Original subtitles

NARRATOR: Deep beneath the tropical waters of the Gulf of Mexico lies a

seething history of piracy, slavery and bitter conflict.

FRITZ: The Gulf of Mexico was the wild west of the sea and it's every man for himself.

NARRATOR: Imagine if we could empty the oceans, letting the water drain away to reveal

the secrets of the sea floor?

Now we can.

Using the latest underwater scanning technology, piercing the deep oceans and turning

accurate data into 3D images.

This time, why did a deadly German U-Boat end up at the bottom of the ocean off

the coast of New Orleans?

JAMES: Within very short range, the hunter becomes the hunted.

NARRATOR: Who was on board this mysterious wreck, from a time when pirates and

slave traders ruled the waves?

How did a single asteroid impact in the Gulf of Mexico

wipe out the dinosaurs around the globe?

KEN: The base of the food chain is knocked out and things begin to starve.

NARRATOR: And how did drilling for oil result in one of the biggest environmental

disasters in US history?

DAVE: In theory, that well should have been easy.

NARRATOR: Draining the oceans shines new light on the secrets of the Gulf of Mexico.

66 million years ago, dinosaurs roam the Earth.

Then, in a geological instant, they are wiped out, around the planet.

Can draining the water from the Gulf of Mexico explain why?

The story begins not in the Gulf but over 1,500 miles away in New Jersey.

This former quarry is one of the most important fossil sites in the world,

because here, paleontologists discover a mass prehistoric graveyard.

-This is the boundary between the cretaceous period, the age of the dinosaurs and

the age that comes after that, the Paleogene.

And what we have here is a bone bed, where we have about 25 fossils per square meter.

Paleontologists have never found an in-place dinosaur bone one centimeter above that

extinction layer anywhere on the planet.

NARRATOR: The absence of dinosaur fossils above this layer can mean only one thing.

They were wiped out by a sudden,

cataclysmic event, 66 million years ago.

-Whatever took out the dinosaurs was global, terrible and instantaneous.

NARRATOR: Experts have offered many answers.

But only one is widely accepted.

-By far the leading explanation is that an asteroid hit the earth

66 million years ago and unleashed hell on earth and took out the dinosaurs

and 75% of life.

NARRATOR: Scientists scour the planet.

Looking for evidence of asteroid strikes.

But none of the impact craters that they find are big enough and of the right

age to be the culprit.

Then, in Mexico's Yucatan peninsula, they find a surprising lead.

Mario Rebolledo, is an expert in a remarkable natural phenomenon found all

over this region.

Sinkholes, known locally as cenotes,

formed by the erosion of soft limestone,

they can be hundreds of feet deep.

Exploring them requires years of experience.

NARRATOR: Mario discovers that many of the cenotes are linked through deep,

subterranean channels.

But that's not all.

They also display a remarkably similar structure.

NARRATOR: When seen from above, an extraordinary picture begins to emerge.

The cenotes form an outline.

It looks like the rim of a gigantic crater.

The most likely explanation is that a massive asteroid strike reshaped this region and then

the sinkholes formed in fault lines around its edge.

Could this be the crater that's linked to the death of the dinosaurs?

Today, millions of years after it was created, the heart of the impact site lies concealed

not just under the waters of the Gulf of Mexico, but under several thousand feet of

sedimentary rock.

The only way to calculate its age and see if it dates from the demise of the dinosaurs is

to analyze rocks from the crater itself.

SEAN: To really understand impact cratering we actually need to pull rocks

from ground zero.

We need to find a place where we know that the damage has been the greatest in

order to get a sense of the way impact craters work.

NARRATOR: In 2016, an international team of scientists drill down from

this specially adapted oil platform.

SEAN: And so, we were pulling up limestone after limestone after limestone.

We're getting ages from the fossils within them.

We know we are at 48 or 50 million years but we're not yet at 66, right.

And then things suddenly jumped in time.

NARRATOR: The team hits a layer of melted rock, indicating an asteroid strike.

And samples confirm that the rocks are 66 million years old,

the exact moment when the dinosaurs died.

Next, the team analyze the rocks to calculate the asteroid's power

comparing their data to that generated by nuclear bomb tests.

-And we can come up with an estimate of the amount of energy released and that turns

out to be about ten billion Hiroshima's.

NARRATOR: Using this data, it's possible, for the very first time,

to create a 3D visualization of the crater, now hidden deep beneath the Earth and discover

how a single asteroid impact in the Gulf of Mexico could wipe out

dinosaurs around the globe.

