Original subtitles

A puzzling web of corridors that appear to lead nowhere.

They're hardly noticed by the general public, but you can't

build an air force without them.

A huge abandoned facility in a remote desert.

This was a hardcore military base, fully prepared to survive

all-out war.

Gigantic steel towers in an industrial wasteland.

They've not just changed western Pennsylvania,

but changed the world and helped build america's 20th century.

And a massive seven-tonne Cannon

left on the edge of an icy mountain top.

It was a real, if you like, war-winner

for the Italians and it was well worth bringing up here.

It still did its job and did it very well.

Once, they were some of the most advanced structures and facilities

on the planet, at the cutting edge of design and construction.

Today, they stand abandoned, contaminated and sometimes deadly.

But who built them, and how?

And why were they abandoned?

♪ ♪

Just outside London is a corrugated iron and concrete building.

It stands amongst the scattered

offices and workshops of an unremarkable industrial estate.

Would you expect to find mysterious

equipment and enormous wooden devices

almost within arm's reach of ordinary people, ordinary houses?

It's really astonishing.

The interior of this lopsided structure is initially mystifying.

Two huge circular apertures with gigantic propellers

lead to a vast concrete tunnel, 230ft long and 140ft wide.

Its incredibly smooth walls

are pierced by veins and hidden channels.

Yet it leads nowhere, simply looping back on

itself in a series of right angles.

The engineers constructing the 24ft-diameter tunnel

faced unforeseen problems that they hadn't encountered before.

The sheer size of it made it

quite difficult in terms of its construction, as well as operation.

What complex process was carried out

in this mammoth tunnel that made such technical features necessary?

And after so much effort, why was it abandoned?

In may 1933, Adolf Hitler created the reich

aviation ministry with former flying ace hermann goering at the helm.

This was a major step towards

the birth of Germany's new air force, the luftwaffe, in 1935.

To Hitler, aerial warfare was the future and soon, the full

weight of Germany's aviation industry was working towards

his program of rearmament.

With some of the best engineers in the world, they began designing a

new breed of aircraft.

Aircraft technology is transitioning

from olde-timey biplanes to what we think of as a modern aeroplane,

and the British government says, "we cannot allow the Germans to get

a technological edge on us."

As an aviation arms race developed,

the British set about building a high-tech research facility.

The farnborough wind tunnel.

This testing facility was designed to allow British engineers to study

aerodynamics and aircraft performance

with far greater accuracy and in more realistic conditions.

A wind tunnel is an absolutely essential part of designing

and building and testing aircraft.

Every element of the aircraft, that's on the outside, affects

aerodynamics, even things like the struts that hold the wheels,

or the way the flaps are designed.

So everything had to be subjected to these tests, and tiny, tiny

little variations can have massive impact on how an aircraft performs.

Creating this complex was an immense challenge.

Beyond its sheer size, every material and component, from

the giant propeller to the concrete walls, had to be carefully selected

and engineered to ensure optimum performance.

Kenny odgers is lead technician

and an expert on the facility.

We're looking at four years of construction

in concrete, asking the people to

work at tolerances, which I find quite frightening.

Every little feature in the tunnel had to

be perfect. The air flow had to be able to move past the walls.

You couldn't have little bolts sticking out.

The louvres had to be exactly right to straighten out the air flow

and not add new layers of turbulence.

In 1935, the 24ft wind tunnel went into operation.

Instead of using scale models, full-sized aircraft were suspended

between the arms of the tunnel so their aerodynamic performance could

be measured and faults corrected.

But the clock was ticking.

Germany's new prototype planes began breaking numerous world records,

demonstrating to the world their technological prowess.

In 1936, the junkers ju 87,

a dive bomber known as the stuka, was rolled out.

Soon after, it was the messerschmidt 109,

which would form the backbone of the luftwaffe's fighter force.

Through late 1939 and 1940, they played a devastating role

in the blitzkrieg tactics that crushed Western Europe

and forced the British army back across the channel.

Over the course of the second world war, the Germans make their

aircraft better and better.

And what's really important for the British is that the British

have gotta be able to improve aircraft ever so slightly

every minute of every day in order to defeat the Nazis.

