Original subtitles

NARRATOR: They're watching you.

More than 5,000 satellites circle the Earth.

Every day, they uncover new, mysterious phenomena

that defy explanation.

Terror stalks an Arizona ghost town.

There were those who believed he had

supernatural powers and couldn't be shot.

NARRATOR: The wrath of Genghis Khan.

Even to this day, it's known as the City of Screams.

NARRATOR: And the miracle waters of the New World.

This water gave them protection against

terrifying diseases.

Baffling phenomena, mysteries from space.

What on Earth are they?

[theme music playing]

NARRATOR: March 11th, 2021.

High over the Arizona mountains,

a satellite captures a strange structure

amongst the barren peaks.

This is a really intriguing image, because this

is surrounded by thousands of square miles of desert.

NARRATOR: Image analysis suggests the structure

consists of vast pieces of stone spread across 1,000 acres,

some at elevations above 5,000 feet.

BELLINGER: Some don't even have complete walls,

so whatever is here, it's in ruins.

What's really striking about this image is, geologically,

we're really high up.

NARRATOR: Drawn by the unexplained alpine structure,

geologist Martin Pepper is traveling into the mountains

to investigate.

Why would people haul all this material way up here

into the hills? It doesn't make sense.

NARRATOR: Beneath these mountains are seams

of gold, silver, and copper.

Arizona is dotted with crumbling mining towns,

but Pepper doesn't buy this explanation.

Typically, these settlements literally

exist right where they're mining,

and so we would see big tailings coming out of some of

these slopes, but I'm not seeing that here.

NARRATOR: From space, it's impossible to assess

the age of these structures,

but clues can lie in the dirt.

Ah, look at this.

This is not recent.

That's old lead solder,

and so we're talking about the 19th century.

NARRATOR: Ascending to the site in the satellite image,

Pepper is prepared for 19th-century ruins.

Check that out.

NARRATOR: He's not prepared for this.

Jeez! Look at the scale of this.

This is monumental.

NARRATOR: The satellite has captured significant structures.

There's evidence of almost 40 buildings, heavily

fortified, with thousands of tons of stacked stone.

Just the width of these walls, you know,

2, 3 feet thick,

shows that whoever built this wanted it fortified

and really strong.

Why would something this big be

out here in the middle of nowhere?

NARRATOR: The geologist returns to the image

that lured him here.

Looking at this image,

zooming in over here,

I can see this green area.

NARRATOR: Pepper heads west.

There it is. Look at that.

Ah, and there's the spring right up there.

NARRATOR: The spring and 19th-century ruins

sit in perhaps

the only navigable route between the Dos Cabezas

and Chiricahua Mountains.

PEPPER: These mountains block what we have west to California,

so this must be some sort of mountain pass.

NARRATOR: Via this mountain pass, it's 400 miles

to the Golden State of California,

the last leg in the most

treacherous migrant route in U.S. history.

In the mid to late 19th century, California was

the destination for fortune seekers,

but getting to California was a very dangerous proposition.

[banjo music playing]

NARRATOR: Census records show that between

1848 and the mid-1850s,

more than 300,000 people flood into California,

lured by the promise of gold.

Wagon trains snake through Arizona's mountain passes.

This water would have been extremely valuable in one

of their stops off as they headed towards the west.

NARRATOR: Disease, starvation, and fatal accidents are common.

Tens of thousands failed to finish a journey which averages

10 graves per mile.

Settlers had to literally run

the gauntlet to go through these passes.

JANULIS: The Spanish name for this pass is

Puerto del Dado, Pass of the Die,

and that's not die as in death,

but as in gambling dice.

Coming through here means you're gambling with your life.

NARRATOR: One gambler not prepared to lose

is New York businessman John Butterfield.

Butterfield's stagecoach was the first truly

transcontinental postal service

and it ran all the way from St. Louis, Missouri,

to San Francisco.

NARRATOR: The massive migration west triggers

a fresh challenge -- how to haul the U.S. mail

to California.

