Episode 1 Dive WWII: Our Secret History

This programme contains some scenes which some viewers may find upsetting

Londonderry is famous for a remarkable siege,

but there is an extraordinary time in the city's more recent past that has been forgotten.

The years when Derry was at the centre of World War II's longest and most decisive battle...

..the Battle of the Atlantic.

To reveal this story, we begin not in the city,

but on the waters of its coast.

Out there on the horizon,

hidden deep beneath the waves,

lie hundreds of forgotten shipwrecks.

Together, they tell the story of an extraordinary conflict.

It lasted nearly six years. 100,000 men died and 4,000 ships were sunk.

Wrecks from the battle still litter the seabed here,

lost, forgotten and out of reach... until now.

One underwater explorer has compiled a unique map.

It charts the lost wrecks of the Battle of the Atlantic.

Now, he and a team of expert divers are going in search of them,

to uncover the lost stories of the battle.

All the hatches are closed.

There is an open locker with live ammunition in it.

What they discover will restore Derry's lost place

in the history of World War II.

The Battle of the Atlantic could not have been won

if the bases on the Foyle had not been available to the Allies.

This is the object of the search today -

a top-secret bunker complex, deep beneath the grass here.

And over 70 years later, the generation who witnessed

first-hand this extraordinary time in Derry share their experiences.

When they came into the hospital,

it was dreadful to see a human being like that.

All you think about is what the people back home will think

when they know I'm dead.

"Bride ship leaves Derry for the US." I really was the first

GI bride to set foot in America.

And there was a lot of animosity, because we were stealing their men!

In this series, we will dive back through history, to uncover

how victory in the Battle of the Atlantic was forged here, in Derry.

Britain was at war in Europe

and increasingly dependent on the United States.

Without American oil, tanks and guns,

Britain's war effort would grind to a halt.

Every week, convoys of cargo ships ferried hundreds of thousands

of tonnes of supplies from America across the Atlantic to Britain.

Meanwhile, Nazi Germany sent its U-boat fleet to intercept

and destroy the convoys.

'In these bomber-laden ships, eastward bound from Canada

'and the USA, lies a threat not only to Hitler's

'campaign against the British Isles, but to his grip on Europe itself.'

It was the U-boats that made the Battle of the Atlantic

the longest and certainly one of the bloodiest campaigns of the war.

But it was from Derry and ports just like it that the fightback began.

It was from here that the corvettes

and destroyers set sail to hunt them down.

Within a year of the start of the war, Germany occupied France.

It gave their U-boat fleet direct access to the Atlantic

and to the packed shipping lanes off Northern Ireland.

The waters off Derry were now a U-boat killing zone,

where no Allied ship was safe.

Effectively, their force has been multiplied

because they can go straight out into the Atlantic.

The Royal Navy now needs a base that is as far

west in the British Isles as they can possibly get,

so the Foyle, the city of Londonderry, and the...what is now

Londonderry Port at Lisahally become truly critical elements.

The Battle of the Atlantic could not have been won

if the bases on the Foyle had not been available to the Allies.

It wasn't just Britain that was aware of Derry's strategic importance.

Extraordinary clues, hidden just outside the city,

show Derry was of huge strategic significance to the Americans,

even before 1941,

when Japan's attack on their Pacific bases pushed the US into the war.

Recently declassified documents discovered in Washington

reveal that even before the Japanese attack on Pearl Harbor,

the Americans were already building a vast European military base,

and they were doing it right here in Derry.

The United States President, Roosevelt,

had said that the United States Navy was going to

help in escorting convoys, and indeed were already doing it.

They were now going to extend that to the point that they

were going to escort convoys the full way across the Atlantic

and they wanted a base on this side of the Atlantic.

A party of US Navy officers came from London to inspect

the facilities that were already present in the city

and along the Foyle.

In early 1941, almost a year before Pearl Harbor,

the US Navy chose to build their very own docks on the Foyle.

Meanwhile, just outside the city, Beech Hill was to be

the site of a military barracks for hundreds of men.

This camp was America's first foothold in Europe - Base One.

But like so many of Derry's wartime stories,

the clues to this lie hidden. Today, Beech Hill is a luxury hotel.

But I've come here to see what is left of America's first base.

The clues are intriguing.

Slabs of concrete where buildings once stood...

..a few Nissan huts, the military's iconic prefab,

and on the far edge of the wood, I find the old perimeter fence,

still marked Base One.

When I first heard about this American European base,

Base One, I was expecting a bit more than sort of overgrown woodland,

but, sadly, this is all that's left of it.

US photographs reveal the true scale of Beech Hill.

They show a four-acre site with over 100 Nissan huts...

..specially built roads,

bomb shelters,

ammunition dumps...

..and accommodation for hundreds of Marines.

A full battalion of Marines was created,

called the First Provisional Battalion, and it was shipped

across and was barracked here and in Springtown

and also down at Lisahally.

Most intriguingly of all, the dates on these documents reveal

construction of Base One was well under way in July of 1941.

