Original subtitles

(dramatic music)

The ancient Chinese military strategist

Sun Tzu wrote that all warfare is based on deception.

And, on the modern battlefield, deception means stealth.

In the 21st century, being unseen to the enemy

has become a dominant focus of military technology.

From deadly snipers

to aircraft that are invisible

to the most sensitive tracking systems.

From surface ships that seem to vanish,

to the ever increasing sophistication

of the silent killers beneath the waves.

The quest to be unseen continues to change

the way we engage in battle.

This is the story of stealth.

(dramatic music)

The role that aircraft play in battle

has changed dramatically since the First World War.

No longer simply airborne observation platforms,

today's aircraft are a vital part

of a mobile attacking force.

And to be as effective as possible, it helps to be stealthy.

In the past, stealth meant a healthy dose of speed

combined with high altitude and a fancy paint job.

But that fanatical drive to go faster and higher

has given way to a more potent ambition,

the ability to operate without forewarning,

to seem to be invisible.

A fifth generation fighter and perhaps the most capable

air superiority weapon in the world,

the F-22 Raptor is the product

of 60 years of active stealth research.

Designed as a successor to the F-15,

arguably the most capable fighter of its generation,

the Raptor was created to meet the threat

from the Russian built Su-35.

Giving the U.S. Air Force an air dominance fighter

that was lethal,

fast, but, more importantly, almost impossible to detect.

It's principle differences to the F-15,

were in two aspects,

the first of those aspects was in observability and stealth.

Unlike the F-15,

which had been optimized for its aerodynamic performance,

the F-22, from the outset, was optimized

so that it could not be seen by the adversary.

So how do you make an aircraft invisible?

You limit what's called it's radar cross-section.

As radar works on the principle of reflected radio waves,

to not be seen requires a surface

that refracts radar signals

so that they don't bounce back to the source.

To help achieve this, the F-22's outer shape is very clean,

great care has been taken to align

all hard edges on the wing, tail and engine inlet

so that the radar return from any given point

is aimed in a number of limited directions.

This results in a few relatively large,

but narrow radar spikes that are difficult to detect

and, if detected, almost impossible to track.

Improvements in the design of radar absorbing materials,

or RAM, contribute to weight savings,

making the F-22, while similar in size to the F-15,

over a ton lighter.

As aircraft speed increases,

the infrared signature also increases due to

the friction caused by air moving over the outer surface.

And so an infrared topcoat is used on the F-22

to ensure that the radar

and infrared signatures are balanced.

Employing the latest turbofan engines,

the F-22 cruises at unprecedented speeds

without engaging afterburners,

a prime source of heat and noise.

And to further reduce the heat signature of the engines,

the plane employees engine vectoring.

The integration of which, combined the ability to reduce

the infrared signature of the exhaust of those engines,

with the ability to vector that exhaust

to increase the maneuverability of the aircraft at speed.

In fact, to the point of which the aircraft

had departed the normal flight envelope.

The result?

The F-22 has a top speed of 2,300 kilometers per hour.

While the Raptor may be one of the most

technologically advanced machines on the planet,

like much of the machinery of war,

it's design stems from the need to overcome

the strategic importance of another invention.

For the F-22, that invention is radar.

(dramatic music)

In 1935, Hitler announced that he was breaking

the First World War Armistice agreement

and was rearming Germany.

Since the war, the rapid increase in airstrike capability,

most notably the emergence of long range bombers,

was viewed as a dire threat.

And so a race began to find a technology

that was able to counter it.

In the early 1930s, the British physicist,

Robert Watson-Watt was working on devices

for tracking thunderstorms.

He had developed a system

of plotting their locations using oscilloscopes.

So when, in 1935, Watt suggested that he could use

similar principles to track aircraft,

the British government jumped at it.

Radar uses the same sort of approach

that a bat uses to navigate in the dark.

If you can send out some form of energy in waves,

then some of those waves will bounce off

and some of them will be reflected directly back to you.

And so if you can set up a system of emission

and receivers that can detect those bounced radar waves,

then you can pinpoint objects that

you perhaps would not normally see visually.

Within weeks of Watts' claim,

a test was conducted employing a BBC radio tower

as the signal transmitter.

Using an oscilloscope, changes in voltage

bouncing back from a test aircraft

emerged as a blip on a screen.

And when the time delay of the signal

was plotted against a calibrated scale,

it pinpointed the aircraft's location.

