All language subtitles for Nazi War Machines Secrets Uncovered S01x2

I'm James Holland, and one of the things
that's always really fascinated me

about the Second World War is the
interplay between man and machine.

In this series, I'm going to go inside
the Nazi war machine.

Travelling across Europe, I'll explore
the extraordinary machines they produced

and uncover rare archives to understand
who built them, how they evolved, and

why they're technically brilliant
designs.

were militarily flawed.

The magnificent fighter planes no rookie
could fly.

You know, the first time you fly a
Messerschmitt 109, you just have to take

leap of faith.

The power of the panthers. If I had come
up against this, I would have been

terrified. But I'm about to learn one of
the biggest cons of them all.

The weapons that couldn't cope with mud
or sand.

Wow. It's got... So little kick on it.
And you hit the target, I'm proud about

you.

The U -boat that were floating bomb.

That was a suicide command.

Absolute horror.

A journey through the heart of the Nazi
war machine.

In this episode, I'll be going to the
depths of the Wolf Packs, Germany's U

-boat arm, a force that threatened
Britain's survival like no other.

I'll be seeking out what made them such
a menace.

The U -boat armies could have just
wreaked havoc with the Allies.

They did play havoc.

And I'll be exploring the extraordinary
and game -changing submarine, the Type

21. We are not talking about evolution
anymore. That's a revolution.

And how they held the key to the outcome
of World War II.

At the start of the Second World War,
Britain ruled the wave.

The Royal Navy was the largest and most
powerful seaborne force in the world,

built to protect its empire and to
defend its nation.

It was a power Adolf Hitler

had to defeat if he had any chance of
winning the war.

And there was only one way to do it.

Britain is an island nation, and it's
almost entirely dependent on supplies

coming from across the sea.

If you manage to cut that supply line,
then you've won the war.

That, at least, was the strategy being
pushed by Adolf Hitler's U -boat chief,

Vice Admiral Karl Dönitz.

A U -boat commander in the First World
War, Dönitz knew firsthand how even a

small fleet of submarines could land a
killer blow against the Allies' vital

supply line.

But Hitler doesn't really seem to
understand this. You know, he's a

continentalist. He's a landlubber. And
this is because Germany is stuck in the

centre of Europe. It does have a
coastline, but it's very small.

And the German way of war
traditionally... has been to fight on

overwhelming firepower at the point of
impact.

Germany has developed blitz warfare,
mechanized warfare, armies on wheels,

juggernauts to crush everything before
them. Come the start of the Second World

War, this is how Hitler intends to do it
again, using firepower and burgeoning

air power to do the hard yards.

Sea power is something he just doesn't
really get.

His notion of a navy was a grandiose
fleet of massive battleships that could

take on the Royal Navy on the high seas.

After all, where's the fun in launching
U -boats when it could be smashing

champagne bottles against giant
battleships?

By the outbreak of war, Dönitz U -boat
fleet was woefully small.

Just 62 vessels and a mere 3 ,000 men.

This beast was the backbone of the
fleet, a Type 7C, and it's the first

going to look at in some detail.

The Type 7s were based on First World
War designs and built in shipyards in

Bremen and Kiel.

Unlike its predecessors... It carried
new sonar equipment, which greatly

improved its ability to search out enemy
shipping.

It was a medium -range combat submarine,
61 .7 meters in length and 6 .2 meters

wide, and carried a crew of 44.

Powered by two 1 ,400 -horsepower diesel
engines, backed up by a couple of

electric motors, it was armed with five
torpedo tubes and a variety of top

-mounted flak guns and cannons.

It could travel at 17 knots on the
surface, but little more than walking

when submerged.

This one is U -boat 995, now permanently
berthed in the Baltic port of Labu in

Germany.

I'm on board to get a sense of the
impact of this vessel on the war, and

was like to be at sea on the Type 7.

Oh, this is a bit of a tight squeeze.

You know, I'm really not sure how much
I'd have fancied going to sleep with a

massive great torpedo above my head.

It makes you realise just how cramped
these Type 7 U -boats were. You know, it

was a terrible place in which to exist.

Lots of men on top of one another.

hardly any fresh water, so you couldn't
shave, you had to grow a beard, and

you'd be away for weeks at a time. The
smell on this place must have been

absolutely horrendous.