At the centre of the wind tunnel, a giant 30ft propeller could blast

a 115mph jet of air across the gap between its two arms.

The mighty fan rotated at up to 250 revolutions per minute,

sucking in air, which span as it left the blades.

This turbulent air was then progressively smoothed as it

flowed through a series of straighteners and deflectors

around the rectangle's corridors.

At the end, it exited the tunnel's

jet toward the test plane as a smooth current of air.

At full whack, the wind was pushing around 4.5

million cubic feet of air, and when you think back over things that

were being tested, ok, everybody talks about the iconic aeroplane,

the spitfire and the hurricane, but we had the westland whirlwind,

a stirling,

then we had the hobby and we had a heinkel.

Testing German aircraft such as the heinkel

helped the British discover secrets of their technology.

By 1940, with the battle of britain raging in the skies,

farnborough continuously honed the performance of British fighter

aircraft, including hurricanes, and the iconic spitfire.

You'll start world war ii where the first models of the spitfire

have a two-blade propeller.

End of the war,

they have an adjustable pitch four-blade propeller.

An adjustable pitch propeller is one of the things that increases

aircraft climb and performance enormously.

And you can't develop propellers without a wind tunnel.

Engineers quickly identified and introduced new

aviation features that helped secure victory in the skies over britain.

Improved engine cooling and reduced drag gave British pilots

an edge in combat.

With the arrival of the famous Lancaster bomber in 1942, it was an

edge they would not relinquish through the rest of the war.

There's a process of the engineering of British

aircraft getting better and better,

while the Nazis are still trying to create

the miraculous super-weapon that is going to win the war for them.

And as a result, the Germans are tripping over their own attempts

to improve their technology.

The Nazis pressed for quantum leaps in aircraft design, including

jet-propelled aircraft,

to turn the tide of war back in their favour.

Meanwhile, the allies focused on incremental changes

and mass-produced proven aircraft.

Wind tunnel facilities such as farnborough played a pivotal role

in establishing air superiority over the luftwaffe and securing

victory in world war ii.

But with the dawn of the jet age, farnborough would gradually be

rendered obsolete.

Having a large tunnel being propeller-driven

wasn't as necessary because you could create high-velocity air

streams using jet engines, and that made an older style like

farnborough obsolete and basically doomed it to the history bin.

Finally, in 1992, its wind tunnels fell silent.

But today, it's designated an historic building.

The heroic struggle fought by the raf in the skies over britain

during those pivotal months of 1940 is well-documented.

Less well-known is the painstaking work

done by men and women at facilities like farnborough,

work that helped give the raf the tools they needed

to win the war.

The farnborough tunnels and the farnborough establishment

itself was an absolutely essential part of the British

military and war effort.

They're hardly noticed by

the general public, but you can't build an air force without them.

In the gobi desert around the Mongolian city of choir,

an empty landscape stretches unbroken across the horizon.

Yet 19 miles northwest of the city, a cluster of isolated strange grassy

mounds spring out of the barren steppe.

They're largely empty areas.

These were miserable places in the middle of nowhere.

Standing 30ft high and 80ft across, each of the 40 mounds is connected

to the next by a strip of concrete, overgrown with weeds.

Nearby, a two-mile-long roadway leads

off towards a range of low hills.

Most bizarre of all

are the rows of crumbling apartment blocks buttressing the background.

But why would anyone build a community in

this vast and remote wilderness?

And why was it abandoned?

In the years after world war ii,

China and the Soviet union had become firm communist allies.

By the 1960s however, diverging ideological

interpretations of marxism led to a breakdown in political relations.

This was exacerbated by disagreements over

how to coexist with the us and it developed into a potentially

disastrous border dispute.

Known as the sino-Soviet split, it brought the two mighty communist

powers to the brink of war.

The reality is that the communists in Russia and the communists

in red China, they couldn't agree on where to have lunch.

Much bigger than communism was the inbuilt rivalry.

As distrust grew,

military forces steadily built up along their borders.

Wedged in between the two adversaries

was the ussr's ally, the Mongolian people's republic.