Five months before the attack on Pearl Harbor in the Pacific,

the United States was preparing for war in Europe, right here in Derry.

But even before the Americans arrived,

Derry was in the heat of the action.

From 1939, British escort ships based in the city were

fighting off attacks by German U-boats along the Ulster coast.

Today, wrecks from both sides lie forgotten on the seabed.

Naval historian Ian Lawler wants to change that.

We are stepping back into 1940, 1941, 1942 and so on.

Is that what it feels like when you dive?

When you're looking at the wreck, you're looking at,

"What am I seeing with respect to the damage?

"Is the bow missing, is the stern missing?

"Can I tell it was a torpedo?"

You can now start to put a few more pieces in the jigsaw.

Following years of research, Ian has created a unique map, one that

he believes charts the lost wrecks of the Battle of the Atlantic.

We have seabed survey data, we have fishermen's fasts,

where their nets caught on things, and we have information from diving.

So what I've done is put it all together on the one chart.

But while Ian's research has confirmed the locations

of hundreds of wrecks, he has not yet put names to all of them.

Each of the red symbols on the chart represents a shipwreck.

About half of what is here, we don't know what it is.

Now Ian plans to dive and identify six wrecks on his map,

which he believes are key to understanding the Battle

of the Atlantic and the role Derry played in the Allied victory.

He is joined by a team of Europe's top deep-water divers.

You can read about it all you want.

You can read all the textbooks, all the source material,

but there is nothing like actually going down and seeing what it is.

Ian and the team will be diving in waters which during the war

were the checkpoint for the Allies' Atlantic shipping.

Every Allied escort group,

every Allied support group that crosses the Atlantic, is going

to tie up in Derry for refuelling and for a couple

of days before it heads back out to do more work in the North Atlantic.

When you realise the Allies moved 85,000 shiploads of cargo

across the Atlantic and each of those ships

assembled into perhaps 600 convoys, will be escorted by five or

six escorts, you get an idea of the scale of what's going on.

The most common of the warships crowding Lisahally were

the corvettes. They were tough opponents.

Of more than 300 built, the U-boats sank just 25,

only two of which were in Northern Irish waters.

But Ian believes his map identifies one of them.

He was tipped off about its location by local skipper Michael McVeigh.

Found it last October.

It really is literally sitting at three, four, five,

six feet off the seabed. Unbelievable.

It was really, really, really, REALLY lucky to find it.

Based on the wreck's location,

Ian has a hunch it is in fact the lost corvette, HMS Hurst Castle.

Now, for the team's first dive, they are planning to explore it.

Rich Stevenson is the dive supervisor

and a deep-water veteran who has dived all over the world.

He is responsible for the safety of the team.

Would it be fair to say that when the ship sank,

she was fighting, potentially?

Oh, yeah, she was fully armed, absolutely.

So, it's probably a good assumption that any armaments or explosives

or missiles, whatever, that we're going to find, could be live?

-Absolutely.

-Yeah.

So I think we are going to employ a common-sense approach today, guys,

we are here to video and document, not to interfere and tamper.

The dive site is 40 miles offshore.

Using his echo sounder, Michael positions the boat over the wreck.

It is now 250 feet beneath them.

At that depth, there is no room for mistakes.

The number of people in Ireland that can dive to that depth,

you could count on, well, your fingers and toes.

It's very, very deep. It's very, very, very dangerous.

There are no errors allowed.

You can't say that going underwater isn't risky, because it is,

because we can't breathe underwater,

so therefore, the risk has to be managed.

I want to keep gas toxicity levels down to a minimum.

Safety is a priority.

The depth of the water puts you into a situation that is just

impossible to recover from quickly.

For three hours, they will rely

on a precise mix of gases to keep them alive.

Prepping the kit requires meticulous attention.

Fully prepped, the dive team drop into the water.

They are descending over 250 feet into the dark of the Atlantic.

For 15 minutes, they swim straight down.

On the seabed, the team has just 20 minutes to explore

and film the wreck.

Ian is looking for clues to prove his theory that this is

the armed corvette Hurst Castle.

She was 250 feet long and weighed over 1,000 tonnes.

The Hurst Castle was also armed with a variety of guns,

depth charges and a mortar. The site could be littered with ammunition.

We have a fair degree of wariness about poking around in amongst

Second World War munitions.

I wouldn't be touching it.

The entire stern has been destroyed. Only the bow section remains intact.

With time running out, the team have found nothing to confirm

Ian's theory that this is the Hurst Castle.

But then he finds his first clue - piles of decaying explosive shells.

After 70 years on the seabed, they are still a real risk.

You wonder what's going to happen next.

All you can do is hope that you're not around when it happens!

Ian examines the shells carefully.

They are important evidence that this was a military vessel.

Then, with only minutes left on the seabed, he discovers another clue.

It is the squid mortar,

a weapon fitted to Second World War corvettes.

It launched depth charges hundreds of yards in front of the ship

with deadly accuracy.

This one is still loaded - a sign the ship went down fighting.

Now you realise just how big a squid mortar is.