In 1857, Butterfield wins

America's largest ever land mail contract --

2,800 miles, five times the length of the U.K.,

through some of the most treacherous terrain on Earth

in a stagecoach.

John Butterfield had a statement

that really stood out -- "Remember boys,

"nothing on God's Green Earth should stop the mail from

getting through."

NARRATOR: Butterfield rounds up 200 coaches,

almost 2,000 horses and mules, and hires 1,200 men.

To win the contract,

He's promised to complete the route in 25 days,

leaving him no choice but to navigate the Pass of the Die.

A small staging post was established at the head of

the pass where

a postal rider would stop for a rest before pressing all

the way on to California.

But a thousand-acre fortified structure is

far more than a small trading post.

PEPPER: Why would this fort be so important

right here? There must have been something

else leaving everybody terrified of a possible attack.

NARRATOR: Coming up, mass slaughter in the mountains.

This place has a long history of bloodshed and unrest.

NARRATOR: And the lost swamp people of South Carolina.

JANULIS: It was the first attempt to settle the shores

of the New World,

and it was an absolute disaster.

NARRATOR: Drawn by remote stone ruins spotted from space...

Jeez, look at the scale of this structure.

...geologist Martin Pepper is high

in the barren mountains of Arizona.

This is monumental.

NARRATOR: He believes these are 19th-century fortifications

overlooking a snaking mountain pass,

the most treacherous migrant and mail route in history.

It's in the perfect strategic position to

protect anybody trying to safely pass through here.

But protect them from what?

Pepper seeks answers in the area around the ruins.

Look at this.

Looks like some sort of a cemetery or something.

NARRATOR: The century-old cemetery may hold

clues about the immense mountain structure.

PEPPER: Colonel Stone,

John Slater, killed by Apaches.

Killed by Indians in the Apache pass.

This is literally right in the middle of Apache territory.

NARRATOR: The formidable Apache control

a 30,000-square-mile territory around the site in

the satellite image.

After five centuries of peace, they are drawn into war.

In the 1730s, the Apache came into conflict with

the Spanish, who were seeking to expand their landholdings

in Mexico.

Their raids against the Spanish

were both savage and calculated.

NARRATOR: Between 1771 and 1776,

the Apaches slay 1,600 Spaniards

and steal 68,000 animals.

They were one of the first groups to

fully adopt the horse and become horseback warriors.

NARRATOR: Spanish horses and guns empower the Apache.

[gun cocks]

Hardened by battles and betrayal,

they defend their land ferociously.

The Apache became so dangerous that it was just

too difficult for people to pass through the mountains.

Passage is vital for the Butterfield Mail Company,

who, in 1858,

broker a truce with Cochise, an Apache leader

renowned for his willingness to embrace white settlers.

BELLINGER: For a few years,

the Apache would allow the postal workers

to go through the pass unscathed.

HORTON: Indeed, they even trade commodities

and so forth with the stage coach.

NARRATOR: It's an unrivaled armistice

sadly shattered

on February 3rd, 1861.

Lieutenant Bascom of the U.S. Army

accuses Cochise of kidnapping

an American child, and in fact, he had not.

But this whole event is gonna

end in bloodshed on both sides.

NARRATOR: Much of it at the Battle of Apache Pass.

BELLINGER: The Apache were prepared to fight,

and they had studied American military tactics.

NARRATOR: In July 1862, 500 Apache warriors ambush

U.S. forces led by Captain Thomas L. Roberts.

Roberts retreats to the Butterfield Mail Depot

and readies his secret weapon,

two 12-pound mountain howitzer cannons.

Nothing the Apache had at their disposal could

compete with the massive firepower

possessed by the Americans.

[cannons blasting]

The Apache would have been terrified with these

howitzers that would literally cut them to pieces.

NARRATOR: 63 Apache are slain by howitzer shells.

The rest flee.

The battle is over.

The war has just begun.

CAVELL: What this event triggers is 25 years of

warfare between the U.S. Army and the Apache.