They had successfully tested radar.

But the range at which the aircraft was detected was short

due to the lack of transmission power

and the relatively low signal frequency.

Watt and his team decided that, to be effective,

the system had to emit waves at a very high frequency.

By pushing the capacities of existing technologies,

they continuously upped the range until, by 1938,

a working system of stations that could detect aircraft

at 160 kilometers was built along the English east coast.

The British successfully developed radar assets

along the coast of the United Kingdom of Great Britain

guarding against the bomber fleets

that the Luftwaffe were sending out

during the Battle of Britain.

Not that the whole process was automatic,

far from it.

In our admiration for radar,

don't let's forget the men and women

in the plotting center, for instance.

At the outbreak of hostilities,

Chain Home, as it was called, consisted of just 21 stations.

By war's end, there were over 100,

all capable of detecting a target threat

at distances of over 250 kilometers.

It was the world's first early warning radar network

to achieve operation.

Radar picks up all planes,

but it enables you to distinguish enemy aircraft

by the constant unvarying pattern.

Allied planes are equipped with apparatus

that varies the oscillation.

In 1939, the British invented another device,

the cavity magnetron oscillator,

and its compactness was a game changer.

So subsequent to the Second World War,

advances in electronics allowed radar hardware

to be reduced in size and volume enough

to actually put them onto air craft.

And so, to this day, we continue to see

radars located in the noses of combat air craft.

Radar rapidly became an all purpose device,

one plane could spot every ship in an enemy fleet or convoy.

The magic eye misses nothing.

Over 12,000 German bombers

were intercepted and destroyed during World War II.

Many of them with payloads that, had they been delivered,

would have decimated Britain and her allies.

Radar prevented that.

And, relatively unchanged,

it has influenced every conflict since.

There's no such thing as dog fighting nowadays.

You don't go Battle of Britain stuff anymore.

Fighters don't see each other.

Their radars see each other but they don't.

Changing the very meaning of stealth,

radar remains, to this day,

one of the most powerful machines of war.

After two world wars, the world slipped into a period

of espionage, secrecy and intrigue.

A war in which stealth was the byword.

It was the Cold War.

The Cold War was a race between

two nuclear armed super powers

to secure political and ideological dominance.

And it fueled a race for technological supremacy.

But who was in the lead?

Who had made the latest breakthrough?

Out of this anxiety came the fastest

non-rocket propelled aircraft ever built,

the Sr-71 Blackbird.

When the Cold War started,

the U-2s were flying all over the world.

During one of the missions, Francis Gary Powers,

one of the U-2 pilots, was shot down.

Three surface to air missiles fired at him.

One of them came close and blew the aircraft up

and blew him out of it.

And so he ended up ejecting.

Powers' capture

was a huge embarrassment for the United States.

President Dwight D Eisenhower reacted swiftly.

He went straight to the top secret Skunk Works division

of Lockheed Martin and placed an order.

He wanted a reconnaissance aircraft that could fly higher

than a U-2, fly faster than a missile

and he wanted it tomorrow.

It seemed impossible.

Building an aircraft that was going to fly faster

and higher than the U-2 had never

even been contemplated before.

No air craft had ever flown that high,

no aircraft had ever flown faster than a missile.

And they were given, finally,

20 months to build such an aircraft.

20 months to create an aircraft

that could outrun a missile meant building an airplane

that could travel at over 4,200 kilometers per hour

at altitudes beyond human tolerances.

Immediately, the designers knew

it couldn't be built from traditional metals,

it needed to be fashioned from titanium.

But America had limited supplies of rutile,

the rare, sandy soil from which titanium is extracted.

The world's largest producer, ironically, was Russia.

Which caused a bit of a problem

because the Russians weren't really excited

about providing titanium to the United States.

So what they did was go to offsite companies,

off shore companies,

and they went and bought the titanium from Russia.

Initial trials found that the heat generated

meant the entire aircraft expanded at speed.

The expansion would have caused a smooth skin

to split or curl.

So they decided that they would have to build the airplane

with the ability to actually grow in flight.

And so the aircraft was built to actually grow

15 inches in flight, from takeoff.

Then there was the question of altitude.

The Blackbird was designed to reach altitudes

into the stratosphere.

But at 24,500 meters, nitrogen in the blood

would make the skin boil.

To combat this pilots, had to breathe pure oxygen

for an hour prior to a flight

to expel nitrogen from their blood.

