NARRATOR: It's the most ambitious expedition of its day.

In 1845, British explorer Sir John Franklin heads into the frozen wilderness of the Arctic to conquer the fabled shortcut to the Orient: the Northwest Passage.

But this grand expedition would never return home.

HUW LEWIS-JONES: There is no story in the history of British exploration that ends as tragically as this.

129 men disappear off the face of the earth.

NARRATOR: Again and again, searchers ventured into this icy wasteland, an effort that continues to this day.

Over time, a meager trail of clues emerged.

Hints of illness, starvation, even cannibalism.

But no sign of Franklin's two ships.

What happened to them?

This maddening mystery has remained unsolved for 170 years.

But now, archaeologists are mounting a far-reaching modern search for Franklin's lost ships.

Ships don't just disappear.

If there is a Franklin expedition ship, we will find that ship.

NARRATOR: Combining 21st-century technology with previously dismissed eyewitness accounts, they make an astonishing find.

RYAN HARRIS: Jabbed my finger right at the screen and kind of lunged for it and said, "That's it, that's it!"

NARRATOR: This amazing journey into the Arctic could solve a mystery 170 years in the making and rewrite the history of exploration.

Search for the "Arctic Ghost Ship," right now on NOVA.

♪ ♪ NARRATOR: The Canadian Arctic.

As the summer of 2014 comes to an end... (ship banging into rocks) ...the ice is closing in.

Working from icebreakers, a team of wreck hunters is scouring the ocean floor with their sonar equipment.

They're searching for two ships believed to have sunk in these frozen waters in the 19th century.

This high-tech mission is only the latest in a long history of failed attempts to solve a perplexing mystery... What happened to the British explorer Sir John Franklin and his crew of 128 fine sailors when they sailed two heavily fortified ships into this Arctic wasteland and then vanished off the face of the earth?

That question has gone unanswered for 170 years.

And now, after weeks of searching, yet another effort, like all those before it, seems on the verge of failure.

Are you worried about that ice coming in?

That's not good.

NARRATOR: In just days, these seas could freeze over completely.

Are you going to stop it?

Yeah.

So, let's head back towards the ship.

NARRATOR: Their window is closing.

The mystery has its origins in 1845, as two great ships leave England on a historic quest to map the fabled Northwest Passage.

European traders had long understood that the most direct route to the Orient lay to the west, if only they could find a way over the Americas.

RANULPH FIENNES: Why not go over the top?

The world narrows as you go up.

Go across the top of North America.

And so the idea was to find what they called the Northwest Passage.

NARRATOR: The approaches from both the Atlantic and Pacific were already surveyed.

But in between, the charts showed a mysterious gap, an area that had defied explorers for centuries.

So in 1845, Sir John Franklin set out to find once and for all whether the gap could be bridged and to claim the passage for the British Empire.

HUW LEWIS-JONES: The fact that there's an empty space on the chart, a terra incognita, that's both appealing, but also an insult to the British Navy.

They need to fill in the lines on the map.

There's power in the ink lines that are drawn on charts.

It's ownership.

It's sovereignty.

It's politics.

NARRATOR: To conquer the Northwest Passage, the Navy put together the best equipped Arctic expedition there had ever been.

Sir John Franklin, a veteran of the Arctic, was chosen to lead.

ANDREW LAMBERT: Sir John Franklin was one of the two or three outstanding polar navigators of the first half of the 19th century.

He combined experience, scientific expertise, and a proven track record as a leader of men.

NARRATOR: 59-year-old Franklin had led two previous Arctic expeditions to survey the coastline of the North American mainland.

During one trip, when supplies ran low, the crew had to eat anything they could to survive, and Franklin became affectionately known as "the man who ate his own boots."

This time, he was better prepared.

He and his crew of 128 men sailed on two specially adapted former warships: HMS Erebus and HMS Terror.

These young men had left behind their loved ones in pursuit of the greatest prize in Arctic exploration.

They knew the ships would encounter ice, so the hulls were strengthened with oak planking up to eight feet thick and reinforced with iron plate.

