[dramatic music] ROB BELL (VOICEOVER): Majestic, powerful, and deadly.

For over 400 years, British ships ruled the waves.

These magnificent vessels helped shape history across the globe.

I'm Rob Bell, and in this series, I'll be exploring six of the world's greatest ships.

In this episode, I step on board a ship that changed the world, the SS Great Britain, a ship that outclassed all the competition.

She was bigger.

She was longer.

She was high-tech.

ROB BELL (VOICEOVER): But her history was anything but plain sailing.

In rough seas, high winds, it was nigh on suicidal.

ROB BELL (VOICEOVER): She would weather a series of maritime disasters-- JOANNE THOMAS: There were leaks everywhere.

The crew basically refused to go any further.

ROB BELL (VOICEOVER): --lose the trust of her passengers-- It was a complete and total public relations disaster.

ROB BELL (VOICEOVER): --and experience an unlikely resurrection.

My father was that bonkers guy who thought he could bring a ship back.

♪ ♪ [dramatic music] One of the most important ships ever built, the SS Great Britain, is a Victorian engineering masterpiece that shaped the fortunes of nations and serves as a blueprint for every ship built today.

With her iron hull and propeller propulsion, she was the most advanced ship the world had ever seen.

During her construction, she was even called the greatest experiment since the creation.

Looking at it today, the SS Great Britain is a big ship.

But for Victorian Britain, her size was monumental.

At 320 feet, she was a hundred feet longer and a thousand tons heavier than her closest rival.

She represented a huge leap forward in shipbuilding and could only have been dreamed up by one man-- Isambard Kingdom Brunel.

[dramatic music] ROB BELL (VOICEOVER): Celebrated in the press as the builder of Britain, Brunel was no stranger to taking engineering leaps and had already built a succession of world firsts.

The Thames Tunnel was the first time anyone had been able to dig under a navigable river.

The Clifton Suspension Bridge was the widest in the world when it was completed.

And the Great Western Railway that connected London to Bristol was the longest in the world.

But Brunel wasn't one to rest on his laurels.

At a backslapping meeting, the directors of the Great Western Railway were congratulating themselves on the completion of their project.

Brunel is said to have drawn on his cigar and jokingly proposed, why not make it even longer?

Why not have a steamboat go from Bristol to New York?

[dramatic music] Brunel's off-the-cuff remark soon became a serious proposition, and he was given the go-ahead to build the SS Great Western, a wooden-hulled paddle steamer.

The ship proved to be a huge financial success, so much so that he was asked to build a sister ship of exactly the same dimensions.

But Brunel was driven more by glory than profit.

He wanted to build an even bigger ship, the largest the world had ever seen.

HELEN DOE: Brunel loved challenges.

And he was living in a really exciting time, when all these new materials, all these new ideas.

So many possibilities.

And that was always the thing that excited him, those possibilities, those challenges.

ROB BELL (VOICEOVER): But Brunel's ambition was restricted by practical concerns.

There were limits to how big a wooden ship could be.

Build it too long and it would snap in half in the first rough sea it encountered.

One possible solution was to use Brunel's favorite building material-- iron.

But it was thought to be totally unsuitable for oceangoing ships.

Any vessels leaving coastal waters needed a compass to navigate by.

And the magnetic field produced by an iron hull would interfere with compass readings.

I know for a fact that north is in that direction, but my compass here says otherwise.

The needle's been thrown off by the thousands of tons of magnetic iron in the hull that surrounds me.

[dramatic music] ROB BELL (VOICEOVER): A huge delivery of African oak was on its way to Bristol for the construction of the new ship's hull.

But then an experimental iron-hulled ship, called The Rainbow, docked at the harbor.

Brunel raced aboard to see how the ship's compass was able to function despite being surrounded by an iron hull.

But the scientists working on The Rainbow discovered a clever workaround solution.

They found that by placing small pieces of metal and magnets carefully around the compass, you could actually counteract the effect of the hull and correct the compass reading.

♪ ♪ ROB BELL (VOICEOVER): This breakthrough was pivotal in the history of shipbuilding.

It allowed bigger, stronger metal ships to be built.

