Original subtitles

Narrator: World war I.

A new stealth weapon brings terror to the oceans.

Delgado: This is a dirty war.

Narrator: Evidence of a naval revolution.

Lost for a century beneath the storm ravaged seas of the british isles.

Imagine if we could empty the oceans.

Letting the water drain away to reveal the secrets of the sea floor.

Now we can.

Using accurate data and astonishing technology...

To bring light once again to a lost world.

Why do three royal navy warships simply disappear?

Grove: The british are shocked.

Narrator: How does a single torpedo change the course of history?

Eoin: For a shop of that size to disappear in

Less than 20 minutes was just incredible.

Narrator: And how do the allies strike back in a battle that changes

Naval warfare forever?

(theme music plays).

Today's superpowers prize one weapon above all others.

The submarine.

The ultimate stealth weapon.

Striking at will.

Delivering its deadly payload from out of nowhere.

But the rise of the submarine started a century ago.

It's a story that begins with a mystery off the coast of holland.

The corpse of an enormous ship emerges.

And not just one.

Three broken giants lie side by side.

How did they get here?

1914.

Britain and germany go to war.

Britannia has ruled the waves for centuries.

Her fleet so massive, how can germany ever hope to win?

Just seven weeks into the war.

Hms aboukir, cressy and hogue scan the horizon near the dutch coast.

Their mission seek and destroy any enemy that dares to threaten british vessels

Supplying the battle fields of France.

Grove: It was there as a screen against serious german surface attack on

These vital cross channel supplies.

Narrator: The three ships are packed with cutting edge technology.

Among the first ever protected by super hardened steel plate.

A whole new class of warship...

Armored cruisers.

Grove: These are powerful ships.

They'll blow you out the water if they see you on the surface.

They're armed with twelve 6 inch guns, two 9.2 inch guns, each.

Narrator: The morning of September 22nd is clear and calm.

There's no enemy in sight.

Yet the three cruisers vanish.

Their last communication, a distress signal.

In the weeks that follow,

Hundreds of bodies wash up along the dutch coast.

Britain's belief that her navy is invincible is rocked to the core.

For a decade, klaudie bartelink has been investigating the fate

Of the lost patrol.

Now she's onto something.

Bartelink: So we're 20 miles off the dutch coast, over there is England,

And over there is the netherlands.

I try to find the three cruisers and figure out what has happened to them.

Narrator: She's on the last known coordinates of the three ships.

115 feet down klaudie and her dive buddy find themselves among piles

Of twisted wreckage.

The wreck site is massive,

Stretching for hundreds of feet into the darkness.

Klaudie's exploration reveals that there's more than one vessel here.

And her lights pick out something else.

Strewn all around shells still in their casings.

Never fired.

Bartelink: I saw a lot of ammunition.

I saw here the boxes with small shells.

It's has to be a military ship.

And on these coordinates they're definitely cressy, hogue or aboukir.

Narrator: A positive id, but in the gloom it's difficult to see how

The ships met their end.

Bartelink: It's very hard to understand the shape of the ship below

Because you only see part of the ships.

And you can't recognize like the bow or something.

It's, it's impossible.

Narrator: High tech sonar scans provide a solution.

Mapping the wrecks in perfect detail.

Allowing us to do something never possible before.

Drain away the english channel to see the lost patrol clearly

For the first time in over 100 years.

The warships bristle with guns.

Including these, innovative side mounted weapons called casement guns.

On the smooth hull of aboukir there's no sign of battle damage.

But near the stern a gaping wound.

On the other two wrecks fatal blows also clearly visible.

Hogue's hull is broken open.

Cressy's interior completely exposed.

Damage like this, far beneath the waterline,

Is hard evidence that a terrible new weapon

Is in play.

Bartelink: So what you see where torpedoes went into the ships.

And I think this is the moment that the naval warfare changed forever.

Narrator: Torpedoes are self-propelled and deadly.

Flying under the waves they strike below the waterline.

Delgado: The torpedo, as initially developed and tested through the 1860s and 1870s,

Is truly refined, in world war I.

Narrator: They are originally fired from ships.

But on the day of the lost patrol the horizon is empty.

The source of the torpedoes must lurk unseen.

Unable to defeat the royal navy's massive battle fleets on the surface.

The germans are deploying new technology under the waves.

They call them, 'unterseeboote'.

U-boats.

The british cruisers are completely unprepared.