Plans from the National Maritime Museum in London show they were also fitted with innovations such as coal-powered steam propulsion, a retractable propeller, and even central heating.

The ships were stocked with three years of food rations, a library, even musical instruments to help pass the time.

(crewmen playing lively dance tune) They were better equipped than any previous expedition.

But how prepared could they really be for a world about which they knew so little?

LAMBERT: It was very much the dark side of the moon as far as the Victorians were concerned.

It was somewhere that had fascinated men for hundreds of years, but they'd never mastered the environment.

NARRATOR: In July 1845, a whaling ship recorded a final sighting of the expedition in Baffin Bay, west of Greenland.

From there, they sailed into oblivion.

In the 170 years since then, despite scores of well-equipped search attempts, only a few meager clues have been found, and no trace of the ships.

In 2014, a crack team of wreck hunters embarks on a fresh search.

Writer and historian John Geiger has been obsessed with the mystery for decades.

To him, this is a once-in-a-lifetime chance to lay the ghosts of the Franklin expedition to rest.

JOHN GEIGER: Been involved in one way or another with Franklin since my 20s.

It's the greatest mystery in exploration history.

There's nothing that compares with it.

It's really important from a historical standpoint to understand what happened to them.

NARRATOR: Only by finding the wrecks can crucial questions be answered.

Exactly why did the expedition fail?

And how far through the Northwest Passage did they get?

It won't be easy.

The wrecks remain lost, largely because searching these icy waters is such a difficult and dangerous task.

In recent years, the government of Canada and its partners have mounted several expeditions, deploying icebreakers and sonar equipment to hunt down the wrecks.

But these costly missions have another purpose.

As global warming melts the ice, interest in extracting the Arctic's natural resources will likely grow.

These surveys will allow safer navigation here in the years to come.

These vessels host a diverse taskforce led by the underwater archaeology team of Parks Canada.

RYAN HARRIS: This is actually our sixth field season searching for Franklin's lost ships.

We're hoping that there's going to be a payday down the road here.

NARRATOR: Despite the calm exterior, the team is desperate for a breakthrough.

In the last six years, they've searched close to 500 square miles of seafloor and found nothing.

They have two key search zones.

One, in the north, is based on clues found by earlier search parties.

Further south, a second zone is based on sightings of a ship preserved in the oral history of local Inuit populations.

But even after six years, there's still a huge area to search.

In the north, sea ice often lingers through the summer, so plenty of this area remains unsurveyed.

This year, they hope to put that right.

GEIGER: We're looking in the very place where Erebus and Terror were last reported by the men who sailed those ships.

You know, if you lose your keys, you generally go back and look for them in the last place you remember seeing them.

NARRATOR: By combining the last known position of the ships with information on prevailing currents, the team has drawn up a northern search zone of some 540 square miles.

So how will they search such a huge expanse of seafloor during the brief Arctic summer?

This year, for the first time, they have a secret weapon.

It's basically an unmanned torpedo that we can deploy pre-programmed and it will literally go out in the sea, follow the route that we've asked it to follow, gather data, and come back with that data.

NARRATOR: This is the Arctic Explorer, a precision piece of military hardware that uses sonar to scan a square mile of sea floor in just an hour.

BERNIER: The sonar itself, which is an acoustic system, that will send a signal to the bottom and recapture it to give a picture of what's on the bottom.

NARRATOR: It produces images like this, showing the seafloor in incredible detail.

Any sign of a ship would show up immediately.

But if there's any hint of ice, the team will have to pull this delicate instrument out of the water.

The last thing they need is to lose their best search vehicle.

For the first two weeks of the search, drifting ice floes have prevented them from deploying the Arctic Explorer.

But their luck may be about to change.

We're seeing a growing surface area of open water.

NARRATOR: A small window in the ice is an opportunity to deploy the Arctic Explorer for the first time.

It's a risk, but just one pass could be enough to reveal a wreck.

It looks like we should try to get into action.

NARRATOR: Wary of rogue ice floes, the team will track the submersible every step of the way.

For several hours, it will track up and down the search zone, scanning an area of a few square miles.