And even today, they still use the same technique to correct the compass.

Back in 1839, Brunel was able to convince his backers that iron was a viable material for building the biggest ship the world had ever seen.

These days, a hull like this would be made from huge sheets of steel.

But Brunel was limited to working with small iron plates.

So you can see here how they've been laid to overlap with one another, just like the timber planks on a traditional wooden boat.

ROB BELL (VOICEOVER): But ships' carpenters couldn't work with the new material.

Iron workers from the industrial heartlands of the midlands and the north flocked to Bristol to build the Iron ship.

♪ ♪ Work took place right here in the same dry dock where she sits today.

Brunel's ambition grew, and soon the hull of his new ship had expanded to twice the size of the Great Western.

Without a name, the workmen simply called her Mammoth.

After two years, Brunel's monumental ship was almost complete.

But as construction came to an end, Brunel saw something that would halt the entire build.

A ship named The Archimedes had arrived in Bristol harbor on a promotional tour.

It was the world's first propeller-driven ship.

Brunel was quick to see how a propeller would be much more efficient in the rough seas of the Atlantic.

On a paddle steamer, the rough seas and big waves can roll the ship from side to side, lifting the paddles clear out of the water, effectively rendering them useless.

But on a propeller-powered ship, the propeller remains in the water, no matter how big the roll, continuously driving the ship forwards.

Brunel insisted that his ship needed to be propeller-powered.

♪ ♪ ROB BELL (VOICEOVER): Brunel may have been convinced, but he needed a way to prove to his backers, and the world, that propellers were the future of steamships.

Always one for doing things on a grand scale, Brunel organized the biggest engineering experiment the world had ever seen.

The most famous test was when HMS Rattler and HMS Alecto were tied stern to stern.

They had identical engineering equipment, identical engines, and the ship with the screw pulled the paddle steamer backwards, which demonstrated pretty dramatically that the screw propeller was the best way forward.

[gripping music] ROB BELL (VOICEOVER): In fact, the propeller that Brunel built for this experiment was so well-designed that the propellers used on ships today are only 5% more efficient.

Even so, his cautious backers wouldn't accept a fully propeller-driven ship.

They insisted that the SS Great Britain should have sales as well, to keep fuel costs down.

[dramatic music] On the 19th of July 1843, the SS Great Britain, the world's first iron-hulled propeller-driven steamer and the largest ship ever built, was ready to be launched.

The scientific world was waiting with bated breath until she was launched to see if she actually worked.

She was built with an iron hull.

People were doubting she would actually float.

ROB BELL (VOICEOVER): 30,000 spectators lined the banks of the harbor, and the SS Great Britain even got the royal seal of approval from Queen Victoria's husband.

Prince Albert came down from London to Bristol on the Great Western Railway, so he was able to get on board Brunel's train to come and see Brunel's ship being launched.

ROB BELL (VOICEOVER): In traditional fashion, a bottle of champagne was to be smashed against the hull of the ship for luck.

But the company director's wife missed the boat as it left the dry dock.

Prince Albert quickly grabbed another bottle of champagne and hurled it against the hull, showering the workmen below in glass, but delighting the crowd, who roared their approval.

Watching the launch of SS Great Britain back in 1843 would have been like seeing Concorde take off for the first time.

And the huge crowds that packed the waterside here marveled at how the genius engineer Brunel had done it again, how he'd taken another huge step forward in engineering.

But he'd made a mistake, one that might have left the world's greatest ship stranded in this harbor forever.

♪ ♪ ROB BELL (VOICEOVER): Her technological breakthroughs could potentially have been her undoing.

♪ ♪ Brunel had made a very simple error.

To power his new propeller ship, he'd needed a bigger engine.

That meant the hull had to be wider.

Now, she sailed out through the dock gates here just fine.

But when it came to getting her out through the harbor lock gates way down the end, the world's largest ship got stuck.

♪ ♪ ROB BELL (VOICEOVER): It's said that that very evening, Brunel took a gang of men to tear down the stonework of the locks.

The SS Great Britain was quickly towed through and down to the Severn Estuary, where her boilers were lit for the first time.