They look like torpedoes - these things are huge.

The squid mortar is a major clue this wreck could be

the Hurst Castle. But the team is out of time.

They need at least two-and-a-half hours to make a controlled

ascent to the surface.

Any faster and nitrogen bubbles could form in their bloodstreams

and kill them.

Finally, safely back on board,

Ian and the team are delighted with what they've discovered.

I thought we were looking at a winch in front of me,

because I saw the cogs. Then it was, "Ooh! That's a squid!"

We got 10 minutes of just excellent footage of that.

-Really pleased with that.

-Yeah, the shot was good.

On an Atlantic cliff top overlooking the very waters

the team are diving, Ian's footage will be

studied by two of the world's leading naval experts.

Dr Randy Papadopoulos is a historian at the Pentagon,

specialising in naval strategy.

Dr Axel Niestle is German

and a world expert on Second World War U-boats.

Ian needs their specialist knowledge to confirm his hunch that this

is the wreck of HMS Hurst Castle.

For a ship that was sunk so recently,

it's much more of a jigsaw puzzle than I expected.

-I'll say!

-But then we found this.

-Well, that's a squid mortar.

-Yup.

-Were there any charges in it?

-There is, definitely. It's loaded.

And here we have a lot of shells, sort of four-inch diameter.

-And lots of live ammunition in there.

-Yes.

-Yup.

-So you have to be careful.

Axel and Randy study the footage carefully, then they consult Allied

naval records, historical documents and plan drawings of possible ships.

Every detail helps in identifying the wreck.

Finally, they confirm Ian has made a remarkable discovery.

The wreck is HMS Hurst Castle.

One of only two Second World War corvettes

ever sunk in Northern Irish waters.

Just talk us through the anatomy of the ship

and how it relates to what you were able to see.

She's got radar, she's also got high-frequency direction finding,

or "Huff-Duff", and most importantly, the squid mortar.

They are very much the state-of-the-art for that time,

and that's the key thing.

Despite their corvette's weaponry, the crew of the Hurst Castle

were unable to repel a torpedo attack by a German U-boat.

The enemy submarine landed a direct hit.

The acoustic homing torpedo would have targeted the loud engines

of the corvette and essentially would have blown her stern off.

It was a decisive strike for the Nazi captain, who

brought his U-boat to within just 20 miles of the Northern Irish coast.

70 years later, it marks Ian's first success in his mission to map

the lost wrecks of this forgotten battlefield.

During the war, all these things are forgotten about,

they are just incidental, they just happened, that's it.

The Hurst Castle was sunk.

So, you know, just a loss in action, that's it.

But it's generally the divers that start to make the discoveries

and try and shed light on what happened.

When you find what you're looking for, that's what makes it,

that really makes it all worthwhile.

Because it marks more than just a wreck.

It marks the position of a war grave,

where 17 men lost their lives, fighting for freedom.

For the crews of any escort ship,

arrival into the protective waters of Lough Foyle meant safety at last.

You can imagine the crew of a convoy escort that have had a really

rough time, coming across the Atlantic,

entering the River Foyle and breathing a huge sigh of relief

and looking forward to all that Derry could offer them.

I remember one former convoy escort sailor writing to me

and saying that the wind seemed to die down

when he got into the shelter of the lough and then the river.

The captain on his ship actually

had "Danny Boy" piped over the loudspeakers.

On entering Lough Foyle, warships then made their way 20 miles

upriver to the docks at Lisahally.

Those war years were the busiest the river has ever seen.

Every week, 100 escort ships steamed up and down this stretch of water.

The docks were crammed with vessels,

all fighting to keep the Atlantic open.

Derry's safe harbour and westerly location made it the perfect place.

So, Naval Command took over two key sites in the city -

Magee College and Ebrington Barracks.

This was the Allies' anti-U-boat academy.

It was here that hundreds of escort captains came to learn

the difficult task of how to hunt down and sink submarines.

It meant that during the Battle of the Atlantic, the skills taught

here made this one of the most important naval bases in the UK.

After every Atlantic mission,

skippers came here to perfect their skills.

They role-played against an imaginary enemy, shared tactics

and were brought up to speed on the latest anti-U-boat weaponry.

Ebrington Barracks became...

It had been a backwater before the war, an army base.

In the course of the war, it is handed over to the Admiralty.

It becomes an essential part of the whole,

if you like, network that was the Allied effort to defeat

the submarines in the Battle of the Atlantic.

So, a huge amount of resources given over to training

and honing those skills to try at last to beat the U-boats.

Very, very much so. I mean, literally as well as being the focal point

of the battle against the U-boats, the physical battle,

it was also the focal point in the training of those who were

taking part in the battle. In fact, there was

a small flotilla of submarines based in the city as well

and their job simply was to go out into the Atlantic, play,

as it were, with the escort groups, act the role of U-boats.

They involved the air in the exercises as well as the surface

ships, and of course, you had a training element also

based in Magee College, where the Royal Navy had its headquarters.

And it is Magee College that may well hide one of the biggest

secrets of Derry's wartime story.

