0:00:07 > 0:00:10We're taking a city break.
0:00:11 > 0:00:16Around our isles, the coast is ringed with cities.
0:00:16 > 0:00:18From the smallest...
0:00:18 > 0:00:20to the grandest -
0:00:20 > 0:00:23their lifeblood's the sea.
0:00:25 > 0:00:29A city can thrive on its coastal connections,
0:00:29 > 0:00:35but it's a relationship that can bring both prosperity and pain.
0:00:35 > 0:00:38Mark's on board to see how navigation
0:00:38 > 0:00:42put one city at the centre of the world's sea charts.
0:00:42 > 0:00:45This is the story of how London,
0:00:45 > 0:00:48a city 50 miles from the open sea,
0:00:48 > 0:00:51became the capital of global navigation.
0:00:52 > 0:00:55And Tessa's going underground
0:00:55 > 0:00:58to investigate a secret wartime threat.
0:01:02 > 0:01:06A forgotten but extraordinary story how, in World War II,
0:01:06 > 0:01:08we stopped the Nazis flooding London.
0:01:11 > 0:01:15Ruth exposes an urban epidemic spread by the sea.
0:01:16 > 0:01:19As the sailors flood into the city,
0:01:19 > 0:01:22a silent danger looms.
0:01:23 > 0:01:27And I'll be immersed in a tidal wave of trade...
0:01:29 > 0:01:34..as I uncover the unsung port all our cities rely on.
0:01:36 > 0:01:40Join us to put the sea back into the city.
0:01:40 > 0:01:42This is Coast!
0:02:13 > 0:02:17For centuries, the beating hearts of our coastal cities
0:02:17 > 0:02:20were the docklands that fed them.
0:02:22 > 0:02:26But today these urban landscapes have transformed
0:02:26 > 0:02:28to suit changing times.
0:02:31 > 0:02:34In Cardiff, redundant docks have been dammed
0:02:34 > 0:02:37to create a freshwater lake -
0:02:37 > 0:02:39a perfect pond for pleasure.
0:02:43 > 0:02:47Bristol's great floating harbour is now a home of heritage.
0:02:50 > 0:02:53And in Liverpool, apartments not ships
0:02:53 > 0:02:56stack up along the waterfront.
0:02:58 > 0:03:04So where has the trade that once filled these docks disappeared to?
0:03:06 > 0:03:10I'm finding out what happens when the sea moves out of the city.
0:03:12 > 0:03:15A journey that's brought me to the Humber,
0:03:15 > 0:03:18to explore an unsung hero of our isles -
0:03:18 > 0:03:21the mega port at Immingham.
0:03:33 > 0:03:37Some seaports grow up slowly over centuries,
0:03:37 > 0:03:40but Immingham sprang up as a super port,
0:03:40 > 0:03:43practically a city in its own right.
0:03:45 > 0:03:50More tonnes of cargo arrive here than at any other port in the UK.
0:03:52 > 0:03:56Its towering skyline marks a dramatic new chapter
0:03:56 > 0:03:59in the story of the sea and our cities.
0:04:01 > 0:04:04Pedal power suits this mini city.
0:04:04 > 0:04:08Immingham's so big it has its own road and rail network.
0:04:10 > 0:04:14A bevy of workers beaver away to keep our coastal trade rolling
0:04:14 > 0:04:16day and night.
0:04:22 > 0:04:25Every cog, ship,
0:04:25 > 0:04:27train and crane
0:04:27 > 0:04:30dances to the tune of our country's needs.
0:04:58 > 0:05:00Go back a century, though,
0:05:00 > 0:05:04and this working landscape looked very different.
0:05:05 > 0:05:08At the turn of the 20th century,
0:05:08 > 0:05:11Immingham was a sleepy backwater.
0:05:12 > 0:05:16How did it spring up into this city of enterprise?
0:05:17 > 0:05:22Immingham was transformed into an industrial powerhouse
0:05:22 > 0:05:25by mountains of coal.
0:05:31 > 0:05:37In the early 1900s, coal was being mined at a ferocious rate -
0:05:37 > 0:05:40black treasure sought across the globe.
0:05:42 > 0:05:44To convey our great export,
0:05:44 > 0:05:47super-sized ships were called on.
0:05:51 > 0:05:55The Humber's urban ports at Grimsby and Hull
0:05:55 > 0:05:57couldn't expand sufficiently.
0:05:59 > 0:06:03So, in 1912, Immingham was purpose-built,
0:06:03 > 0:06:06opened in pomp and circumstance
0:06:06 > 0:06:08by the King himself.
0:06:11 > 0:06:14100 years on, coal mines have closed
0:06:14 > 0:06:18but Immingham is still awash with the black stuff.
0:06:21 > 0:06:24Today, though, the traffic's going in reverse.
0:06:28 > 0:06:31Surprisingly, coal is still king here,
0:06:31 > 0:06:33but rather than shipping it out,
0:06:33 > 0:06:36huge boats now bring coal in.
0:06:38 > 0:06:40They're importing tonnes of it.
0:06:46 > 0:06:49This might look like a minnow nudging a whale,
0:06:49 > 0:06:52but these tiny tugs are incredibly powerful,
0:06:52 > 0:06:56and they have to be, because some of the ships sailing into Immingham
0:06:56 > 0:06:59weigh 200,000 tonnes.
0:07:05 > 0:07:08Overseeing this mountainous operation
0:07:08 > 0:07:11is port director John Fitzgerald.
0:07:12 > 0:07:15How much coal's actually passing through this port now?
0:07:15 > 0:07:18Well, this year we're on track for about 14 million tonnes.
0:07:18 > 0:07:22I'm quite surprised because, you know, I'm not the only one
0:07:22 > 0:07:25who thought that Britain was decarbonising
0:07:25 > 0:07:27and heading towards renewable fuels,
0:07:27 > 0:07:29and yet we're surrounded by...
0:07:29 > 0:07:31literally, mountains of the black stuff.
0:07:31 > 0:07:37Nearly 50% of all the electricity generated in the UK
0:07:37 > 0:07:39is generated from coal,
0:07:39 > 0:07:42and that, effectively, means that the coal here at Immingham
0:07:42 > 0:07:45is powering well over three million homes.
0:07:49 > 0:07:53As we struggle to end our dependence on fossil fuels,
0:07:53 > 0:07:55Immingham helps keep our lights on.
0:08:01 > 0:08:02Out there in the North Sea,
0:08:02 > 0:08:05there's always another coal ship waiting to come in,
0:08:05 > 0:08:07then another then another,
0:08:07 > 0:08:10vessels queuing up to disgorge their cargoes
0:08:10 > 0:08:15into this energy capital on England's east coast.
0:08:16 > 0:08:20I'll embark on a 24-hour exploration of this vast site,
0:08:20 > 0:08:26to see how the port's kept on call for cargo around the clock.
0:08:45 > 0:08:48One advantage of using the sea as a highway...
0:08:50 > 0:08:54..this city traffic flows without the traffic jams.
0:08:57 > 0:09:01Deep-water city docks export British cars across the world.
0:09:05 > 0:09:07But 300 years ago,
0:09:07 > 0:09:12a maritime mystery made global sea trade much more difficult.