Sweat, oil, rotten food, a really
physically incredibly tough

environment in which to live and try and
fight a war.

The U -boats lie in waiting.

Four, five and six of them together.

Working in flotillas.

Operating in wolf packs, the U -boats
targeted Britain's lifeline.

The merchant ships supplying goods and
materials from the United States and

Britain's colonies around the world. If
we cannot bomb them out, then we will

starve them out.

The wolf packs were staggeringly
successful.

Between July and October 1940,

The U -boats alone tanked nearly 1 .5
million tons of shipping.

They will stalk a convoy for days at a
stretch, fighting their time until the

chance of wind and weather offers the
fattest prize to their torpedoes.

This was a mammoth achievement, which
cemented the U -boat's reputation as the

undetected superweapon the Allies
desperately needed to destroy.

This is their song.

We're sailing against England.

For Admiral Karl Dönitz, using his crews
to starve Britain into submission

remained the key to winning the war.

But without Hitler's full backing, he
had a problem.

He didn't have enough boats, and he
didn't have enough men.

To help me understand Hitler's failure
to grasp the potential of the U -boat,

I've been joined in U -boat 995 by the
historian of the German Navy

Dr Jan Witt.

One of the things I find just so
extraordinary is, because Britain's an

nation, everything, everything it needs
for war has to come through the

Atlantic. So if you can stop those
supply lines, you're well ahead of the

So why is it...

that Germany starts the war with a U
-boat arm which is just 3 ,000 men

Very simple to answer, because only in
the early 1930s they started to build

up, at first in secret, then also
openly.

But it takes a long time to build up a
new U -boat arm

from scratch.

And so they could only reckon that these
U -boats would be available in late

1940, early 1941.

So you have always this kind of delay.

But as Hitler is very, very aware, you
know, the whole German way of war is to

fight wars very quickly and get them
over and done with because they can't

sustain a long war. Well, you name the
problem.

Hitler wasn't thinking in maritime
terms.

He followed straight away a land -based
strategy.

So, if you bring it to a nutshell, the
Second World War was a maritime war.

The decisive battle fleet was the
Atlantic. This was something that Hitler

understood fully.

Had Hitler prioritized the creation of a
large U -boat fleet before the war,

there's every chance he'd have won.

There's a basic rule of supply and
demand for any fighting fleet. Have one

of your vessels on combat patrol, one
third traveling to or from patrol, and

third at base on training, maintenance
and repair.

This meant that throughout all of 1940,
there were never more than 14 U -boats

on patrol in the Atlantic at any one
time.

And that was simply not enough to win
the war.

One of the many triumphs of Nazi
propaganda was to convince the world

Wolf Pact roamed the seas at will, but
their limitations were soon to be

exposed.

These were not, in fact, submarines as
we understand them now, but

essentially surface vessels with the
capacity to die for a very limited

of time, a matter of a couple of hours
before they had to come up for air.

As Allied anti -submarine technology
swiftly improved, so losses of both

and men increased.

Admiral Dönitz was finding he just
didn't have enough trained and

crews to replace them.

First thing that strikes me is there's a
heck of a lot of wires and

dials and turning handles and so on. The
training for this must be enormous.

Yes, it needs up to six months to train
a U -boat crew because everyone on board

has to be fit with all these kind of
handle and rules so they know what to do

just a case of emergency.

If you have only an expert in the diving
process and he gets killed or injured,

you have a severe problem, especially
when you're submerged.

So they took care that anyone on board
knew how to handle the diving process.

The gruelling training and long voyages
built a powerful esprit de corps among

the crew, from the newest recruit to the
commander.

Just think about the men that are...

taking command of these U -boats by the
middle stages of the war.

The average age of a crew member is
about 20 years old.

Think of the awesome responsibility on
their shoulders.

You're out at sea for up to weeks on
end, on your own, and you are in

The decisions you make are literally...

a matter of life and death. No matter
what you think about the Second World

and the part that Nazi Germany played in
it, you cannot help but have an

enormous amount of respect for the young
men that were commanding these U

-boats.

The Battle of the Atlantic exposed the
limitations of the Type 7 U -boat.

There were simply not enough of them to
destroy the Atlantic merchant convoys,

and the superiority of Allied air power
and radar technology made them much

easier to detect.

The pilots have at their beck and call
the swift and deadly destroyer escort,

packing a murderous wallop in her gun.

