Original subtitles

- As you walk through these tunnels,

I find them to be chilling and haunting.

- Looking at these structures

as an engineer, it's just unreal.

- We can only assume that what we see

is just the tip of the iceberg.

- [Narrator] 1940, Hitler has finally

conquered a piece of Great Britain.

An archipelago in the English Channel

has fallen under German rule, land that was once

characterized by quaint, rolling English countryside

would be completely transformed by Nazi concrete.

- 20,000 tons of concrete and steel every single month.

- [Narrator] One island in particular would become

irreparably marked by Hitler's unrelenting obsession.

Transformed the isle of Guernsey

into an impregnable fortress.

- Hitler was defending an island the way

that he would attack an island.

- [Narrator] But for what purpose?

Why would the Third Reich invest so many resources

into fortifying such an insignificant island?

Was this purely an attempt at maintaining

a foothold into occupying Britain?

Or was there something else that the Nazis were protecting?

- What did Hitler have planned here?

[engaging dramatic music]

- [Narrator] Hitler sets his sights on conquering Britain.

It would be the country that would

unexpectedly pose the greatest challenge.

- England was the one country that alluded him.

They were standing alone.

The French rolled, everyone rolled.

The United States was not yet in the war.

This is the one country that was opposing him.

- [Narrator] Even under continuous attack

Britain staunchly defended her borders,

refusing to give ground or surrender.

That is with one small exception, the Channel Islands.

- Guernsey is a quaint, pastoral island

off the French coast in the English Channel, quiet, slow.

- What could be more British than

the rolling countryside of the Channel Islands?

The pubs, the winding lanes, it's

quintessential Britain at its best.

- Beautiful countryside surrounded by the seas,

the Channel Islands, and then there's these beast

concrete structures almost everywhere you look.

- You cannot visit the island of Guernsey

without seeing the Nazi footprint.

It's visible everywhere even today.

The island is filled with bunkers

and the remnants of anti-aircrafts,

machine gun pillboxes and observation towers.

This was really a Nazi stronghold.

- [Patrick] Now the island has descended

into the pinnacle of German fortress.

It's a festung in the Nazi word.

- The materials required to do that, the coordination

required to have the labor force available

to make these structures and in such a short period

of time that it's very difficult to understand

the magnitude of this operation.

- [Narrator] By June 20th the isle of Guernsey

had been partially evacuated and completely demilitarized.

Only 10 days after that the occupation began.

- Long before there was the American

shock and awe, there was blitzkrieg.

You hit them on land, sea, air, artillery,

infantry, cavalry, all at the same time.

- So the British have watched the way

that the blitzkrieg has just rolled through France

and the Low Countries like a knife through butter.

They know better.

They know this ground is worthless to the Allied cause.

- Guernsey and the Channels are symbolic but not strategic.

Yes you get a little bit closer to Britain than France

but incrementally so and it's irrelevant.

- And sadly for the Channel Islands, they were given away.

Almost as a vacuum they're left open

for the Nazis to invade.

- [Narrator] The Germans waste little time transforming

these peaceful islands into part of the German universe.

At first taking a soft power approach they install

local communities, rebuild the roads,

and amazingly switch which side they drive on.

They changed the time zone and currency,

and banned British radio as a means of introducing

German culture to the island's formerly British citizens.

- The Germans arrived on the island

and suddenly the island had gone from a democracy

to being occupied by a fascist dictatorship.

- And of course the construction work

begins almost immediately.

Hitler takes a close, personal supervision

in making sure that the transformation that happens

in Guernsey is exactly in line with his vision

for the rest of Europe and indeed the rest of the world.

- [Narrator] With little resistance Hitler now views

Guernsey as the model occupation, but his vision

for the island was more than anyone could have foreseen.

- In terms of the large fortifications built over here

the quantity that you find on this island is unbelievable.

There was in excess of 900 large structures built

and on top of that you've got all the smaller fortifications

that were built for trench-line type positions.

- Hitler saw these fortifications always

as a sign of strength, of power.

The Nazis were very into symbolism and they weren't

going to build fortifications and then take them down.

- And so for him, nothing was too much.

He wanted to make sure that the best structures

with the best engineering was available at Guernsey.

He was not willing to take any chances with building things

that would potentially crumble because of some mistake.

He was just not willing to take that chance.

- Enter Organization Todt.

- [Narrator] Just one year after the total invasion

Hitler would task Organization Todt to undertake

the building of some 200 strong points

on Guernsey, now code named Gustav.