0:09:15 > 0:09:19In the 18th century, sailors had no way of knowing
0:09:19 > 0:09:21their precise position at sea.
0:09:25 > 0:09:29How would cracking the question of navigation
0:09:29 > 0:09:33put our capital on every mariner's map?
0:09:41 > 0:09:44For centuries, London's made the most
0:09:44 > 0:09:47of its narrow link with the sea.
0:09:47 > 0:09:50Mark's discovering how the city became
0:09:50 > 0:09:52the centre of the maritime world.
0:09:56 > 0:10:01The most important location for any sailor at sea
0:10:01 > 0:10:04is marked by a single line
0:10:04 > 0:10:09drawn through a surprisingly urban setting -
0:10:09 > 0:10:10London.
0:10:10 > 0:10:12Or, more precisely, Greenwich.
0:10:14 > 0:10:18This is the home of the Prime Meridian,
0:10:18 > 0:10:23the reference line for every ship at sea.
0:10:23 > 0:10:25But how did it end up here?
0:10:27 > 0:10:30This is the story of how London,
0:10:30 > 0:10:33a city 50 miles from the open sea,
0:10:33 > 0:10:36became the capital of global navigation.
0:10:44 > 0:10:48Our story starts some 300 years ago,
0:10:48 > 0:10:53with a maritime mystery that perplexed sailors around the world.
0:10:55 > 0:10:58It may sound unbelievable today,
0:10:58 > 0:11:01but up until the 1700s, sailors could not determine
0:11:01 > 0:11:04their exact position at sea -
0:11:04 > 0:11:07it was all a matter of guesswork.
0:11:10 > 0:11:16In sight of the coast, seafarers could navigate using landmarks.
0:11:17 > 0:11:21But in the 18th century, global trade was growing.
0:11:22 > 0:11:24For ships to cross oceans,
0:11:24 > 0:11:29sailors needed a new way to work out their location.
0:11:29 > 0:11:34To understand more, I'm meeting with historian Simon Schaffer.
0:11:34 > 0:11:36- Hi!- Hi!
0:11:36 > 0:11:38Simon, why in the 18th century
0:11:38 > 0:11:41was there this sudden need to know where we were?
0:11:41 > 0:11:44Up till then, most trade routes
0:11:44 > 0:11:47and most military enterprises that mattered
0:11:47 > 0:11:50had been local, they'd been European,
0:11:50 > 0:11:52and that meant you could navigate along the coasts.
0:11:52 > 0:11:58But now, from the late 1600s, early 1700s, Britain goes global,
0:11:58 > 0:12:01big time, and that means
0:12:01 > 0:12:04long-range voyages across oceans
0:12:04 > 0:12:07where you could not stick to the coasts.
0:12:07 > 0:12:10There were two places in particular that really mattered -
0:12:10 > 0:12:14the West Indies, where the sugar trade was based,
0:12:14 > 0:12:16and the East Indies and India,
0:12:16 > 0:12:18where spices were imported.
0:12:21 > 0:12:25Why where ocean voyages so difficult?
0:12:26 > 0:12:30300 years ago, sailors could determine
0:12:30 > 0:12:33how far north or south they were,
0:12:33 > 0:12:35thanks to the sun.
0:12:36 > 0:12:39This was their latitude.
0:12:41 > 0:12:46But no-one knew how to measure how east or west they were -
0:12:46 > 0:12:48longitude.
0:12:49 > 0:12:53So, if solving longitude was so important,
0:12:53 > 0:12:56why hadn't anyone come up with a solution?
0:12:58 > 0:13:01Even the world's top scientists were stumped.
0:13:04 > 0:13:09In desperation, the Government took a novel step.
0:13:09 > 0:13:14In 1714, they threw the question open to the general public.
0:13:16 > 0:13:19Men across the country brought their solutions to London
0:13:19 > 0:13:25to be examined by a government committee like no other -
0:13:25 > 0:13:27the Board of Longitude...
0:13:29 > 0:13:31..a panel of the great and good,
0:13:31 > 0:13:33Britain's brightest brains.
0:13:35 > 0:13:39They offered a huge cash prize to anyone clever enough
0:13:39 > 0:13:42to crack the riddle of longitude.
0:13:43 > 0:13:48Unsurprisingly, hundreds of submissions flew in.
0:13:48 > 0:13:54Inventive, beautiful but sadly harebrained schemes.
0:13:56 > 0:14:00Decades passed with no practical solution.
0:14:00 > 0:14:05The Board of Longitude became a national joke.
0:14:06 > 0:14:11A very good example of this is this image made by William Hogarth
0:14:11 > 0:14:13in the 1730s,
0:14:13 > 0:14:16which is a picture of Bedlam -
0:14:16 > 0:14:19the vast and sprawling London madhouse -
0:14:19 > 0:14:23and Hogarth was put right in the middle of this picture
0:14:23 > 0:14:25of a lunatic asylum -
0:14:25 > 0:14:30a man scribbling, and the man is drawing a longitude scheme.
0:14:32 > 0:14:37After years of head-scratching, what had the board come up with?
0:14:37 > 0:14:41There was one concept they all agreed on.
0:14:42 > 0:14:46The secret to determining longitude was time.
0:14:48 > 0:14:50BELL TOLLS
0:14:50 > 0:14:53As long as you know the time at a fixed point like Greenwich,
0:14:53 > 0:14:57then you can work out where you are anywhere in the world.
0:14:58 > 0:15:01Because the Earth rotates,
0:15:01 > 0:15:03the sun rises in the east,
0:15:03 > 0:15:07so midday will be earlier on this side of Greenwich
0:15:07 > 0:15:10and later on this side.
0:15:10 > 0:15:14These lines represent lines of longitude.
0:15:14 > 0:15:18It takes two hours for the sun to travel
0:15:18 > 0:15:21from one line to the next.
0:15:21 > 0:15:25So, if it's noon at Greenwich,
0:15:25 > 0:15:26it's...
0:15:26 > 0:15:292pm here...
0:15:29 > 0:15:31and 10am here.
0:15:32 > 0:15:36That time difference between local time
0:15:36 > 0:15:38and Greenwich time
0:15:38 > 0:15:41could be converted to distance from Greenwich.
0:15:41 > 0:15:44Local time was easy -
0:15:44 > 0:15:46when the sun was highest,
0:15:46 > 0:15:48they knew it was noon.
0:15:48 > 0:15:52But how could they keep track of time in Greenwich?
0:15:53 > 0:15:59300 years ago, this was the only kind of clock sailors had.
0:16:02 > 0:16:05Pendulum clocks just don't work on board boats.
0:16:07 > 0:16:11They needed a new method to keep Greenwich time.
0:16:11 > 0:16:16Fundamentally, there were two approaches that seemed viable.
0:16:16 > 0:16:20One was carrying Greenwich time with you in a box -
0:16:20 > 0:16:23that meant building a very reliable and accurate clock.
0:16:23 > 0:16:27The other was observing the time of events in the heavens
0:16:27 > 0:16:29using astronomy.
0:16:31 > 0:16:35In 1764, the two leading methods
0:16:35 > 0:16:38were trialled on a voyage to Barbados.