NARRATOR: In 1864, to defend Apache Pass,

the U.S. military establishes the structure

in the satellite image, Fort Bowie.

Fort Bowie will become Ground Zero to

try and deal with this Apache menace.

This was an original window that they then bricked up

and most likely it turned into

a rifle opening to shield the shooter

in case of attackers.

[gunshot and indistinct shouting]

NARRATOR: The war pits U.S. generals against legendary

Apache tactician, Geronimo.

While Geronimo was hugely important to the Apache nation,

he was never actually a chief.

He was known as a shaman.

There were those who believed he had

supernatural powers and couldn't be shot.

NARRATOR: Led by their invincible shaman,

Geronimo's Apache take advantage

of their local knowledge.

JANULIS: They used guerilla warfare tactics,

which means hit and run, retreat back to the mountains,

and then do it again.

ALBERTSON: There was really no quarter on either side.

The United States Army committed 5,000 of

the active duty army to chasing down Geronimo.

NARRATOR: The war claimed tens of thousands of casualties.

The fallen are buried in desert graves

like those by the fort

in the satellite image.

Fletcher, 1880.

Unknown Apache child.

Another Apache child, 1885.

Oh, wow, son of Geronimo himself.

Little Robe.

NARRATOR: In 1886, Geronimo surrenders,

effectively ending the Apache Wars.

After a quarter-century of conflict,

friend and foe rest side by side.

PEPPER: This showed that they came to some sort of truce

to bury them right here in the same cemetery.

NARRATOR: The ruins of Fort Bowie and its cemetery

are reminders of all who fell at Apache Pass

and a stark warning from American history.

What we can see from space was the beginning of the end,

before the Apache were broken and put onto reservations.

And even though it's peaceful and tranquil now,

this place has a long history of bloodshed and unrest.

NARRATOR: Coming up, killer seas.

Whatever has happened here, it's not good.

NARRATOR: And red dawn.

These innocent-looking circles are a key zone of the Cold War.

NARRATOR: October 1st, 2020.

The Landsat 8 satellite scans

the U.S. Eastern Seaboard captures

something bizarre spreading from

South Carolina's coastline.

KOUROUNIS: This image is absolutely shocking.

Typically, the waters off of Winyah Bay,

South Carolina, would be beautiful blue-green,

but it is stained brown.

SZULGIT: This is no small plume.

Whatever is leaking to the ocean is big.

NARRATOR: Something in Winyah Bay estuary

is pumping millions of gallons

of rust-colored water into the Atlantic Ocean.

I think it's safe to say that whatever has happened here,

it's not good.

NARRATOR: Satellite images taken over the Carolinas

two years earlier could offer a clue.

In 2018, tremendous amounts of rainfall caused flooding

that overflowed pig farms,

and there were literally floods of pig manure

leaching out into the nearby watersheds.

NARRATOR: North Carolina's hog farms house

around nine million pigs,

which each pump out around two tons of manure a year.

The 2018 floods create fecal tsunamis

so large they can be seen from space.

A flood of pig manure turned the rivers brown, and it really

bears a striking resemblance to what we're seeing

in this image here.

NARRATOR: Yet what puzzles analysts is that there are

reports of similar plumes dating back many centuries.

They are often referred to as blackwater.

The long history of people recording this blackwater

tell us that it predates industrial pollution,

so that's probably not the cause of it.

NARRATOR: What's more, the historical reports claim

that the noxious-looking waters possess strange

healing properties.

SZULGIT: They say that drinking in and bathing in

this water actually helped with their condition.

NARRATOR: The first accounts of blackwater date

to as far back as 1526.

HORTON: A Spanish pioneer settler called

Vazquez de Ayllon

arrived with over 500 fellow Spaniards,

and they planted a colony

close to the mouth of the river.

SZULGIT: When we think of the difficult conditions

that early settlers faced,

we think of them freezing to death in the winter

or having battles with indigenous peoples.

