

He now set his sights on Britain, just a short distance

across the water.

Britain was in huge danger in the summer of 1940.

The Germans threatened to bomb us into submission.

They were massing on the continent,

they were assembling barges.

Hitler had planned an operation which he called Operation Sea

Lion which was set for the 15th of September 1940.

And the British thought that invasion

was a real possibility.

NARRATOR: Hitler now had charge over French airfields

just 20 miles from the British coast.

c His bombers and fighters could now reach London,

and their lethal payloads were forcing both the public

and the government to seek shelter where they could.

His plan was to destroy Britain's Air Force

and leave the island open to invasion.

RAF fighter command was a prime target,

and if it was to survive the assault of the Luftwaffe

it would have to go underground.

These two items about 40 German bombs,

they both weigh 1,000 kilograms that's around

about 2000 pounds.

This item here is a blast with.

About 80% of this of this weapon contains explosives.

NARRATOR: Blast weapons exploded upon impact

and caused maximum damage above ground.

They were easily countered by underground bunkers,

but such shelters were extremely vulnerable to another weapon

in Hitler's arsenal.

This particular weapon is called an easel.

Is a penetrating weapon designed to penetrate bunkers or harden

targets.

It's got this Tonyan strap system, which

means it's going to be used by dive bombers that

can accurately hit the target.

80% of his weapon is steel, only 20% explosive

NARRATOR: Although it contained little explosive,

the pencil shape and extreme weight of a penetration bomb

meant that it could burrow through metal, brick,

or concrete before detonating at high pressure

deep in the ground, the original bunker buster.

The only response to these penetrating bombs

was to take the bunkers deeper underground.

Churchill was enormously excited by warfare.

And the warfare that was going on in the summer of 1940

was the Battle of Britain, the airborne assault on Britain

and the bombing which got slowly nearer and nearer London.

And Churchill he'd like to do this,

he like to go to the front.

And the front line during the Battle of Britain

was in the Underground headquarters at Oxbridge.

NARRATOR: Oxbridge was one of a new generation

of top secret deep level bunkers that lay far below the range

of German weapons.

With special military permission,

we can now head down 60 feet to the operations room of London's

fighter command.

In the summer of 1940, this room offered Britain a lifeline.

Buried deep in an open excavation,

the Oxbridge bunker is a simple thick walled box

on substantial concrete foundations.

For added protection a six foot slab of reinforced concrete

was laid on top.

Two exit passageways were constructed,

and then the hole was filled with sand and Earth.

It was designed to be virtually invisible from the air.

The bunker comprised 40 rooms over two levels.

It was completely self-sufficient

with its own generators, ventilation system,

and telecommunications.

But the crowning glory of this underground command center

was the plotting room.

Ready for action as war was declared,

Oxbridge was for a time the most important operations room

in Britain.

The Prime Minister was a frequent visitor.

Joan Fanshaw serving in the bunker in 1940

secretly recorded his visits.

It was quiet against all rules and regulations

to keep a diary, but I kept on throughout the war.

And I used to hide it in my gas mask container.

NARRATOR: One particular visit stands out.

September the 15th I was on duty till nearly 1

because Churchill was upstairs and we could not change over

in a blitz.

NARRATOR: That blitz was to prove the heaviest daylight

raid of the war.

On September 15th 1940, London held its breath.

200 heavily armed German bombers were approaching.

And if Hitler could destroy Churchill's air defenses,

the path to invasion lay open.

All records of sightings were channeled

into the plotting room.

First reports of German aircraft came from radar stations

on the coast.

These were then translated into map positions

by plotters like John.

if it's the were enemy aircraft,

it would say h, hostile and it would

say how many aircraft there were and at what height

they were flying.

As soon as they touched the coast,

the observer corp took over and picked up the aircraft

and they passed them to fighter command headquarters.

NARRATOR: The station controller reacted to the latest

information.

He sent up fighter squadrons to intercept the German raiders.

Churchill knew it was make or break.

This was the pivotal day of the Battle of Britain.

Churchill sat there absolutely enthralled

as the plotters pushed the indicators across the board

and as the lights lit up to show the Germans coming

and the British squadrons rising to fight them.

You can imagine it would become extremely busy

because then we come across our own squadrons here.

3 and 3 has come from North hote and that

means there are 22 aircraft in it flying at 22,000 feet.

So the controller could get them up to the ride height

to oppose the enemy aircraft coming in.

NARRATOR: Facing over 200 German aircraft,

Oxbridge threw everything it had into the fray.