While the SR-71 was designed to rely largely

on altitude and speed to avoid detection,

it did have significant stealth capability.

The underside of the fuselage

was drawn out like a small boat,

which limited radar cross-section.

Special radar absorbing alloys were incorporated

in saw tooth sections on the aircraft skin

and the wings and tail fins were tilted inwards,

reducing direct radar reflection.

We did have defensive systems, but again,

our defensive system primarily was speed.

Faster you go and the higher you go.

That was how we got away from things.

The first operational Blackbird flight

was in December, 1964.

When it flew, it became, and it remains,

the fastest jet powered aircraft ever made.

With the capability of achieving a staggering top speed

of over 3,500 kilometers per hour.

It's top speed's well over Mach 3.2.

The SR's the only manned airplane that's ever done that.

But Mach 3 was a different world.

You can't imagine how quick you can get lost

at that speed if something fails.

You can get really lost, really quick.

32 were built, none were shot down.

It was only because of the development

of satellite surveillance technology

and high operational costs that the SR-71

was eventually retired in 1998.

It was a cost issue.

Flying the SR-71 was not cheap.

You know, every estimate

I've ever heard was a million dollars a flight,

whether or not it really was I don't know.

But that's a lot of money.

But the lessons learned from its design

proved invaluable in developing

the next generation of stealth aircraft.

And that aircraft was the F-117 Nighthawk.

It looks like it shouldn't fly.

And it deserves its nickname, the Wobbling Goblin.

But, though it may be ugly,

the F-117 is another cutting-edge design by two names

that recur in relation to stealth aircraft:

Skunk Works and Kelly Johnson.

Johnson led the design of the SR-71.

And the Nighthawk was one of his last projects.

Born after combat experience in Vietnam,

where increasingly sophisticated surface to air missiles

repeatedly downed U.S. heavy bombers.

I mean in Vietnam, I think the tally

was up to over 800 missiles fired at the SR.

The most striking thing about the Nighthawk

is it's faceted design,

which incorporates the most sophisticated

stealth thinking of its time.

This meant that, despite it being the same size as an F-15,

it appears on radar screens the size of an average bird.

One of the main reflectors of radar

is actually the fan face.

And so modern self designed to try and hide

that fan face from direct view.

The F-117 did this in an interesting way.

The designers at Skunk Works

set the engines deep within the airframe.

The inlet screened with rotatable louvers

to deflect any radar signal.

The Skunk Works team also added noise minimization

to counter the whine that jet engines produce,

making the Nighthawk unnervingly quiet.

The F-117 Nighthawk was the first production,

truly stealth design that had been optimized

from the beginning for reduced observability.

Principally again in radar cross-section,

but also in infrared signature.

The result is an aircraft that is quiet,

all but invisible and extremely lethal.

During the early morning hours of January 17th, 1991,

in response to Saddam Hussein's invasion of Kuwait,

a fleet of Nighthawks slipped over Baghdad

unseen by Iraqi radar and neutralized 37 targets.

Over the ensuing weeks,

they would strike with remarkable accuracy.

Less than three percent of

the American aircraft in Iraq were Nighthawks.

Yet they accounted for 40% of all strategic targets hit.

And of the 64 made, only one was ever lost in combat.

But while the F-117 was deadly, it carried a limited payload

of just two laser guided bombs of up to 900 kilograms each.

The next challenge for aircraft designers

was to create a strategic weapons platform

that combined stealth with massive firepower.

An assessment published by the U.S. Air Force

concluded that two of these aircraft,

armed with precision weaponry,

could do the job of 75 conventional aircraft.

It's the B-2 Spirit,

the latest generation of stealth aircraft.

With a wingspan of 52 meters, the B-2 is big.

And yet, when a former head of the U.S. Air Force

was asked the size of its radar signature,

he described it as, "Insect category."

Conceived during the Cold War

to infiltrate the Soviet air defense network

and attack targets with nuclear weapons,

the B-2 Spirit is a high lift, low drag flying wing design.

(exploding)

(dramatic music)

Engineers have long known that flying wings

have minimal radar signature.

They surmised that, properly shaped and constructed

using advanced composite materials,

they could create the ultimate penetration bomber,

undetectable by radar.

So almost 80% of the B-2 is constructed

out of a woven carbon graphite composite.

With the aid of modern supercomputers,

the outer skin was shaped to deflect radar energy in a way

that is far more subtle than the Nighthawk.