As tensions Rose, this Soviet satellite

state found itself at the centre of a potentially explosive situation.

Mongolia is something of a

contested area and, in fact, this heated up back in the early 1960s.

It got to the point where there

were some serious, not just skirmishes, but actual battles.

The Soviets created the Mongolian people's republic

as a puppet state to buffer them against Chinese attack.

The Soviets are really concerned that, as China modernises,

as China grows stronger, that Russia and China will fight a war.

In response, the Soviet union deployed

hundreds of thousands of troops near the Mongolian border with China.

They were backed up by a formidable network of air power.

A key component was the bayantal air base.

This was home to the 126th fighter aviation regiment.

A huge new base designed to provide a first line of defence against

any Chinese attack on the Soviet union's satellite state, Mongolia.

This base is massive. The runway's two miles,

with hardened bunkers where they could hide their aircraft from even

the most serious aerial attack.

At the air base, there were 1,800 men, and the associated families

that were in charge of the aeroplanes, as well as

the maintenance and running of the facility.

This was a hardcore military base,

fully prepared to survive all-out war.

In 1970, red army engineers rapidly laid foundations in the vast expanse

of the Mongolian steppe.

In keeping with the secrecy that surrounded its construction,

the cost of this massive installation is still unknown.

Work at bayantal faced a number of unique challenges.

This was a long way from the typical Soviet air bases in Europe.

A whole town had to be built from scratch for the Garrison and their

families, with every last nut and bolt brought in from the ussr.

One thing the Soviets were really good at was building massive

infrastructure in the middle of nowhere. It would be difficult

to build a two-mile runway, you know, ten miles outside of Moscow.

Imagine doing it in the middle of nowhere,

thousands of miles away from your normal sources of supply.

What you see on this base is how much effort,

resources and money the Soviets poured into their defence system.

In 1972, bayantal became operational.

Surrounded by anti-aircraft missile batteries and a network

of defence bunkers, the base was formidably well-protected.

Hidden within its blast-proof shelters was a deadly strike force

that included dozens of mig-21s and 23 fighter jets.

At the air base, there was a squadron of mig-21s, which,

at the time, was a top-of-the-line fighter interceptor,

so a supersonic jet that would deal with any airborne threats

that would come from the Chinese.

It's one of the ten great aircraft of the cold war.

The us encountered the mig-21 in the skies over north Vietnam,

where it was a formidable opponent.

It was fun to fly, fairly easy

to maintain, and the people that flew it liked it and trusted it.

While the aircraft were high-tech, conditions at the base were brutal.

In the summer, temperatures reach 40 degrees celsius, while in winter,

the icy winds blasting across the desert steppe could bring

everything to a stop at minus 40.

The problems that they faced on base were both from a maintenance

perspective, keeping the machines

operational in the desert environment, as well as morale.

Keeping people motivated to live in such a stark and barren place

was quite a challenge.

Yet bayantal remained on a state of

high alert throughout the 1970s and '80s as tensions continued.

At this point,

China's interests are clearly opposed to Soviet interests.

And as long as Chinese and Russian interests are opposed,

there is always going to be tension between Moscow and Beijing.

And that tension is gonna be stretched right across Mongolia.

Bayantal air base helped prevent China from taking direct military

action against the ussr and all-out war was narrowly avoided.

When mikhail gorbachev came to power in 1985, he made a determined effort

to ease tensions.

Just a few years later, in 1989, the Soviet union was collapsing

and bayantal no longer had the funds to be maintained.

This was not a country with a lot of money at the time.

It's part of the reason the Soviet union ultimately collapsed, was

the need to spend so many precious resources building and maintaining

this far-flung network of expensive military facilities.

And this base shut down, as did hundreds of others.

In December 1989, the bayantal air base was abandoned.

Today, this once-vital air base is a ghost town.

The base is largely abandoned now.

None of the structures are used for the original purpose.

Native people, the Mongolia, can be found on the base, but not

in the buildings themselves. They live in and amongst

the buildings, using them for shelter from the environments.

But largely, the buildings are completely empty

and abandoned.