It became almost impossible to find space to put these blocks

all together, and the plots were all getting mixed up

and you get mixed up with your person next door.

It was a madhouse, it really was.

At one crucial moment during this extraordinarily tense,

dramatic time, air Vise Marshal Park was in charge

of the whole operation told him that there were no more

reserves.

NARRATOR: Every available fighter plane

was committed to the battle.

Both the British and the Germans suffered heavily

through the day.

There were wild claims from each side over the number of planes

shot down.

Churchill was intensely moved by the Oxbridge experience

and he went home excited, elated, exhausted thinking

that the British claims that we had shot down 185

German aircraft was correct.

It wasn't correct, we shot down about a third of that,

about 60.

Nevertheless, it was the culmination

of the Battle of Britain, something

that he had witnessed at first hand.

And it marked the end really of the German attempt

to attack Britain by air during the daylight.

NARRATOR: The secret bunker at Oxbridge

was never discovered by the Germans.

Without it, fighter command might have been wiped out.

Because of it, Britain retained control of the skies.

Hitler abandoned his plans for invasion

and switched his tactics from attacking the Air Force

to bombing civilians.

Churchill and his government would now

be in the firing line.

They were in urgent need of a bomb proof bunker in Central

London.

There began one of the most incredible secret construction

projects of the war.

Under this building in Central London is a massive bunker.

With over 200 rooms, it would be the hub of Winston Churchill's

wartime world.

With German bombers wreaking destruction on London,

this secret underground complex would provide

a refuge for Churchill and his government

in the most desperate of times.

London becomes a most extraordinary focus

for world attention.

It's the most dangerous place in the world,

it's the most dramatic place in the world.

And at the center of it all is Churchill who actually

is himself in the firing line.

NARRATOR: When the blitz began, there

were loud calls to evacuate the government from London.

But Churchill feared this would lead to widespread panic.

He resolved to stay in the capital

and see it through with his people.

Churchill enjoyed the bombing.

It was a kind of huge pyrotechnic display.

And sometimes in his tin hat, he would

go up onto the roof of what is now the Treasury

and look at this splendid firework display,

puffing away at his cigar throughout.

He realize of course the horror of this,

but always in him there was a kind of schoolboy

that was a delight in the drama of action and warfare.

NARRATOR: But when his own home took a direct hit Churchill,

reluctantly accepted the need for bomb proof quarters.

Just 100 yards from the Houses of Parliament,

a substantial government building

with extensive basements was identified as being

perfect for Churchill's needs.

On the first floor would be his living quarters.

The basement would provide protected office space

for political and military leaders

and down in the subbasement sleeping

quarters for his staff.

For many years, the cabinet war rooms

were a closely guarded secret.

But studies of declassified papers

now reveal the full story.

This is the way that Churchill and those coming

to work in the cabinet war rooms or to visit the cabinet war

rooms would have arrived in the building

and he would have walked up the staircase.

And ahead of them they would have

seen a pair of glass doors.

As they got close they would have noticed that there was

a small hole in the middle with a machine gun pointing out

through it.

NARRATOR: Guarded by heavily armed Marines,

the suite of first floor rooms provided for the Prime Minister

was known as the Annex.

At one end where Churchill's private map rooms, at the other

was his living quarters, a dining room, a living room,

and a bedroom each for Mr and Mrs. Churchill.

But these rooms were not safe from bombs.

With Hitler intensifying his night attacks

on London in late 1940, Churchill and his government

took shelter in the basement rooms below.

These offered some protection, but they were still not

bomb proof.

Substantial reinforcement was ordered.

What followed was one of the most amazing

secret construction projects of the war, the erection of a bomb

proof slab over the basement cabinet war rooms.

Well, they started to reinforce the cabinet war rooms

by putting in a timber structure.

Eventually they changed it to putting in a steel structure,

but that wasn't considered safe enough.

And so eventually they started to build

a massive concrete detonator slab which

was thought to be proof against 250 kilogram bombs.

NARRATOR: The principle of the detonator slab was very simple.

A thick crust of concrete lay above the basement.

Rather than penetrate it, a bomb would explode

and the rooms below would be shielded.

But the engineering was more complex.

If you imagine a bomb falling from maybe 15,000 feet.

It can reach a speed of 1,000 feet per second.

So that's an awful lot of kinetic energy hitting

the roof of the shelter.

So if you actually deal with that

and have a slap of some sort that

will resist that sort of impact this

is a big engineering challenge.