To make

matters

worse, by May 1943, Hitler was facing a
new threat.

The victory in the Battle of the
Atlantic meant that the Royal Navy could

from defence to attack along the
extended coastline of Nazi -occupied

The German Navy had to come up with a
new plan.

Trouble was, was how to deal with the
mass of Allied shipping that was going

be crossing the Channel.

You know, it was going to be very
crowded, very congested waters.

They didn't want lots of large -scale
submarines. What they wanted was

that had comparatively small range.

but was small, very hard to detect, and
which could maneuver very easily and get

close to enemy shipping and sink it. And
this was the birth of the midget

submarine.

This 1945 American documentary takes up
the story.

The development of the midget submarine
by the Germans is another chapter in the

story of sneak craft attack.

The first to be developed was the one
-man MOLK.

It was not very successful.

Its range was limited, and it was slow
and cumbersome.

After two 15 -boat sorties, in which all
craft were lost, she was abandoned.

Her successor was the streamlined
beaver, which sacrificed strength for

The beaver, or beaver, had one pilot and
was equipped with two torpedoes.

It was just seven metres in length and
weighed three tonnes.

Powered by an Opel truck motor for
service travel, it had a battery

electric motor when underwater.

Work on the first prototype began in
February 1944 and was completed in less

than six weeks.

It then underwent a mere two weeks of
testing before it was accepted into

service.

was still small enough to be launched
and maintained at quickly constructed

strategic points.

These midget subs were soon to prove
more dangerous to their crews than the

enemy.

To find out just what the thinking was
behind these extraordinarily dangerous

machines, I'm going to the Technic
Museum in Spreyer, just south of

I'm meeting up with a former submarine
radio officer, Ulrich Zorn of the German

U -Boat Association.

I mean, I can only imagine what it must
be like having to set sail in one of

these with a torpedo strapped to you.
Alone.

Yes, I mean, that's horrendous. And
anxious, I think. And how long would you

expected to stay in that?

Two days?

One day? Two days, three days, up to
four days were the beavers too.

The beavers had many losses.

Did they? What was the percentage loss?

One says 69%, others say more than 70%,
75%.

And what were the problems?

Demonship, material damages.

Right.

So were they not particularly well
constructed?

They were constructed at the end of the
war.

So it's cheap.

And at the end of the war, they had less
material.

They had problems with training for the
crew. Right. So you're sending an under

-trained individual, one man, in a
vessel, which frankly isn't as good as

might be. Yeah.

And so put that together.

For example, the engine in the Beaver
was a normal petrol motor.

He has problems with explosives, and you
have carbon monoxide, and lots of crews

died by carbon monoxide poisoning.

Oh, my God.

In 15 sorties using 163 Beavers, 53 of
them,

almost a third, failed to return.

Weber was being used as a stopgap until
the new midget sub, Seehund, was ready.

At just 12 metres long and weighing 15
tonnes, the Seehund was the largest of

the lot.

Equipped with a diesel engine and an
electric motor, it was both fast and

to manoeuvre.

It carried two torpedoes flung either
side of the hull.

and was the most successful of all the
midget submarines, sinking some 90 ,000

tons of enemy shipping.

The Zeehund had a crew of two, a
commanding officer and a leading

We're sitting in front of a Zeehund.

It's a pretty small submarine, and it's
just horrendous conditions on it. You

could say horror conditions.

There were two men living in the boat.
Right. A commanding officer.

and his engine officer.

He fired the torpedoes at command, and
the fish slipped off the track on its

to the target.

They only had two wooden seats.

They had no heating inside the boat. The
other problem was the meals.

They only had a small electric cooker.

Inside? Inside. They had no toilet in
the boat, so they got special low

-fiber meals on the boat for 10 days
maximum.

So you would stay up for 10 days. Yeah,
they could stay up to 10 days. If they

had to do... Had to do their business.
They put their feces into small tin

containers. And when they surf it, they
threw it outside the boat. There was a

horrific smell in that boat. Yeah, yeah.
They didn't get real sleep.

You can't sleep on that, can you?
Because you've got to control the whole

the whole time.

Yeah, and so they got trucks.

During the war, it was fairly common
practice for both the Allies and Nazi

Germany to use drugs to enhance the
performance of their front -line troops.