- From the Great Wall of China to the Pyramids

the world has not seen an organization

with this kind of track record.

They're the ones that build the autobahn,

they build the Siegfried Line, they build the Atlantic Wall,

it's remarkable what this organization does.

- It is the men and more importantly the material

to build Hitler's vision for a thousand year Reich.

- This was warfare that was happening

on a huge territory right across Europe.

So to choose to implement Organization Todt

onto Guernsey meant something really, really big.

- The idea that they could build fortifications

over a 1,600 mile range from Norway to northern Spain

is unimaginable but they did it,

and they did it quickly while fighting a war.

- [Rob] Hitler's got big, big plans for this place.

- [Narrator] Hitler decides the Islands

are not adequately defended.

He orders more men, more tanks,

and more defenses to be constructed.

The island is so important that the Inspector

of Western fortresses is given direct supervision

of the island fortification and required

to provide biweekly progress reports.

- Their main concern was to do whatever Hitler wanted.

- Hitler authorizes an unlimited budget.

If you come in and you say we need X number

of tons of concrete, check we can do that.

We need X number of tons of steel, check.

And oh in Guernsey we have to ship it across the Channel

and the British Navy controls the Channel.

Oh we can do that, check.

- I'm sure they questioned whether or not all of this

was necessary but at the same time I'm also sure

they had that technological curiosity themselves.

- When we're building structures today

we want efficiency of construction.

When you look at the structures that they built

they didn't look at economy; it wasn't relevant.

Whatever it took they had to throw

everything they had at it.

- [Narrator] Hitler signed off

on all plans with the expectation

of impregnable force within just 14 months.

- And if you were gonna do that,

that kind of thing doesn't happen overnight.

- I can't imagine doing it then

without the tools we have today.

It seems unfathomable.

- [Narrator] Why would the Nazis put so much effort

into something that the British essentially abandoned?

What secrets does this island fortress hide?

And what will it tell us about the dark plans the Nazis had?

Though Germany has successfully conquered most

of Western Europe, Britain refuses to capitulate.

The blitzkrieg on England is in full swing.

In the midst a former tiny British island

is completely overhauled by the occupying Germans

to become an impregnable fortress utilizing

a stunning amount of workforce and materials.

- Having gained such a stronghold on Guernsey

you can understand installing some defensive structures

to help you defend the island,

to keep you at that stronghold.

- 65 square kilometers, you could expect

a few fortifications, a machine gun nest,

some mines, or maybe some batteries near the port.

- But to put together these defensive positions

all the way around the island, the number of troops

on there, the radar, the radio,

the communications that they had there.

- The Islands are so small and resource poor you're not

gonna use those to run the Nazi war machine

across the continent of Europe.

Strategically it makes no sense.

- And remember this is territory that is not

strategically important for the British at all.

So it just makes you wonder why Hitler needed

and felt it was so important

to his plans to keep Guernsey his.

There must've been something more.

- [Narrator] With 16,000 workers overseeing

20,000 tons of steel and concrete being poured

and erected every month Guernsey was turned

into one of the most fortified islands

on Earth in just over a year.

- It's almost like Hitler commissioned a fortress island.

- You have 12,000 German soldiers come to the island,

thousands of forced laborers come to the island,

all of a sudden it's no longer your island.

It becomes very Germanic in its feel.

- [Narrator] Organization Todt brings

in an astounding number of forced labor, over 16,000

ultimately and sets a murderous construction pace.

- [Rob] The amount of labor brought in was pretty much

one worker for every three residents.

- Forced labor was something the Nazis always relied on.

It was there M.O.; they used it everywhere.

The laborers did only what they needed to do

to stay alive and they were worked mercilessly.

The sheer workload working around the clock

despite the weather, brutal conditions.

- As part of Hitler's extreme plan for this island

and how he was gonna achieve that, that meant

20,000 tons of concrete and steel

being erected every single month.

That's roughly about how much it takes

to build, say a modern sports stadium in a big city.

- It's a huge amount of concrete and it's unrealistic

to put that on a 65 square kilometer island.

- You think about how long that takes nowadays:

you're not talking months, you're talking years.

- [Narrator] But was the fortification

of the island truly strategic or a product

of Hitler's paranoia and obsession

with holding what was once British territory?

As German bombs fall on London,

Hitler sees his model occupation

of the British Channel Islands

come under threat and he won't allow it.

- So originally when everything was going well

for Hitler he was planning to invade Britain,

but now the tide of the war is turning,

Hitler must be getting nervous.