I'm sure a lot of trial and error

went into establishing the necessary thickness to defeat

the largest of the bombs that might be directed

at an important target.

NARRATOR: The slab was laid over a framework of steel beams cut

into the walls of the ground floor.

In complete secrecy, some 900 beams each weighing over a ton

were lifted by hand into the building.

On these beams a bed of corrugated troughs was laid.

Then six feet of liquid concrete was pumped in.

Eventually an area the size of a football field was covered.

It was exposed section of the slab,

you can see the thickness of concrete.

You can also see the troughing which supports the concrete,

and then the steel beams underneath.

NARRATOR: This enormous construction project

took 18 months to complete.

Work carried on 24 hours a day around Churchill

and his government.

And while he hated the constant banging and whistling

of the workmen, the prime minister's fascination

in their work was noted in his secretary's diary.

The PM appeared and bidding may bring a torch led me

away to look at the girders in the basement intended

to support the building.

With astonishing agility he climbed over girders, balanced

himself on their upturned edges some five feet above ground

and leapt from one to another without any sign

of undue effort.

Extraordinary in a man of almost 66

who never takes exercise of any sort.

NARRATOR: Eventually some 200 rooms

were reinforced for government use.

Of primary importance to Churchill

was the cabinet war room.

He regularly met here with his ministers

and military commanders to discuss strategy.

It was in this room that some of the greatest decisions of World

War II were made.

But none of those decisions could

have been made without up to the minute intelligence

reports which came from the map room.

This was the nerve center of the basement complex.

This is where all the information came in from all

the different theaters of war.

There were people sitting around this table who

were on to the telephone taking notes, ringing

and giving other people pieces of information.

And the whole purpose of it was that daily they

could make an assessment of the state of the war.

NARRATOR: Around a tight cluster of desks,

military staff received and passed

on the latest information from battle zones around the world.

It came in via radio, telephone, and telegraph links.

All the information that came in was plotted onto maps.

The one on the wall is the convoy map

and you can see from all the thousands of pinholes in it

where they were following all the different movements

of the ships across the different oceans.

NARRATOR: There were literally hundreds

of maps on the walls covering up to the minute land and Naval

operations across the globe.

Operating 24/7 irrespective of air raids, the map room

was Britain's eye on the world that never slept.

There was office space allocated to dozens of secretaries,

clerks, telephonists, and guards.

The cabinet war rooms could sustain the essential machinery

of government underground.

And in order to work around the clock sleeping accommodation

was provided.

Senior staff enjoyed private quarters at basement level,

but the Junior staff had to descend 20 feet further

into the dock.

This was a claustrophobic warren of rooms in the subbasement.

And it's exactly the same layout of rooms

as you had above, but you had a very much shorter headroom

as you can see from this mind your head sign.

And so people would come through here

and then go off into their dormitories.

NARRATOR: Just four feet high in places, the dock

was damp and infested with rats.

But it did at least offer a safe berth away from the bombs.

Churchill and his government now considered themselves

safe in their basement war rooms,

but there was a real danger that the Prime Minister would be cut

off from the outside world.

The intense bombing was tearing London's communication system

to shreds.

One of the first targets that an enemy tries to hit in a war

is your communications center.

If they can knock out your radio transmitter,

if they can knock out your telephone lines,

if they can knock out your telegraph,

they're going to do it.

NARRATOR: London's cables were being cut as fast as they could

be laid.

Churchill was safe in his bunker but he

knew that without communications he could not direct the war.

The remarkable tunnel system that he ordered in response

to this threat remains a state secret to this day.

One of the great secrets of Churchill's lost world

remains under central London today classified and fully

operational.

Nightly German bombing raids were tearing the city's

communication system to shreds.

This secret tunnel network was built deep underground

in response.

German bombers are trying to take out not only people.

They're trying not only to terrorize the population,

they're trying to take out the main command and control

points that link London with the rest of the world.

What's important is not only the population hold out.

It's not only important that Churchill survives,

but Britain's communications survive the blitz.

NARRATOR: If Hitler's severed London's telephone, telegraph,

and radio networks, Churchill's voice

would be cut off from the rest of the world.

The fight was on to protect the capital's communications.

London's international radio telegraph and telephone network

stemmed from the Faraday exchange,

the hub of a network of landlines

350,000 miles in length.

By securely connecting the cabinet war rooms to Faraday,

Churchill would enjoy direct communications

with his armed forces and over 70 countries among them

the United States.