Mainly, these were amphetamines and
methamphetamines, although the Nazis

actually curtailed their use before the
Allies did.

What's really strange, then, is that
towards the end of the war, it is the

Kriegsmarine who are starting to
reintroduce these drugs, and not just

methamphetamines, which, after all, is
crystal meth.

but cocktails of methamphetamines with
pure cocaine and other drugs beside.

And they were carrying out experiments
with these drugs on prisoners at

Sachsenhausen concentration camp.

Then having done that, then issuing them
to the crews of these midget

submarines. When you're talking about
clutching at straws, I mean, these were

really desperate measures.

The last of these so -called submarines
was probably the most dangerous of the

lot. A German human torpedo.

The operator enters the control torpedo,
which is actually a standard 21 -inch

German torpedo minus the warhead.

This floating bomb had several
variations.

The Negev and the Martin.

At its simplest, it was a one -man
torpedo with the pilot sitting at the

in a plexiglass bubble.

The real torpedo, the child, was slung
below the mother.

She carried it to within close firing
range of the target.

But the pilot couldn't see underwater
well enough to make an attack, so he had

to surface to get within firing range.

These vessels were to prove more
terrifying for the pilot than for the

The first ones beached harmlessly.

They were the subject of more curiosity
than alarm.

Later models of the Martin, like the one
at the Technic Museum, replaced the

plexiglass bubble with a more
substantial diving belt.

Here we are in front of a Martin. The
Martin was called a one -man torpedo.

That's just mad, isn't it?

I mean, you can imagine, again, what you
must be feeling like going off of that.

I mean, the controls you've got
presumably are quite limited.

Yeah. You had only a small lever, like
in a plane cockpit.

Right. The low silhouette of the craft
running awash with only the dome visible

made the run -in on a dark night
relatively easy.

But once he had fired his torpedo and
his presence was known, he was quite

helpless against counterattack.

I don't understand it. Quite often the
mechanism by which you detached yourself

from the torpedo didn't work. Yeah. So
you ended up hurtling off with the

torpedo and effectively becoming a
kamikaze bomber. Yeah.

Normally the pilot jumped out of the
torpedo.

They had equipment like combat diver
equipment, rubber suit, closed circuit

breathing system. Right, right, right.
But you still had to be picked up,

Yeah, yeah. Hope getting picked up, for
example, mine searching units.

Are most of these operations at night?

Yeah, yeah. So the chances of you being
spotted and found on the sea at night?

Zero. Wow.

The losses sustained in these inhumane
vessels were immense.

The average age of a Martin pilot was
19.

some 60 % of them were lost.

Another of Adolf's surprises, a human
torpedo was driven ashore near Anzio.

His one -man crew, a 17 -year -old
Kriegsmarine, a six -month veteran, is

and defiant.

But that didn't stop the Nazis training
up the next generation of would -be

suicide submariners.

Well,

as a submariner yourself, you would
never have wanted to be in one of these,

would you?

For me, that would be absolute horror.

That's not... Right.

Me going on a submarine, for me, that
was a suicide command.

Yeah.

Richard's submarines were a desperate
attempt to disrupt the cross -channel

invasion. But if they had any chance of
winning the war, they needed to disrupt

the Atlantic sea lanes.

And for that, they needed something much
bigger, much more revolutionary.

Something that could change the fate of
the war.

With the war entering its final phase,
It was clear the days of the Type 7 U

-boats as an effective fighting force
were over.

The Nazi is forced to the surface.

Immediately a torrent of gunfire has
turned on the triple sub.

It is doomed.

The terrible death toll and loss of
vessels have made it nigh on impossible

Admiral Dernis to fight on.

This is the Laboue Naval Memorial.

Built in 1936 to remember those U -boat
crews and sailors lost in World War I.

It's now been expanded to include all
who died in both World Wars.

Inside, a mural is devoted to every
vessel lost by the Kriegsmarine.

By the beginning of 1943, Admiral
Durnett at last had the numbers of U

he'd wanted.

But his young and inexperienced crews
were going to pay a terrible price

they were still using the same U -boats
they'd been using at the beginning of

the war and simply hadn't kept pace at
all with the technological advancements

of the Allies.

The hunters had become the hunted.

Only the introduction of a revolutionary
new vessel could possibly give the

Kriegsmarine a chance to turn the tide
in the war at sea.