Although the public interest was huge for the launch of the ship and the building of the ship, unfortunately, that did not translate into ticket sales because there was so much skepticism about whether the ship would float and how she would fare.

Could she carry enough coal to actually get to New York under steam?

There was so much doubt about this new technology that only 45 of the 350 tickets were sold for her maiden voyage to New York.

[majestic music] ROB BELL (VOICEOVER): The public might have lacked confidence in the SS Great Britain, but she proved them wrong, with Captain John Hosken skillfully navigating her across a stormy Atlantic in 14 days and 21 hours, a new record.

When she arrived in New York, she was welcomed by thousands and thousands of visitors.

People would come down to the harbor site to see this magnificent ship.

She was the largest ship in the world at the time.

She was the most technologically advanced.

She was a wonder to behold.

There were thousands and thousands of people who actually bought tickets just to be given a tour around the ship.

ROB BELL (VOICEOVER): As New York fell in love with the SS Great Britain, some of her crew fell in love with New York, so much so that a number of them deserted, leaving the ship shorthanded.

[tense music] ♪ ♪ Captain Hosken had no option but to set sail on his return journey home from New York with a skeleton crew.

And in the middle of the Atlantic, as the ship faced brutal weather conditions, the lack of men would prove disastrous.

♪ ♪ ROB BELL (VOICEOVER): As the winds whipped the ship from side to side, threatening to capsize it, the captain ordered that the sails be taken down immediately.

♪ ♪ ROB BELL: Taking in the topsail was a dangerous, labor-intensive job at the best of times, but in rough seas, high winds, and with a lack of crew, it was nigh on suicidal.

And as the sailors battled with the halyard, a rope that fixes the mainsail, powerful winds took hold of the sale, snapping the topsail mast like a twig, seriously injuring two men.

♪ ♪ ROB BELL (VOICEOVER): The sailors were rushed to the ship's surgeon, where one had to have his arm amputated.

[dramatic music] The SS Great Britain fared even worse on her second journey, running aground off the coast of America, damaging her propeller.

[soft music] She had to be put into dry dock in New York for repairs, where engineers realized she'd lost two of her six propeller blades.

This is what the propeller would have looked like before it hit the seabed.

But with two blades missing, it would no longer be balanced and wouldn't work properly.

So the engineers took the decision to remove a third blade.

Off it comes.

And with the remaining three blades being evenly spaced, they believe it would work almost as well as when it had all six.

They were wrong.

[dramatic music] HELEN DOE: The propeller broke again, and the ship had to largely proceed under sail.

After that, they put it in a completely new design of propeller.

ROB BELL (VOICEOVER): After just two transatlantic trips, the ship's owners, the Great Western Steam Ship Company, were forced to pay for a costly refit.

All the Great Britain's troubles had reinforced the public perception that this advanced ship was a leap too far, and only 28 passengers bought tickets for her third Atlantic crossing, less than 10% capacity.

♪ ♪ But the SS Great Britain's third journey silenced her critics, breaking the world record for an Atlantic crossing.

HELEN DOE: The Great Britain could make the transatlantic journey under 14 days and had the potential to do much more.

The average sailing packet could, with a good following wind coming from New York, do it in possibly, if they're lucky, three weeks, but it could take three months.

ROB BELL (VOICEOVER): So a trip on the SS Great Britain wasn't just about speed, but reliability, too.

And this soon had an effect on ticket sales.

For her fourth trip to New York, 180 passengers bought tickets.

This was three times more than had ever previously traveled aboard.

The Great Western Steam Ship Company must have finally felt that their huge investment might pay off.

But on one cold September night in 1846, their hopes would be dashed.

As the passengers on board readied themselves for their first night at sea, disaster struck.

The ship hit the bottom of the ocean again and shuddered to a sudden halt.

Waves crashed over the hull as the crew fought to free her.

Everyone on board must have been terrified.

It was a passage that Captain Hosken had done many, many times before on his previous ship and now on the Great Britain.

Inexplicably, when he was heading south of the Isle of Man, instead of turning north to go around Ireland, he ended up with the ship in Dundrum Bay.