Only when the sub returns can they access the images, hoping against hope for a glimpse of a wreck.

When Franklin set sail in 1845, he was aware that his ships could be trapped in sea ice for at least one winter.

But in 1847, after two years with no word, Lady Jane Franklin put pressure on the authorities to start looking for her husband and his crew.

Rescue missions were sent from Britain and America.

And in 1850, near the entrance to the Northwest Passage, a joint search team turned up the first clue.

Graves.

Of three sailors who had died during Franklin's very first winter in the Arctic.

Even in the 1840s, this many fatalities so early in a mission was unusual.

LAMBERT: This shouldn't happen.

Three men should not die in the first winter of an Arctic expedition.

They've only been out of Britain six months.

What's killing them?

NARRATOR: With Erebus and Terror st uck in the ice, these graves indicate Franklin's expedition spent their first winter here at Beechey Island, well north of the modern search zone.

Overwintering was something they'd anticipated.

Burying three of their crew was not.

One of the graves was marked with a quote from the Bible.

(bell ringing) "Thus saith the Lord of Hosts; consider your ways."

Puzzling.

It's ominous.

Has something gone wrong?

Do they sense that something is going to go wrong for the rest of the expedition?

NARRATOR: Over a century later, in 1984, archaeologists exhume the bodies to try and work out how they died.

The corpses were shockingly well-preserved in the frozen ground.

Tests revealed high levels of lead in their systems.

Lead was a common pollutant in 19th-century England.

But it could also have come from piping in the ship's water system, or even from the solder used to seal canned food.

Innovations designed to protect the men from the rigors of the Arctic.

But the tests didn't prove that lead poisoning was the cause of death, so this clue only deepened the mystery.

In the search zone, the Arctic Explorer has scanned a few square miles near the last position of Erebus and Terror recorded by the crew.

Back on the ship, the team downloads the data to get their first glimpse of the Arctic seafloor.

DAVE SHEA: As you can see, there's not a lot of features in this particular area.

BERNIER: So, this is sterile completely.

There's nothing, right?

Yeah.

NARRATOR: With no discoveries in the first pass, they're eager to press on with the search.

But there's a problem: the ice, which had briefly opened up, is back.

GEIGER: As hard as it may be to believe, this is somewhere in the Arctic.

In parts of the Arctic, this is as good as it's going to get this year.

NARRATOR: Global warming means the amount of summer sea ice in the Arctic is in long-term decline.

But from one year to the next, the picture is far more complex.

Just because there's a warming trend due to global warming doesn't mean that you won't have variations.

Modern-day ships can still encounter difficult ice because the year-to-year variations in this part of the world can be just extreme.

You can go from no ice one summer to completely landlocked ice, where the ice goes from coast to coast, in another summer.

It's hard to predict.

The Arctic has always been an incredibly variable place.

NARRATOR: In 2014, unusually extensive sea ice is now threatening to shut down the search here entirely.

It's frustrating because the team is so close to the suspected last location of Franklin's ships.

But how do we know these crucial coordinates?

After the discovery of graves in 1850, several more search expeditions were sent to the Arctic.

And in 1859, nearly 15 years after Franklin set sail, the next tantalizing clue was found on King William Island, nearly 400 miles south of the burial site.

Here, in a stone cairn, men of the Franklin expedition had left a single, handwritten note.

LEWIS-JONES: The note, an incredible document of the fate of the Franklin crews.

How can a piece of paper hold fortune in its hands?

This is the most important object that has been recovered.

NARRATOR: This precious piece of the Franklin puzzle is now held at the National Maritime Museum in London.

CLAIRE WARRIOR: It was standard naval practice to issue these kind of notes with a standard blank form that would be filled in when necessary.

The notes were then placed in tubes like these.

They could be just left for people to find information about the expedition.

NARRATOR: The note explains that from Beechey Island, the expedition sailed over 350 miles south to coordinates near the coast of King William Island.

Here, the men spent their second winter in the Arctic, and the message ends with the upbeat words "all well."

But scrawled around the edge of the note is another message, written a whole year later.

A shocking turn of events that must have filled the surviving men with despair.