They needed a submarine that could
change the face of the war.

This is U -boat 2540, the Wilhelm Bauer,
docked in the museum harbour in

Bremerhaven.

It's a Type 21.

And it's a vessel I've long wanted to
see for myself.

It's the only surviving example of what,
to my mind, was one of the most

brilliant military designs to have
emerged during the Nazi era.

In order to try and understand the
impact this machine was to have on the

of submarine warfare, I'm now on board
with naval architect Alexey Konovalov.

I'm just really interested about what a
leap forward the Type 21 was.

We are not talking about evolution
anymore.

It's a revolution.

For the first time, the submarine was
optimized for submerged operation rather

than for surfaced.

The Type 21 really was astonishing
because it was the world's first proper

submarine.

So earlier models of submarine had
actually been, strictly speaking,

submersibles. What that means is that,
yes, they could operate under the

surface, but only for very limited
periods of time, and also at much

speeds.

What really made the Type 21 stand out
was, because of its revolutionary hull

design, greater numbers of batteries and
the fuel it used, it could actually

operate faster.

under the surface than it could on the
surface, and for much longer periods

underwater than early models like the
Mark VII, the Type VII.

That really was massively revolutionary.

It was the first German vessel to be
produced in modular form.

Construction began in 1943, with a total
of 133 boats being completed as

assembly yards in Hamburg, Bremen and
Danzig.

More than 250 feet long and displacing 1
,620 tons, the Type 21

packed six torpedo tubes capable of
firing more than 23 torpedoes.

It carried a crew of 57, could achieve a
top speed of 17 knots submerged, and

survived underwater for up to 75 hours.

It was also the first U -boat to be
fully streamlined.

All periscopes and radar masts were
fully retractable, and even the flak

were built into streamlined turrets.

Its unique air -breathing snorkel
enabled it to remain submerged to

batteries, something modern submarines
still do to this day.

Well, up in the conning tower, this is
absolutely amazing, isn't it? I mean,

dials and tubes.

Everywhere. I mean, when you're thinking
about submarines, this is kind of what

you imagine, isn't it? But who would be
up here and when?

This room is used by the commanding
officer to lead the attack.

So he sits right behind you on the
attack periscope.

Right. So I sit on here.

And I've got two pedals. So is this for
controlling, turning it around? Yes. So

this can rotate? The whole turret can
rotate.

And this presumably is where they've
gone, but this is where the optics would

have been. So I'd be here controlling
where I want to go, moving around.

It's just amazing.

Precision engineering, isn't it? It
really is.

Actually, when looking at the level of
mechanical engineering now in the 21st

century, the kind of precision is not
much better than World War II.

We just put more electronics and
intelligence in it. But then you look at

and you can sort of understand why.

We make our way down from the conning
tower to the mess room, where we can

down on the huge complement of batteries
that gave the Type 21 its immense

power.

So these are batteries.

This is half of the battery capacity
this submarine actually has.

Really? They increased the amount of
batteries times three, and the power.

of electric drive times 10.

Right. I mean, they do look like giant
car batteries, don't they? Yeah, because

this is the same principle. They are
more sophisticated because they have

additional system for acid circulation
and so on, like every modern submarine.

So, presumably, the faster you go, the
more revolutions you need, the more

you're using, the quicker they use up
their energy.

Yes, exactly.

For this reason, until today, every
submarine without air -independent

propulsion has very low endurance when
running at high speed.

They can run for many hours at 3, 4, 5
knots.

Right. But if they have to go for 70
knots, it's just about for a couple of

hours.

This is the only footage I've been able
to find of the Type 21SC.

U -boat 2513 was surrendered to the
Americans, and this is taken as they

evaluating its design and performance.

It was information that was to prove
invaluable to the future of submarine

design.

I just find it absolutely stunning that
in the era of the Second World War

you're creating something as
sophisticated as this. I mean, you look

someone has to invent this, someone has
to design this, and teams of engineers

have to create it. It's a very complex
thing, isn't it?

Yes, and without modern computer -aided
design technology, it's just some

guy standing and drawing something.

I couldn't imagine just doing this for
months and years without a computer.

Yep.

I really do think this Type 21 is
absolutely amazing.

And, you know, I just can't help
thinking that the Nazi regime had a

opportunity with this that they just
didn't exploit at all.