Key to victory in the Battle of the Atlantic was the vast

logistics of coordinating over 100 armed escort vessels with

thousands of convoy ships crisscrossing the ocean.

You are dealing with an effort, then,

that perhaps deals with a million people that are trying to

make sure that the Battle of the Atlantic comes to

a successful conclusion from the Allied side.

It is a tremendous undertaking from their perspective,

arguably one of the largest endeavours ever made by

human beings in any conflict, then or since.

At the heart of this massive undertaking was Magee College.

But the full extent of its role has been shrouded in secrecy.

Historian Jonny McNee is determined to unearth it.

He is convinced the college lawns hide a vast, covert command bunker.

From here, they were controlling

the convoys coming in from America,

the convoys going out,

deciphering codes that they were

intercepting from the German U-boats and then doing

the tactics of organising the RAF coastal command airfields.

Jonny's research indicates the bunker was staffed by Navy brass.

But throughout the war, their underground headquarters

remained top-secret to all but a very few.

It just operated in lone isolation here,

people were working in buildings on the top of the bunker complex,

only those of the highest security clearance were allowed to

go down into the bowels and work underneath it.

So, bunker life went on here

and Derry was completely ignorant to its existence.

During World War II, it was part of a wider command network,

coordinating the entire operation of the Battle of the Atlantic.

There was three of these bunker complexes in the United Kingdom,

one in Whitehall, one in Derby House in Liverpool, and this one here.

The other two were working out of the basements

of existing large buildings.

This has been purpose-built, this is the closest point to the

actual Battle of the Atlantic proper, as it is being raged.

70 years later, finding evidence of something

so top-secret has been tough.

Jonny has searched military records

and discovered mention of the bunker in just a handful of documents.

Looking through any of the records into this,

you're talking half a dozen pages of information at the most that

let you know there was something here.

While the official evidence may be scarce,

Jonny has located a compelling description from an eyewitness

and it has given his team of archaeologists

a starting point for their search.

All we have is one testimony from a senior Wren who

worked in the area, who talks about going into the shed,

down a set of concrete steps, along a warren of corridors

and into a mapping room, a cipher room, a decoding room,

so this is the object of the search today.

The team are using ground penetrating sonar to search

the area beneath the college lawns.

And the technology begins to throw up

enticing clues to Derry's secret past.

I'm seeing down 10 metres into the ground here,

so as well as objects in the near surface,

I'm seeing geology as well, which is quite exciting.

Alistair quickly picks up readings that suggest

they could be right over the underground bunker.

Stop, whoa! Hang on. That's good. That's good.

A really nice, clear anomaly.

Even I can see that!

Starting at a metre, 1.5 metres,

with a load of interference coming off a significant object.

Interestingly, just where we went over that bit of rough ground...

-Yes. So...

-..which quite often is the case.

-Just about here, then.

That's it, starting there.

Very sparse grass, this is nice, this is soaked, very damp.

It's a good indication that the bunker may still remain.

Pictures from the corresponding naval command centre

in Liverpool give an idea of the potential size

of the command centre in Derry and the rooms it might have contained.

Oh, Jonny, this is good. A really nice anomaly.

Lots of ringing beneath it,

which is exactly the sort of thing I would see with a hollow or

a grave, or something of that size.

Could that be, like, a stairwell entrance,

-or am I getting too excited?

-No, you're not getting too excited.

-No, like a tunnel.

-Right.

It's a tantalising clue, but Jonny will have to wait

until excavations can begin to uncover the truth.

Today's discovery could be only the first in solving

the mystery of Derry's secret bunker,

and further proof of the city's role

at the centre of the Allied Atlantic campaign.

This would have been the nerve centre for continuing that fight,

deep beneath the grass here.

Every week, a growing number of survivors from the convoys,

many of them badly wounded, were coming ashore.

For this city especially, it was a dramatic

illustration of the growing human cost of the Battle of the Atlantic.

Once the sirens went, we had to come out

and get to the Waterside Hospital on our bicycles.

You just couldn't believe it, seeing first-hand, you know,

what you would hear of on the news.

Esdale Johnson was 17 when war broke out.

Like hundreds of teenagers,

she volunteered for the St John's Ambulance and worked in the

makeshift hospital set up to deal with casualties as they came ashore.

There was no difficulty treating the men,

because they were very brave and very...

..glad to be ashore.

They were just glad to be in a hospital, they said there was

a lot that weren't saved and they were glad to be saved.

Esdale remembers treating two survivors

picked up days after a torpedo attack.

They had been adrift in lifeboats

and exposed to the worst of the Atlantic's weather.

They were in a small boat, and they were

frozen in the shape of a letter L when they came into the hospital.

We couldn't get them to lie down.

If you lay on the back, the feet came up, it was very sad.

I remember, I would be bandaging their feet one day and then

when I would go back again, I would find, you know, that

the toes were coming off. I remember that vividly.

You just couldn't believe it,

it was dreadful to see a human being like that.

It was.