First, the entire Gulf must be drained away.

As the water recedes, it reveals a vast continental shelf running

around the coastline.

The crumpled plain is thick with sediment, but the crater is still hidden under

thousands of feet of rock.

66 million years of geology must now be rolled back, draining away layer upon layer

of sedimentary rock, until the impact site begins to emerge, a sight that no living

creature has witnessed for 66 million years.

The crater is immense.

Over half a mile deep and 120 miles wide.

Around its edge towers the outer rim, formed by rock ejected from deep

within the Earth's crust.

Now, by studying the crater's profile, it's possible to determine the size and speed

of the asteroid.

It's over 7 miles wide and it travels at 40,000 miles per hour.

And the crater's dimensions tell us something else.

30,000 cubic miles of rock are displaced here.

Vast amounts hurled into the atmosphere, setting off a devastating chain of events.

-It blows a hole in the ground about the size of the State of Massachusetts.

Now all that rock, it gets pulverized, thrown up through the earth's atmosphere.

It starts to orbit the planet and when that rock comes back in,

it's got a tremendous amount potential gravitational energy.

it heats up the atmosphere to toaster oven or pizza oven temperatures,

frying everything that doesn't have a place to hide.

NARRATOR: Almost every living creature within 600 miles is killed by

this deadly fireball.

But those further away do not escape.

-Later that day the tsunami waves wash up on the shore.

These could have been hundreds of feet tall, maybe even half a mile tall when they hit

here, and they would have run up through the continent.

Animals that are still alive would have heard the wave coming for them

but wouldn't have seen it in the darkness.

NARRATOR: But the asteroid strike becomes a truly global disaster for

one specific reason...

where it hits Earth.

This part of the planet contains rocks high in Sulphur.

On impact, the Sulphur is vaporized and blasted high above the Earth.

-Well that Sulphur combines with the atmosphere and becomes sulphate aerosols and

sulphate aerosols are excellent at blocking sunlight.

NARRATOR: This deadly cloud shrouds the planet and the Earth begins to cool.

By studying the crater in more detail it's possible to see new evidence of how the

crater's shape makes the Sulphur cloud even more deadly.

The north-east rim is open.

The asteroid hits deep water here absorbing some of the impact and

thirty minutes later the ocean rushes back in.

Water vapor from this tsunami combines with the Sulphur to form

sunlight- blocking gases in even larger quantities.

-The plankton in the ocean can't do photosynthesis and pretty soon the base of the

food chain is knocked out and things begin to starve.

NARRATOR: Lack of sunlight means the entire planet experiences an average cooling

of 47 degrees Fahrenheit for up to 16 years.

Only the toughest plants and animals survive.

The dinosaurs do not.

One question remains, was this event unique or could it happen again,

this time wiping out human-kind?

-There are other near-Earth objects out there, asteroids just like the one that took

out the dinosaurs and we do not know where they all are.

Every day, scientists are discovering more and more asteroids that have the power

to menace our earth.

SEAN: Now, we think we've tracked all the big ones.

So, we don't think there is another event that is just around the corner,

but that doesn't mean we shouldn't keep making sure, given the circumstances.

NARRATOR: As we drain the Gulf of Mexico further, it's possible to reveal areas

where humans are drilling thousands of feet below the sea bed

to exploit a natural resource formed 100 million years ago...

oil.

But how did a failure while drilling in the Gulf of Mexico turn into the biggest oil

spill in US history?

NARRATOR: The economy of the Gulf of Mexico is driven by oil.

This vast, oil rich basin accounts for 17% of total US crude oil production.

Nearly half of America's oil refining capacity sits along the Gulf coast.

But it's offshore that the scale of the infrastructure needed to bring oil to the

surface is truly staggering.

Using the latest data and visualization techniques, draining away the waters of

the Gulf of Mexico exposes an extraordinary underwater world,

normally hidden in the dark depths of the ocean.

But how did an accident here cause the worst environmental disaster in the history of the

Gulf of Mexico?

Pumpjacks like these, introduced in the 1920s, can only extract oil in very small

quantities, on land.

DAVE: An old well like this is perhaps producing only 10 barrels per day of oil.

This is old technology.

This is on the twilight of an oil field.

You can tell that because it's nodding up and down.

That means that the pressure in that reservoir down there is low.

It's about ready to be finished.