But really, the most dangerous thing they faced was disease.

NARRATOR: During the age of discovery, disease is

the principal cause of death among sailors and settlers.

Scurvy alone kills two million, typhus, typhoid, and dysentery,

countless others.

Back then, sailors would have been in these terribly septic,

horrible conditions where disease would be rife by

the time they arrived on their vessels.

NARRATOR: For the Spanish settlers in 16th-century

South Carolina, locating a clean water supply is critical,

but the state's fetid waterways are

a petri dish of bugs and possible infections.

Not only

does it provide contaminated water sources,

but also becomes a breeding ground for mosquito that can

spread diseases such as malaria and dengue fever.

NARRATOR: Faced with this onslaught

of waterborne horrors,

the Spaniards find sanctuary in the blackwater

seen from space.

When we look at where the water feeding into this

river comes from, it's passing through

a lot of swamps and wetlands,

so it's gonna be interacting with a lot of

decaying plant matter,

and that's going to make it pick up certain things.

NARRATOR: As the rivers move through

forests and wetlands towards the sea,

rotting plant matter leeches tannins

and organic molecules called phenols into the water.

All these natural compounds in the water basically

make it self-sterilizing,

allowing it to be very safe to drink.

NARRATOR: The healing properties of blackwater helped

the South Carolina colonists

to establish the first European settlement on

the continental United States,

but their stay is short-lived.

The minute this settlement gets to shore,

everything goes wrong -- their supply ship grounds

and cuts off their means of escape, their lifeline.

They rapidly run out of food and resources, because they

don't know the landscape and the colonists

start dying of starvation.

NARRATOR: A month after their arrival,

the Spanish flee, and their settlement is swallowed by

the swamp.

It was the first attempt to settle the shores

of the New World, and it was an absolute disaster.

NARRATOR: Five centuries later, a hurricane hits the site of

the Spanish colony,

generating the giant plume of blackwater captured

from the skies.

As it spreads across the Atlantic,

it prevents sunlight from penetrating the ocean,

leading to a mass die-off in the depths below.

SZULGIT: It's ironic that the dark water

that we see in the satellite image

that would have been a calling card

to early settlers for health and invigoration

turned out to be death to the oceans

hundreds of years later.

NARRATOR: Coming up, setting fire to runways.

Hey, in wartime, you're gonna

try pretty much anything to be effective.

NARRATOR: And the city that enraged Genghis Khan.

This was obviously a very bad decision.

NARRATOR: February 11th, 2020,

478 miles above southwestern England,

a satellite captures this image.

What you've got here is an airfield,

that much is obvious.

But then when you look at it a little bit more closely,

you realize there's something very, very unusual indeed.

There's a bunch of circles and also rectangles,

and what's interesting is there's a great deal of

precision to the shape and the placement of them.

NARRATOR: Each of the mysteries shapes

is around 400 feet in diameter.

It also looks like there's no sign of life.

So if this was active, it must have been decades ago.

NARRATOR: Analysts turned to local land registry documents

for clues.

Looking at the records, this is St. Eval,

an RAF coastal command station from the Second World War,

very active from 1938 to 1945.

NARRATOR: The airbase is one of 444 airfields

the British build during World War II,

with enough combined runway to stretch

from New York to Hong Kong.

PAVELEC: The base is close to the coast,

so it was given the orders of finding

and destroying German submarines out in the water.

NARRATOR: Over the course of the war,

hunter-killer aircraft from the base helped destroy over

200 U-boats threatening

American lives and Allied supplies.

Yet, as they return from their missions,

many pilots encounter an unexpected and deadly threat.

Basically, England's got this dual problem of heavy fog

and then a lot of industrial waste

coming up in clouds from the factories,

and those two combined and make almost, like,

a pea soup that pilots could not see to land in.

NARRATOR: The clouds of dense fog and smog,

which envelope wartime Britain,

claimed the lives of numerous pilots.

They force Prime Minister Winston Churchill

to develop an extraordinary solution,

one that could explain the weird shapes in the image.