ROB BELL (VOICEOVER): The ship had run aground and couldn't be moved.

In the morning, a rescue mission to evacuate the VIP passengers was immediately mounted, as news of the accident reached England.

It was a complete and total public relations disaster for everyone, and Brunel was absolutely beside himself with fury.

JOANNE THOMAS: He writes a letter in which he expresses his disappointment in that he describes the Great Britain as a useless saucepan lying around on the beach.

So he's very upset about nobody really looking after her.

ROB BELL (VOICEOVER): Brunel took matters into his own hands, designing breakwaters to protect the ship from the rough Irish sea.

The Great Britain was in Dundrum Bay for nearly a year before she was salvaged, and in that time she was exposed to winter gales, storms, waves crashing in.

So it's a marvel that she survived.

Any wooden ship would have broken up in those storms on the beach.

ROB BELL (VOICEOVER): The Dundrum disaster had bankrupted the Great Western Steam Ship Company.

Brunel's revolutionary ship was to be sold off.

ROB BELL: The world's largest and fastest ship, which had also been one of the most expensive, was put up for auction in Liverpool.

Three years earlier, her build cost had come in at an unprecedented 120,000 pound, and her owners had been forced to spend thousands more on rescues, refits, and repairs.

Embarrassingly, the SS Great Britain failed to meet her reserve price, set at just 4,000 pounds.

And with no buyers stepping forward, it looked as though she was destined for the breaker's yard.

[soft music] ROB BELL (VOICEOVER): Finally, however, after two years, a company called Gibbs, Bright & Co.

bought the ship in December 1850.

Her new owners got a bargain and only paid around 15% of the 120,000 pounds Brunel and the Great Western Company had paid to build her.

An air of failure began to hang around the SS Great Britain.

But no sooner had the ship changed hands than her fortune started to look up.

And it was all down to this stuff-- gold.

[dramatic music] ROB BELL (VOICEOVER): Just two months after the sale of the SS Great Britain, prospectors near Melbourne struck it rich and triggered the Australian gold rush.

Suddenly, Australia wasn't just a convict colony, it was a place to make your fortune.

The small trickle of migrants wanting to head to Australia became a mighty flood, and the SS Great Britain's size made her an ideal budget passenger transporter.

JOANNE THOMAS: She no longer was a first-class, luxurious passenger liner.

She had to accommodate those people who wanted to go and try and find their fortune on the goldfields.

Those were people that couldn't afford to buy a first-class passenger ticket.

So the majority of the ship was given over to third-class accommodation, where all you would get is a bunk bed, and that's pretty much it.

ROB BELL (VOICEOVER): The refit more than doubled passenger capacity, taking it from 360 berths to an impressive 730.

She'd been designed to cross the Atlantic, a journey of just over 3,000 miles.

But her new destination would be Melbourne, 12,000 miles away.

This route took her down through the Eastern Atlantic, right around the very tip of South Africa.

She had to navigate some of the worst seas sees in the world off the Cape of Good Hope and then cross the vast Southern Indian Ocean to Australia.

For the owners, it was important their ship was able to reach Melbourne without having to refuel along the way.

Coal here, for these ferocious boilers, was cheap in Britain and in Melbourne, but prohibitively expensive anywhere in between.

[light music] ROB BELL (VOICEOVER): And on her first journey, in August 1852, the winds of the South Atlantic bested the SS Great Britain's steam engine, and she ran out of coal near St.

Helena.

The SS Great Britain's new owners decided it was time for a radical change.

To save money on the mammoth journey to Australia, she would change from being a steam-powered ship assisted by sail to the exact opposite.

From now on, the Great Britain would be a sail-powered ship assisted by a propeller.

That sounds like a simple switch, but there was a problem with this logic.

ROB BELL (VOICEOVER): When the ship was under sail power with the engine off, the redundant propeller would drag in the water, slowing her down.

The solution they came up with was this-- a retractable propeller.

And mounted on this cradle, it could be lifted clear out of the water on a winch system like this when the ship was under sail.

This significantly reduced the drag of the ship through the water, allowing them to power down the engines, saving precious coal.