NARRATOR: In the 1940s, oil companies discover a far more productive source,

below the waters of the Gulf of Mexico.

Here, the oil doesn't need to be pumped.

It flows.

And the reason lies deeply embedded in the unique geology of the Gulf.

JAMES: The Gulf of Mexico is one of the more oil rich areas on the planet because out beyond

us was once an ancient swamp 300 million years ago.

That swamp now is not only under the water, it's underneath the earth.

And as a result of pressure and heat all of that organic material has been

transformed into oil.

NARRATOR: To produce an oil field, three things are essential.

A layer of kerogen, the organic compound which creates oil.

A permeable rock such as sandstone known as 'source rock' for the oil

to accumulate in.

And a trap: a layer of impermeable rock above, to prevent the oil dissipating.

By drilling down through this hard layer, it's possible to extract the oil and gas from

the reservoir below.

And the Gulf's continental shelf provides the perfect base for

offshore drilling platforms.

-When you look out over the Gulf of Mexico and you see this flat expanse of water,

most people don't realize that this is very shallow.

You can go 50 to 100 miles out but it's only 100 feet deep.

NARRATOR: Since the first platform was constructed just a mile offshore,

the network has expanded greatly.

Around 3,500 platforms now sit off the coast.

But it's only by draining the ocean that it's possible to see the sheer scale of the

infrastructure hidden beneath the waves.

As the water recedes, these huge structures are left high and dry.

There are more oil platforms here than in the rest of the world combined.

In the 1970s companies begin to move off the continental shelf into ever deeper waters

to tap into even bigger reserves.

Operating in the Gulf's very deepest regions, up to 10,000 feet below the waves,

where conditions are extremely hostile.

DAVE: It is completely black.

Temperature down there is just above freezing.

You're drilling another sometimes 20,000 feet below the seabed and it gets

extremely hot.

So you have this big contrast between something that's very hot to something that's very

cold, let alone the extremely high pressures that we have.

NARRATOR: Today, there are around 50 deep-water rigs sited in the Gulf.

Continuing to drain its waters beyond the continental shelf reveals the huge scale of

infrastructure needed to bring oil to the surface from these super-deep wells.

Clusters of well-heads control the flow of oil and gas from deep below the sea bed.

The pressure in the wells can reach up to 22,000 pounds per square inch.

The well-heads connect to a central manifold, up to 100 feet high,

which controls the flow of oil and gas from across the oil field up

to the production rig.

The rig separates the oil and gas before they're transported to shore by pipeline some

stretching for hundreds of miles as they wind their way along the sea bed.

An incredible 43,000 miles of pipeline snakes across the floor of the Gulf.

With oil reserves close to shore now becoming depleted, companies continue to search

the Gulf of Mexico for new, more productive oil fields.

Special rigs, costing nearly half a million dollars a day to operate,

drill exploration wells called wildcats, reaching miles below the sea bed.

One such rig is called the Deepwater Horizon.

DAVE: The Deepwater Horizon is an exploration drilling rig.

We use what we call mobile drilling units to come in and drill the initial well.

If we find oil we run casing down there we cement it off and then we move that

exploration rig off location and then come back later to put on

the production equipment.

NARRATOR: In 2010, the Deepwater Horizon strikes oil 50 miles off the coast of

Louisiana in an area codenamed Macondo.

-In theory that well should have been easy in that the water depth

about 5000 feet.

We have been drilling in 5000 feet of water since 1979.

The pressure wasn't too high either.

However, we are in a very potentially dangerous industry.

REPORTER (over TV): Now another major story developing in the Gulf of Mexico.

Eleven people are missing after an explosion and fire on an off-shore oil rig.

REPORTER 2 (over TV): The explosion happened aboard a mobile offshore

drilling unit called the Deepwater Horizon.

It erupted with 126 people on board.

NARRATOR: The cement lining, designed to seal the well before the rig moves away,

has a leak in it allowing oil and gas to force their way up to the rig and ignite.

After burning for two days, the rig sinks.

The eleven missing workers are never found.

In the aftermath, 60,000 barrels of oil per day escape into the Gulf.

With the well-head a mile underwater and the oil pressure so high,

engineers can't stop the flow.

-In the immediate aftermath of the disaster even while the well was flowing the

government stopped all deep-water drilling in the Gulf of Mexico and rightly so

until we could figure out what had happened and what you need to do to be sure not only it

doesn't happen again but if it does happen that you have equipment so

that you can stop it immediately.