WALTERS: What the scientists come up with is

this ingenious idea, and it's called FIDO.

Now, FIDO is not a big dog.

What FIDO stands for is

Fog Investigation and Dispersal Operation.

The idea is to run pipes on either side of the runway

and then flush them with fuel that ignites, and so it

basically illuminates the runway,

enabling the pilots to land safely.

NARRATOR: The infernos generated by burning

120,000 gallons of fuel an hour

also help to disperse thick fog above the runway.

PAVELEC: It seems a little counterintuitive

to set fires along

the side of the runway where you're trying to land,

but hey, in wartime, you're gonna

try pretty much anything to be effective.

NARRATOR: Between 1943 and 1945,

the FIDO system saves the lives

of 10,000 British and American aircrews.

But closer analysis reveals the mystery shapes

aren't connected to this fiery flight safety system.

MUNOZ: If you zoom in, and you look at

the center of these circles,

you see sort of an antenna-type structure.

NARRATOR: Declassified military files confirm

that these are transmitter stations,

ones that played a vital role in

events that unfolded after World War II.

In the immediate aftermath of the Second World War,

the United Kingdom was in a very difficult position.

It had prevailed in the victory,

but the economy was devastated.

NARRATOR: Britain's role in the Allied victory in World War II

cost the nation around $1 trillion

and leaves its industries and defenses in ruins.

As the Cold War dawns, this makes it highly

vulnerable to an attack from its former ally, Russia.

There was a period of time that we thought

that World War III was going to begin in

Berlin and that it was going to continue with an all-out

Soviet attack on the United Kingdom.

[people shouting]

NARRATOR: Fearing a possible communist invasion,

the U.S. dramatically ramps up its military presence

in Britain,

including at an airbase to the south of the site

in the image.

At any given time during the Cold War, there would have

been thousands of U.S. troops,

and not just the troops, but the aircraft

and the weapons capability

should there be some kind of conflict.

NARRATOR: Much like during World War II,

perhaps the greatest threat to peace comes from submarines.

During the Cold War, the Russians build around

1,450 subs and have the largest,

most powerful fleet in the world.

To track this menace, the U.S.

and Britain turn to the Hawker Siddeley Nimrod,

a passenger jet modified for

clandestine maritime surveillance.

The Nimrod was an incredibly interesting

aircraft -- essentially,

it was like the Swiss army knife.

It could be equipped with weapons,

torpedoes, or for intelligence, surveillance,

and reconnaissance operations.

NARRATOR: With a range of almost 6,000 miles,

Nimrods relentlessly comb the ocean for Russian subs,

relaying critical surveillance data back to the site

in the image.

Pilots are authorized to deploy

B-57 tactical strike nuclear depth bombs

on any intruders into British waters.

If you look at it, you would see basically a passenger jet,

but a passenger jet filled with either high-powered

weaponry or very sophisticated equipment.

NARRATOR: During its 40-year lifespan,

the Nimrod flies countless missions over hostile waters,

helping to repel the Soviet threat.

Today, evidence of its vital yet overlooked role at

the front line of the Cold War remains, visible from space.

WALTERS: These innocent-looking circles

are a really highly protected key zone of the Cold War.

It's one of the most secure places on Earth at the time.

NARRATOR: Coming up, attack of the scourge of God.

If you resisted, no mercy was shown.

NARRATOR: And the $60 billion hoard.

If you're a treasure hunter,

you might want to get out there now.

NARRATOR: August 19th, 2018.

A satellite orbits the Sistan Basin in southern Afghanistan,

140,000 square miles

of some of the most inhospitable terrain on Earth.

KOUROUNIS: In every direction, for hundreds of miles,

there's nothing but emptiness and sand dunes.

NARRATOR: Yet closer analysis reveals mysterious evidence of

human presence in these inaccessible,

Taliban-controlled wastelands.

MORGAN: There's a larger outer circle,

and then a smaller inner circle

with some structures inside of it -- it looks enormous.