And a new alternate high frequency radar absorbent coating

is applied to each B-2.

It's four turbofan engines are internally mounted

and have an exhaust temperature control system

to minimize thermal signature.

And its weapons capability is up to a devastating

18,000 kilograms in a single payload.

That can include a mix of weapons, allowing it to engage

up to four different target types on any mission.

It can also carry air to surface missiles

with ranges up to 370 kilometers,

allowing it to stand off and attack

from well outside a conflict zone.

Capable of attack missions

from altitude's above 15,000 meters,

with a range of more than 11,000 kilometers unrefueled,

at over 18,000 kilometers with a single refueling,

the Spirit has the ability to fly to any point on the globe

and engage a target without ever being seen.

While stealth technology is essential

to modern aerial combat,

on the ground, different tactics are needed.

During covert operations,

to take out a target from a distance

requires a weapon that is both silent and deadly.

Up until the end of the 19th century,

armies marched into battle with soldiers in orderly lines,

wearing brightly clad uniforms to aid identification.

But when a small Boer force,

either concealed in the landscape

or using skirmishing techniques, very nearly defeated

the mighty British empire in South Africa,

it ushered in a new way of fighting.

We know it as guerrilla warfare,

a tactic that values stealth over strength.

In 1898, at the Battle of San Juan Hill in Cuba,

750 Spanish regulars delayed the advance

of 15,000 U.S. troops.

The Americans were armed with single-shot rifles,

the Spanish were using the same rifle as the Boer

in South Africa, the Mauser 93.

The first major war that the U.S. army had fought

since the American Civil War

was the Spanish-American war of 1898.

In that campaign, the Americans realized

that their existing rifle was obsolete

and they needed to come up with a new design.

The Americans paid $200,000

to license the design from Mouser

and modified it at the U.S. Armory in Springfield.

They installed adjustable iron sights at the front and rear

to assist accuracy at range

and reduced its barrel length by 300 millimeters,

creating a hybrid long gun that could serve

as both a service rifle and a carbine,

making it easier to handle.

And so, the M-1903 Springfield was born.

The Springfield has a muzzle velocity

above 850 meters per second,

over 250 meters per second faster than his predecessor.

Meaning its effective range was doubled to almost 550 meters

and absolute range was increased to well over 3000 meters.

This vastly improved range of the Springfield

was in part due to the decreased

aerodynamic drag of the French Spitzer round,

which replaced the standard bullet's rounded nose

with a pointed tip.

And it was smooth and reliable

under the worst battlefield conditions.

The Springfield rifle was a robust design.

New recruits in that vastly expanding army,

which the Americans created in the First World War in 1917,

found it relatively easy to train

and become competent in the weapon.

10 to 15 shots a minute was easily achievable.

With the shooter able to fire

from a safer range using smokeless powder,

making them far more difficult to detect.

Over three million were produced.

The Springfield rifle was renowned

for its reliability in combat,

and it was such a sound design

that a sniper variant of the rifle

continued to be used during the Second World War,

more than 40 years after the original design was conceived.

In the hands of an expert marksman,

it could reliably take out a target at over 1.5 kilometers.

Add an optical sight,

and what you had was a potent specialist weapon.

And they gave a name to the man who operated such weapons.

They called them snipers.

When Germans on the Western Front

began consistently claiming lives

firing across seemingly impossible distances,

the Allies initially assumed it was potluck.

It wasn't until they began moving through German positions

and stumbled upon rifles equipped with telescopic sights

that they understood what had been happening.

Really the story of the sniper and the sniper rifle

begins in earnest in the First World War.

When each of the participant nations

realize they needed a much more precise version

of their infantry rifle, their standard,

usually bolt-action, infantry rifle.

And that's really what these early sniper rifles were.

The British wasted no time

in emulating the German tactic.

And they elevated it to a new level.

They established training camps where British snipers

honed their shooting skills and learned to gain

advantageous positions using improvised camouflage,

known as ghillie suits.

The underside of the ghillie suit

is reinforced with heavy canvas

to help pad a sniper's torso during hours or days

of lying on his stomach.

Camouflage netting is attached.

To this is added shredded hessian

and other frayed materials,

as well as elements of local vegetation.

Early snipers often acted alone, many used iron sights,

but optics helped realize a rifle's potential.

It meant that you didn't have to line up mechanically

your front and your rear sight with your eye,

with the target.

You just have to put the cross hairs on the target.