(coughing) NARRATOR: Franklin was dead.

There's no mention of how he died, but the note goes on to say that nine officers and 15 sailors had also passed away.

Something was going seriously wrong.

LEWIS-JONES: The loss of any leader in the middle of an expedition isn't good news.

Particularly so when you're stranded in the middle of nowhere in a hostile environment.

NARRATOR: The captain of HMS Terror, Fr ancis Crozier, was now in command, and he had a problem.

His note implies that rather than breaking up, the sea ice remained frozen solid throughout the summer of 1847.

The ships were trapped, and the men faced yet another winter stuck in the heart of the Arctic.

So, why had the ice failed to melt?

Climate scientists collect and study ice core samples to reconstruct past weather conditions.

During warm summers, ice on the surface will melt, leaving characteristic pale bands in the core.

But dark areas, lacking in these distinct pale bands, indicate times with far colder summers.

And ice core data shows that the Franklin expedition coincided with a period of at least 30 years with especially frigid conditions.

Based on the ice core record, the Franklin era was the least favorable in terms of ice conditions in the past 700 years.

This period was unusually cold, and so he really was unlucky with the timing of his expedition.

Just an unfortunate confluence of events, and it's nothing that he could have anticipated.

NARRATOR: Mother Nature had dealt a cruel blow.

But with the fate of 105 ailing men in his hands, the note reveals that Captain Crozier decided to make his move.

He ordered the men to abandon the ships and march south toward Back's Fish River, knowing that beyond there was a British trading post.

Setting off, they faced a daunting trek of over a thousand miles to reach it.

Exactly why he attempted that journey or whether he really believed they could make it, the note doesn't say.

It is the most enigmatic of clues.

It's just enough to locate them in the landscape.

It's just enough to tell you that something terrible has happened.

It's just enough to point you in the right direction to follow them.

But there's so many things that are not there.

NARRATOR: The coordinates in Crozier's note are the basis for the team's northern search zone.

But winds and currents mean the ships could have ended up anywhere within this huge area.

And in 2014, sea ice has plagued that area all summer.

It's been a sort of cat-and-mouse game.

We feel like we have a break, we feel like we have a shot, and then the ice shifts and the doors close.

NARRATOR: In a couple of weeks, these seas could freeze over completely.

Knowing that time is short, the team sends up a helicopter to find gaps in the ice.

MAN (on radio): You can get to our position right here.

It's at least eight to ten miles in open water.

Actually, that's excellent.

GEIGER: The good news is that to the north of us, there is a large opening.

And this is right where we want to be.

It's right in the primary search zone, so essentially, we have a shot here.

BERNIER: We're waiting to launch the first mission of the day.

We're going to look at a first block of four kilometers long.

There we go.

Now the waiting starts.

Do you have a visual on it now?

NARRATOR: But just an hour into the search, ice is spotted drifting across the Arctic explorers' path, and the run is aborted.

BERNIER: This morning, we had a window, and very rapidly, that opening closed on us from all sides.

The ice is moving quickly around us again, capturing us, trapping us.

NARRATOR: The northern search zone is huge, and the ice makes for slow progress.

With time running short, the team abandons this area in favor of the southern zone, where there's less ice and some additional clues.

The team began looking here six years ago based on eyewitness accounts of the plight of Franklin's men preserved by Inuit oral tradition.

Oral tradition is a very important aspect of Inuit culture and Inuit life.

That's how we learn about where to go and get the food, or you may know about these ice conditions in the springtime.

Oral history had to be very, very accurate, because if it was not, it could mean death.

NARRATOR: According to Inuit accounts, expedition survivors were spotted many times as they marched south.

Those sightings were later passed on to search parties, including one remarkable story gathered in 1869 by American explorer Charles Francis Hall.

It describes a dramatic face-to-face encounter between the Inuit and one group of Franklin's men.

According to the story, an officer walked forward, shouting the Inuit word for friend.

(speaking Inuit) NARRATOR: Some believe this was Captain Crozier, who had learned some Inuit words on a previous expedition.

(speaking Inuit) NARRATOR: The Inuit provided seal meat for his starving crew.