0:16:40 > 0:16:43First up, the astronomical, or lunar, method.
0:16:45 > 0:16:49This uses the clockwork nature of the sky at night
0:16:49 > 0:16:52as a huge celestial timekeeper.
0:16:55 > 0:16:58All you need is a sextant to measure
0:16:58 > 0:17:02the angles between the moon and certain stars.
0:17:04 > 0:17:06Once you've got your angle,
0:17:06 > 0:17:11you can work out what time it is in Greenwich - easy.
0:17:11 > 0:17:15But the maths back then, took over four hours.
0:17:17 > 0:17:19Fiddly calculations aside,
0:17:19 > 0:17:22the Barbados trial showed the lunar method
0:17:22 > 0:17:26to be accurate to within one degree of longitude.
0:17:29 > 0:17:33But that could still mean a ship was more than 60 miles adrift.
0:17:33 > 0:17:36Surely there was another option?
0:17:37 > 0:17:40Next up, a sea clock,
0:17:40 > 0:17:45submitted by an unknown carpenter from Yorkshire, John Harrison.
0:17:47 > 0:17:49The rocking motion of ships
0:17:49 > 0:17:53interrupted the timekeeping of pendulum clocks,
0:17:53 > 0:17:59but Harrison had spent years perfecting a new design.
0:18:00 > 0:18:04Harrison's clock was like none other.
0:18:04 > 0:18:06In fact, it wasn't a clock,
0:18:06 > 0:18:08it was modelled on a watch.
0:18:10 > 0:18:13Using springs instead of a pendulum,
0:18:13 > 0:18:16the watch only lost 40 seconds
0:18:16 > 0:18:18during the seven-week Barbados voyage.
0:18:20 > 0:18:25At last, sailors could carry Greenwich time with them.
0:18:26 > 0:18:28This incredible clock
0:18:28 > 0:18:31had finally solved the problem of longitude.
0:18:31 > 0:18:33The end, surely?
0:18:34 > 0:18:38Harrison thought he'd cracked longitude -
0:18:38 > 0:18:41the board, however, thought otherwise.
0:18:44 > 0:18:47Harrison was the greatest clockmaker of the age,
0:18:47 > 0:18:52and it had taken him years and years to build his marine watch.
0:18:52 > 0:18:55That was ONE watch.
0:18:55 > 0:18:59That scheme would only work if every mariner had a watch.
0:19:01 > 0:19:04The board rewarded Harrison,
0:19:04 > 0:19:09but refused to give him recognition for cracking longitude
0:19:09 > 0:19:13until accurate sea-going clocks could be mass produced.
0:19:15 > 0:19:17Harrison never lived to see it.
0:19:20 > 0:19:26It took another 40 years for clocks to become commonplace on our seas.
0:19:28 > 0:19:32In the meantime, sailors across the world
0:19:32 > 0:19:35persevered with the lunar method.
0:19:38 > 0:19:40And it was astronomical data
0:19:40 > 0:19:45compiled here in Greenwich that became their bible,
0:19:45 > 0:19:48with far-reaching consequences for the city.
0:19:50 > 0:19:53The astronomers here in Greenwich
0:19:53 > 0:19:56began to make books exactly like this.
0:19:56 > 0:19:59This is the book called The Nautical Almanac.
0:19:59 > 0:20:05On these pages, the distance of the moon from a list of stars
0:20:05 > 0:20:09is tabulated with exquisite precision,
0:20:09 > 0:20:14based on the longitude of Greenwich as zero.
0:20:14 > 0:20:17Every mariner who used these tables
0:20:17 > 0:20:21would be assuming that Greenwich was the origin of time,
0:20:21 > 0:20:24and therefore the origin of longitude.
0:20:26 > 0:20:30Those British books circulated around the globe.
0:20:30 > 0:20:33All used Greenwich
0:20:33 > 0:20:35as their reference point.
0:20:36 > 0:20:41Most mariners acquired the habit of looking to London
0:20:41 > 0:20:43to work out their location.
0:20:44 > 0:20:48In 1884, a world conference
0:20:48 > 0:20:51confirmed our capital's connection to the sea.
0:20:53 > 0:20:56When it came to a vote, it was official -
0:20:56 > 0:20:59Greenwich was sanctioned
0:20:59 > 0:21:01as the Prime Meridian,
0:21:01 > 0:21:04the line of zero degree longitude.
0:21:23 > 0:21:27Greenwich remains the centre of the maritime world.
0:21:29 > 0:21:32But where is the capital's once-thriving sea trade?
0:21:35 > 0:21:38Out towards the edge of the Thames Estuary
0:21:38 > 0:21:42a new mega port has been taking shape,
0:21:42 > 0:21:44London Gateway.
0:21:52 > 0:21:57Around our isles, we've constructed large out-of-town ports.
0:21:59 > 0:22:01When every second counts,
0:22:01 > 0:22:03how do they get goods off the sea
0:22:03 > 0:22:05and into our cities?
0:22:09 > 0:22:12I'm caught up in a hive of activity at Immingham.
0:22:20 > 0:22:24Global sea trade demands that ships keep moving.
0:22:26 > 0:22:29Delays cost companies and, ultimately, us.
0:22:31 > 0:22:34The volume of traffic here is relentless.
0:22:37 > 0:22:41Connecting everything are these roll-on/roll-off trailers.
0:22:48 > 0:22:52A 24-hour operation, overseen by Mark Reeve.
0:22:54 > 0:22:56We bring a vast amount of cargo in.
0:22:56 > 0:23:00It can be anything from food, timber, steels,
0:23:00 > 0:23:03chemicals, as well - import and export.
0:23:03 > 0:23:06So a very wide and diversified cargo.
0:23:06 > 0:23:09How long do you have to turn a ship around? To get it out again?
0:23:09 > 0:23:12Something like the vessel that's come in from Esbjerg in Denmark today -
0:23:12 > 0:23:15200-plus trailers in, 200-plus trailers out -
0:23:15 > 0:23:18- we can turn that around in six hours.- That's shifting!
0:23:18 > 0:23:21Yeah, that's going some. That's going some.
0:23:29 > 0:23:32The container port is just one district
0:23:32 > 0:23:34in this city-sized enterprise.
0:23:35 > 0:23:39More fiddly cargo is delivered by the boatload
0:23:39 > 0:23:41and moved by the tonne.
0:23:42 > 0:23:44Heavy lifting - which presents me
0:23:44 > 0:23:47with the opportunity to realise a boyhood ambition.
0:23:49 > 0:23:53After ten years on Coast, I, Nick Crane,
0:23:53 > 0:23:56finally get to do a story on cranes!
0:24:03 > 0:24:07Crane driver Chris Jubb is showing me his elevated office.
0:24:09 > 0:24:12Not a lot of space in here, is there, Chris?
0:24:12 > 0:24:14No, they're only built for one, Nick.
0:24:14 > 0:24:16What are you unloading here?
0:24:16 > 0:24:18Today, we've got 13,000 tonnes of salt coming from Egypt.
0:24:18 > 0:24:20- Is that road salt? - That's road salt, yeah.