To understand the battle that raged off Derry's coast, Ian and the team

need to track down the deadly enemy and see it with their own eyes.

They are on the hunt for a submarine.

The German U-boat fleet consisted of various types of sub,

but many shared common features -

a long, narrow hull,

a raised central section known as the conning tower,

periscopes for seeing above the waterline,

a snorkel, a retractable air intake for the diesel engines,

and of course, torpedo tubes.

All these features will help the team to identify today's wreck.

It's lying in deep water, 30 miles off the coast.

But with a storm blowing in, the team need a head start

to get there, and they are setting off before light.

When they come out of the water,

it'll be blowing a force 5 to 6, so we'll just need to be careful.

'There is a small craft warning in operation.

'South-west winds will reach force 6 during today

'along Northern Irish coastal waters.'

The wreck is in 200 feet of water.

Michael uses sonar to scan the seabed

and position the boat accurately.

As the wind picks up, the divers have to make their careful

preparations in a six-foot swell.

There's the wreck coming up now, you can see about four metres

there, the top of the wreck is about 60 metres down.

Rich briefs the team to keep the dive as short as possible.

Today isn't the day to be taking risks.

Let's try and keep it to two-and-a-half hours,

because we are chasing the weather today, lads, there is

some bad weather coming in, you can feel it brewing already.

-OK, guys, the shot's in.

-The team drop over the side.

As they descend, Michael keeps his eye on the weather.

220 feet beneath him,

the divers' torches reveal the decaying remains of a German U-boat.

The wreck is at least 200 feet long.

The team scours its length, looking for clues as to how it sank.

The U-boat's hull is largely intact.

But then they locate an area of huge damage.

The section in front of the conning tower is barely recognisable.

The sky periscope is bent flat across the hull.

Everything points to this U-boat being

the victim of catastrophic damage.

Ian discovers a magazine still loaded with bullets.

All these clues could identify the U-boat and explain why it sank.

As soon as he is on board, Ian reveals what the team has seen.

All the hatches are closed. But the conning tower is a mess.

There is an open locker with live ammunition in it.

-There is live ammunition?

-Absolutely.

-You saw it?

-Yup.

There's piles of bullets.

That's why you're the expert, Ian!

It's a great result for the team.

They have discovered vital clues that could identify the U-boat

and explain why it sank.

But now, a storm is closing in and after a good day's work,

they face a grim trip home.

In the Atlantic in World War II, it was no different.

The weather could be as vicious as the U-boats.

Seas like this, and far worse, were typical of those

experienced by the North Atlantic convoys and their crews.

Looking at the sea on a day like today,

you see how it all happened, you can actually put a picture on it.

It really does make you appreciate the sacrifice these people made

and just how brutal the war that went off here was.

You don't just have to contend with that,

but you're contending with people trying to kill you.

Back onshore, the team's footage has intrigued naval experts

Randy Papadopoulos and Axel Niestle.

Something unusual must have happened to this U-boat.

-This is the control room periscope.

-OK.

-You can see it's been absolutely flattened...

-Yes, yes.

-..against the...

-Perforated.

-But it must have been up

to be torn off. It would be consistent

with something driving across the top of the conning tower.

-And here is the head of the snorkel.

-Oh, yes.

That's right, very distinctive. If the mast is up,

it means the snorkel was being used to run the submarine's diesel

engines while she was submerged beneath the surface of the ocean,

and that means she was operating very shallow

and was attempting to charge her batteries before going back

deep and running on batteries alone.

There was an area where one of the life-raft containers had been ripped off,

there is a space and they're all missing.

This is one thing we did not spot on the dive. There.

-We nearly missed it.

-That's the hatch.

-And it's open.

-It's open, yes.

-It's open.

This is not a normal situation,

because this means it had been used as an emergency exit,

and this is very interesting

in explaining the situation which had befallen this boat.

It is consistent with the boat being rammed

and being evacuated at a later point of time.

-Rammed while snorkelling, probably.

-That's it.

-Yeah.

This evidence is critical in narrowing down which U-boat

the team has found.

And after crosschecking German archives with British

and Canadian records, Axel and Randy arrive at one conclusion.

The wreck is U-1003, a German submarine that came to a sudden

and unexpected end.

Well, after much deliberation

and some pretty impressive detective work, you have now

determined that the wreckage we saw there was that of U-1003 -

a plan of it here, a classic Type 7 U-boat,

-the backbone of the Wolfpack Fleet.

-That's right.

Here we have a photograph of the 1003 while on its first patrol.

You can see the snorkel installation and all that,

which makes up a late-war Type 7C.

This made them very capable fighting machines

and very dangerous to the Allied shipping.

According to the survivor reports,

this boat was scuttled about 60 miles north-west of Inishtrahull.

She's snorkelling very close to the surface

and is accidentally rammed by a Canadian escort vessel,

it wrecks her snorkel and her periscopes,

which makes it much harder for the U-boat to operate.

The Allies realise, "Well, we've hit something, probably a U-boat,

"we'd better start depth charging, in fact." And they do.