Grove: What they weren't expecting was this covert, underwater attack,

Which is carried out with great skill.

Narrator: Unfired ammunition on the sea-bed shows that the cruisers

Don't put up much of a fight.

By the time they spot torpedoes running the battle is already over.

Delgado: U-boats are a game changer.

Narrator: The way the drained ships lie close together reveals

That they were sitting ducks.

As the first goes down the other two race in to rescue survivors,

Giving u-boat number nine

The perfect opportunity to pick them off with ease.

They still lie where they fell.

Side by side.

Grove: The sinking othe three cruisers, aboukir,

Hogue and cressy, demonstrated the power

Of the submarine perhaps more than anything else.

Narrator: The dutch authorities bury the british dead with military honors.

Bartelink: In the netherlands it was big news.

It was in all newspapers because in one and

A half hour almost 1500 men died and 13 of them were teenage boys,

So it was a very big story.

And they were buried here, honorably.

There were soldiers along the road,

They paid a lot of attention to it.

Narrator: U-boats are so effective because german engineers have

Overcome some massive technical challenges.

And how they manage this can still be seen because, remarkably,

The very first u-boat survived.

Koerver: This is u-1, germany's first submarine, over 100 years old and

You could make some 5 or 6 hours submerged with electric engine

At slow speed 5-6 knots.

Narrator: Electric engines power the 139 foot long vessel when under water.

Its batteries are recharged by 2 gasoline engines,

Which run the u-boat on the surface.

Koerver: We have two different pairs of engine.

Two gasoline and two electric motors,

So it's like a modern car, a hybrid system.

Narrator: U-1 can dive to 100 feet and travel submerged for 50 miles.

But for their crew,

U ats are unforgiving places.

There's deafening engine noise, exposed electrical circuits.

And if sea water gets into the batteries deadly chlorine gas will quickly spread.

Mccartney: If you're serving in submarines,

You've got a higher change of dying than

You have if you're on the western front.

Narrator: U-boats maybe dangerous for their crews,

But they're lethal to their enemies.

And the germans have boats almost three times bigger

Than u-1 on the drawing board.

During 1915 germany expands its fleet to over 50.

And that's just the start.

Koerver: The climax was reached with the number of 125 available submarines,

Means around 30, 40 submarines were at sea daily.

Narrator: And this expanding u-boat force doesn't just have military

Targets in its sights.

Grove: There were elements in the german navy who quite deliberately wanted

To achieve what you might call a form of maritime terrorism.

Narrator: The killer u-boats target a world-famous ship in

An attack that shocks the world.

By 1915, no allied ship is safe.

Off ireland's southern coast,

Eoin mcgarry investigates what happens when the german navy

Dramatically escalates its campaign.

Eoin: It's under the water, you can look around, you don't know where it is,

You don't know where it's going to attack from.

How do you attack back?

Narrator: U-boats entering service in the second year of the war could dive almost

Twice as deep as u-1 and run submerged for 80 miles.

Increased range means they can now strike deep into the atlantic.

And soon the german navy is making the most of its killer technology.

Beneath this buoy lies the wreck of one the most iconic ships in history and

Its shocking secret.

Eoin is one of a select few experienced enough to make the dive.

It's so deep he must breathe a special mix of gases to stay alive.

Eoin: It's like the everest of diving, it's just within the realms of

Safety and the limitations of your qualifications.

Narrator: He heads down over 300 feet into the darkness.

This twisted wreckage is all that remains of one of the most luxurious passenger

Liners ever built.

But for over a century the power of the sea has taken its toll.

Eoin: On a huge wreck like 798 foot long it still lies as a huge hulk

On the sea floor.

It's festooned with fishing nets,

Discarded fishing nets, tangled fishing nets.

It's a dangerous dive.

Narrator: It also hides clues to an atrocity so shocking,

It changes the course of the war.

This is the wreck of rms lusitania.

On may 1st 1915...

Lusitania leaves new york for britain.

Like her ill-fated rival titanic,

This massive liner has been engineered to be unsinkable.

On board nearly 2000 souls.

Eoin: It was like a floating 5-star hotel.

In one end of it and then for the third-class passengers it was still

A luxurious way and fast way of crossing the atlantic.

Narrator: Six days later,

Lusitania is just 12 miles from the irish coast.

Her captain has been warned that u-boats are in the area,

But lusitania can surely outrun any threat.