NARRATOR: The mystery crumbling edifice covers

two million square feet of desert.

There are no trees, there's no water,

no other signs of habitation,

just this large structure that obviously took a lot

of effort to build in the middle of nowhere.

NARRATOR: Dialing up the magnification reveals

the structure is defended by a series of concentric

walls up to a mile long and 30 feet thick.

Military expert Sam Cavell studies them for clues.

The architecture here is very

reminiscent of Islamic military fort design.

It looks like the kind of structural elements

you would expect to see

in something that dates to about the 13th century.

NARRATOR: It appears the giant desert fort

was designed to defend against

the onslaught of perhaps one of the most dreaded forces in

all human history.

In the 13th century,

one of the greatest threats to this area would have been

the Mongol Empire,

led by one of the most fearsome warriors of all time,

Genghis Khan.

NARRATOR: The Mongols' journey to these deserts begins

in the Central Asian steppes in 1206 A.D.

Mobilizing 100,000 highly trained horseback warriors,

Genghis Khan sweeps west, covering up to 100 miles a day,

conquering all in his path.

Over the next 160 years, he and his descendants slaughter

up to 40 million people,

creating a 12-million-square-mile empire

that stretches from the Pacific in the east

to Poland in the West.

Mongolians were known simply for barbarity.

They were known for moving in and raping,

pillaging, and plundering everything that they could get

their hands on.

1219 A.D., the Mongol Horde,

known as the Scourge of God, reaches Afghanistan, ruled at

the time by the Khwarezmian Empire.

To defeat it, Genghis unleashes the fury of

200,000 soldiers.

The Mongol invasion of Afghanistan was

especially brutal.

JANULIS: He would give quarter to those who submitted

to his army at the beginning,

but if you resisted no mercy was shown.

NARRATOR: In 1221, the Mongols lay siege to

a city to the north of the site in the image.

In the process of the siege,

Genghis Khan's favorite grandson is killed.

Now, this is going to force instant

and absolutely brutal retribution.

KOUROUNIS: This was obviously a very bad decision.

This enraged Genghis Khan.

NARRATOR: To avenge his grandson's death,

Genghis deploys the first heavy gunpowder explosives ever

used in combat to slaughter every man,

woman, and child in the city

and surrounding region.

Khan's wrath knew no bounds.

This city was put to the knife.

Everybody was killed, brutalized, and tortured.

Even to this day, it's known as

the City of Screams after this massacre.

NARRATOR: What puzzles analysts is that the site in

the image appears to have been spared from Genghis's rage.

JANULIS: This fortress continued to seemingly thrive

for hundreds of years after

the surrounding cities and fortresses all fell to

the Mongol threat.

NARRATOR: Studies suggest the key to its survival lies in

its groundbreaking use of concentric defenses called

curtain walls.

This kind of circle fortress is something that the Islamic

armies were the first to perfect.

JANULIS: But each fortified wall around the city

creates a kill zone between the next.

It's like taking over a castle multiple times,

and this was a critical military innovation,

and that may be why this city continued

to flourish when everyone around them did not.

NARRATOR: Some 50 years after the Mongols' invasion

of Afghanistan,

Christian knights are confronted by the same defenses

during the Crusades.

Their bloody encounters lead to a transformation in

the design of forts and castles across the globe.

JANULIS: Because the Crusaders saw just how hard it was

to attack one of these types of fortifications,

they brought it home with them

and started building it themselves.

NARRATOR: Over the following centuries,

castles mimicking the Islamic design spring up across Europe

and beyond.

MORGAN: Ultimately, you will see them

spreading to North America.

You get forts in the United States that are

built during the 19th century

that are the expression of an art that began in Afghanistan.

NARRATOR: Today, the fort that helped to spark

this extraordinary revolution

in military architecture worldwide is being swallowed

by the desert.

But for now, its secrets are still visible from space.

It's fascinating that with the most modern technology

available to us, we can look down

and see this thing that tells us so much

about who we are today and where we came from.