- So Hitler must have assumed that at some point

the British are gonna come for Guernsey and take it back.

So he has to plan for that.

- What Hitler's done is turned

this island into an impregnable fortress.

You can't walk more than five meters before bumping

into some kind of armament, or some kind of fence or post.

It literally means that you've got line after line

of defense, heavy artillery, pillboxes,

MG 42 rapid fire machine guns,

soldiers all around the island,

all of them looking out waiting for the boats to come.

- And that's when he really kicks into

the next phase of his installments on Guernsey.

- [Narrator] Anticipating the British

would come back to reclaim what was once theirs

Hitler sets out to secure Guernsey's perimeter,

starting with observation towers

that would keep an eye on the horizon for imminent attack.

- All of a sudden there's these big observation towers

with these thin observation slits around them

looking like they were almost built by aliens.

Looking very futuristic, very bizarre

in terms of their shape and they're haunting therefore,

and they stand out in stark contrast to a wind-swept field,

plus the sheer size of them, and you can understand

an observation tower because you need to see

a certain radius and so you get a perimeter of the island.

But these things are massive.

- Today if our intention of those structures was just

to triangulate they'd be really skinny

very efficient structures maybe made out of steel

or something different but because these were under attack

potentially they had to be made of very thick concrete

to be able to withstand bombing and shelling.

And so the design considerations in a war scenario

were different than what we might build today.

- [Rob] The original plan was to build observation towers

around the coast of Guernsey so they'd be able to spot

and triangulate the exact position of any approaching ships.

- [Patrick] The towers are designed to work in pairs.

Soldiers positioned inside the towers spot an enemy ship

which was what the Germans feared would come.

They triangulate the position,

which gives their artillery the ability

to hit those ships with pinpoint precision.

- Triangulation is a really important tool

that they used in the war to identify

where a ship is and where it might be going.

MP3 would sight where a ship was out in the ocean

and would identify its speed and direction.

It would relay that information to MP4

which would have similar data and then you could use

very simple trigonometry and propose where that ship

may be going and how long its gonna take to get there.

- And once they triangulate to that position

that message would need to get communicated

to a command center where they could make a decision

on how they were gonna deal with it.

- These observation towers would have been

extremely fortified because the destruction

of one tower would have meant that their triangulation

would have been completely off.

- But the other thing is the communication system.

This is a rather rural, sleepy island from yesteryear.

They had to build a communication system

so they could talk to the people in the bunker,

each observation tower could talk

to the people at the coast.

So this is a very elaborate project.

- So for an island that's only 65 kilometers

six observation towers of the size that they were

would have been overkill but I think one

of the more important things we need to remember

is Hitler was defending an island

the way that he would attack an island.

- At all costs Hitler forbade giving up

the island of Guernsey and with the threat

of invasion feeling ever more real

it felt that the triangulation that was done

from the observation towers was a little bit primitive.

It didn't act fast enough.

- They realized that simply sighting off towers

in the middle of the bad weather of the Channel

is never gonna be sufficient.

- [Rob] The next phase then was to upgrade and install

stereoscopic systems which could act much

more accurately and much more time effectively

to defend against any oncoming vessels.

- [Narrator] But Hitler wasn't taking any chances.

If the enemy did end up making it up to the beaches

of Guernsey they would find themselves confronted

with a massive defensive array of minefields, barbed wire,

and trenches full of German soldiers.

- In addition to all the fortification structures

that were built you've also gotta bring in

all the weaponry and the armaments that you're gonna use,

all the ammunition that Hitler thought

would be required to defend this island.

You gotta bring that in.

You gotta get it to all the points around the island

and some of these guns, you know

it's not like they're packed down into neat little boxes

that you could pop into the back of a trailer

and head it up onto the cliffs.

These are huge guns.

The logistics again, everything about Hitler's plans

on Guernsey just seems difficult

and it feels like a problem,

but he was insistent it was gonna happen.

- [Narrator] The observations and defenses

of Hitler's fortress island all but guaranteed

the British would never drop anchor on Guernsey.

But the Germans were taking no chances with the Nazi prize.

They also kept an eye to the skies.

- What the Germans start off with

very rapidly becomes completely obsolete.

- Manual triangulation is somewhat primitive.

It requires math, it requires time, and it's speculative.

That ship could change in the course of while you're doing

your calculations and relaying information.

- But then the Germans bring in the best in the business,

the best radar system they have, the Freya system.