NARRATOR: To seal the Macondo well, engineers design a solution from scratch...

a capping stack to latch over the well-head, working remotely at incredible depths.

By the time the well is sealed 87 days after the blowout, nearly 5 million barrels of

crude oil have escaped.

The worst environmental disaster ever to strike the Gulf of Mexico.

The wreck of the Deepwater Horizon now lies on the sea bed.

But it's not alone.

Human commerce began in the Gulf of Mexico hundreds of years before the oil and gas

industry took hold.

As the water continues to drain away, an extraordinary relic of the region's maritime

history is about to be revealed from a time when the Gulf became a superhighway for

pirates and smugglers trading in the most valuable 'commodity' of the age...

human life.

NARRATOR: Oil and gas exploration means the seabed of the Gulf of Mexico is

surveyed in fine detail.

And the search for oil regularly uncovers long-lost shipwrecks.

Including a mysterious ship 150 miles south of New Orleans.

As the water of the Gulf of Mexico continues to drain away,

it will be exposed to the sky for the first time in 200 years,

giving an extraordinary insight into a period renowned for piracy,

smuggling and slavery.

Who was on this mysterious ship and what was its cargo?

Sitting at the mouth of the great Mississippi River, New Orleans,

in the early 19th century, expands rapidly.

FREDERICK: New Orleans was basically a bustling maritime entrepôt.

I mean, this was one of the largest ports in the western hemisphere and

it was situated centrally in the Gulf of Mexico.

And so, you have hundreds of ships coming and going, importing,

exporting all sorts of different kinds of trade goods,

but you're also seeing an increase in illicit activity from slave trade to smuggling,

and, and this place is just booming.

NARRATOR: Hard evidence of this extraordinary period of maritime history

is extremely rare.

Then, in 2011, an oil company identifies a wreck, giving it the name 'The Monterrey'.

FREDRICK: This particular shipwreck lies on the sea floor at an approximate

depth of 4500 feet or almost a mile,

which makes it really difficult to get to, but it also means it's going

to be that much better preserved because the temperature at that depth is

four degrees Celsius and that really slows the rate of decomposition.

NARRATOR: The team launch a state of the art remotely operated vehicle,

or ROV, to investigate.

FREDRICK: The ROV takes four hours to get down to the sea floor

and so, you know, there's this anticipation.

When the ROV hits the floor and cruises up to this particular site and we lay our

eyes on the shipwreck for the first time, we're astounded, we're excited.

Because what we're looking at is a largely intact ship almost a mile deep in the

Gulf of Mexico and it was just mind-blowing.

NARRATOR: As the ROV travels over the wreck it sends back tantalizing glimpses

of the ship and its contents.

-At this depth in the ocean it's pitch black, there's no light,

you can't see anything unless you light it up.

So, when we're working on sites like this in particular, we're only getting snapshots

or small glimpses of the site itself.

We don't have the entire picture while we're viewing the ROV footage.

NARRATOR: The ROV also captures precise data from on-board sonar equipment.

Combining this with the latest visualization techniques, it's now possible to drain

the ocean and pull the plug on more of the Gulf of Mexico, letting archaeologists view

the wreck from any angle and examine it in unexpected detail.

Will seeing it for the first time in 200 years help them discover what it was doing,

how it came to lie on the sea bed and the biggest mystery of all: who was on board.

As the water recedes, the ship is revealed.

The bow, sheathed in copper to protect against

marine organisms, still intact and the anchor still stowed.

Chain plates, once used to secure the rigging, indicate it had two wooden masts,

long lost to the ocean.

With the water gone, six cannon lay exposed to the sky.

And around the stern, lying on the sea floor, a cache of muskets.

JAMES: What struck me was this was a ship that was very long and narrow

particularly at the bow.

It struck me as almost being like a clipper ship, a specific type of vessel that

came into the fore really in the early 1800s.

NARRATOR: Clippers were perfectly suited to the Gulf of Mexico due to

their shallow draft,

ideal for navigating the Gulf's coastal waters and marshy bayou.

-What also struck us was that it was armed.

It had cannon, and there were muskets, was it a warship, was it something else?

NARRATOR: Is it a privateer?

-A privateer is basically an individual that has written permission or letter of marque

or letter of commission from a respective government giving them permissions to capture

ships, to make incursions on enemy soil in the name of that particular country.