It makes it sound simple, it's not.

But as sniping became more effective,

so too did countermeasures.

We can see the classic contest between offense and defense

beginning to take place.

We have snipers who are highly trained,

and we have the opposition, in this case the Germans,

developing armor to protect themselves.

The increasingly mechanized

battlefields of World War II

dramatically changed military tactics on the ground

and naturally armies across the world

began to look at the potential for specialist snipers

to inflict damage on more than just men.

But how on Earth does the individual infantryman

harness physics in a portable weapon to perhaps kill a tank?

It's an extremely difficult thing to pull off

and different answers were arrived at.

Early anti-tank or anti material weapons,

as they became known, were extremely cumbersome.

More mobile than an artillery piece, but only just,

the British Boys anti-tank rifle of World War II

was over one and a half meters long,

weighed almost 20 kilograms

and required a crew of two to operate.

And their story kind of peters out

as tank armor just gets too thick to defeat reliably.

And there's a point in the Second World War

where the anti-tank rifle becomes

absolutely useless, essentially.

But tanks were not

the only armored vehicle on the battlefield.

A weapon was still needed that could stop lighter armor.

And to make that weapon difficult to detect

meant reducing its weight, suppressing its noise

and taming the incredible recoil forces it would generate.

In the 1980s, a weapon arrived

that filled all those criteria,

the Barrett M82.

The Barrett M82 sniper rifle is the benchmark

large caliber anti material rifle

that revolutionized the field of military sniping.

Referred to as a multi-role weapon system,

the M-82 has an effective range of over 1,800 meters.

But anti-personnel work is not the weapon's primary purpose.

It is more commonly deployed against hard targets

like buildings,

armored vehicles,

parked aircraft

and communication systems.

To create a weapon of this power and portability

first required a reduction in weight.

There's a constant quest to lighten all weapons,

but especially weapons that tend

to be very heavy and cumbersome.

Simply because you can use them much more flexibly.

To achieve this, the Barrett's barrel is fluted,

a design that also improves heat dissipation.

Elements of the stock are constructed

using lightweight plastics,

but what's truly unique about the Barrett

is it's buffer system.

The entire barrel is set on rails

and travels back 3.8 centimeters against springs,

a revolutionary development that allows it to be fired

from the shoulder, unaided by tripod bracing.

The Barrett's recoil operated system

sacrifices a little accuracy for low recoil,

which is very important when firing

an extremely powerful cartridge

like the 50 Browning machine gun cartridge.

All of this allows the M82

to deliver previously unheard of levels of energy

and distance with low observability.

A sniper rifle capable of putting a 50 caliber round

through the block of a truck engine

from over a kilometer away.

But the effectiveness of a modern sniper

is enhanced not just by the rifles they use.

Advances in glass manufacturing

have led to massive increases in standard magnification.

And the increasing use of transparent polymers

has greatly improved

the light transmission of modern scopes.

Such scopes fitted to rifles like the M110 Sniper System

equip the sniper with what is a true precision weapon.

With the M110 that precision begins with the barrel.

If you think about the microscopic

imperfections in a rifle barrel,

every one of those can upset the bullet very, very slightly.

And so, if you're able to go down to that microscopic level

and if you're able to remove all of those imperfections,

in theory, you will have an ultra precise bore.

Something that they couldn't have dreamed of in 1918.

The M110's 50 centimeter chrome-plated barrel

is made from the highest quality modern steel

with greatly reduced imperfections.

It also features what is called 5R rifling.

The important thing with sniper rifles

is that you minimize barrel vibration

when you fire the projectile.

And that is so important for accuracy because,

as you fire the projectile,

the barrel may have a tendency to vibrate.

And if you minimize the amount of vibration,

then that's going to improve the level of accuracy.

5R rifling reduces projectile damage,

ensuring the projectile remains more uniform.

And a more uniform projectile

translates into less vibration and improved accuracy.

The changing nature of battle

revealed the limited engagement capabilities

of traditional single shot bolt action rifles.

This was particularly problematic in urban Iraq

during the U.S. led invasion,

where non-repeating sniper rifles

became a tactical liability.

With a larger 20 round magazine,

a sniper carrying an M110, who finds themselves under threat

can easily switch the weapon into automatic mode,

allowing them to fight their way through to safety.

Two weapons in one and yet extremely accurate.

In the hands of a skilled sniper,

the M110 can group 10 shots fired rapidly

over a distance of more than 90 meters

within a radius of less than one and a half centimeters.