- On MP3 the Germans installed a Freya radar system

which was way more advanced than the radar systems

the British had at the time.

- And it had a technology called IFF

which was Identify Friend or Foe,

which allowed you to not only spot an object

but potentially tell is that an enemy or is that a friend.

- So Hitler has taken a proactive decision

to invest in Guernsey once again.

- It supposedly had a range of 100 miles.

This system could detect any ship or plane

coming in within a long radius to sound the alarm,

scramble the soldiers, get them in position,

and then as soon as the ship enters the range

of the big guns, they just start hitting 'em.

- [Rob] These Freya radar systems

are cutting edge technology.

These don't exist all around the Nazi empire.

- There's always the risk in deploying any state of the art

technology, Enigma, or the Freya radar system,

that if the defensive position is overrun

the enemy now has the technology

and what may have taken you years,

teams of scientists at a great financial burden

to develop, they can reverse engineer

and have it almost instantaneously.

Rationally one would think that every Freya radar system,

every Enigma machine, every advanced technology

needs to be along the main French coast

where you anticipate the D-Day, the Allied landing.

- [Narrator] And this is where

the German firepower gets serious.

Coordinates from range finders and radar were

to be passed Batterie Dollman, trenches, and gun pits

housing four 220 millimeter guns

each with a range of 22 kilometers.

- Whenever, wherever the British decide to attack Guernsey

Hitler intends with the Dollmann battery to be his answer,

a phenomenal firepower capability

that will blast the British ships out of the water.

- The firepower that existed on Batterie Dollmann

is quite phenomenal; it had four 220 millimeter cannons

with a range of roughly 22 kilometers each.

To put that into perspective that's

a tenth of the way to mainland Britain.

- They could control 360 degrees around the island.

Any ship or landing craft that's coming

will be under a barrage of fire.

- [Rob] There are very few ships who have guns

with the range that Batterie Dollmann had

which would have given Hitler

a huge advantage defending this island.

- When these guns fire there's a huge amount of energy

behind propelling that projectile 22 kilometers

and that force needs to be dissipated through

the base of this gun into the concrete

and into the earth surrounding it.

If that gun is not anchored down properly

to this massive concrete the energy

will be dissipated through deflection

and it could cause damage to components,

and so the structure itself is integral

to the operation of these guns.

- But it's not just big guns.

It's reinforced concrete.

There's anti-aircraft.

There's machine guns.

There's mines.

There's barbed wire and there's

a whole elaborate complex below it for ammunition,

ventilation systems, barracks for the soldiers.

This is probably one of the more formidable

batteries in all of Nazi Germany and it's on Guernsey.

- The Germans know that when the British come,

because for them it's when not if,

they'll be bringing the biggest guns they have

to bear on their destroyers and on their landing craft.

So the Germans have to bring the best answer

they have to that, well they brought it.

- Were those structures built to last?

Hitler not only wants to keep this as a strategic

as part of his of propaganda, we're on British soil,

it was also part of a much longer term plan

and part of his vision of a one thousand year Reich.

So maybe that end goal is the reason

why so much happened so quickly.

- [Presenter] But Batterie Dollmann was just the beginning.

The Germans had far more firepower in store

for anyone who dared cross into Guernsey airspace or waters

and as the war effort continued Hitler would even

start to move his defenses underground.

Hitler has created an island fortress out of Guernsey.

He pours more resources proportionally

on the small, sleepy island of no strategic importance

than almost anywhere else on the Atlantic Wall.

The Germans have brought in massive guns,

built fearsome bunkers and towers,

and installed state of the art radar,

but nothing seems more mysterious

than the vast tunneling underground.

- As the war progresses the British and the Allies

make two attempts to hit mainland Europe,

key German fortifications, most notably at Dieppe.

That gives the Germans every reason to believe

that the next site they're gonna come for is Guernsey.

- Hermann Goering, the head of the Luftwaffe

boasts that the Nazis will control the skies.

That never happened.

The Allies controlled the skies through much of the war.

So Hitler and the Nazis know they're gonna get bombed.

So what's the answer? Tunnel.

- Hitler decided to go underground because

he wanted to make sure that his troops were protected

from any air fire, or from any ships

that would have come too close to the island

that could have possibly been undetected.

- So he orders that this enormous complex

of underground tunnels and bunker systems are built.

He builds 29 tunnels and down there he had

munition stores, he had hospitals built down there,

he had its own water reservoir, its own water supply.