[dramatic music] ROB BELL (VOICEOVER): With the ship's engineering problems finally fixed, the next voyage to Melbourne took a respectable 65 days.

And passengers' experiences of those 65 days depended on what type of ticket they'd bought.

Here we are, Simon, sat in the luxury opulence of this first-class dining lounge.

Tell me, who were the first-class passengers making the trip?

SIMON POTTER: They're all very well-off.

Some of them are probably going out to invest.

They're looking for entrepreneurial opportunities, do some business.

They might be merchants.

They're people who've got money.

So they can travel.

They can pay almost 100 guineas or something to take quite a luxurious trip.

I imagine the service here would have been first-class.

How does what the experience was in here compare to other areas of the ship?

What you've got here in terms of food and service was like the best hotels in London.

It was the best.

In steerage, it's small.

It's cramped.

There was a fair amount of segregation then, was there, between the different classes of people on the ship.

Yeah.

So depending on what type of ticket you've got, it depends where on the boat you can spend your social time, not just where you sleep, but which parts of the boat you've got access to.

But the food is so awful in second-class, once they start running out of fresh food, a lot of people buy an upgrade.

And they come and eat here, and that causes quite a lot of tension.

Because the people who've paid 95 guineas, they want to have an exclusive experience.

They don't want people of slightly, maybe less social standing coming and joining them.

[light music] ROB BELL (VOICEOVER): Ensuring that the second- and third-class passengers knew their place was the job of the captain, and one man in particular was famed for his harmonious running of the ship.

Captain John Gray stood 6 feet tall and, despite weighing almost 17 stone, liked to lead by example.

He was very respected with the crew, because once a week, he would climb to the top of the mainmast just to prove to them that he could do the work he would ask them to do.

♪ ♪ ROB BELL (VOICEOVER): Gray was renowned for his swift justice and once pummeled a passenger with his bare hands after he was found drunk in the brandy stores.

But despite this, Captain Gray seems to have been loved by the crew and passengers alike.

Scores of diary entries mention his good spirits, how he'd stop to play a game of checkers and encourage people to exercise on deck.

A baby born on board was even named after him.

[light music] ROB BELL (VOICEOVER): John Gray was the most celebrated captain in the British merchant fleet and was the SS Great Britain's longest-serving master at 18 years, until his leadership was mysteriously cut short.

On the night of the 25th of November 1872, as the ship was in the mid-Atlantic, the captain complained of a pain in his bowels and went to bed early.

Later that evening, a steward looked in on him and reported that he'd seemed better, was sat at his desk writing a letter.

Then, at around midnight, Gray was seen leaving his cabin, heading towards the deck.

That would be the last time anyone saw Captain John Gray.

♪ ♪ ROB BELL (VOICEOVER): The next morning, a servant brought Gray a cup of tea and found his cabin empty.

The entire crew searched the whole ship from top to bottom, but there was no sign of the captain anywhere.

He'd vanished.

JOANNE THOMAS: There was no way of getting a message ahead to Liverpool.

The ship comes into port on Christmas Day in 1872, and Captain John Gray's wife and his two daughters were waiting for him on the quayside.

It was only then that they found out the sad news that their father and husband had disappeared at sea and would never be joining them again.

♪ ♪ ROB BELL (VOICEOVER): Captain John Gray's body was never found, and the circumstances in which he vanished have never been explained.

[soft dramatic music] Despite the loss of Captain Gray, the SS Great Britain continued to thrive.

During her years as a migrant transport ship, she made her owners a fortune, carrying a total of 15,000 passengers to new lives in Australia.

This ship played an integral role in forging the Australian nation.

Today, it's claimed that an incredible quarter of a million Australians are direct descendants of migrants who traveled aboard the SS Great Britain.

[tense music] ROB BELL (VOICEOVER): But after 25 years, passenger numbers dwindled, and the SS Great Britain began a slow decline.

She was no longer the biggest ship afloat.

Brunel had beaten his own record and built the SS Great Eastern, which was over double the size of the Great Britain and could carry 4,000 passengers.