But Faraday lay over two miles away and cables at street level

were vulnerable.

Churchill urgently needed a bomb proof system

to get his cables safely across the city,

and this spawned a remarkable deep level tunneling project.

Hidden under Whitehall far below unsuspecting Londoners

lies the first phase of this secret project.

Still classified and a potential terrorist target,

we can only piece together this tunnel story

from fragmentary evidence.

We're here in Trafalgar Square,

the tourist heart of London.

Down there, we have Whitehall, which

is the heart of the British government.

Under Whitehall is a tunnel, a top secret tunnel

built during the Second World War

to house and secure the government communications.

NARRATOR: C Building a two mile tunnel from Churchill's war

rooms to Faraday was beyond Britain's wartime resources.

But a shorter 800 yard tunnel was

begun between Trafalgar Square and the Houses of Parliament.

It would carry government communication cables deep

under the street.

Initial excavations 100 feet down in the clay soil

were consolidated by cast iron segments bolted into rings.

Section by section, the 12 foot diameter tunnel

progressed along Whitehall.

It was to carry a total of 40,000 government telephone

and telegraph wires toward the National Network.

Starting in late 1939, miners and engineers

protected from air raids worked day and night.

They completed the tunnel in just 18 months.

As well as cables, the large bore tunnel

provided workspace for hundreds of telecoms operators

and engineers.

But there remain the problem of the last mile and a half

to reach the Faraday exchange.

The solution the tunnel engineers found

was as simple as it was brilliant.

C We have a cable tunnel running all the way

along Whitehall from parliament to Trafalgar Square,

but that's no use unless it can talk

to the rest of the network.

In London we have a large tube network

waiting to carry cables.

It's called the London underground.

So if you can link from the communications tunnel

into the London underground, you can get pretty much anywhere.

NARRATOR: The extensive tunnels of the London underground

were perfect for connecting Churchill's communications

to the outside world.

Cables from the cabinet war rooms

fed directly into the Whitehall tunnel

where they traveled to Trafalgar Square.

There they connected with a tube tunnel heading

South under the River Thames.

At Waterloo station, they switched tunnels

and headed North again back under the river.

At Faraday telephone exchange they

surfaced in a specially constructed shaft.

This is Faraday building.

By linking across from Whitehall through the tube tunnels

to Faraday, Whitehall was now in touch with the world.

NARRATOR: But getting the cables safely across town

was not the end of the story.

The Germans understood the significance of Faraday

and targeted it heavily.

In one night in December 1940, almost 25,000 bombs

were dropped in the area.

The exchange urgently needed protection.

A bunker was planned.

But we're not talking about an underground bunker here,

we're talking in terms of a citadel,

a bomb proof citadel being built on the surface simply

to protect what was inside that building.

NARRATOR: A huge concrete fortress

began taking shape next to Faraday to house an emergency

telephone exchange.

Built above ground to save time, it

had foundations 10 feet thick with walls and roof to match.

It was windowless.

Its steel doors weighed four tons

and it was gas proof and bomb proof.

It could hold out for months under attack.

Under this formidable concrete shield,

government communications were patched into the National

Network.

They were then sent back out of the city

via the underground railroad.

The Whitehall tunnel and Faraday citadel

were immensely successful in keeping Churchill's

communication channels open.

As Britain gained allies in Russia and the United States,

this was ever more important.

But the arrival of American troops in London

brought further security risks.

In 1942, President Roosevelt since his commander, the man

who will lead Allied forces to retake Europe, General Dwight

Eisenhower here to London to run the war.

But London is one of the most dangerous places

to be on the face of the Earth.

How do you protect your commander?

There has to be a safe point that will protect Eisenhower

and his communications.

NARRATOR: A new generation of Nazi weapons

were set to flatten London.

If he was to survive and lead the allies to victory

in Europe, Eisenhower would need a different kind of bunker.

Far under central London is the deepest underground bunker

built in Britain during World War II.

This awesome bomb shelter safely housed General Eisenhower

after his arrival in Britain, and was the focal point

of Churchill's new alliance with America.

For two years Britain had fought the war on its own,

but after Pearl Harbor Churchill wanted

to build that special relationship with Roosevelt

into something which is a political and strategic plan

to defeat Germany, Japan, and Italy.

To do that, he needed to build that informal relationship

into something where he could have access to the President

day in day out.

NARRATOR: Eisenhower was the key to Britain and America

fighting a successful war as Allies.

He set up his headquarters in the shadow of the US embassy

in Grosvenor Square.