By taking your defensive operation underground

you're protecting with the earth above you

your troops, your munition stores, your command

or your senior command that you'd have on the island there.

- So these are self-contained units that can fight

even if another unit that is supposed

to be reinforcing it or supporting it is overrun.

- This underground maze is almost

like an island within an island.

It is quite literally humming and thriving with life.

- When you're considering tunnels today

we try to limit our earthworks.

We don't want to build tunnels if we don't have to

because they're costly, and they're dangerous,

and penetrating the earth is a science in and of itself.

When you look at the scale of the tunnels

at Guernsey island, it's massive.

There was major intent behind these tunnels.

They were building a city.

They were building a habitat under the earth.

Trying to fathom why they would have gone 75 feet

underground, I can't see a reason to go that deep,

Even if you went 10 feet underground you would be covered.

- [Narrator] Organization Todt put thousands to work.

Digging, laying explosives, and carving out earth.

Forced workers from Eastern Europe were brought in

along with conscripted labor to build

an underground fortress on Guernsey.

- Constructing a network of tunnels that big

is no mean feat of engineering.

- Mining is a really dangerous undertaking.

We have a lot of technology today

that helps us mine safely.

Back in the war these efforts were not well developed

and you could tell by these fortifications

that life expenditure was not a concern

for Hitler and the team, building these tunnels

80 feet underground potentially is a difficult task.

But when you tunnel through the earth you need

to create structure to sustain

the loads imposed by the earth above the tunnels.

We use shapes such as arches or circles

which are very strong shapes

when they have a pressure applied on all sides

and then they would have to build formwork

against the tunnel back and walls

and then they would have to pour concrete

and let that concrete set up before

using these tunnels for their intended usage.

It is a very inefficient mode of construction.

It's very slow, it's painstaking,

and it's very dangerous.

- But each one of these bunkers was designed

to be a self-contained unit.

- They would have had to have their own separate systems

in order to support their troops.

They would have had to have their own septic system,

their own communication system.

The ventilation system in these tunnels

was quite sophisticated, not only to make sure

that the workers would have had enough

to continue their jobs but also

that once the construction was completed

that the troops that were expected

to live down there and survive down there had enough oxygen

to breathe and to maintain their condition.

There were also gas detection systems so that if

too much gas accumulated in one location

it could easily shut off certain sections

of the tunnel to exhaust those areas.

- There are so many variables to consider

when you bring construction underground

that the problems increase tenfold.

- [Narrator] Overall 244,000 cubic meters of rock

excavated out of all the Channel Islands,

only a little less than the total 255,000 cubic meters

of earth excavated for the rest of the Atlantic Wall.

- This is no skin deep trench system.

This is highly designed, highly considered,

highly well-thought underground maze.

The amount of earth that the Germans were prepared

to dig out means that the entire island rises

because they have to put it somewhere.

- We're talking about several kilometers of tunnels.

That is a lot of excavated material.

Planning for that and where is it gonna go,

and what are you gonna do with it, that's another problem.

The island's essentially growing.

Were displacing material underground

and bringing it to the surface and altering the landscape.

- The funny thing for me about these tunnels

is that they weren't necessarily joining

all of the locations above ground.

This was effectively its own

self contained underground city

and you don't go to those kind of lengths

unless you're planning on staying.

- [Narrator] 16 of 29 planned tunnels were completed

before Organization Todt workers were sent

to fortify other areas of the Atlantic Wall.

They left behind miles of tunnels, a city underground,

what nefarious plans did Hitler have for these tunnels?

And who did he imagine would stay so long underground?

Were the tunnels merely intended to guard against

Allied bombing or did Hitler have plans

for these tunnels after the war?

- As you walk through these tunnels

and think Nazi soldiers were living here several decades ago

I find them to be chilling and haunting.

- It's really quite spectacular when you think

that the preparations and the work

on these tunnels went on for three and a half years

even as it became clear, surely even to Hitler himself

that this island was no longer important.

It was only when the workers were pulled away

from the island to go back to Europe

that the work finally stopped.

- [Rejeanne] These tunnels are almost 80 years old

and the fact that they're still standing

could be an indication as to just

how superiorly they were built.

- Hitler had intended Guernsey to be

part of his shiksha and his destiny,

but that wasn't having to be done.

In fact the tunnels were eventually used

just to house injured soldiers.

- When I think about why would you go to that effort

to take something underground,

to build a city and shelter for people underground.

It can't be spotted from above,

that is shrouded in secrecy,

that stems from danger really, and fear.