You know, they don't start this until
1943, and yet they've got the

the know -how, much earlier than that,
and they just don't do anything about

It's just this really bizarre
prioritisation.

You know, just imagine if these had been
around in the early part of the war.

The only way to really dent the Allies
is by destroying their shipping.

This. is the weapon that could have done
that.

And yet, incredibly, only two ever go on
war patrol right at the very end of the

war. It's a massive opportunity miss for
the Nazi regime, and thank goodness for

that.

This particular U -boat never saw combat
service and was scuttled by its crew in

1945.

And as I'm about to find out, it was
lucky to be built at all.

As the Second World War moved towards
its endgame, the Nazis made one more

desperate roll of the dice.

On the 18th of February, 1943, Joseph
Goebbels announced a new phase for the

Germans, that of total war.

The entire country was to be mobilized
in its defense.

An armaments production was to be
increased threefold.

Rapid construction of the Type 21 U
-boat was seen as vital to this

but Nazi Germany's meagre resources were
becoming ever more stretched by the

Allied bombing campaign.

Most of their shipyards now lay in
ruins, so a very special, very secret

assembly facility needed to be built
that was immune to Allied attack.

One with walls and a roof so thick,

No bomb would be able to smash it.

It's early 1943, and the Nazi high
command urgently needs to get the Type

-boat in the water.

The Valentin assembly plant is to be
their answer.

Built of reinforced concrete, It would
be the largest fortified U -boat

in Germany, at 426 metres long and 27
metres high.

The walls alone were to be four and a
half metres thick, the ceiling an

extraordinary seven metres at its
thickest.

The engineers were given just 22 months
to build it, and it was built largely by

slave labour.

For the past ten years, museum curator
Dr. Markus Meyer has been refurbishing

the rundown factory as an example of
German engineering construction, but

as a symbol of the horrors of war.

So how many people are involved in
constructing something quite as enormous

this? We're talking about...

8 ,000 slave workers a day plus 2 ,000
engineers, German workers and guards.

And who were these workers?

They were slave workers from all over
Europe. They were concentration camp

inmates. Yes. And they were inmates of a
local police camp.

And presumably conditions were not good.
No, they were very, very bad.

One of the biggest problems was to get
enough food.

Most prisoners had a weight of about 46
kilograms after a short period of time.

That's just nothing.

There was basically just soup.

Cabbage soup with cabbage as an idea of
cabbage.

So not enough calories to stay alive
just by doing nothing. And they had to

very, very, very heavy work.

Carrying stacks of cement, metals,
everything.

The living conditions were quite bad.

And do we have any idea how many people
died as a result of building this? We

cannot say the exact number, but about 1
,300 are proved.

Of the 10 ,000 to 12 ,000 men who worked
on the construction, it's now estimated

that as many as half perished in the
process.

From the perspective of today, this
looks like an act of gargantuan folly.

It was dreamed up by Dönitz, by then a
grand admiral, in collaboration with

Hitler's favourite architect, Albert
Speer.

In the aftermath of the war, both these
men honed a carefully cultivated image

of being good Nazis, not really
supportive of the worst of the regime.

It's an image that looks more than a
little shaky in the shadow of the

bunker.

Why are they doing this?

Dernis knows that the U -boat war is
over. I mean, really? Is a Type 21 going

come in to make a difference? I mean,
can he possibly believe that? It's hard

say if he really believed it. I think,
in a way, he did. But it's kind of

delusional at that point.

But the thing is, total war means not
achieving a kind of rational goal

in a war, getting resources, getting
territory.

Total war means we are in the end fight
and there's just one survivor. Yeah.

There's no chance. It's all or nothing.
All or nothing. So if you have the

technology to build a Type 21, which is
potentially a game changer, it's worth

going and building a 400 meter long
bunker. Exactly. Yeah.

By any cost.

Right. Money.

Yeah, and if it costs 6 ,000 lives in
the construction, nobody cares. This is

really one of the last straws they had.

And it's madness.

Yeah, yeah. And that's the special thing
about this bunker.

Inside, it's completely logical.

Right. But outside, it's madness.

The madness lay not just in the
construction.

but in the belief that a building this
size could be kept secret.

I was off to photograph Hamburg.

Unbeknown to the masterminds behind the
Valentin, the Allies had been watching

its construction from the very start.

Coming in over the target, I started the
automatic camera.