0:24:20 > 0:24:25What are the qualities you need to be a dockside crane-driver?
0:24:25 > 0:24:28I've heard it likened to the same as an airline pilot
0:24:28 > 0:24:30on takeoff and landing,
0:24:30 > 0:24:31the concentration that's needed.
0:24:31 > 0:24:34So how much salt can you lift up in one go?
0:24:34 > 0:24:36- It's 12 tonnes of salt in that grab. - That's a lot.
0:24:36 > 0:24:39On top of the world up here, aren't you, looking down on the port.
0:24:39 > 0:24:42The pinnacle of a manual-grades career.
0:24:42 > 0:24:43NICK LAUGHS
0:24:47 > 0:24:49Chris makes it look easy,
0:24:49 > 0:24:53but guiding this massive grabber into the precise position
0:24:53 > 0:24:56to dump its load into the hopper
0:24:56 > 0:24:58takes skill and experience.
0:25:01 > 0:25:03How long to train me to do something like this?
0:25:03 > 0:25:05You're looking at least a year.
0:25:05 > 0:25:07Yeah, I can believe it.
0:25:07 > 0:25:09I might not have a year,
0:25:09 > 0:25:12but I can't come all this way without having a go.
0:25:13 > 0:25:18Chris has a novel challenge in store for a novice like me.
0:25:18 > 0:25:22Have I got the spatial awareness to drive a monster crane?
0:25:22 > 0:25:24We're about to find out.
0:25:29 > 0:25:33Well, there's an awful lot of controls in here.
0:25:33 > 0:25:35The only two you'll be looking at today
0:25:35 > 0:25:37are the basic controls -
0:25:37 > 0:25:41which is the jib lever, for slewing left to right,
0:25:41 > 0:25:45and your right-hand lever, which is for lifting the grab,
0:25:45 > 0:25:47lowering the grab, opening the grab and closing the grab.
0:25:47 > 0:25:50- Shall I give it a go? - Give it a go, yeah.
0:25:50 > 0:25:54Nice and gently. Slow...slow. Ease the lever back gently.
0:25:54 > 0:25:56You need a light touch as a crane-driver.
0:25:56 > 0:25:59Them small movements are the key movements.
0:26:01 > 0:26:05If you want to try and position yourself over that traffic cone there.
0:26:05 > 0:26:08- OK...- We'll try and grab hold of the traffic cone.
0:26:08 > 0:26:10Once you think you're somewhere over it,
0:26:10 > 0:26:12just gently bring her down.
0:26:12 > 0:26:14Now start looking out the window.
0:26:14 > 0:26:15Am I going to knock it over now?
0:26:15 > 0:26:18If I try and do a grab now... A bit lower maybe?
0:26:20 > 0:26:22Oh! Now I've knocked it over. I'm doomed!
0:26:24 > 0:26:27Oh, yes! Got it! Bingo.
0:26:27 > 0:26:30Gently lift her up. Gently lift her up.
0:26:30 > 0:26:32Well done. NICK LAUGHS
0:26:32 > 0:26:36You're the first person I've ever taught to grab a cone before.
0:26:36 > 0:26:38That's so difficult!
0:26:38 > 0:26:41- But could you do that for eight hours a day?- I'd be drained.
0:26:41 > 0:26:43I'd be absolutely drained.
0:26:44 > 0:26:47I think I'll leave the heavy lifting to the professionals!
0:26:51 > 0:26:54That was great fun. I've always wanted to drive a crane.
0:26:54 > 0:26:58It's amazing what a hands-on business our sea trade still is.
0:27:05 > 0:27:09Our great cities weren't only built on the back of trade.
0:27:18 > 0:27:22On the south coast, major cities owed their existence to the Navy.
0:27:27 > 0:27:29As the Royal fleet grew up,
0:27:29 > 0:27:32so did a vast and varied population.
0:27:38 > 0:27:41As they know in Portsmouth.
0:27:56 > 0:27:58This is our oldest naval base.
0:28:03 > 0:28:06In its docks, the city proudly displays ships that brought
0:28:06 > 0:28:08victory to our isles.
0:28:10 > 0:28:13But there's a less-celebrated story here, too.
0:28:15 > 0:28:17In the 19th century,
0:28:17 > 0:28:21naval ships and their sailors carried disease from overseas.
0:28:23 > 0:28:27Ruth is exploring how the port put the city in peril.
0:28:28 > 0:28:31# The captain's daughter, I suppose
0:28:31 > 0:28:33# Could be called an English rose
0:28:33 > 0:28:36# What would you think if I propose?
0:28:36 > 0:28:39# The pox she gave to me a dose... #
0:28:39 > 0:28:40It's February 1856,
0:28:40 > 0:28:43and the Crimean War has just ended.
0:28:43 > 0:28:46The Royal Navy is heading back into Portsmouth,
0:28:46 > 0:28:49but as the sailors flood into the city,
0:28:49 > 0:28:52a silent danger looms.
0:28:55 > 0:28:59The Royal Navy was plagued with a sexually transmitted disease -
0:28:59 > 0:29:02over a third of the men admitted to hospital had syphilis.
0:29:05 > 0:29:07The statistics were staggering.
0:29:07 > 0:29:09In one year alone,
0:29:09 > 0:29:12the Royal Navy lost 77,000 working days
0:29:12 > 0:29:15to sickness from syphilis.
0:29:18 > 0:29:20The Government saw syphilis
0:29:20 > 0:29:22as a threat to national security.
0:29:22 > 0:29:26Our naval cities were on the front line of a war.
0:29:30 > 0:29:32So, what exactly is syphilis?
0:29:33 > 0:29:36The disease scandalised Victorian Britain,
0:29:36 > 0:29:39and it still has the power to shock.
0:29:39 > 0:29:43Medical historian Pauline Price has some disturbing images.
0:29:45 > 0:29:50The primary symptoms would be hard lumps called chancres,
0:29:50 > 0:29:53and then you would end up
0:29:53 > 0:29:57perhaps coming onto this stage, this is the secondary syphilis,
0:29:57 > 0:30:01and you've got a lot of pustules around the chest, on the face,
0:30:01 > 0:30:05and that would make you feel very tired, very ill.
0:30:05 > 0:30:08That might disappear after about six weeks,
0:30:08 > 0:30:10and then you might have
0:30:10 > 0:30:13a period of 5 to 20 years where it was latent -
0:30:13 > 0:30:15hadn't gone away, but you had no symptoms.
0:30:15 > 0:30:20And then you would start developing the tertiary symptoms,
0:30:20 > 0:30:21and these are even worse,
0:30:21 > 0:30:25and you can imagine the results of these is usually death.
0:30:25 > 0:30:27So, what could people do to treat it?
0:30:27 > 0:30:31They would have various forms of mercury treatment -
0:30:31 > 0:30:33they might make it into pills,
0:30:33 > 0:30:34a lotion.
0:30:34 > 0:30:37Mercury's a really poisonous substance, isn't it?
0:30:37 > 0:30:39The effects on the body are truly vile.
0:30:39 > 0:30:41Well, that was the Victorian idea,
0:30:41 > 0:30:44that you were purging your system, so if you salivated,
0:30:44 > 0:30:46if you vomited, then you're getting out of the system
0:30:46 > 0:30:48the things that are making you ill.