Eoin: The lusitania was doing 24 knots when she was cruising and

If you look off the stern in the lusitania you could

Put 60 water skiers across the water and she could pull water skiers,

She went that fast.

Narrator: So why does this super liner,

Built to be invincible, never arrive?

300 feet down...

Clues are hard to spot.

But feeding precise 3-d scanning data into powerful animation software

Means we can now reveal the wreck of

One of the most famous ships that ever sailed.

Lusitania slowly emerges back into the light.

32,000 tons of scarred and twisted metal.

She lies tilted on her starboard side part sunken into the sea bed.

Can this be linked to how she sank?

Now seeing under the sea floor, itself it's possible to reveal

Something never seen before.

Evidence of a fatal blow.

Here under the water line the unmistakable hallmark of a torpedo strike.

U-20 has been ordered to stalk these waters.

Not only hunting warships...

Liners too.

The u-boat unleashes a single torpedo, like an assassin's bullet.

Eoin: If you could imagine being on the deck of the lusitania being six,

Seven story's up and looking over and you see this thing coming at

You and you know it's gonna hit you and you know exactly what it is...

That must be daunting.

Narrator: Lusitania is built to take on huge amounts

Of water yet still stay afloat.

How could a single shot,

Send a ship this big to the bottom?

The drained wreck reveals the hull is snapped clean in half.

And the tip of the bow severely damaged.

Evidence the liner hits the sea floor with tremendous force.

Now at last we can reconstruct lusitania's final moments.

The torpedo blows open a hole.

Lusitania is travelling so fast that her momentum forces tons of water in.

She plunges into the atlantic taking nearly

1,200 men, women and children with her.

Eoin: She's almost driving herself underneath the water.

And even if the props were stopped she still was 32,000 tons

Still being driven forward.

Narrator: There's hardly any time to launch life boats.

Eoin: She was gone in 20 minutes which must have been just terrifying

For the people on board.

Narrator: Lusitania's speed hasn't saved her.

It's killed her.

She hits the sea bed so fast that her huge hull snaps in two.

Many hundreds of bodies wash ashore nearby.

Buried in mass graves in ireland.

As the whole world reels in shock.

Delgado: The germans were seen as murderers,

They were seen as villains.

Narrator: U-boats are now a terror weapon.

But it's a risky strategy.

The loss of american civilians on lusitania and

Further u-boat attacks on american shipping,

Pushes the us towards joining the war.

The german navy knows that the clock is ticking.

Delgado: The germans know that they have a short window in which they can

Try to win the war.

If they can get enough subs out there,

If they can have advances on the battlefield,

Then they have a chance.

Narrator: The killer u-boats launch a new campaign

To crush their enemy outright.

Waged here just off the coast of britain.

But the battle is about to get a lot tougher for everyone.

Narrator: Lurking beneath the surface.

Unseen, unchallenged,

The u-boat seems invincible.

Delgado: To counter the threat of the german u-boats,

The royal navy in particular

Didn't have much that they could throw at it.

Narrator: U-boats can hide themselves within sight of any british port.

The enemy is at the gates.

After sinking lusitania the u-boat fleet doubles to over 100 vessels.

They're planning to land a decisive blow.

Grove: We will sink enough ships to stop britain importing and

This will defeat the british,

Who are the lynch pin of the allies before the americans,

Who might well declare war, can bring their power to bear.

Narrator: Britain's ports are the final destination for a vast

Maritime supply chain.

Thousands of merchant ships bring vital food,

Munitions and supplies from the british empire and the usa.

Delgado: The need to support the war in europe sees a massive shipment of

Men and material across the atlantic,

As well as the movement of ships in and around the british isles.

The germans know this and the submarines are sent out to take those ships out,

With deadly effect.

Narrator: If the german u-boats can cut the flow of supply ships,

They can starve britain into submission and they'll stop at nothing to do it.

Mccartney: It's a total war. Civilians are targets.

Merchant seamen are targets. This is what total war is.

It's not a war between sailors and soldiers.

It's a war in which everybody is involved and everybody will be sacrificed.

Narrator: This war rages most fiercely here in the irish sea,

Just outside the important port of liverpool.

In these seas bangor university's survey vessel,

Prince madog is on a mission.

Mccartney: There she is.

Narrator: Marine archaeologist innes mccartney has

Joined forces with oceanographer mike roberts.