- [Narrator] If Hitler wanted a propaganda tool

Guernsey was it but then why continue to fortify it?

- There must be something bigger going on here.

- [Narrator] If propaganda isn't the main reason

for Hitler's island madness what is and why go underground?

The Germans have constructed a massive fortress

out of a quaint island in the British Channel

fully anticipating English forces

to come storming back for their territory.

With eyes to the sea and skies around Guernsey

the Germans watched and waited for enemy attack.

With a coordinated system of locating

and tracking enemy boats and planes

Hitler arms the isle of Guernsey to the teeth.

- There were 11 batteries installed around Guernsey,

each with guns bigger than the last,

but the most fearsome, the most intense of them all

was Batterie Mirus right in the center of the island.

- So the size of these guns that were at Mirus,

which is about the largest battery in all

of Nazi Germany's defensive system,

the range of these guns is over a 1000 football fields.

- Mirus, essentially has the distance of the entire island.

It's very clear that Hitler was taking

absolutely no chances with Guernsey.

He's placed four of the biggest guns he can bring to bear on

the island ready to repel the British attack when it comes.

- [Narrator] But why place a gun battery

so far from the coast?

How do you defend an island from the inside?

With the biggest guns you can get your hands on,

four fearsome gun pits make up Batterie Mirus.

- And they were all manned by 72 soldiers.

That is a heck of a lot of effort for just one gun.

- You need a massive crew to fire these kinds of guns.

You need the support systems

in terms of communication, observation.

- [Narrator] Each gun could turn 360 degrees

and cover a 50 kilometer range.

- With a range of 50 kilometers per gun

Mirus essentially has the distance of the entire island.

- The drawback is how on Earth

did they get 'em to the island?

- Four Russian cannons were captured from the Finns.

They were brought back to Germany

where they had new bases installed on them.

The guns were then transported from Germany

to Saint-Malo via railroad where they were then

lifted and put onto barges using 100 ton cranes.

- Those barges also needed to sustain this load

and they're traveling across the Channel

which is susceptible to storms and weather.

When they arrive at Guernsey island that port

was not likely equipped to deal with these large loads.

They probably had to build another gantry train there

to lift these cannons off of the barges and onto a skiff.

This skiff apparently moved at eight kilometers

an hour, which is very slow.

The skiff had to travel over land

all the way to the battery.

Once they had the cannons at the site they were again

lifted into place and set on their foundations.

- So just to place the guns involved

an entire engineering marvel, a logistical feat.

- That is a really big journey for cannons.

That is a lot of people involved,

a lot of equipment, and a lot of planning.

- I mean the sheer operation to bring these guns

into place is, it's gargantuan.

- All of the logistics around the guns

and the battery itself, the materials

that were acquired to build that,

the cranes, the logistics, the infrastructure,

none of that's native to Guernsey.

All of this has had to been installed

by the Nazis at some point.

- When you think about the magnitude of effort

to bring these cannons to the batteries,

to build these batteries in the first place,

Hitler is not gonna give up this island.

There is so much invested here.

He wants to keep this island and I don't know why.

- I think what a lot of the structures say

about the Nazi Reich is something

that was very important to them which was propaganda.

- It was part of that power that

they wanted to exercise over the world.

- How they made their presence known to all around.

- It's very clear that their investment

in defending Guernsey is absolutely critical.

- [Narrator] After a tremendously long journey

the guns are lowered into four 21 meter concrete pits.

Behind each pit a 31 by 31 meter bunker

containing shell cartridge and fuel storage,

accommodation for 72 men, and a ventilation system.

The walls were made of reinforced concrete two meters thick.

The gun itself was 15.8 meters long and was mounted

on an armored turret that could rotate 360 degrees.

- You don't want to be even possibly thinking

of approaching that kind of battery

because quite frankly any ship and as well as any aircraft

would have been completely annihilated.

- Just about every naval gun that existed at the time

would be in range of these guns.

So there's no sitting off the coast comfortably

as the shells of your opponent fall harmlessly

into the water; you would come under assault.

- [Patrick] You don't just do this for

your typical bunker or your typical fortification.

- The Nazis fortified almost every place they took

'cause they intended it to be a permanent occupation.

- Something about this island is absolutely critical

to Germany's war effort and Germany's war vision.

- [Narrator] Test runs of the guns

were captured on film and sent back

to Germany for use in German propaganda.

Hitler reveled in the optics.

Guns so powerful they caused windows

and greenhouses in the area to shatter.