14 escort ships rushed to the area,

dropping depth charges on the injured sub, but U-1003 escapes.

She hid on the seabed

while her crew worked frantically to repair the damage.

For the commanding officer, it was a fatal test of his nerve.

The impact of the stress imposed on him, he obviously panicked.

On the third day after the collision,

under the constant threat of aerial attack,

he decided to scuttle the boat,

in order to save the crew, of course,

but in the way he did it, he sealed the fate of the crew.

He did it in the middle of the night,

he did it under very adverse weather conditions,

without proper preparation, so setting to the lifeboats

in the night is not the ideal conditions for saving the crew.

It's interesting, isn't it, when you look back at these pictures,

you just have to wonder if any of them did survive?

In the botched evacuation, 33 German crewmen died.

The remaining 16 were rescued by an Allied corvette.

But U-1003 sank beneath the waves, to be forgotten for 70 years.

As the war against the U-boats intensified,

so did the ranks of troops in Derry.

There were 20,000 Royal Navy personnel and 10,000 Canadians.

But most conspicuously of all, 5,000 Americans.

What was the reaction of the locals in Derry to this influx?

First of all, when they came,

it was one of, "Where are these people from?"

In fact, some local people actually thought they were women,

because they were dressed so gaudily.

And people here tended to dress in a rather staid and old-fashioned

manner, so suddenly here was Hollywood on their doorsteps.

The 36,000 troops stationed in Derry doubled the city's population

and transformed daily life as they fitted in with the locals.

They worked alongside them in the docks, some even had their

lives saved in the area's hospitals and on occasion, they fell in love.

Young Derry women couldn't wait to hit the town to meet

the handsome foreigners.

After you came out of the factory during the day, you went home

and you got yourself all dressed up as best you could,

California poppy and a fist of powder and lipstick and away you went.

Derry's dancehalls were the place to head.

They were full of American sailors, unwinding after

the stress of crossing the Atlantic and looking for fun.

You never were a wallflower, you'd always get up and dance,

even if they couldn't put one foot past the other!

Local women may have enjoyed dancing with the Yanks, but Derry's

menfolk found it hard to compete with the Americans' fancy footwork.

The Americans had their own method of dancing, you know,

jazz and all this sort of thing.

And the girls around here seemed to fall for that.

There was two ways to get to our street,

and I remember one night,

I had one at one end of the street and one away down the other end

of the street, I went to see which was the best looking!

The Americans took the girl away from you!

They were great, big, burly fellas with big boots,

and we were quite excited, really.

I remember my mum saying,

"Well, thank goodness Maureen's not old enough to get herself

"involved with any of these young men!"

But little did she know!

The war lasted long enough that I did get involved.

Can you remember getting that picture taken, honey?

For Maureen Archibald and Robert Mathis, Derry's role

in the Battle of the Atlantic was a happy twist of fate -

one that eventually led to pictures of Maureen being

printed in newspapers across America.

Through my job, I met Bob's commanding officer

and he said to me, "I have a young fellow in my outfit that

"would like to meet you," so eventually we did get together.

So, he's not one to go to dances, but I got him out on the floor

and he didn't do too badly at all, he wasn't too bad.

He thought he was terrible, but I thought he was pretty good.

And Maureen was convinced by more than just his dancing.

Within a year, she agreed to marry him.

Word of an American falling for a local girl set tongues wagging

and crowds turned out for her big day.

I just couldn't believe it.

It was packed with people who I didn't even know,

but they had heard there was going to be an American wedding,

so they all came to the Cathedral that day.

"A charming wedding was solemnised in Derry Cathedral

"on Thursday morning, when Miss Maureen Archibald became

"the wife of Petty Officer Robert Lawrence Mathis, United States Navy."

Maureen and Bob's wedding made a big splash, and that was just the start.

When Bob was posted back to the States and Maureen packed

her bags to go with him, the flurry of headlines continued,

this time, on both sides of the Atlantic.

"Bride ship leaves Derry for the US.

"65 young women bound for the various parts of the United States..."

When you think of it,

16 hours' advance notice to get ready to leave your family!

I didn't realise it at the time, but they came and asked me

if I would be the one to go off the ship first.

And I didn't realise what I was up against until I got off the ship.

Because I actually was, supposedly, and I think I really was,

the first GI bride to set foot in America.

Maureen and Bob left New York for his mum's house

in South Bend, Indiana, but wherever they went,

America's first GI bride couldn't escape her newfound celebrity.

All these American women reporters were waiting for me.

"City's first war bride arrives, smiling."

They were really throwing questions at me.

There was a lot of animosity, I would say, from the American girls,

for stealing their men!

Throughout the course of the war in Northern Ireland,

1,500 other women stole the hearts of American military men

and joined their new husbands in the US.

But it was Maureen who blazed the trail to America,

where she was known as the first GI bride.

The dive team's next expedition is to the wreck of a notorious

German submarine, one that stalked the entire Atlantic,

but brought tragedy to one family right here in Northern Ireland.

It's difficult to get lost on a submarine, I think.

But it's good to have a starting point.