Using the latest scanners,

Their ambitious plan is to locate every victim of this battle.

And discover what happens when the u-boats try to starve britain into submission.

Roberts: In world war I this stretch of water was a very, very dangerous place to be.

Narrator: Every merchant ship runs the gauntlet to make it through

This corridor of death.

Roberts: It must have been terrifying knowing what could happen at any moment.

Narrator: And prince madog's survey is uncovering the massive scale of the killing.

Roberts: Immediately beneath us are the remnants of a protracted battle, a

Battlefield effectively which contains the remains of many,

Many hundreds of shipwrecks.

Narrator: The sonar scans reveal the scattered bodies of the u-boats victims.

They prey on any type of vessel, thousands perish.

Innes and mike study one wreck closely.

A ship heavily laden with cargo for the war effort.

Mccartney: We know from the position of where it is, combined with the length and

Other details, that we can see that this is the wreck of ss apapa.

Narrator: 4:00am.

Nov 28th 1917.

Ss apapa is almost at the end of her journey from west africa.

As well as cargo, she's carrying 119 passengers.

Including many women and children.

Soon they'll be docking safely at liverpool.

They hope.

Mccartney: It's coming into the danger zone where the u-boats are waiting.

Narrator: Us-96 is in the perfect position.

Mccartney: The u-boat had maneuvered round and was between the land and the ship.

Undetectable against the background.

Fires a torpedo which struck apapa in the stern.

And it immediately began to sink.

The captain on the apapa ordered the women and children to be put into the lifeboats,

So the lifeboats are swung out and they're put down on the rail.

Narrator: Though apapa is already sinking, u-96's commander heinrich jess,

Isn't finished with her yet.

Mccartney: At this point u-96 has fired its second torpedo,

What the commander referred to as the killing shot.

And it was being hit the second time while everybody was evacuating and

It caused 77 people to die.

Narrator: The dead civilians onboard apapa make this one of the most

Infamous u-boat attacks ever.

But it's just one of many.

Under orders to sink a monthly quota of 600,000 tons of shipping,

U boat attacks are relentless.

Grove: In fact, at one month, April 1917, they get to 800,000 tons,

It's quite massive.

They're doing better than they expected.

Narrator: National survival is on the line,

How can the british fight back?

Delgado: Not only do german submarines improve and change during the

First world war,

But also the means by which to find them and sink them, also begin to change.

Narrator: Prince madog has found dozens of wrecks.

Now she picks up a new signal from the sea floor.

Unlike any seen so far.

Is this evidence of an under-water counter offensive?

Mccartney: Skinny and tube-like with a central high point.

This is a classic submarine wreck.

Narrator: Among the wrecks surveyed in the killing zone,

This is the only u-boat.

So, if u-boats are so dominant here in 1917,

What is it doing on the sea bed?

Prince madog's detailed scan makes it possible to drain back the

Waters and investigate.

It's an amazingly well-preserved u-boat.

Frozen in time.

And this fearsome killer's 200 foot long body looks completely undamaged.

Accurate measurements from the high res scan means innes can identify

Exactly which u-boat this is.

Mccartney: The distance from the bow to the conning tower, to the stern,

And all of that matches up

Exactly correctly for u-87.

Narrator: It's an incredible discovery.

U-87 is one of a whole new class of long-range ocean-going hunter killers.

It's faster than previous u-boats and carries twice as many torpedoes.

A deadly threat.

Mccartney: U-87 was the best type of submarine the germans were capable of

Making in 1916 to 1917.

Narrator: What could its mysterious fate tell us of the desperate struggle

To stop the killer u-boats?

Narrator: The wreck of u-87 sits on the sea bed.

Apparently intact.

But over 500 feet across the drained ocean floor,

Another much smaller piece of wreckage comes to light.

It appears to be the very tip of u-87's stern.

What's it doing here?

Aboard survey vessel prince madog,

Innes mccartney reviews records of u-87,

Detailing her mission, and learns more about the day she is destroyed.

Mccartney: Christmas day 1917, u-87 encounters a small convoy.

And torpedoes a steamship.

The u-boat's periscope is subsequently spotted.

Narrator: Royal navy patrol boat p 56 has u-87 in its sights.

Mccartney: The chances of any of these patrol boats ever seeing

A submarine was remote and when they did everything gets used to take them out.

Narrator: And she's carrying a new kind of anti-submarine weapon.