NARRATOR: Coming up, hunting shipwrecks from space.

It's easier to identify massive holes

with hidden treasure.

Every day for five decades,

NASA's Landsat program has been scanning our planet,

mapping its constantly evolving surface.

As one of the space agency's satellites travels over

a patch of sea to the north of Belgium,

it captures something that doesn't make sense.

FANARA: What we're seeing here is vast ocean,

and we're also seeing wakes from boats.

But then if you look in the middle,

there are these trails with no vessel

attached, like phantom wakes.

NARRATOR: The ghostly trails are almost three miles long.

CAVELL: There's got to be something sizable under

the water that is creating this disturbance

so that we can see it from satellite images.

NARRATOR: Marine scientists head to the location

and study the seabed using multi-beam sonar.

MORGAN: These are images of the sea floor

and they shoot right through all that silt

and sediment to reveal what's actually going on,

and it appears that there is

a nest of shipwrecks in this position.

FANARA: What is happening here is that the currents moving

around these ships are causing the sediment

to come to the surface.

NARRATOR: From the Phoenicians, through to the Romans

and Vikings, the waters around the wrecks

witnessed trade and warfare throughout antiquity.

But closer analysis suggests these wrecks

are casualties of more recent history.

WALTERS: If they were sunk, you know, before that,

the boats weren't made out of metal, so they rotted away.

CAVELL: One of the vessels is broken completely in half.

I mean, there is some really violent action that has

taken place on this ship, and the question is what?

NARRATOR: Analysts cross-reference the wrecks'

locations with 20th-century maritime records.

PAVELEC: It turns out that these two ships are American

Liberty ships,

the Samsip and the Samvern, that were sunk during

the Second World War.

NARRATOR: Liberty ships were a class of wartime cargo

vessel and a lifeline between America and her allies

during the darkest days of the conflict.

The Liberty ship was a reflection of the exigencies

of the war effort.

They had to be made quick, and they didn't have to

last forever.

WALTERS: They were known as the ugly ducklings,

because they weren't pretty -- it didn't matter.

They got the job done.

NARRATOR: The Liberty ship program was one of

the most astonishing feats of engineering in military history.

Between 1941 and 1945,

18 shipyards across the U.S.

churn out almost 3,000 of these crafts,

each capable of carrying 10,000 tons of

vital supplies to a war-torn Europe.

Part of the hull was poured concrete,

which made it a really quick turnaround

to actually construct these ships.

WALTERS: They were producing these ships

in a matter of hours -- that's extraordinary.

NARRATOR: Yet these workhorses of war

are also virtually defenseless, and many ships

and their crews don't survive the conflict.

These Liberty boats were quite slow

and incredibly hard to maneuver.

So at the end of the day,

these ugly ducklings actually ended up being sitting ducks.

CAVELL: More than 200 would actually be sunk.

But ultimately, more Liberty ships are

produced than the Germans can sink.

And so this is the key to victory.

A discovery of the remains of two lost

Liberty ships is of great interest to historians.

But the satellite image has

a much greater significance than that.

MUNOZ: These sort of trails or plumes in the middle of

the ocean are red flags that could indicate

a shipwreck underneath.

This could really help governments and authorities

identify other shipwrecks

that could be scattered across the world's oceans.

NARRATOR: There are an estimated three million

shipwrecks spread across the ocean floors.

Until now, the resting place of many

of these vessels has been a mystery.

CAVELL: It's a needle in a haystack

operation to try and locate shipwrecks.

But the satellites can look down all day long, any day

they need to, and they can recognize these plumes.

NARRATOR: What intrigues many isn't just

the location of these wrecks,

but what they hold.

Over the years,

around $60 billion dollars of treasure has been claimed by

the ocean depths,

and now, it may be possible to hunt for it from space.

It's really exciting to now realize that we have

a clue into where these shipwrecks might be.

So, if you're a treasure hunter,

might want to get out there now.