Bayantal air base shows that nuclear armageddon could have started

not just in cold war Europe, or the United States,

but even in the vast desert wastelands of Mongolia.

Like most military installations, this one was never used in war,

but that's not necessarily how you measure

the success of an investment in military infrastructure.

If it prevented a conflict, then it did its job as well.

On the other side of the planet, in Pittsburgh, Pennsylvania

is a perplexing wreck of rusting metalwork.

A steel and concrete mass rises above the trees that grow along

the banks of the monongahela river.

It's really peculiar-looking and you're thinking it's some sort

of steam punk theme park. It's that weird.

When you first see the Carrie furnaces,

you're taken right back to an age of huge industrialisation,

with these enormous plants.

The scale of this unusual construction dwarfs nearby

buildings.

A mighty chimney soars 280ft high and a row of rocket-shaped silos

are flanked by two 110ft-high pipe-covered steel towers.

Connecting them all is a mid-air rail

line that seemingly leads nowhere.

When people first see these,

I think they're just struck by how big they are.

This crazy collection of pipes and tubes, and intricate plumbing

on a massive superhuman scale. It's kind of mind-blowing.

What exactly took place in this jumble

of pipework, concrete and steel?

And why was this gargantuan facility abandoned?

At the turn of the 20th century, an explosion in building

and transportation across the usa created huge industrial need

for steel.

Iron and steel were the backbone

of the development of north American infrastructure.

Every building, every highway bridge,

every car, every train, every ship

and tank, they all contained steel that came from Pittsburgh.

This was the birth of america, really, the industrial revolution,

the empire state building, the Brooklyn bridge.

Every city had its proud structures that came from this

dangerous, complicated process of producing steel.

This dangerous process involved the smelting of iron ore.

But not enough could be smelted to keep up with

the ever-expanding steel production.

Ron baraff is a director at rivers of steel heritage.

He works to preserve the history of industry

and steel in western Pennsylvania.

They made iron that not just changed western Pennsylvania

but changed the world, and helped build america's 20th century.

Us steel came up with a solution to the bottleneck.

These are Carrie furnaces 6 and 7.

The extraordinary towers

were designed to produce more iron for the production of steel.

Really what you're doing is melting rocks.

It is a manmade volcano that is reducing three basic ingredients.

Iron ore,

coke - which is coal that's baked and is carbon - and limestone.

And you're subjecting it to an immense amount of heat and reducing

it down to iron, which is then

transported from this site across the river and converted into steel.

These furnaces were purposely built near Pittsburgh.

This was because of the extensive

natural deposits of coal that exist in

the nearby appalachian basin.

In that part of america, you have a lot of structures in the earth's

crust, which have brought coal,

have brought limestone and have brought iron ore

close to the surface, and you need those three things to make iron.

Building began in 1906.

It was no easy task creating these 90ft-tall combustion chambers.

Made of 2.5-inch-thick

steel plate, they are lined with thousands of bricks capable of

withstanding temperatures of almost 2,000 degrees celsius.

A system of counterbalanced cars was designed to carry tonnes of ore,

coke and limestone up an inclined ramp

to be emptied into the furnaces.

We can think of the furnace as, like, a giant test tube with a big

bunsen burner underneath.

We're adding in the chemicals to make the reactions to get

from a solid rock with iron in it, to liberating free iron as a metal.

And we do that by reacting the iron with the coke, to free the iron,

and we also add calcium to get rid of all the silica.

All of this is happening in mid-air.

Suspended in mid-air, this big push of air up,

material coming down, the coal burden coming down, being heated,

and the iron rains out.

In 1907, the new furnaces began operating.

The process of emptying the white-hot iron

from the furnaces and into

the waiting rail cars made for hazardous working conditions.

This was not a job for the faint-hearted.

This is a tap hole here behind me.

It's a Clay plug that's drilled out. The drill's right in front

of me here, so it drills through, the iron starts

flowing, iron goes down this runner and through a hole in the floor.

Then hopefully, stationed directly

below that hole in the floor is a bottle car or ladle car.

Fatalities were high.

Injuries were extremely high.

Fatigue was always a problem.