If we kind of cross over, so we're not in each other's way.

The hull probably is going to be lying on its side.

So we'll just wait and see, it's going to be complete pot luck.

Skipper Michael is bringing them

10 miles offshore to the location of the wreck.

But the currents right now are so strong that making

the dive will be a challenge.

The tide is going at about 0.6 knots,

which makes it hard for the divers with all the stuff they carry,

they can't really swim more than half a knot.

For Rich, the strong tides mean timing

when the divers get in the water is critical.

We don't want to take unnecessary risks and of course,

if something goes wrong

and you've got current compounding that, it can go doubly wrong.

As soon as the tide slows, Michael grabs his opportunity

and drops a grapple down to the wreck.

OK, go ahead. OK, guys.

And the dive team waste no time in dropping over the side.

190 feet beneath the surface, there is little light reaching the seabed.

But the team can make out the wreck of a U-boat.

In the darkness, Ian manages to take measurements.

At 24 feet wide and 245 feet long,

they have found an enormous submarine.

The team see the telltale shape of the conning tower,

and its periscope.

And on the starboard side, they find the snorkel assembly.

On early model U-boats, once submerged,

the air supply to the diesel engines was cut off

and the sub relied instead on slow, battery-powered motors.

A snorkel was an extendable air intake which allowed the sub

to use its diesel engine underwater.

It meant the U-boat could travel faster and with greater stealth.

A typical U-boat launched torpedoes through tubes in the bow.

But this wreck has two additional torpedo tubes at the stern.

This distinctive feature will help identify the submarine.

Ian carefully guides our two experts through the footage.

The snorkel, rear torpedo tubes

and positioning of the periscope mean only one thing.

All of these suggest a Type 9 U-boat.

The Type 9s were key to the German Kriegsmarine.

Over 150 saw active duty.

But after studying naval records,

Axel and Randy have narrowed down the possibilities to just one.

It is another success for the team. They have identified U-155.

She was a notorious submarine that dealt a tragic blow to one

family here in Northern Ireland.

This was one of the real workhorses of the U-boat flotilla,

and 155 has a very long, and productive, one would say, career.

U-155 was a devastating opponent.

Huge diesel tanks gave it enough range to cross the Atlantic

four times non-stop.

Meanwhile, its snorkel allowed it to remain submerged for hours on end.

If you think of a Type 9 U-boat,

it's built for long-range operations.

The boats had usually to stay submerged for up to 20 hours

a day, only surfacing at night to recharge the batteries.

The crew of U-155 made the most

of their boat's range, stealth and weaponry.

From its base in France, it crossed the entire Atlantic,

using its snorkel to stay submerged nearly the entire time.

This submarine made it, undetected, all the way to Florida.

Imagine a U-boat built in Germany, based in France,

able to operate in the Florida Strait,

just 40 miles off the coast of southern Florida, that's very,

very close indeed to the US coast at that time, and really very

startling, of course, to the American defenders of the area.

In April 1943, just 40 miles from Key West, U-155 sank two giant

tankers, bringing the Battle of the Atlantic into America's backyard.

This deadly sub was one of the Germans' 10 most effective U-boats.

Throughout its career, it lost only five crew

and inflicted terrible losses on the Allies.

26 ships had been sunk and over 900 lives lost at sea.

Amongst them was that of a naval officer from Ulster.

He left behind a young widow and a family.

David Brew had not yet been born when war broke out

and his father joined the Navy.

In 1939, he joined the Royal Naval Volunteer Reserve

and married my mum, and that year, we have a wedding photograph.

We then have him on HMS Dunvegan Castle,

with some of his officer colleagues, these are dated 1940.

David never got to know his father.

But today, he has a precious keepsake.

A postcard sent to him by his dad when he was just nine months old.

In March 1942,

he posted this postcard

from New York. It's addressed

to me, but obviously,

it's directed at my mum.

But it says, "Dear David,

"how would you like to come and live here with me

"and bring your mother with you?

"Hope you are being a good boy and taking care of your ma. Daddy."

It must have been written with some longing, er...

to be home and to be safe with his family.

In New York, John Brew joined the crew

of the aircraft carrier HMS Avenger.

In the early hours of the morning, HMS Avenger passed through

the Straits of Gibraltar on her way to Glasgow.

On board, John Brew would have been looking forward to what

he hoped would be an uneventful and speedy passage home.

But they weren't alone. Hidden deep beneath the waves,

the captain of U-155 already had the convoy in his sights.

The U-boat ace in command of U-155 was Adolf Cornelius Piening.

We have an extract from his war diary here,

which gives a narrative of the actions taken by him.

When he first spotted the convoy, it was at a distance of five miles.

So then he closed in, in order to attack.

And then he fired a total of six torpedoes

at the targets on the rise.

Piening's aim was deadly.

He hit three ships, one torpedo igniting the Avenger's bomb store.

The massive explosion tore the 9,000-tonne aircraft carrier in two.

It sank in less than two minutes. Over 500 men were killed.

One was David's father, John.

This is the telegram my mum received.