0:30:48 > 0:30:50And if you did go through with the treatment,
0:30:50 > 0:30:52would it actually cure the syphilis?
0:30:52 > 0:30:55No, it wouldn't. They just didn't have the science.
0:30:55 > 0:30:58So you used this because it was the best they had.
0:31:01 > 0:31:04With no cure in sight,
0:31:04 > 0:31:06the silent killer spread.
0:31:06 > 0:31:10Our cities were soon a breeding ground for the pox.
0:31:12 > 0:31:16This is a copy of a caricature from the early 1800s
0:31:16 > 0:31:20showing a typical Portsmouth dockside scene -
0:31:20 > 0:31:23lewd goings-on, sailors rollicking with prostitutes,
0:31:23 > 0:31:27an inebriated woman being carried off.
0:31:27 > 0:31:30And it was these loose women, rather than the sailors,
0:31:30 > 0:31:33that were to be the focus of the Government crackdown.
0:31:35 > 0:31:38As the Government sought ways to control the epidemic,
0:31:38 > 0:31:42a shadowy underworld came under the spotlight.
0:31:42 > 0:31:44I'm with historian Fern Riddell.
0:31:44 > 0:31:47We know that in Portsmouth in this period
0:31:47 > 0:31:50there were about 2,000 prostitutes working.
0:31:50 > 0:31:52There's a real strong link, it seems,
0:31:52 > 0:31:55between sailors and prostitutes, isn't there?
0:31:55 > 0:31:57They'd be somewhere the men could come and stay,
0:31:57 > 0:32:00they'd look after their money, give them a social life.
0:32:00 > 0:32:03And it really was very much a companionable relationship.
0:32:03 > 0:32:06- Because there were no barracks for the sailors, at all, in town?- No.
0:32:06 > 0:32:09When they arrived off the ships there was nowhere for them to stay?
0:32:09 > 0:32:13None at all. You wanted somewhere you could actually lay your head,
0:32:13 > 0:32:16and some company different from the men that you'd stayed with
0:32:16 > 0:32:18the entire time you were at sea.
0:32:18 > 0:32:24# Get six of me, comrade To carry my coffin...#
0:32:24 > 0:32:29As syphilis spread, popular songs made clear who was held to blame.
0:32:29 > 0:32:35# ..Bad luck to the girl that gived him the pox... #
0:32:35 > 0:32:39"Bad luck to the girl that gived him the pox."
0:32:39 > 0:32:42The sailors blamed the prostitutes for their sickness,
0:32:42 > 0:32:44and the Government did, too.
0:32:47 > 0:32:52In July 1864, Parliament passed the first Contagious Diseases Act -
0:32:52 > 0:32:53this is it here.
0:32:53 > 0:32:58Its purpose? To control prostitution and venereal disease
0:32:58 > 0:33:01in order to increase the efficiency of the Navy.
0:33:02 > 0:33:05The Act introduced draconian new measures
0:33:05 > 0:33:09to control sexually transmitted disease...
0:33:09 > 0:33:11aimed squarely at women.
0:33:11 > 0:33:15Under the Act, any woman who was suspected of being a prostitute
0:33:15 > 0:33:17could be examined - forcibly -
0:33:17 > 0:33:19in the most intimate way.
0:33:21 > 0:33:23While sailors walked free,
0:33:23 > 0:33:26women suspected of having the disease
0:33:26 > 0:33:29were sent to aptly named lock hospitals.
0:33:31 > 0:33:33The shame of the city,
0:33:33 > 0:33:36these prison-like wards have long since disappeared.
0:33:36 > 0:33:39But Fern can paint a picture.
0:33:39 > 0:33:43They were really stark and depressing places to go,
0:33:43 > 0:33:46and each woman was responsible for their own treatment.
0:33:46 > 0:33:51So they'd go from having a horrible, really horrible, internal exam
0:33:51 > 0:33:54when they were proved to have a contagious disease,
0:33:54 > 0:33:56to then treating themselves,
0:33:56 > 0:33:58to then being examined by a doctor
0:33:58 > 0:34:00to see if the treatment was working.
0:34:00 > 0:34:02And that was for their entire time
0:34:02 > 0:34:04that they were incarcerated in the lock hospitals,
0:34:04 > 0:34:08which could be from three to six to even nine months.
0:34:13 > 0:34:16One woman was especially outraged by the law.
0:34:17 > 0:34:21Josephine Butler was a Christian from a middle-class background.
0:34:21 > 0:34:24Heedless of potential embarrassment,
0:34:24 > 0:34:27she attacked the Contagious Diseases Act.
0:34:27 > 0:34:31She toured the country to argue the prostitutes' cause.
0:34:31 > 0:34:33I'm following in Josephine Butler's footsteps.
0:34:36 > 0:34:38Despite the odds stacked against her,
0:34:38 > 0:34:43Josephine set up a campaign group to repeal the Act targeted at women.
0:34:44 > 0:34:46She took to the stage to voice her dissent.
0:34:48 > 0:34:53"Women turn to prostitution out of starvation, hunger.
0:34:53 > 0:34:56"Two pence is the price in England of a young girl's honour."
0:34:58 > 0:35:00What were her main arguments?
0:35:00 > 0:35:02Well, she has three main points.
0:35:02 > 0:35:06So, firstly, she manages to inspire compassion for a class of women
0:35:06 > 0:35:08that most people would have ignored.
0:35:08 > 0:35:11Secondly, she exposes this horrific double standard
0:35:11 > 0:35:15of the fact that you would treat women, but you wouldn't treat men.
0:35:15 > 0:35:18And that, I think, really grabbed a lot of people's attention.
0:35:18 > 0:35:22"We must protest against the purchase
0:35:22 > 0:35:24"of physical health of soldiers,
0:35:24 > 0:35:30"at the cost of introducing so much darkness and immortality."
0:35:30 > 0:35:34This is what really grabs the whole community together -
0:35:34 > 0:35:36the fact that she exposes the Government as really being
0:35:36 > 0:35:38incredibly immoral.
0:35:38 > 0:35:42And they're basically legalising and regulating prostitution,
0:35:42 > 0:35:46which to the Victorians was absolutely unthinkable.
0:35:46 > 0:35:50# Come, my good friends and a story I'll relate
0:35:50 > 0:35:54# I spied a brave comrade all dressed in white flannel
0:35:54 > 0:35:58# Dressed in white flannel and cruel was his fate... #
0:35:59 > 0:36:02It was this final argument that struck home.
0:36:02 > 0:36:04By regulating prostitution,
0:36:04 > 0:36:07the Government appeared to be condoning it.
0:36:08 > 0:36:10A groundswell of popular opinion
0:36:10 > 0:36:13backed Josephine Butler's cause,
0:36:13 > 0:36:17but it took 19 years' hard campaigning
0:36:17 > 0:36:20until Josephine finally received a telegram
0:36:20 > 0:36:23with momentous news.
0:36:23 > 0:36:26It's dated 1886, and simply read,
0:36:26 > 0:36:28"Repeal received royal ascent."