But there was no way they could support so many men, so the Inuit left, knowing that sharing any more of their food would have been suicide.

So the men continued to march southward.

According to Inuit accounts, they dragged small boats laden with supplies.

LEWIS-JONES: If they stop, they die.

So they walk and they pick themselves up and they try and head south, pulling the ships' boats behind them.

FIENNES: The word "cold" as we know it takes on a different meaning.

You feel like you want to roll up in a fetal ball all the time.

You become inactive, weak-willed, you don't want to do anything other than sort of creep into some place where there's no wind and no cold.

NARRATOR: It was a horrific ordeal for the malnourished crew.

But Hall's report wasn't the first time Inuit accounts of the expedition had reached England.

In 1854, the explorer Sir John Rae spent time with another group of Inuit, who described a particularly grisly discovery.

When the story was reported in the British press, all hell broke loose.

So this is 1854.

This is The Times, October the 23rd, and here's John Rae's letter in all its gory detail.

"The bodies of some 30 persons were discovered.

"Some were in a tent, others under the boat, "which had been turned to form a shelter.

"From the mutilated state of many of the corpses "and from the contents of the kettles, "it is evident that our wretched countrymen "had been driven to the last resource: cannibalism as a means of prolonging existence."

It's a horrendous, horrific truth for a Victorian public to hear.

Heroes don't eat each other, least of all naval heroes.

NARRATOR: To many in Britain, the stories of cannibalism were an insult.

And none other than Charles Dickens leapt to the men's defense.

He dismissed the Inuit accounts as "the chatter of a gross handful of uncivilized people, with a domesticity of blood and blubber."

But in 1992, archaeologist Anne Keenleyside carried out extensive research on bones that had just been discovered on the coast of King William Island.

Fragments of fabric and buttons found with them indicated that they were members of Franklin's crew.

This site map shows the distribution of the bones that we uncovered at the site.

On this end of the site, there is a scattering of bones.

They're fairly widely scattered.

And then, as we move towards this end of the site, you see a dense concentration of bones in this area here.

The first bone in which I identified a cut mark was a left pelvic bone.

I turned it over, uncovered it, lifted it up from the soil, and found a distinct cut mark clearly identifiable as a mark that was not made by an animal.

These kinds of human-made cut marks tend to have a V-shaped cross-section, depending on the shape of the blade.

(coughing) NARRATOR: These marks appear as though they were made by metal knives used to strip flesh from human bones in a last desperate bid to survive.

It seemed to corroborate the Inuit accounts of cannibalism.

In its disgust, 19th-century Britain had rejected those stories as unreliable folklore.

But in doing so, they'd also overlooked important clues to the whereabouts of HMS Erebus and HMS Terror.

The Inuit told explorers that one of Franklin's ships was crushed by the ice before sinking off King William Island.

But oral traditions also preserve clues about the fate of the second ship, which supposedly remained intact.

Could this information help to narrow down the search?

Here on modern-day King William Island, Louie Kamookak has spent 30 years compiling information passed down through the generations.

He discovered clues embedded in Inuit culture itself.

LOUIE KAMOOKAK: With the elders involved, we collected all the place names in this region because place name is one way oral history is passed down.

Oral history is passed down by speaking, telling stories, but it's also in the place names.

There's places like, past Simpson Strait, (speaking Inuit)-- a Boat Place.

That's the story where one of the ships was when it was still afloat.

That's why it called a Boat Place.

NARRATOR: This "Boat Place" is found well south of King William Island.

Based on that and other Inuit accounts, Parks Canada has drawn up its southern search zone.

And with the north blocked by ice, all efforts are now focused here.

HARRIS: So, what do we have?

A detailed oral history that really, you know, helps us define where to start looking.

It were not for information provided by the Inuit, we would have no reason to start looking for Franklin's ships down in the Wilmott and Crampton Bay.

NARRATOR: Teams from Parks Canada and the Arctic Research Foundation have scoured the seafloor here in recent years.

And that work continues now, using towed sonar units.

MAN: That's the safety cable for the sonar.