"Deeply regret to inform you that your husband, John Sydney Brew RNVR,

"has been reported missing, presumed killed, on war service, stop.

"Letter follows." That's, um, that's the deadly...the deadly message.

Many, many more such telegrams were sent out

to devastated families of Atlantic crewmen.

The battle claimed the lives of 70,000 Allied sailors

just like John Sydney Brew.

As the intensity of the battle grew, so did Derry's involvement.

By 1941, the city's docks were the cornerstone of the Allied defence,

with 50 escort ships based on the Foyle.

The city was now a clear target for Hitler's Luftwaffe.

I don't know what time of night it was, I had gone to bed.

And then I suddenly heard the siren going.

We were so used to it, we didn't pay any attention to it,

until we heard the drone of the aeroplane.

We were very familiar with the drone of British aeroplanes,

but I recognised this one was different.

German bombers were now in the skies over Derry.

After months of drills and false alarms,

volunteers rushed to man the defences for real.

I was about 15 or 16 years of age at the time, and I had joined

the air raid precautions, and I ran down Dunfield to get to the post.

I seemed to be on my own, I don't remember anybody there,

but by that, the anti-aircraft guns on Corrody Hill,

the high ground across the river here, they opened up.

Suddenly, there were two terrible explosions.

And a blue light flashed through the room.

The ceilings all came down, the windows came in,

everything was in darkness,

I followed my mother downstairs, it was all broken glass,

I was screaming, I remember that, I went down to the living room,

there was no windows left, what was there was all twisted and turned.

I was just sat there and everything was so quiet, very, very quiet.

The German mines had fallen directly on Messines Park,

a residential street to the north-east of the city,

where the houses were full of frightened families.

The rescue crews scrambled into action.

When we heard the bombing,

then we rushed in our ambulance

down to the area

and found that the house was pretty well wrecked.

A horrific scene awaited them.

An entire street corner had been destroyed.

That was quite a sight.

Arms and legs sticking out of the rubble.

A girl was blown out of her own bed

and had arrived in a field in front of her house.

In the hospitals, nurses were waiting to receive the wounded.

You certainly got your eyes opened, you know, as to what a bomb could do.

I remember this poor woman with all the holes in her.

I didn't expect that.

But it must have been shrapnel.

Oh, it was an awful time for the locals around Messines Park.

The German bombs tore through six houses, completely destroying them.

It was an unexpected attack in the middle of the night

and it caught families completely unaware in their beds.

14 people on that one street corner were killed.

Many believe the German bomber was lost and that it dropped

its load, believing it was over Belfast or Liverpool.

But historian Richard Doherty

has uncovered evidence to prove otherwise.

15th April 1941, a lone bomber drops its payload over the city.

Some people have regarded that as a rogue,

as a mistake on the part of the Germans. But you are not so sure?

There is a myth that the raid was by a bomber that lost its way.

It wasn't, it was clearly targeted. This was a planned attack.

Richard has discovered German reconnaissance photographs,

taken high above the city.

On them are clearly marked the city's strategic targets.

It shows us the shipyard at Pennyburn,

it shows us barrage balloons, anti-aircraft guns,

the flak site out here, for example, anti-aircraft site at Corrody Hill.

It shows Ebrington Barracks quite clearly,

the bridge, it marks the railway stations

and the railway goods yards.

Literally everything that is of military value is marked.

They didn't send reconnaissance aircraft over for nothing.

So, there was a clear target in mind that night?

The clear target was the Navy dockyard at Pennyburn,

which is marked here as number eight by the Germans.

Despite the extensive German reconnaissance from the skies

over Derry, on the night of the actual attack,

their bomber made a fateful miscalculation.

They were aiming for the dockyard.

They were aiming for the dockyard here, but the mines actually

landed, the one which caused most destruction, here at Messines Park.

The bombs that they dropped were not actually bombs, they were mines.

They were intended to explode in the air above the ground,

blast downwards and flatten it. And we saw the horrible effects

of those on the houses of Messines Park.

The cost of that German mistake can be counted in Derry City Cemetery.

14 dead men, women and children,

killed as they slept in their beds at night.

Their names are a tragic reminder of the price Derry paid

for joining the fight against the U-boat.

But it was a fight that had to be won.

Throughout 1941, Britain's war effort was

still in peril as German submarines continued to hammer Allied shipping.

The U-boats seemed unstoppable.

An Allied victory in the Battle of the Atlantic was

far from certain, but the Allies had one more trick up their sleeves,

one that would turn the entire tide of the campaign in their favour.

Next time, Derry helps the Allies to victory

by helping them into the air...

Basically, the U-boats daren't operate on the surface any more.

..and the children of heroes relive their parents' bravery...

-Down a bit. Up a bit.

-Dangerous job, that is!

Mum must have been nervous and anxious about him

all the time he was away.

..while the dive team set out to find Hitler's deadliest U-boat.

You see just how deep and how big the hull of the submarine is,

I mean, it's amazing to see. It's just something else.

Subtitles by Red Bee Media Ltd