0:36:28 > 0:36:31No longer could a women be forcibly examined
0:36:31 > 0:36:35or locked up in a hospital without her consent.
0:36:35 > 0:36:38# There's a hole in his boots...
0:36:38 > 0:36:40# Bad luck to the girl... #
0:36:40 > 0:36:45In 1905, the real enemy to our cities was identified - not women,
0:36:45 > 0:36:50not the sailors that visited them, but this -
0:36:50 > 0:36:53Treponema pallidum, the spiral-shaped bacterium
0:36:53 > 0:36:56responsible for syphilis.
0:36:56 > 0:36:58But only after the Second World War,
0:36:58 > 0:37:01when penicillin became widely available,
0:37:01 > 0:37:06did the threat to our cities finally subside.
0:37:06 > 0:37:08# I might have been cured
0:37:08 > 0:37:10# By those pills of white mercury
0:37:10 > 0:37:15# Now I'm a young man cut down in my prime... #
0:37:29 > 0:37:33We're exploring the sea and the city.
0:37:35 > 0:37:38A journey that's brought me to the Humber.
0:37:43 > 0:37:46Just 13 miles from the port of Immingham,
0:37:46 > 0:37:50a finger of land reaches into the sea.
0:37:52 > 0:37:54This is Spurn Head.
0:37:57 > 0:37:59At its tip is a control centre...
0:38:02 > 0:38:07..directing cargo ships safely into Immingham's busy port.
0:38:17 > 0:38:20Now, I'm following this flow of traffic,
0:38:20 > 0:38:23and it holds some surprises.
0:38:32 > 0:38:35This is a gateway for global commerce.
0:38:35 > 0:38:38But it isn't only cargo that washes up here -
0:38:38 > 0:38:42these huge ships are also homes.
0:38:47 > 0:38:52Seafarers are forever in transit between destinations,
0:38:52 > 0:38:56so ports like this become temporary cities for the stateless.
0:38:58 > 0:39:01Yesterday, the Greek-owned Elena Ve,
0:39:01 > 0:39:04with its Filipino crew arrived from Russia.
0:39:06 > 0:39:09These globe-trotting ships spend months at sea.
0:39:10 > 0:39:12Far from their own cities,
0:39:12 > 0:39:16what do the crew do when they arrive on our shores?
0:39:17 > 0:39:19I'm meeting Colum Kelly.
0:39:19 > 0:39:22We're going on board the Elena which has come from Russia
0:39:22 > 0:39:24bringing some coal.
0:39:25 > 0:39:28Colum is Immingham's very own chaplain.
0:39:28 > 0:39:32He helps throw an anchor to a restless flow of visitors.
0:39:35 > 0:39:38As the Elena's vast hold gives up its cargo...
0:39:39 > 0:39:42..the crew are getting a break in the mess room.
0:39:44 > 0:39:46- Hi, guys. ALL:- Hey.
0:39:46 > 0:39:47What's for dinner tonight?
0:39:47 > 0:39:50- Pork. Pork.- Yes.
0:39:50 > 0:39:53Who's been longest on this ship? Contract?
0:39:53 > 0:39:56- These guys. - These guys? How many months?
0:39:56 > 0:39:58About nine months. Nine months.
0:39:58 > 0:40:00So you must miss your families dreadfully in that time?
0:40:00 > 0:40:03Yes, that's what we do when we are in port.
0:40:03 > 0:40:06We try to find internet access
0:40:06 > 0:40:08just to have contact with our families.
0:40:08 > 0:40:10Well, tonight's your lucky night
0:40:10 > 0:40:12because I've brought you some internet access -
0:40:12 > 0:40:14and the good news is, it's free!
0:40:14 > 0:40:16- ALL:- Yay!
0:40:17 > 0:40:20It's not often an internet connection gets a round of applause,
0:40:20 > 0:40:23but this ship and its 20-strong Filipino crew
0:40:23 > 0:40:26have been at sea for weeks.
0:40:28 > 0:40:32Column's Wi-Fi is a long-awaited lifeline home.
0:40:33 > 0:40:36- This is my daughter. - Your daughter?
0:40:36 > 0:40:38Yes, sir. I miss her so much.
0:40:38 > 0:40:40I bet. How old is she?
0:40:40 > 0:40:41Er, eight years old, sir.
0:40:41 > 0:40:43- Well, you're a very lucky man. - Thank you, sir.
0:40:43 > 0:40:46Is it difficult for you to stay in touch with your family
0:40:46 > 0:40:48- when you're on the ship? - Yes, of course, sir.
0:40:48 > 0:40:52The longest voyage I have ever experienced in a vessel is 42 days.
0:40:52 > 0:40:55- 42 days on one voyage?- Yes.
0:40:55 > 0:40:57- Where were you going from? - From America to China.
0:41:01 > 0:41:05In port, they only get six hours off at a time.
0:41:05 > 0:41:09Even so, the chaplain tries to give them a good taste of Britain.
0:41:12 > 0:41:15You must have had some strange requests over the years?
0:41:15 > 0:41:17There was an Indian crew, and I said,
0:41:17 > 0:41:19"Well, do you want to go to the cinema, to a supermarket,
0:41:19 > 0:41:22"or want to go into the city and do a big shopping?"
0:41:22 > 0:41:23And the captain says,
0:41:23 > 0:41:27"They'd like to be taken somewhere where they could walk on grass."
0:41:27 > 0:41:29Oh. Heartbreaking.
0:41:29 > 0:41:31How simple a request is that?
0:41:32 > 0:41:36With the coal disgorged, this crew is ready to sail again.
0:41:39 > 0:41:41But where in the world,
0:41:41 > 0:41:42they won't know until word comes
0:41:42 > 0:41:45from the owner in Athens.
0:42:03 > 0:42:05For centuries, the coming and going of boats
0:42:05 > 0:42:07has brought opportunities
0:42:07 > 0:42:08for city folk...
0:42:10 > 0:42:13..giving them freedom to travel the world.
0:42:15 > 0:42:18To find a city that's been shaped
0:42:18 > 0:42:19by that spirit of adventure,
0:42:19 > 0:42:23there's nowhere better to look
0:42:23 > 0:42:24than Liverpool.
0:42:32 > 0:42:36This city not only transported goods across the sea,
0:42:36 > 0:42:38but also people.
0:42:40 > 0:42:42The quayside once bustled with liners,
0:42:42 > 0:42:47offering Liverpool's youth a route to adventure.
0:42:49 > 0:42:52Transatlantic trade has long dried up,
0:42:52 > 0:42:56but the sea still inspires the young to run free.
0:43:05 > 0:43:09Today, their routes are just a little bit more imaginative.
0:43:13 > 0:43:16I'm Ryan Doyle, and this is my city - Liverpool.
0:43:21 > 0:43:24Liverpool is just one of the coolest cities -
0:43:24 > 0:43:26every major road runs to the coast.
0:43:26 > 0:43:30It's like a city that's had half of it opened up to the ocean,
0:43:30 > 0:43:34so you don't have that inner-city claustrophobia.
0:43:38 > 0:43:42Free-running is expressing yourself through movement
0:43:42 > 0:43:44so you can set yourself a destination
0:43:44 > 0:43:47and try and get there as creatively as you can.