We don't want to lose it.

NARRATOR: The data comes in live, so team members keep their eyes glued to the screens.

Winter is coming, and their search window will soon close.

But just as hopes are beginning to fade, exciting news comes from a different source entirely.

For many years, a separate team led by anthropologist Doug Stenton has also been looking for clues on land.

In 2014, they're combing small islands in the southern search zone for evidence of Franklin's men.

And on September 1, it's helicopter pilot Andrew Sterling who makes a stunning find.

ANDREW STERLING: Just walking on the beach, sort of something caught my eye at the side and it just looked out of place, the color behind a rock, so I just went over to investigate it.

NARRATOR: Could this be the breakthrough the team has been hoping for?

We all looked at it and went, "Well, this is from a ship."

We didn't know what it was.

We're not marine archaeologists, per se, but we all thought this just has that... you know, we all just sensed it.

NARRATOR: The object is stamped with characteristic marks known as broad arrows, signifying British Royal Navy property.

It was just unmistakable, what the significance was.

An indisputable indication that this came from a Royal Navy ship and undeniably from either Erebus or Terror.

NARRATOR: The object is quickly identified from the ship's plans as the metal fitting that supports one of the ship's cranes.

And it was found in the heart of the southern search area, close to the Inuit sightings.

HARRIS: This large iron object, very close to where the Inuit report that they encountered one of these ships.

To find this in that vicinity is very, very exciting, and it really told us that we were barking up the right tree.

NARRATOR: At last, it all seems to be coming together.

This find is the most important discovery since the cairn note over 150 years ago.

Are they finally on the verge of solving the Franklin puzzle?

With winter approaching and their search window closing fast, the Parks Canada team scrambles to scan the surrounding seafloor.

HARRIS: My colleague and I were manning the side-scan sonar station.

We were both looking at the sonar monitor, and there it comes.

And you have this really unmistakable outline of a shipwreck.

No doubt what it was.

Started to scroll down the monitor.

And it wasn't even halfway onto the screen before you really knew what you were looking at.

Jabbed my finger right at the screen and kind of lunged for it and said, "That's it, that's it!"

BERNIER: When I saw the image of the ship coming down, I just... it cut my legs, literally.

"Oh, my God, this is going to be a treasure trove of information, "and we are going to really open up a window directly into history."

NARRATOR: It's a pivotal moment in the Franklin story.

Thanks to the Inuit oral history and, ironically, to the ice that forced them south, the team has finally located one of Franklin's long-lost ships.

GEIGER: This is a great moment for exploration.

We've been searching for, you know, 160 years for answers to what happened to the Franklin expedition.

The best equipped, most finely prepared and trained expedition that had ever set out for the Northwest Passage, and to have it literally obliterated, end in mass disaster, no survivors and no ships, it's been a confounding mystery.

To finally have something significant, to finally have a ship, is just incredible.

I've spent most of my adult life dreaming of this day, and, you know, it's here.

Scientists have located one of the ships from the fabled Franklin expedition.

...found one of two ships used to search for the Northwest Passage.

...teams have finally hit the jackpot.

So an absolutely incredible day for those people, some of whom have spent, you know, a good chunk of their life's work... NARRATOR: For underwater archaeologists Marc-André Bernier and Ryan Harris, it's the find of a lifetime.

But they're desperate for a closer look, so before the seas freeze for another winter, they dive down to see the ship with their own eyes.

HARRIS: I'd caught a glimpse of the timber on the seafloor.

Followed along its length.

Just growing in anticipation and excitement, and then, you know, boom!

Towering overhead, out of the haze, loomed the bulk of this stately shipwreck a full five meters tall.

That sensation of finally laying a hand on the side of this storied shipwreck is quite a remarkable experience that I'll never forget.

NARRATOR: The wreck lies just 36 feet below the surface, but murky water and piles of broken planks make it difficult to see.

Among the timbers, a familiar shape catches the eye.

BERNIER: Is that a gun?

HARRIS: It's a cannon.

BERNIER: Incredible!

Is that two of them?

HARRIS: Yeah.

There's so much to see, it boggles the mind.