-Privateering is basically state sponsored piracy, in which the privateer gets a cut

of the action and the rest goes to the state that's licensed them.

NARRATOR: In the first two decades of the 19th century there are hundreds

of privateers in the Gulf of Mexico.

But as the ocean drains even further away from around the Monterrey,

there's a twist to this story.

The wreck is not alone.

As the water disappears, a complete picture of the entire sea floor begins to emerge for

the very first time, revealing the remains of two other ships,

each containing further clues.

-It's really exciting to have one shipwreck but when all of a sudden you go from one to

three it gets incrementally more exciting because now we're not talking about just

one wreck we're talking about a potential convoy.

NARRATOR: Wreck A, the first ship discovered, is heavily armed with cannon and muskets

for close quarter combat, leaving researchers to think it could be a privateer.

With wreck B, it's clear that the wooden hull has been consumed by the ocean.

But its cargo is still intact.

It's carrying animal hides, a valuable commodity at the time and frequently traded.

Treated and rolled for shipment, they are well preserved by the cold waters.

Wreck C, exposed to the sky for the first time in 200 years, is a larger,

three-masted vessel.

But amongst this wreck, there's no cargo to be found.

-What does that mean?

Well it means the ship was either sailing in ballast, that is empty,

or it had a cargo that was perishable, and that perishable cargo could have

been everything from rice or grain, to one possibility being a very sobering thought

and that is it could have been carrying people.

It may have been a vessel engaged in the illegal slave trade.

NARRATOR: The trans-Atlantic slave trade sees slaves violently captured and

shipped from West Africa, and then forced to work on US plantations.

Although owning slaves remains lawful, the import of new ones is outlawed by

Congress in 1807.

Great Britain also bans the trade and uses its navy to hunt down and

capture slave ships.

With much money still to be made,

smugglers continue to bring captured African men,

women and children through the Gulf of Mexico and into its maze of channels and

waterways, aiming for New Orleans and its slave markets.

Is wreck C involved in this brutal, callous business?

-Now we didn't see manacles or anything of that sort but in this period, when it's lost,

it's entirely possible, as we know from other cases, that people were simply locked

below in the hold, and with those that were most capable of trying to escape

being tied up.

NARRATOR: The team begin to piece together the evidence.

-In thinking about these ships as a convoy, we can hypothesize a

variety of scenarios.

The first would be it's an armed escort with two merchant ships that need protection to

get from one port to another.

It could be a privateer with two prizes that it captured.

In looking at the cargo on the second ship we have stacks and stacks of cow hides.

Those would have brought a great price at the market, even if you were smuggling.

NARRATOR: To unravel the mystery further, they select a range of artifacts and bring

them to the surface.

They could reveal once and for all who was on board.

AMY: One of the unique things about this particular shipwreck Monterrey shipwreck-A

was the cannons and the presence of muskets.

Those were all British types, British military musket types.

They were absolutely ubiquitous in this region during the first half of the

19th century, so having British muskets on a ship does not mean that it's

a British vessel.

NARRATOR: The crews' nationality remains a mystery.

But there are other clues that may tell us what caused the ships to sink.

AMY: A portion of the collection that was recovered were navigational tools.

The importance of these tools was so great that you would have wanted to have taken

those with you so leaving them on the ship is foreboding and you know,

it suggests that maybe everyone perished.

NARRATOR: The Gulf of Mexico is notorious for a particularly violent force of

nature: hurricanes, giving rise to one likely scenario.

JAMES: All three of them were running together in what clearly was a

very violent storm.

You had a quick moment to look on the horizon, see the other guys there and

then their lights disappear if it's at night or they disappear in a squall.

And the next thing you know the Gulf is coming over your own decks and you're being

dragged down into the depths, and into the darkness.

NARRATOR: The Monterrey group of wrecks provides a new insight into the maritime

history of the Gulf of Mexico,

at a turning point in US history.

FREDRICK: The Monterey shipwrecks are important because they're evidence of that

transition to the birth of a new nation.

How trade continued while the Spanish empire crumbled.

Why New Orleans was such an important part of this interregional,

burgeoning global trade.

And that's what those shipwrecks speak to and that's what they're symbolic of.

NARRATOR: The Monterrey wrecks are not alone.

As the water drains away further, leaving the darkest depths of the

Gulf of Mexico exposed,

one of the most extraordinary stories of all is about to be revealed:

a state-of-the-art WW2 submarine, not American but German.