0:43:48 > 0:43:51It's just exploring what the body's capable of.
0:43:53 > 0:43:54The sea... It's in my blood.
0:43:54 > 0:43:57My father was half Irish, my mother is half Irish.
0:43:57 > 0:44:00I don't know why, just something about the Irish Sea.
0:44:00 > 0:44:01I'm connected to it.
0:44:09 > 0:44:12The Liverpool docks - it's a maze of architecture,
0:44:12 > 0:44:16unexplored architecture, that we need to use to our advantage.
0:44:16 > 0:44:19You know, you don't really get to know an environment
0:44:19 > 0:44:21until you've jumped all over it!
0:44:40 > 0:44:42A lot of these kids like to play Spider-Man
0:44:42 > 0:44:44and play all the PlayStation games,
0:44:44 > 0:44:47but I like to go out and actually physically be Spider-Man.
0:44:53 > 0:44:56The River Mersey flowing right through Liverpool.
0:44:56 > 0:45:00If we want, we can go on a boat and just hit the open seas
0:45:00 > 0:45:01because a lot of free-runners
0:45:01 > 0:45:03are always up for the adventure,
0:45:03 > 0:45:05and there's nothing more that says
0:45:05 > 0:45:07adventure than the open sea.
0:45:19 > 0:45:22We're on a metropolitan maritime journey.
0:45:22 > 0:45:25A story of profit...
0:45:25 > 0:45:27and loss.
0:45:32 > 0:45:37For centuries, the sea has provided for our cities.
0:45:37 > 0:45:39But when the tide turns,
0:45:39 > 0:45:42our greatest ally can become our worst enemy.
0:45:51 > 0:45:53Head down our east coast,
0:45:53 > 0:45:58and chunks of land have been eaten by ferocious waves.
0:46:03 > 0:46:06We've witnessed the devastating impact of the sea
0:46:06 > 0:46:08on small coastal settlements,
0:46:08 > 0:46:14making it clear what catastrophe the water could wreak on our cities.
0:46:22 > 0:46:26They must defend themselves from the sea in London.
0:46:36 > 0:46:41People and property are protected by the Thames Barrier
0:46:41 > 0:46:44and the city's stone embankments.
0:46:47 > 0:46:51But go back 75 years, and there was a storm brewing in Europe.
0:46:53 > 0:46:56Hitler wanted to bring the city to its knees.
0:46:56 > 0:46:59Would the power of the tide be London's Achilles heel?
0:47:03 > 0:47:07Tessa is uncovering a hidden chapter in the story
0:47:07 > 0:47:08of the Second World War.
0:47:14 > 0:47:17I've got with me a top-secret wartime document.
0:47:19 > 0:47:22It says here, "Warning. This publication must not leave
0:47:22 > 0:47:26"the custody of the person to whom it has been supplied,
0:47:26 > 0:47:29"nor may it be taken or sent abroad
0:47:29 > 0:47:33"without the authority of the Hydrographer of the Navy."
0:47:33 > 0:47:36What's in this secret document?
0:47:36 > 0:47:39London's tidal bible.
0:47:41 > 0:47:44The surging tide raises the level of the Thames
0:47:44 > 0:47:46by up to eight metres.
0:47:50 > 0:47:52During the Second World War,
0:47:52 > 0:47:55one man saw this twice daily deluge
0:47:55 > 0:47:58as a threat to Britain itself.
0:47:59 > 0:48:03The document has been written by this person, Peirson Frank,
0:48:03 > 0:48:05and here he is,
0:48:05 > 0:48:07London County Council's chief engineer.
0:48:09 > 0:48:12Frank's fear of the high tide
0:48:12 > 0:48:15sprang from bitter experience.
0:48:15 > 0:48:20In 1928, the Thames had poured into the city,
0:48:20 > 0:48:22a storm overwhelmed the Embankment,
0:48:22 > 0:48:24the Underground flooded,
0:48:24 > 0:48:28people in basement flats drowned.
0:48:28 > 0:48:31Then Peirson Frank had been powerless.
0:48:32 > 0:48:3512 years later, as the Blitz rained down,
0:48:35 > 0:48:38Frank knew that if Hitler had the tidal bible,
0:48:38 > 0:48:40accurately placed bombs
0:48:40 > 0:48:45could demolish London's flood defences at high water,
0:48:45 > 0:48:47unleashing the sea on the city.
0:48:53 > 0:48:56London had nearly drowned by accident,
0:48:56 > 0:48:59could Hitler now drown it by design?
0:49:02 > 0:49:06If so, Peirson Frank knew where the Nazi bombers would strike.
0:49:08 > 0:49:12The Embankment protects the heart of the city from the sea.
0:49:14 > 0:49:18Archaeologist Gustav Milne has pieced together evidence
0:49:18 > 0:49:21of a secret that's been kept for over 70 years.
0:49:23 > 0:49:25This is the scar of a bomb
0:49:25 > 0:49:29that struck here on 16th March 1941,
0:49:29 > 0:49:32and the hole was very rapidly filled.
0:49:32 > 0:49:35What makes you sure this is the site of a bomb?
0:49:35 > 0:49:39Well, we know it's a bomb simply because all the granite facing
0:49:39 > 0:49:41that was there is now spread out
0:49:41 > 0:49:43over a great 18-metre arc,
0:49:43 > 0:49:45right the way round here.
0:49:45 > 0:49:48So, 70 years on, it's still lying on the riverbed?
0:49:48 > 0:49:49Still on the riverbed.
0:49:51 > 0:49:56A co-ordinated bomb attack on several targets at high tide
0:49:56 > 0:49:57could have crippled the city.
0:50:01 > 0:50:03Power and phone lines would be cut,
0:50:03 > 0:50:06the water supply contaminated -
0:50:06 > 0:50:10losing London might have meant losing the war.
0:50:11 > 0:50:15Gustav has found scars from 122 bomb strikes
0:50:15 > 0:50:17to London's flood wall.
0:50:20 > 0:50:23Attacks that worried the Government so much
0:50:23 > 0:50:25they took action to cover them up.
0:50:27 > 0:50:32What I've got in here is the logbook of the snappily named
0:50:32 > 0:50:37Thames Flood Prevention Emergency Repairs Service.
0:50:37 > 0:50:39The team was led by Peirson Frank,
0:50:39 > 0:50:41and it was so secret
0:50:41 > 0:50:44no-one even knew it existed.
0:50:47 > 0:50:52Gustav has spent years researching this covert team of workers.
0:50:53 > 0:50:55If you look at this photograph,
0:50:55 > 0:50:57it shows the team in action.
0:50:57 > 0:51:01What you can see here is this great line of 5,000 sandbags,
0:51:01 > 0:51:06and they are blocking up a gap in the riverside wall.
0:51:06 > 0:51:08And why was this unit such a secret?
0:51:08 > 0:51:11Because they didn't want to alert the Luftwaffe
0:51:11 > 0:51:14to the extreme vulnerability of low-lying London,
0:51:14 > 0:51:17and they didn't want to affect the morale of Londoners,
0:51:17 > 0:51:20who had already been faced with being exploded to death,
0:51:20 > 0:51:24so they didn't want to make them fear drowning, as well.