You know, working in these plants, especially early part of

the 20th century, you were an old man if you were in your 40s.

It would eat you up and spit you out.

During the American 20th century,

furnaces 6 and 7 proved a phenomenal success.

Each producing up to 1,000 tonnes of hot iron every day.

In 1910, 60% of

the usa's entire steel output was coming from Pittsburgh.

And Carrie furnace was particularly efficient,

thanks to its hot metal bridge,

which took molten iron straight

to the heart of the homestead steel works across the river.

This helped production keep up with spikes in

demand for steel in war time.

During world war ii, 180 tonnes

of molten iron were shipped across the bridge every single hour.

At its height, and you're looking

second world war on, these furnaces alone,

just this complex of furnaces, were outproducing Great Britain.

You know, the Pittsburgh region

was outproducing all of the axis powers together.

This region gained the moniker of the 'arsenal of democracy'.

This was the heart of america's industrial might.

But as the years went by,

the way the furnaces operated became increasingly outdated.

It was incredibly dangerous, absolutely incredibly dangerous.

The force of the pressure inside this furnace, the amount of gases

that are in there...

It is a constant balancing act.

You have too much pressure build up in these vessels, they can explode.

It requires team work, it requires everyone being on that same page,

and understanding that they're trying to tame a volcano.

By the 1970s, demand for iron from the Carrie furnaces had dropped off.

Even more seriously, this early 20th-century

technology was raising serious concerns about safety.

This is heavy industry we're talking about.

The conditions for the men working at the Carrie furnaces would have

been like working in hell.

Extremely hot, you're working around molten iron.

Soot in your face, the fumes.

Just the heat, the oppressiveness of that environment would have been

unbelievable and the risk of injury or even death

were all around you, all the time.

You had these high temperatures, toxic fumes, dangerous work that

required a lot of skill.

This was work for very, very tough, motivated people.

In 1978, time ran out for the two giant furnaces and their fires

were extinguished for good, leaving the site abandoned.

The rest of the Carrie works around the region were deemed too dangerous

and contaminated.

So they were all demolished.

Furnaces 6 and 7 however, still survive.

Designated a national historic landmark in 2006, they are now

a local tourist attraction.

Where we're standing, in 1907, this was the high tech of its day.

And, you know, it's the building of america's 20th century.

It happened in places like this.

Across the Atlantic ocean

in the Italian alps, the cresta croce Ridge

sits 10,000 feet above sea level, amongst the rugged mountain tops.

On the brink of an almost vertical cliff

stands an 11ft Cannon. It's supported by a steel cradle

and two huge wooden spoked wheels.

The idea people could move something so massive on top

of a mountain so high

really is a testament to what humans can do.

There is no doubt about the purpose of this

six-tonne steel Cannon.

More of a mystery, however,

is why it's perched here on this barren mountain top.

If I came across an old Cannon like that in the middle of the Italian

alps, I would be utterly amazed, because how did this get there?

And why was it abandoned to this icy wilderness?

Since its formation in 1871,

the nation of Italy had been attempting to build up

its army and Navy to protect itself from their chief adversary, Austria.

In 1915, Italy entered world war I, taking up the allied cause against

the austro-Hungarian empire.

For Italy, it was a war of barbed wire, machine guns and, above all,

heavy artillery along the northern border in the Italian alps.

The Austrians had, for centuries, dominated Italy,

along with the French.

And what the Italians see in the first world war

is those Austrians coming across the passes yet again,

to try to dominate the country that the Italians had only just built.

And the Italians had to stop it.

In 1916, there was a critical danger that Austrian troops would breach

Italian mountain defences and break through what was then the border

between Italy and Austria, just by the cresta croce Ridge.

The artillery piece was the prime

killing weapon of world war I, and Italy's success in defending

this mountainous border would hinge on its effective use.

You would never beat the Austrians

unless you got heavy artillery up into the mountains in Italy.

One or two guns will dominate a large amount of territory

in a mountain terrain.

The Italian army, however,

was desperately short of modern heavy guns.

The only solution available was an outdated gun from 1888.

The 5.9-inch g-model Cannon.