- That's the kind of power Hitler had installed on Guernsey.

- And Hitler loved this.

He loved to use that footage as propaganda

to help to show exactly how powerful he was

to the soldiers that he was training

as well as to the rest of the world.

- [Narrator] If the war was almost lost

and supplies limited this island

was no longer remotely important.

Yet even then Hitler forbaded surrender at any cost.

Why?

By 1943 Hitler, the Organization Todt,

and 12,000 German soldiers had transformed

the rugged isle of Guernsey into an impregnable fortress.

Batteries and observation towers guarded

the island's coast as the forced workers

dug a complex of tunnels deep into the the island's core,

but the Germans left one thing above ground

until well into the war, the one thing they overlooked.

- You know in the early days of the blitzkrieg

the Germans were absolutely overwhelmed with confidence.

They've had it so easy.

So when they initially arrived they set up

their communications in the La Collinette Hotel.

Previously it had been the plaything for British tourists.

Now it's the center of German activity

and military activity on the island.

- Prior to the war La Collinette Hotel

was a nice little getaway for the British

to come over and get some Channel Island sun

for the weekend perhaps and actually not much

of that changed when the Germans first moved in.

It was all still quite quaint in there

but now it was their communications

and command center for the whole of the island.

- But if the Battle of Britain teaches the Germans anything

it's how vulnerable ground radar systems

and communication systems are to air attack and bombing.

They just proved it to the RAF during the Battle of Britain.

Once the Nazis felt La Collinette was more vulnerable

they moved their command center underground

into a bunker that they built especially for it,

but this wasn't any kind of bunker.

- [Narrator] Hidden away in a secret bunker

was the entire Naval Command.

- The importance of this bunker is once again

portrayed by what technology they had down there.

This was state of the art.

They could communicate directly with Berlin

or Paris and they had Enigma machines

that were programmed with their own codes

specifically for the Channel Islands.

- [Patrick] The Naval HQ on Guernsey becomes absolutely

critical to the German's ability to wage war,

U-boat war on the Allies and on Britain itself.

It's the primary mechanism by which Hitler

intends to strangle the British islands.

- This bunker was the center for all the information

coming in from the U-boats in the English Channel,

from the observation towers above

and it was communicating directly with Berlin

even after Paris and France had fallen.

- [Narrator] By 1942 the Americans

had declared war on Germany and were well

on their way to support the British.

An Eastern front had opened after Germany

had provoked their former ally Russia.

Meanwhile on Guernsey the headquarters

connecting Hitler to the Islands

remained vulnerable above ground.

Things were changing.

In 1943 work began on a bunker to house a new HQ.

The communication equipment would move less than a mile

to a bunker built on the grounds of the hotel.

- Organization Todt was once again called upon

to oversee the building of this secret hi-tech bunker.

This bunker's absolutely critical.

- The Organization Todt need to get this right.

So they bring in two industrial, enormous concrete mixers

to pour the concrete for a communications center,

a generator, and a command HQ bunker.

- The bunker consisted of three separate rooms or chambers.

One was the communications room.

A separate room to generate its own power from and thirdly

there were the barracks to house the high command.

- [Narrator] The communications coming into HQ

from Berlin and France became more and more desperate.

As the Americans joined in the war

and a second front developed, Hitler's high command

began to whisper about his island madness.

- Hitler and the Nazis knew the Allies were coming.

From '43 on they were preparing for the invasion.

Here's an irony: they never finished

all the gun casements at the site of D-Day,

but they finished all the gun casements at Guernsey.

That makes no sense.

- In his mind Hitler must have had a bigger,

more important plan for Guernsey and the Channel Islands

because if you think about in the context

of everything else that's going on it makes no sense

to put so much effort into keeping that stronghold.

- Oh Hitler got a lot of opposition initially

from a lot of his generals when some still felt

like they might be able to speak their mind.

- And within Hitler's own high command there begin

to be whispers and murmurings about Hitler's island madness,

why he's keeping such an interest on this small island.

- In 1941 he was already issuing orders

to heavily fortify and defend the Islands,

way before any of the work was ever done

on the Atlantic Wall and the rest of mainland France

and extending up to the northern reaches of Norway.

We can see that that interest stemmed from very early days

and even when the Germans were preparing to invade Russia

they were at that point withdrawing artillery units

which had been designated to attack Russia

and actually bringing those artillery units

to Guernsey, and Jersey, and Alderney, to defend the Islands

and the German army high command were like

we need these units, why are they being sent here?