But intelligence reports in 1942 suggested

that the Allied Supreme Commander would not be safe

there.

Germany had developed lethal new rocket weapons.

Soon they would be able to release them on London.

The effect would be devastating.

The V1 one was the first of the German revenge weapons.

It was in all essence, an unguided aircraft

and used a post jet engine for propulsion.

It carried a war of around about one ton.

It was not enormously accurate, but it was well able to hit

a large target like London.

You could hear the V1 coming, which

was a distinctive nickname of the doodlebug.

It was vulnerable to being shot down by aircraft, in particular

the latest jets.

It was also vulnerable to anti-aircraft artillery.

That led directly to the development of the V2

its big brother weapon.

This only carried the same size warhead as a V1 but it's one

massive advantage was we could not hear this weapon coming.

It was launched into the stratosphere

and would re-enter after the engine had burnt out.

The first indication of a V2 attack

would be the explosion as a weapon hit the ground.

NARRATOR: The massive potential these rockets had for blast

and penetration caused great concern amongst Britain's

engineers.

They feared that London's underground shelters

were no longer safe.

One effect of detonating occurring deep in the soil

particularly in something like London clay

was that it confines the explosion

and thereby intensifies, it makes it much more powerful

than it would be if the same explosion was to take place

in the open at ground level with pulse of energy

this ground shock wave rushes out at supersonic speed

away from the center of the explosion.

So in a way London was its own worst enemy you might say.

It had soil conditions that allowed bombs

to get deep and also soil that transmitted

the effects of the explosions very efficiently.

NARRATOR: With the lethal threat of V weapons hanging overhead,

Eisenhower was provided with the first of a new generation

of ultra deep bunkers.

With rare permission to gain access,

we can reveal the full extent of Ike's London bunker.

Prewar plans to enlarge an underground station close

to the American embassy were co-opted,

and using established deep tunneling techniques

a tubular bunker was developed.

Using a pair of concrete blockhouses,

parallel shafts were dug by hand through the London clay.

c They went to a depth of 120 feet.

Small bore access tunnels were then dug away from the shafts

before two large tunnels 16 feet in diameter were constructed.

Again, the work was done by hand.

These two larger tunnels provided the main body

of the shelter.

Divided into two floors they could accommodate

as many as 8,000 people Eisenhower

took possession of his bomb proof bunker in late 1942.

60 years later, it remains off limits and just as impregnable.

It is now London's deepest and safest store

for confidential documents.

It hasn't changed since Eisenhower occupied it.

This is the lift, the lift that Dwight Eisenhower had

installed to make sure he was safe in supervising the war

effort from this bunker in London.

Not only is this one of the most central points

for communications, this is one of the deepest points

in London.

You're 120 feet underground here.

There's no way that the personnel can

be killed or captured.

This becomes the unseen command post, the unseen headquarters

for Eisenhower the rest of the American staff linking

the Americans with their British Allies.

Eight men from the 318 special service battalion

were brought here working through these tunnels.

In 29 days they put in 1,400 communication lines.

In normal conditions, three months.

In less than half that time these eight men

set up the vital link that allows Eisenhower to reach out

to Churchill and Roosevelt and establish the winning strategy.

NARRATOR: With sensitive transatlantic telephone lines

passing through his bunker, Eisenhower installed SIG Sally,

a high tech voice scrambling system to ensure

that conversations were secure.

A hot line from the White House was set up

to link Roosevelt directly with Churchill in the cabinet war

rooms.

It was disguised as Churchill's private bathroom.

Thanks to Ike's bunker the President and Prime Minister

enjoyed unbroken and secure communications on a day

to day basis.

This tunnel provides the center, the center

for what will become the unseen effort to win

the war in Europe.

NARRATOR: Ike's bunker provided a springboard

from which he orchestrated the fight back against Hitler.

After D-day, Allied forces pushed into northern France.

They captured the airfields and rocket launching sites

that had terrorized London.

From his secret underground world,

Churchill had saved Britain and with General Eisenhower led

the Allies to victory in Europe.

This Lost World has retained its mystery for 60 years.

Largely absent from the history books,

the secrets of its wartime role are only now giving themselves

up.

Who knows how much remains classified or to what extent

this world of bunkers and tunnels

was extended after the war?

With the British government facing new threats in the form

of nuclear, biological, and chemical weapons,

and the very real dangers of global terrorism,

it is likely that any further secrets under London streets

will remain buried for many years to come.