NARRATOR: Directly over the wreck, the Canadian Hydrographic Service carries out more sonar work to create a virtual image of the entire site.

The masts have been swept away by drifting sea ice, but the hull of the ship is in one piece.

Holes in the deck even allow the divers to get their first look inside the ship.

HARRIS: And you could look forward and see murky features.

Just an incredible sensation of being inside.

That's where they would have spent long, harrowing winters through the dark Arctic nights.

It's just an absolutely remarkable sight, and the fact that it still stands intact, it allows you to sort of place yourself there.

You feel this connection with the past.

It's really quite astonishing.

NARRATOR: To cap it all off, there is one last prize.

HARRIS: And I hear John call over on the headset, saying, "You're not going to believe this, but I found the bell."

And I thought I must have misheard him, but sure enough, I went over and there was the ship's bell, lying in plain sight, right on top of the upper deck.

NARRATOR: Embossed on the side is the year that Franklin set sail: 1845.

(bell ringing) A poignant reminder of the terrible events that played out on this ship 170 years ago.

(bell ringing) Today was an extraordinary day.

I've never had the like of it in my entire career, and I probably never will after this day.

This wreck site without a doubt is one of the most extraordinary things I've ever laid eyes on.

It is absolutely an underwater archaeologist's dream.

NARRATOR: To identify which ship they've found, the team takes measurements from the high-resolution sonar data.

This image here kind of shows a good perspective for extracting length measurements.

NARRATOR: According to the 1845 plans from the National Maritime Museum, the dimensions of Erebus and Terror were subtly different.

Carefully comparing the sonar image with the plans, only one of the ships is a perfect match.

The wreck must be HMS Erebus, Fr anklin's flagship.

The sonar data is used to produce this three-dimensional reconstruction.

The wreck will be explored in great detail in years to come, but it's already produced an extraordinary idea that could rewrite the history of Franklin's expedition.

Both ships were originally thought to have been abandoned off King William Island, much further north, so how did Erebus move 100 miles to the south?

HARRIS: So where the wreck of Erebus is found, it actually happens to be protected, almost surrounded by a barrier of small islands and islets.

What we ask ourselves is how this ship arrived at that location.

NARRATOR: Satellite imagery from the Canadian Ice Service shows that ice in this area tends to drift south with the wind.

Could this have carried Erebus so uth?

Or might there be another explanation?

HARRIS: You see the tendril of ice coming down the bottom of the screen, and that's being expelled into the Queen Maud Gulf.

So it's not terribly surprising that at least one of the ships ultimately would have been directed towards Wilmott and Crampton Bay.

What is less clear, however, is how it could have gotten through this tangled web of small islands and shoals, how it worked itself into a protective pocket of where we find it today.

NARRATOR: Harris and Bernier believe it's unlikely that the ice could drag a ship intact through the maze of reefs and shoals.

But there is a more plausible idea suggested by a further clue in the Inuit accounts.

When Erebus was last seen above water, smoke was rising from the ship as if it were inhabited.

Had some of the crew returned to the ship from their attempted march south, and could they have steered her to where she now lies?

It's a possibility that might rewrite the history of the expedition.

The ships had already navigated through a significant stretch of the Northwest Passage to reach King William Island, but the wreck lies close to the mainland, where the coast had already been surveyed by previous expeditions coming from the west.

So if survivors did pilot Erebus to this spot, they had bridged the gap on the charts and completed the goal of their mission.

LEWIS-JONES: Now these men, that last surviving band, a final fire before the flame goes out.

These men have, in effect, completed the final link in the chain of the Northwest Passage.

But that is so far from their minds at that moment.

These men are thinking nothing of fame or records.

They're thinking of the following day.

NARRATOR: Inuit accounts mention a few sets of what they called white men's footsteps heading inland.

A last trace of the remaining souls.

In navigating the ship to where it now lies, those men may have found the final link of the elusive Northwest Passage.

Whether they succeeded or not, the wreck of HMS Erebus is a monument to exploration and to the sacrifice of all 129 men of Franklin's lost expedition.

An amazing discovery.

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