To stay useful, the Great Britain would once again undergo a refit, but it was a humiliating step backwards.

The gold rush was coming to its end in the 1870s, and the Great Britain was getting older.

She was an old ship by then.

Actually, she became uninsurable as a passenger ship in 1876, so her owners decided to sell her on.

Her new owners converted her to a sailing ship.

So she was completely stripped of her luxurious fittings inside.

She was stripped of her engines and converted to a big sailing ship to carry cargo.

[dramatic music] ROB BELL (VOICEOVER): Her first voyage as a coal-carrying cargo ship led to more embarrassment.

Powered by sail only, the ship that was once the fastest in the world took a shameful six months to reach San Francisco.

But it wasn't all bad news.

Because of her size, she could carry so much cargo that she was actually hugely profitable as a sailing ship.

♪ ♪ ROB BELL: But in February 1886, as the ship was sailing around Cape Horn, she hit gale-force winds.

The crew reported to Captain Henry Stap that the coal was shifting in the hold, making the ship dangerously unstable.

They pleaded with him to seek shelter on the Falkland Islands.

He refused to listen, until the gale ripped off the front topmast.

JOANNE THOMAS: There was a fear that her decks might be strained.

There were leaks everywhere.

So the crew basically refused to go any further and said, we have to turn back.

So the captain relented and put into the Falkland Islands.

ROB BELL (VOICEOVER): But the ship was now almost impossible to steer and ran aground twice, seriously damaging her hull before limping into port.

JOANNE THOMAS: From there, telegrams were sent to her owners, who then decided it was too expensive to repair her, and she would just be sold off as an insurance loss.

[dramatic music] In 1886, the SS Great Britain was bought by the Falklands Corporation for 2,000 pounds and used as a floating fuel store.

From the hull up, this entire space would have been piled full of coal.

But after almost 50 years in this rather demeaning role, her usefulness had run out.

They punched holes in the sides of the hull and scuttled her on the ocean floor in Sparrow Cove, where she was left to the elements.

[emotional music] ROB BELL (VOICEOVER): Over the next 30 years, the Islanders got used to the sight of this giant, decaying hulk rusting on their shoreline.

♪ ♪ They would even row out to the old ship to explore its vast hull and enjoy picnics on the 100-year-old deck.

Then, in 1967, a vicar and naval architect, Ewan Corlett, wrote a letter to The Times.

It was an impassioned plea to save what he called one of the few truly historic ships still in existence and the forerunner to all modern ships.

Corlett's letter persuaded a group of financial backers that it just wasn't fitting for a British national treasure to be left to rot on the other side of the world.

Soon, Corlett was on his way to the Falklands to work out how to bring the ship back home to Bristol.

[dramatic music] My father was that bonkers guy who thought he could bring a ship back.

He fixed things, and one of the things he was going to fix was the Great Britain.

My father was able to visit the ship on the Falkland Islands and carried out a very thorough survey of the ship.

His survey suggested that she was deteriorating exponentially, and if she hadn't broken in two within five years, he'd have been very surprised.

Time literally had run out for her.

ROB BELL (VOICEOVER): Corlett knew that something had to be done, and fast.

He came up with a plan for floating the ship over a pontoon barge and lifting her right out of the water.

[dramatic music] ROB BELL (VOICEOVER): On the 24th of April 1970, the SS Great Britain made her final transatlantic crossing on the back of a giant floating pontoon.

She was headed for the city of her birth, Bristol, and the very dry dock where she'd been built.

♪ ♪ But strapped to a raft was no way for one of the greatest ships in history to return to her home port.

At the mouth of the River Avon, the SS Great Britain was released from the pontoon for the final leg of her last-ever journey.

Tens of thousands of Bristolians turned up to see the magic moment when the SS Great Britain, floating unassisted, was towed under another of Brunel's amazing achievements, the Clifton Suspension Bridge.

On the 19th of July 1970, exactly 127 years to the day since her launch, the SS Great Britain was backed into the very dock where she was built, with only inches to spare.

[brooding music] The conservationists that had fought to bring the ship home could now get to work on putting her back together.