What was Nazi submarine U-166 doing in the Gulf of Mexico?

And how did it meet its end?

♪ ♪

NARRATOR: December 11, 1941.

Hitler declares war on the United States.

NARRATOR: When the US enters the war, a new battleground opens up...

The Gulf of Mexico.

Today, by draining away its dark waters, it's possible to reveal secrets from this

desperate period of conflict, when a ruthless battle to rule the waves comes to America's

own shores and solve a mystery which has baffled historians for over 70 years.

Immediately after entering World War II, the US faces a deadly peril,

off its eastern seaboard.

Nazi U-boats.

Their objective is to disrupt Allied shipping bound for Europe, at the source.

The U-boat commanders are highly experienced, having honed their skills

in battle since 1939.

The United States is completely unprepared for them.

ERIC: Ships were escorted across the North Atlantic in convoys both ways.

But once they got into American coastal waters they were unescorted,

and they were therefore easy targets for the U-boats.

NARRATOR: To make matters worse, the US government fails to impose a blackout.

Ships sailing along the coast at night are perfectly silhouetted.

Sitting ducks.

-And this was a key vulnerability the Germans noticed,

and they sent their submarines in to exploit it.

NARRATOR: German submarine commanders call it 'American shooting season'.

Between January and June 1942, more tonnage is sunk off the U.S.

coast than the Allies have lost during the previous two and a half years,

as the Nazis try to starve Britain of vital supplies.

The U Boats then take the war into the Gulf of Mexico.

And the reason is oil.

-Most of the world's oil at this time came through the Gulf of Mexico,

hence it was the equivalent to the Arabian Gulf today.

NARRATOR: It's not just oil tankers.

Any Allied ship is seen as fair game.

JAMES: A U-boat skipper did not want to pass up on the opportunity to sink what might

be a valuable cargo of a specific commodity, be it foodstuffs,

be it machinery or parts.

He couldn't know for certain, but he did know that if he sent a ship to the bottom he

was aiding the German war effort.

NARRATOR: One such ship is the Robert E Lee.

ROB: The Robert E. Lee was a passenger freighter.

It was coming from Trinidad up to New Orleans and it actually was carrying American

construction workers and also a lot of other passengers that were victims

on previous U-Boat sinking's.

NARRATOR: As the Robert E Lee approaches New Orleans,

U-166 is on patrol.

One of the latest German long-range submarines, U-166 is capable of traveling across

the Atlantic without the need to refuel.

A thoroughbred ocean predator, commanded by battle-hardened Captain Hans Gunther Kuhlmann.

ROB: Hans Gunther Kuhlmann had not had a lot of success during this mission.

He had sank a couple of small boat, including one that was just a few tons.

It actually bore the same name of his wife, Gertrude.

And so as soon as he saw a large vessel over 5,000 tons, it was a big target and it was

an opportunity for him to get some tonnage under his belt.

NARRATOR: The details of the battle, including the fate of U-166,

for years remain one of the Gulf of Mexico's greatest mysteries.

Rob Church is a marine archaeologist for a company performing surveys of the

sea floor for the oil and gas industry.

When a wreck is discovered, his job is to assess its historical importance.

-So, this is a typical inspection class ROV.

It is a 3,000-meter rated system.

On this particular one right now we have three camera arrays here.

We have the two stereo cameras for collecting 3D video.

We have the HD camera above them for collecting high resolution video.

We also have a seven-function manipulator arm which allows us to be able to pick up

things on the sea floor; collect samples, also ah set out experiments, etcetera.

And then we have a scanning sonar.

This allows us to detect targets on the sea floor to inspect or we can also use it

navigate around shipwrecks.

NARRATOR: While conducting an oil pipeline survey using an ROV similar to this,

Rob Church comes across a wreck.

ROB: We approached from the stern and you could see the railing,

you could see the decks of that passenger freighter

and there was no doubt at that point that we were looking at the Robert E. Lee.

This was a thrilling moment.

And to see a boat like the Robert E. Lee,

which is really a beautiful wreck site, it was incredible.

NARRATOR: Over 5,000 feet down, the ROV scans the site collecting valuable data.

From this, it's possible to drain away the ocean and see the drowned vessel as she is

today but this time, exposed to the sunlight.

As the water pours away, the wreck of the Robert E Lee is revealed in extraordinary

detail, providing new evidence on her final moments.

The bridge is gone, unable to withstand the forces of drag as the ship plummeted

through the water.