0:51:27 > 0:51:29People's worst nightmare
0:51:29 > 0:51:31was a flood underground,
0:51:31 > 0:51:34below the Thames in the Tube.
0:51:35 > 0:51:40During airstrikes, stations became makeshift bomb shelters.
0:51:40 > 0:51:42But what if a tunnel was hit
0:51:42 > 0:51:45and the river above poured in?
0:51:46 > 0:51:48The horror was unimaginable,
0:51:48 > 0:51:50but the fear very real.
0:51:52 > 0:51:56How could those helpless underground be protected?
0:51:57 > 0:52:00Thousands of people use this Tube every day,
0:52:00 > 0:52:04but I wonder how many notice the remnants of a metal door.
0:52:07 > 0:52:10When the air-raid siren sounded,
0:52:10 > 0:52:13heavy steel floodgates slid into place...
0:52:15 > 0:52:18..to seal off tunnels running under the Thames.
0:52:21 > 0:52:24This is one of the actual flood-proof doors
0:52:24 > 0:52:26fitted during the Blitz.
0:52:26 > 0:52:28It's now out of use,
0:52:28 > 0:52:30but during the war, every tunnel
0:52:30 > 0:52:33that ran under the Thames had one of these.
0:52:35 > 0:52:37If the tunnel behind was breached,
0:52:37 > 0:52:40the Tube network SHOULD stay safe.
0:52:42 > 0:52:44But at night, in the chaos of war,
0:52:44 > 0:52:48it was hard to tell if bombs were falling in the river.
0:52:49 > 0:52:52If a bomb hit the Thames and flooded one of those tunnels,
0:52:52 > 0:52:57how would they know without literally opening the floodgates?
0:52:57 > 0:53:03Once again, the city's engineers devised a remarkable counter measure.
0:53:04 > 0:53:07Hydrophones.
0:53:07 > 0:53:09Basically, underwater microphones -
0:53:09 > 0:53:12and they were placed on the bed of the Thames,
0:53:12 > 0:53:15close to every one of the Tube tunnels under the water.
0:53:15 > 0:53:18LOUD EXPLOSION
0:53:21 > 0:53:23It was an astonishing scheme.
0:53:23 > 0:53:27Sound waves would detect where the bombs were landing.
0:53:27 > 0:53:30So, how did it work?
0:53:30 > 0:53:34Thames hydrographer John Dillon-Leetch can demonstrate.
0:53:34 > 0:53:37What we have here is two hydrophones,
0:53:37 > 0:53:39and if we take this target
0:53:39 > 0:53:42and we say this might be a bomb during the Second World War
0:53:42 > 0:53:44and we drop it into the water,
0:53:44 > 0:53:48like so, the ripples there would represent sound waves.
0:53:48 > 0:53:52And they would be timed from the time they're received here and here,
0:53:52 > 0:53:54and by looking at the difference between the two times
0:53:54 > 0:53:56we should be able to calculate
0:53:56 > 0:53:59the approximate position of the bomb.
0:54:00 > 0:54:04The wartime hydrophone signals were interpreted by skilled analysts
0:54:04 > 0:54:07at South Kensington Tube station.
0:54:09 > 0:54:13Test recordings show sound waves from a Thames tug boat.
0:54:13 > 0:54:16ENGINE HUM, SPLASHING WATER
0:54:16 > 0:54:20And even the sensitivity to a single rifle shot.
0:54:20 > 0:54:21RIFLE SHOT
0:54:24 > 0:54:27Then, on 9th September 1940,
0:54:27 > 0:54:31the Luftwaffe loomed over London.
0:54:31 > 0:54:33Sirens sounded.
0:54:33 > 0:54:35SIRENS WAIL
0:54:35 > 0:54:38The electronic ears under the Thames were made ready,
0:54:38 > 0:54:40floodgates slammed shut.
0:54:42 > 0:54:46Then analysts received the signal they'd been dreading.
0:54:48 > 0:54:52Beneath the river, a section of the Northern Line had been hit.
0:54:59 > 0:55:02Thanks to the hydrophones the flood gates were kept shut,
0:55:02 > 0:55:04the water contained.
0:55:06 > 0:55:11Families sheltering in the Tube escaped...none the wiser.
0:55:15 > 0:55:20So, what of London's guardian angel, Peirson Frank?
0:55:20 > 0:55:24It turns out his fear of Hitler using the tidal Thames
0:55:24 > 0:55:27to destroy the city was well founded.
0:55:29 > 0:55:31Just not in the way he had imagined.
0:55:33 > 0:55:35Hitler didn't flood London,
0:55:35 > 0:55:38but his air force did turn the tide against us.
0:55:41 > 0:55:43Instead of hitting at high water,
0:55:43 > 0:55:47on the night of 29th December 1940,
0:55:47 > 0:55:51Hitler struck the city with incendiary bombs at low tide.
0:55:53 > 0:55:57Firefighters struggled to get enough water from the Thames
0:55:57 > 0:56:00to extinguish the blazes.
0:56:00 > 0:56:01The city burned.
0:56:03 > 0:56:06It was a tragic night for London,
0:56:06 > 0:56:09but had Hitler turned the sea against the city,
0:56:09 > 0:56:12then the story of the Blitz and even the outcome of the war
0:56:12 > 0:56:15could have been very different.
0:56:32 > 0:56:35We've been exploring the sea and the city.
0:56:38 > 0:56:40An urban coastal landscape
0:56:40 > 0:56:43continually transforming with the times.
0:56:46 > 0:56:49Old city trade routes welcome
0:56:49 > 0:56:51a flow of new ideas.
0:56:52 > 0:56:54And in the mega port of Immingham,
0:56:54 > 0:56:57a new opportunity awaits.
0:56:58 > 0:57:01For 100 years, coal has been the kingpin of Immingham,
0:57:01 > 0:57:05but this port is building its future on a new fuel.
0:57:11 > 0:57:15Wow, this is absolutely enormous!
0:57:17 > 0:57:22This soaring tower is being built to store a new generation of energy.
0:57:22 > 0:57:28This is biomass - mainly wood pulp from sustainable forests.
0:57:29 > 0:57:34Such biomass may provide up to a tenth of our electricity -
0:57:34 > 0:57:37the pellets stored in these huge silos.
0:57:40 > 0:57:44Our small isle would struggle to grow enough trees,
0:57:44 > 0:57:48so we rely on the sea for imports.
0:57:49 > 0:57:53Biomass could cement an exciting future for this port,
0:57:53 > 0:57:55harnessing the coast
0:57:55 > 0:57:58to the changing needs of our country.
0:58:05 > 0:58:09Life around our shores continues to transform...
0:58:10 > 0:58:14..but the precious links between sea and city endure.
0:58:21 > 0:58:23For thousands of years, we've built settlements
0:58:23 > 0:58:25along the edge of the sea -
0:58:25 > 0:58:27the great provider,
0:58:27 > 0:58:29the global highway.
0:58:29 > 0:58:30Now, as ever before,
0:58:30 > 0:58:34the coast lies at the centre of our national life.