Nicknamed 'the hippopotamus', it was designed to fire a 60lb shell

over a distance of six miles.

Easily outranged by more modern guns,

it was all that Italy had available to defend its borders in 1916.

When you needed fire support, you wanted not small mountain guns

that you could transport on the back of a donkey - everybody had those.

You needed heavy artillery.

On 9 February, 1916,

the hippopotamus Cannon arrived in the valley below.

It faced a daunting journey up the mountains near the town

of passo del tonale.

If the town was captured, Austrian troops would have

a clear run to the vital manufacturing city of Milan.

The gun had to be sited on a Ridge blocking the Austrian advance.

With no roads and the mountains covered in deep snow,

the only option was to manually haul the 6.6-tonne Cannon thousands of

feet up the mountain, in temperatures of 20-below.

Well, as an engineer and as an amateur mountain climber, the idea

of taking a Cannon and hauling it up is almost impossible

to imagine, because of the weather and the snow conditions,

and just the absolute misery that those men had to go through.

Professional mountaineer Cain Olsen is visiting the Cannon

to better understand exactly what those men went through.

To imagine, you know, 18-year-old, 19-year-old kids,

you know, hundreds of them, to get this up here in lots of

snow, from a mountaineering point of view, it's incredible.

Freezing temperatures weren't

the only obstacle faced by these young soldiers.

During the gruelling march upward, they were twice buried by avalanche.

Members of the tow team were killed.

Yet the mountain troopers and artillerymen had to

dig out the Cannon and continue the long haul.

Now, the friction capacity of snow is very much a function of

the weather conditions, so cold, dry snow is almost like sand.

So imagine dragging a heavy weight

through a sand dune, where wet, sticky snow is almost like mud.

And so

there's really no great way to drag a heavy weight through snow.

Despite this, after 78 days of incredible effort,

the Cannon arrived at its first firing position.

But the initial location proved problematic.

The Austrians were positioned on that Ridge over there.

And from its original position, the Austrians were just a bit too

far away, so that's why they had to then move it over onto cresta croce

and from cresta croce, they could easily hit the Austrians.

Italian artillerymen faced yet another problem, as historian

David Caldwell-Evans has discovered.

There's virtually no recall mechanism on this gun.

When you fire it, it's gonna slam straight back

and there's nothing you can do about that, other than

try and stop the roll back.

Each wheel had a wooden wedge behind it, and when it fired,

the wheel would rock back up, come up the wedge, and then slide

back into position again.

That was the only way they had of stopping it,

basically recoiling straight off the back of the mountain.

Austrian troops were stunned to find themselves under bombardment by

a Cannon twice the calibre of their own mountain artillery.

Shelters dug deep

into the ice, snow and rock were pulverised by the enormous shells.

It not only stopped the Austrian advance in this sector,

but went on to provide covering fire for Italian counter-attacks.

This was the largest-calibre gun

at high altitude anywhere in the first world war.

The Austrians had nothing to compete with it.

So, although it was obsolete, although it was well past

its sell-by date of world war I,

it still was bigger than anything else up at this altitude.

What this gun is doing really is saturation fire.

For two long years, the battle above the clouds ebbed to and fro.

The two sides simply battered each other and, of course,

the mountain positions gave you a very important advantage.

In 1918, Italian troops stormed forward with the help of the g-model

gun atop cresta croce Ridge and drove the Austrians back

for good.

When world war I came to an end,

the obsolete hippopotamus was simply abandoned.

Today, the surviving heavy guns

of world war I are gathering dust in museums across the globe.

Yet the extraordinary hippopotamus still stands where it fired its last

epic shots.

It was a real, if you like, war-winner

for the Italians, and it was well worth bringing up here.

Although it was out of date, although it didn't compare with

more modern guns

in use in France, it still did its job and did it very well.

The story of the cresta croce Cannon is a reminder that a decisive weapon

doesn't have to be technologically advanced,

it just has to be in the right place at the right time.

Now abandoned, they were once on the cutting edge

of human engineering.

Within these decaying structures are the echoes of history.

They speak of war and terror,

but also of exploration and human endeavour.

Captioned by ai-media ai-media. TV