The deck gun on the stern is in the stored position showing the attack

is sudden and unexpected.

And lying next to the wreck are two lifeboats.

The speed with which the ship goes down does not give the crew time to deploy them.

Experts calculate that it takes just three minutes for the Robert E Lee to sink.

But one important part of the puzzle remains unanswered.

What happened to the U-boat that fired the deadly torpedo?

As the water continues to drain away from the wreck of the Robert E Lee,

one of the Gulf of Mexico's biggest maritime mysteries is about to be solved.

NARRATOR: July 30, 1942.

The German submarine U-166 fires a fatal shot at the merchant vessel,

Robert E. Lee off the coast of New Orleans.

It sinks in three minutes.

But the Robert E Lee is not alone.

It's escorted by a submarine chaser Patrol Craft 566, captained by Herbert Claudius.

ROB: The indications are that the U-Boat had no idea that the patrol craft was

bearing down on them.

They were proceeding at periscope depth watching the

Robert E. Lee sink.

It wasn't until the patrol craft got within range and began actively pinging sonar

against the hull that they first apparently realized they were under attack at that

moment and began to dive.

JAMES: Within very short range, the hunter becomes the hunted.

NARRATOR: As Patrol Craft 566 passes over the U-boat,

Captain Claudius fires two rounds of depth charges.

Unable to confirm a kill, he turns his attention to rescuing survivors

of the Robert E Lee.

The fate of U-166 remains unknown.

Two days later a US Coast Guard plane spots a U-boat surfacing 140 miles away.

It drops a single depth charge and the U-boat disappears.

The plane crew is credited with sinking U-166.

But despite extensive scanning of the sea floor,

no trace of a wreck is ever found.

-Finding something that so many people had looked for so long it's kind of you know,

it takes an element of luck.

NARRATOR: Studying a sonar scan of the sea bed around the Robert E Lee,

Church spots a mysterious object, less than two miles away from the wreck.

ROB: So, as I first saw the image I realized it had potential.

But it was about 50, 60 feet short of the dimensions of a Type 9C German U Boat.

NARRATOR: What was this mysterious wreck, 140 miles away from where U-166 was

believed to have sunk?

Could it be the missing sub?

Further draining of the ocean uncovers the truth.

As the water recedes, light begins to pour onto this mystery vessel.

The conning tower of a German U-boat gradually appears, its antenna unretracted

indicating it dived suddenly and under duress.

Next, its hull is exposed to the sky for the first time in over 70 years.

The configuration of the conning tower and deck guns exactly matches

the missing U-166.

And from another angle, the reason the sonar image is short suddenly becomes clear.

The U-boat's bow is missing, blown off by a massive explosion.

As the water continues to drain away, the missing section is revealed,

lying 500 feet away.

A depth charge alone could not have caused such catastrophic damage.

So, what happened?

-It appears that after one of the depth charges breached the pressure hull that it probably

set off an internal explosion which then ripped the bow section off.

ERIC: When the submarine dived, perhaps torpedoes became loose and it was more

likely that an explosion would occur.

This was a successful depth charge attack and it was clear that this was actually

sunk as claimed by the submarine chaser.

NARRATOR: 22 people lost their lives on the Robert E Lee and all 52 perished on the U-166.

The two wrecks are now considered a war grave and cannot be salvaged.

Draining the ocean is the only way to bring the wrecks to the surface and

in the process set the record straight.

With the U-boat discovered lying less than two miles from the Robert E Lee,

there can be no doubt who sank it.

The kill is now credited to Herbert Claudius, captain of Patrol Craft 566.

Soon after the sinking of U-166, the tide begins to turn in the Battle of the Atlantic.

-Inevitably, the Allies were able to push back against the U-boat assault thanks

to a variety of factors.

Increased surveillance, more convoys, as well as the ability to strike from the air,

the U-boats were steadily defeated.

NARRATOR: Nevertheless, during the Second World War, while operating in US waters,

the German navy sends 609 Allied ships to the bottom of the ocean with the loss of

only 12 U-boats.

Of those, only one submarine is sunk in the Gulf of Mexico...

U-166.

Looking below the waters of the Gulf of Mexico has solved long lost mysteries and

brought deadly secrets back to the surface showing that the story of North America:

through trade, war and even the death of the dinosaurs can only be fully

seen and understood by draining the oceans.

Captioned by Cotter Captioning Services.