- But toward the end of the war things did change,

In one respect they started to run out of food.

Guernsey is a small relatively resource poor island.

So everything had to be shipped in,

coal, fuel, food, but the British

still control the seas and the Germany Navy,

the Kriegsmarine was defeated.

So by the end Germany's having

a rough time resupplying Guernsey.

They are running out of food.

German soldiers are starving.

The local islanders are starving.

German soldiers were antsy

probably anticipating an invasion.

They heard about D-Day and people started to turn

on one another and it got a little dicey toward the end.

- By 1943 it's clear to most of Hitler's sane generals

that there's absolutely no reason to continue

to pour so much material, so much energy into these Islands.

That begs the question why is Hitler

so obsessed with the island of Guernsey?

- [Narrator] The tides of the war had turned.

German troops battened down the hatches

and waited for news from Paris and Berlin.

In the coming months and even after it had become

clear the Germans had lost the war,

Hitler would hold onto this island with everything he had.

All of this for 65 square kilometers of farmland.

Hitler's island madness has transformed

a small island in the British Channel

to a monstrous fortress bristling with armament.

In less than five years the island has been fortified

using 616,000 cubic meters of steel and concrete,

about 10% of the materials used in the entire Atlantic Wall.

Observation towers and 11 batteries guard

the Guernsey coastlines and Enigma machines

sending coded messages to nearby U-boats,

other Channel Islands, and Berlin.

After the war when deported islanders returned

to their island home they'll find it marred

by evidence of Hitler's mania.

It's a far cry from the quaint island in the British Channel

whose economy was based on tomatoes and tourism.

- The invasion Hitler feared for

so long actually never came.

Even on D-Day the Channel Islands were completely bypassed,

flown over, the boats circumnavigated it.

- As the war progressed and the tides turned

for the Germans they continued

to pour resources into Guernsey island which seems strange.

There were so many fronts that needed attention

and the resources required here were substantial.

- And the irony is that Guernsey's never invaded.

It never plays a role in World War II.

It becomes almost an afterthought.

It's folly.

- These enormous artillery pieces,

these heavy rapid fire machine guns,

they're all whispering in the wind.

They're all standing silent because the Allies don't come.

Hitler got it wrong.

Instead he leaves over 12,000 soldiers trapped on the island

bypassed when the Allies make their move on Normandy.

- Hitler's madness about Guernsey, his obsession

led in part to the Nazi undoing at D-Day.

More defenses should've been built along the French coast

proper rather than on a tiny island offshore.

- When supply lines were cut off from Guernsey

and the troops and the residents

were starving on the Islands, even then

Hitler insisted that it be defended.

- If Hitler had not been so obsessed with Guernsey

and if had put the emphasis, the amount of guns,

construction, time, and energy, and soldiers from Guernsey

at Normandy you would have had 12,000 more soldiers,

dozens and dozens more massive guns, bunkers, mines,

so by him focusing so much on Guernsey it helped us

to take D-Day in a little less bloody way.

- [Narrator] Was Hitler's refusal to give up the Islands

lunacy from a mad dictator in decline?

What dream was he desperately clinging to?

- Guernsey remains a mystery.

There is no rational or good explanation why Hitler devoted

so many resources to this tiny, insignificant island.

- Even today when you see what's left of the fortifications

that were installed on Guernsey, the way there were designed

and built tells you that this was not just a temporary

defensive mechanism that Hitler wanted to install.

Hitler had intended Guernsey to become

an impenetrable fortress, the vanguard

of his thousand year Reich.

- Thankfully that never actually materialized.

- Instead it became a slowly corroding

testament to his island madness,

the only time that he got a foothold on British soil.

- And to the bitter end though it was in Nazi hands.

- [Narrator] Though Guernsey would eventually

be given up without a fight, Hitler

would not live to see its surrender.

10 days after Hitler took a fatal dose of cyanide

and a full 24 hours after HQ got the message

the war was over German forces surrendered

aboard the HMS Bulldog in St. Peter Port.

But what if the war had gone the other way?

If the Channel Islands had been only the beginning

in Germany's occupation of British territory?

What would have become of Pleinmont, Mirus,

and all these underground structures?

We may never know what dark

plans the Nazis had for Guernsey.

Was it a toehold on his enemy's land

that Hitler simply refused to give up at all costs?

Was it part of a longer term strategic plan

we haven't been able to unearth?

Those secrets lie buried under decaying structures,

symptoms of a terrifying dream and dark time.

[dark engaging music]