Marcus has uncovered some old files in
the British National Archives, which

an insight into the quality of their
surveillance.

What the British get out of their air
surveillance...

documented um first note is from i think
may 43 right uh

okay there's something going on let's
check it out and after that we have

reports every three to five months
getting much more precise every day

right um even drawings of the bunker
okay just taken by by exploring

the photographs they took Right. And
their special interest was the thickness

the roof. Right.

They were waiting for the building to be
well into construction, but not so

complete they would be unable to
penetrate it.

From the reconnaissance photos, the
Allies correctly worked out that one

the roof was only five metres thick, not
seven.

On the 27th of March 1945...

617 Squadron, the Dam Busters, struck
with bombs known as Grand Slams.

These 10 -tonne high -explosive
earthquake bombs couldn't penetrate 7

concrete, but they could break through
5.

And that was the part that was
successfully targeted.

Well, Marcus, that's a pretty big hole
in the roof there. Is that the fatal

blow? That's one of the two fire blows,
yes.

Yeah, wow.

And it was caused by a 10 or 12 ton
bomb.

Yeah, a grand slam. A grand slam.

Yeah, and this looks very much like the
remains of one of the grand slams that

was dropped.

It's amazing, isn't it, that after all
those months of construction, just a

couple of bombs, and that brings the
whole thing crashing down to a halt.

Yeah, all the planning that went into
this place were basically useless,

this was...

Highly visible.

I mean, how could it be anything but?

Yeah, you couldn't camouflage it. No.
This bunker could have been built only

because the Allies let it happen.

They could have destroyed it from day
one. They didn't because so many

were used here without any danger to
anyone. At that point where they

okay, the Germans will finish the roof
finally up to seven meters.

They just flew this one attack.

Right. One.

And two bombs hit, and this whole
project was gone.

You know, on one level, this place is
just so impressive. To think that this

built, you know, in the second half of
the Second World War, on such an

scale, is just incredible.

But on another level, this is just
absolutely insane.

I mean, you know, Germany is losing the
war. Yes, they've got the Type 21, but

they simply cannot build enough of them.
And this is not going to be the answer,

because let's just say they do manage to
complete the construction of this, and

it isn't actually bombed.

The final assembly of the U -boats, the
Type 21, is going to be here.

This would have been a dry dock. You
fill it up with water, and then you sail

out. But you sail it out into the River
Visa, and that isn't deep enough to

submerge one of these submarines.

So they would have to sail all the way
down the river, quite a long way to the

North Sea, above the waterline.

And there is just no way, by that stage
of the war, that the RAF or American

planes are not going to be able to spot
that.

and destroy them en route. It's just
inconceivable.

And to imagine any other course was just
so illogical, so irrational.

And it just underlines, I think, just
how crazed the senior leadership

in Nazi Germany had become. I mean, what
were they thinking?

The war was over.

The U -boat fleet was destroyed, with an
appalling loss of life.

At the start of the war, the U -boat arm
had been just 3 ,000 men strong.

By the war's end, ten times that number,
more than 30 ,000 had been killed.

Had Hitler been a halfway competent
military strategist, and had Dönitz got

way in 1939, the war might have ended
very differently.

I think what's so amazing about the U
-boat arm is you can see the potential

there. You can see how a properly
equipped modern U -boat arm could have

wreaked havoc with the Allies.

But it's too little, too late, and not
enough focus.

Well, it's the problem if you try to
fight the world.

with a handful of ships.

Yes, exactly.

It was the right strategy to follow, but
with very limited means.

And from a mere military point of view,
that was the key problem.

They had great successes, but in the
end, they simply ran out of breath.

While Dönitz failed in his attempt to
sever the vital Allied supply lines

the Atlantic, no one can doubt the
achievements and sacrifices of the U

arm, nor the astonishing developments in
technology that it inspired.

You are aboard one of the newest attack
submarines in the US Navy.

It had a fundamental influence on post
-war submarine development in both

America and the Soviet Union.

In the years since World War II...

The rapid development of underwater
technologies has thrust the submarine

the forefront of the naval balance of
power.

Such was the legacy of the Type 21.

Submarines today are faster, better
equipped, and have longer endurance than

ever before.

It demonstrated the Nazis' faith in the
power of technology.

Perhaps given more time, it could have
even helped them win the war.