An underwater bomb, called a depth charge.

Delgado: A depth charge is an explosive that is set,

Once launched or rolled off the side or

The back of a ship, to detonate at a set depth.

Narrator: The british captain gets as close to the last sighting of u-87

As he can and fires a volley of depth charges.

But is this what sinks the u-boat?

Can this small fragment give us an answer?

Some force has left it 500 feet away from the u-boat.

But the edges of the wound look clean not jagged.

Could a depth charge do this?

Engineer: Can you confirm the range is clear for firing, over.

Man (over radio): Confirmed, the range is clear.

Narrator: At a remote defense testing facility in scotland

Demolition experts are trying to understand

What effect an underwater blast can have on a u-boat.

Sensitive equipment measures the forces a depth charge unleashes outside

And inside the hull.

Engineer: 60 seconds.

Misselbrook: I wouldn't want to be in a submarine when that happens to it,

Cos it's a very violent event.

(air horn)

Engineer (over radio): 5-4-3-2-1.

(explosion)

Narrator: The blast creates a pulsing shock wave.

But is does not crack open the hull.

However, the test reveals that depth charges can damage subs in other ways.

Misselbrook: The direct shockwave excites the submarine, shakes it,

Vibrates it until equipment fails.

Narrator: If this array of fragile pipes, valves

And hatches breaks, that threatens the u-boats survival and

Exposes its biggest weakness.

Delgado: By setting a depth charge off underwater the blast is intended

To rupture the seams, to break systems,

To rattle the crew, to concuss them.

Mccartney: Depth charges had the immediate effect of driving

The u-boat to the surface.

Narrator: On the surface there's nowhere to hide.

P 56 seizes the moment.

Grove: A good way of sinking submarines, was just to ram them.

They were vulnerable to this.

They could be cut in half or have bits,

Chunks taken out of them, by a ship ramming them.

This would sometimes perhaps damage the ship,

But on the other hand, on balance it was better

To sink the submarine and ramming is very important.

Narrator: Risking sinking itself,

The patrol boat heads on a collision course with u-87.

The drained wreck bears the scars of this incredible clash.

The impact cleanly slices off the rear end,

Leaving the fragment intact.

It sinks to the bottom,

Followed quickly by the crippled u-boat.

Mccartney: As the submarine was sinking the patrol boat that,

That had rammed it could see the germans

Inside the submarine so we know it was opened right up.

Narrator: The german's have been wreaking havoc in the irish sea for months.

But now u-87's crew meets its own terrible fate.

Delgado: Submarines were known to their crews sometimes as steel coffins.

I think it's an apt analogy because when we find one of these,

Sitting on the bottom,

Particularly one lost in combat,

You realize that the crew is still inside.

Narrator: The wreck of u-87 reveals that new technology plus some luck

And courage could defeat a u-boat.

And by the end of 1917,

The royal navy has a new a force dedicated to the fight.

Mccartney: The anti-submarine division

Is charged with looking at every single means of technology,

Every single means of strategy available to it,

To combat this threat and it develops a whole raft of

Different ways of dealing with it.

Narrator: The counter attack means taking the war to the u-boats both

Above and below the waves.

Delgado: They also develop the undersea mine as a more effective weapon and

Ultimately build a,

A fortress wall, a barrage as they call it,

Of mines to keep the germans from approaching.

Narrator: Around british coasts huge forests of deadly floating bombs

Now protect shipping.

These massive mine fields sink u-boats and deter attacks.

By the middle of 1918 the kill rate drops off from its peak at 800,000 tons per month,

To under 400,000 tons but that's still a lot of sunken ships.

Delgado: For all of the work being done to counter the german u-boats,

They reign supreme.

Narrator: Conventional weapons are still not landing a decisive blow.

The british must use a secret stealth weapon of their own.

Narrator: The english channel is where the battle to defeat the u-boats

Reaches its climax.

By 1918 its entrance blocked by a huge minefield.

But off plymouth sonar scans reveal the outline of a wreck.

It's similar to apapa, a cargo ship.

Does this mean that despite all allied counter-measures u-boats

Still threaten in these waters?

Historical wreck researcher steve mortimer is heading out to take a closer look.

For over 4 years he's been searching for a lost legend.

And this wreck is exactly what he's looking for.

Mortimer: Today we're looking to dive a shipwreck that was sunk in 1918

After a battle with a german u-boat.