And just like at her launch, the SS Great Britain would receive the royal seal of approval from the queen's husband, with a visit from Prince Philip during the renovations.

But even after her rescue and restoration, the ship's problems were far from over.

Now, this may be called a dry dock, but it was anything but dry.

And in 1999, a team from Cardiff University made a shocking discovery.

After an inspection of the hull, they found that it was still rusting away.

And at that current rate of decay, the SS Great Britain would totally disintegrate within 25 years.

In fact, these leaky walls and the salty sea atmosphere in here, this was one of the worst places in the world to try and preserve a rusty ship.

[tense music] ROB BELL (VOICEOVER): To help tackle the problem, the SS Great Britain has a full-time rust expert on hand.

So, Nicola, tell me, what is rust exactly.

And how does it form?

Why does it form?

So rust is a type of corrosion, and corrosion forms when iron is in contact with both moisture and air.

And this causes a chemical process where the iron combines with the oxygen in the air to form iron oxide, or rust.

You notice, actually, that there is a lot of rust here on the bottom section of the hull but not up above.

Why is that?

That's because this bottom part of the hull was submerged under the sea for nearly 130 years.

The sea is full of sodium chloride, or salt.

And those chloride particles from the salt get embedded in the iron, and that acts as a catalyst.

So that speeds up the corrosion process even further.

And the top part of the ship isn't soaked in saltwater.

In fact, it's getting constantly washed by the rainwater, which then keeps the chloride concentration nice and low.

How dry do you need the air to be to properly conserve a ship like this?

We had some researchers from Cardiff University help us to answer that question, and they told us that at around 20% relative humidity, we could slow down the rate of corrosion so that the ship would last for more than a hundred more years.

ROB BELL: How does that compare with outside, say-- I mean, what is that difference roughly?

In Bristol, on a day like today, it could be 90 or even higher percent relative humidity.

[soft dramatic music] ROB BELL (VOICEOVER): Thousands of miles away, the United States Air Force had faced a similar problem when working out what to do with their reserve planes so they didn't rust away when not in use.

Their solution was simple-- park them in one of the driest places on the planet, the Arizona Desert.

So what the conservationists here needed to do was recreate the dryness of the Arizona Desert in Bristol.

And that's what this enormous dehumidifier does.

It has the rather imposing name, Deep Thought II.

Its twin brother, Deep Thought I, does exactly the same thing, but inside the ship.

♪ ♪ All of these ducts along the length of the hull, continuously blowing out this warm and very, very dry air, you can feel it sucking the moisture out of you.

♪ ♪ ROB BELL (VOICEOVER): And the glass plates that surround the ship create the roof for this giant dehumidification chamber.

The glass ceiling on the dock here not only helps regulate the humidity, it also gives this quite strange sensation that you're underneath the water alongside the hull of the ship.

[dramatic music] ROB BELL (VOICEOVER): An engineering solution worthy of Brunel himself set to preserve the ship for generations to come.

♪ ♪ Last year, 300,000 visitors traveled from all over the globe to marvel at this incredible engineering achievement of the Victorian age.

Referred to as the grandmother of all modern ships, Brunel's leap forward in shipbuilding transformed not only maritime transport, but the world.

Every working ship, from cruise liners to oil tankers and aircraft carriers, used the blueprint drawn up by Brunel of a metal hull and a propeller.

And she continues to inspire a new generation of engineers.

I was sitting outside here having my lunch, and a school party of about 14 seven or eight-year-olds came out.

I think my father would have really loved that.

Because maybe one of them-- I'm getting choked up.

Maybe one of them would have become an engineer.

[dramatic music] ♪ ♪ ROB BELL: In her lifetime, the SS Great Britain has traveled more than a million miles, carried over 30,000 passengers, and survived more storms, scuttling, and groundings than any modern liner could ever resist.

And for me, this ship's true legacy is her endurance.

She's been a first-class transatlantic steamship, a wind-powered coal barge, and left to rot in the rough South Atlantic seas for decades.

And yet, 175 years after she was launched, she still stands strong.

♪ ♪ [theme music] ♪ ♪ ♪ ♪ ♪ ♪ ♪ ♪