We've been looking for her for a number of years,

Today we've got a really hot target.

She's lying in 65 meters, we think, something like that.

All we can do is go down,

See what we find, and see if we can identify her.

Narrator: Among the thousands of defenseless cargo ships sunk by u-boats

In these deadly waters, steve's target is special.

The shape and size of the hull,

Proof that this was built as a cargo ship.

And the mangled wreckage shows that it met a violent end.

But the murky conditions obscure further secrets.

Only draining away the english channel can fully uncover the wreck.

And reveal the extraordinary truth.

The hull is twisted and bent.

The bow torn open.

Classic torpedo damage.

But there's a totally unexpected discovery too.

Naval guns.

Military hardware on a cargo ship.

For steve mortimer it's the evidence he's dreamed of.

Mortimer: Fantastic!

That must be it, that must be it!

The engine's on the stern of the ship,

There's two big guns on the stern.

It can't be anything else.

That must be hms stock force.

Narrator: Stock force is a legendary british secret weapon.

Codenamed a 'q' ship.

Delgado: The q-ship is a warship disguised as a merchant vessel.

Mccartney: It is a ship that is trying to pretend to be something it isn't,

And in this particular case,

To look innocent, but it is in fact far from innocent.

Narrator: She may look like a harmless cargo ship,

But stock force is heavily armed.

Four-inch naval guns,

Like those on a cruiser or destroyer sit on platforms

That can be folded away and hidden below deck.

Grove: It's one type of stealth against another type of stealth.

Narrator: Under a directive from admiralty chief winston churchill,

The royal navy has

Deployed q ships since the submarine menace first began.

Mccartney: It's thought to have been at least 200 ships and they vary from the very

Smallest little fishing vessels,

Even single mast sailing ships,

Right through to large merchant ships.

Narrator: The sailors on board are not merchant seamen,

They're fighting men,

Practiced in the art of deception.

July 30th 1918.

As stock force sails along the english channel,

Her job isn't to transport cargo,

But to lure a u-boat to attack.

She spots a periscope.

The trap can be laid.

What happens next makes stock force and her crew famous.

Their story immortalized in a silent movie.

With great skill u-80 has crept through a minefield and strikes first.

Mortimer: Most of the bridge is destroyed.

Some members of the crew are trapped.

Narrator: Stock force starts to sink.

The crew rushes to abandon ship.

But it's all part of the trick.

Mccartney: They were even trained how to tip the lifeboat over

While they were dropping it,

So just to make the whole thing look very amateurish.

The crew would then be off and the u-boat would then move in to close

Quarters to finish off the ship.

Narrator: U-80 takes the bait,

Surfacing to inspect its handiwork.

Stock force's captain harold auten holds his nerve.

Mortimer: Auten waits until the u-boat is in the optimum position to attack it

And then shouts,

"let's go", ordering his crew to fight back with everything they've got.

Grove: In would come the submarine,

Down would come the covers over the guns and

Battle would commence.

Mccartney: It would be a hell-fire of shells pouring into it.

Grove: You have to be able to hold your nerve even if your ship is sinking.

And open fire and continue firing on a platform that is going

Glug, glug, glug into the ocean.

Narrator: The u-boat is hit,

The captain of stock force escapes only moments before

His ship goes down.

Commander harold auten wins the victoria cross.

Britain's highest award for valor.

At last the allies are neutralizing the u-boat threat.

And cargo ships now reach britain in well protected cooys.

There are simply not enough u-boats left to stop the flow of supplies.

Delgado: If the germans had been able to keep producing more submarines,

They might very well have won the war.

Narrator: When the exhausted germans finally surrender in November 1918,

They are forced to hand over their u-boats.

Mccartney: Before 1914, there isn't a great deal of understanding about

What the submarine can really do.

But by 1918,

Everybody knows, it's a lethal weapon.

Narrator: No-one knows this better than the man

Bent on resurrecting german naval power in the 1930s.

Delgado: The nazis,

Well aware of the success of the u-boats in world war I,

Adopt that technology and adopt those strategies yet again.

Narrator: In the second world war,

The nazis launch over 1100 new and improved u-boats.

And once again they devastate allied shipping.

Crewed by brave and remorseless men,

The killer u-boats revolutionize naval warfare.

The ancestors of the super-subs that silently and secretly

Dominate the oceans today.

Captioned by cotter captioning services.