Stealth on land relies on silence,

camouflage and guile.

But in the wide expanse of the open ocean,

it's much more difficult to hide.

At sea, the stealthiest place

from which you can do damage to enemy shipping

is not from the surface, but below it.

(dramatic music)

On the morning of the 5th of September, 1914,

HMS Pathfinder, the lead ship of the British

Pathfinder class of cruisers was spotted

by the German U-boat U-21.

Stalking her at periscope depth,

U-21 fired a single 50 centimeter torpedo.

At a range of 600 meters.

Within minutes, she was lost.

It was the first sinking by a U-boat in World War I.

Thousands more were to follow.

Many naval people in the beginning of the 20th century,

regarded the submarine as a really underhanded weapon,

a weapon to be used by the coward.

Yet the ability to approach unseen

and to reap damage revolutionized warfare at sea.

The Unterseeboot, or the U-boat as they became known,

was more a submersible ship than a submarine

as we think of them today.

They were fast on the surface,

they could do something like 17 knots.

But dived only about seven.

So they would do most of their hunting on the surface

and then dive for the attack.

There were many Allied submarines.

But what made the U-boat superior

and gave it its tactical edge

was its diesel electric propulsion system.

The Germans had long understood the value of diesel engines

and led the world in their design.

In 1915, a reliable four stroke diesel engine was produced

that far outstripped the performance

of any Allied equivalent.

The U-boat could keep pace

with most merchant ships of the day.

With a range that allowed them

to choose their time to attack.

Using electric motors to get them within range,

they would surface and either engage

with deck mounted guns or torpedoes.

U-boats quickly became

the most prolific killers on the seas.

While in 1914 German surface ships sank 55 ships,

compared to only three by U-boats,

the following year, this was reversed

with U-boats sinking 396 Allied ships

compared to only 23 by surface craft.

Between 1914 and 1918, nearly 10,000 ships,

thousands of planes and dirigibles,

and more than 100,000 mines were deployed

to combat a U-boat fleet which totaled just 340 submarines.

The Allies may have eventually won the war on land

but the success of the U-boat campaign

underscored how important and devastating

submarine warfare could be.

A lesson that was repeated

to an almost decisive effect in the Second World War.

(dramatic music)

The Type VII U-boat was the workhorse

of the German submarine fleet during World War II.

They were designed really for service in the North Sea

and in the Western approaches to Europe.

They were very effective in their job of trying to cut off

sea communications to Britain.

And there were more Type VII U-boats built

than of any other submarine ever.

Over 700, in fact.

But the Type VII was more an evolution

rather than a revolution.

They were kind of small submarine and,

in terms of their technology, they will little changed

from the submarines of World War I.

With similar size and similar capability.

Additions included large external tanks

holding 33 tons of extra fuel, which increased range,

and supercharged diesel engines

gave a slight increase in overall speed.

Improvements in the efficiency of the electric motors

extended the time they could remain submerged

and they carried an increased load of torpedoes.

But it was improvements in shipboard communications

that was their deadliest asset.

It allowed German submarines to hunt in groups,

groups that became known as wolfpacks.

Well a wolfpack was a group

of submarines operating together.

They could be very, very effective

because they could surround a convoy

and attack it from multiple directions all at once.

Undoubtedly, one of the most

formidable assets of the Axis Powers

in the present phase of the war is the U-boat.

Initially they were very effective

in disrupting supplies to Britain.

In the first six months of the Second World War,

Britain lost more than 300 ships,

while the Germans lost just 17 submarines.

And, as the war spread with America's entry,

so too did the Battle of the Atlantic.

The U-boat campaign,

certain to be intensified,

is Hitler's greatest hope of staving off defeat.

He has hundreds of U-boats at sea now.

He'll undoubtedly have more.

The answer is to destroy them.

Good luck began to run out

as submarine countermeasures evolved.

Allied air patrols over the North Atlantic

became more effective and radar became more available,

which made them very vulnerable.

If you want to combat an air attack on a submarine,

you have to stay well submerged and keep out of the way.

And that was difficult because, like many early submarines,

the Type VIIs were basically a surface ship,

which could dive.

The Germans realized they needed a way

to carry out such operations while remaining submerged.

And the answer to that was the snorkel.

The Germans adopted the Dutch snorkel and retrofitted it

to quite a number of the Type VII submarines,

which made them much less vulnerable.

Although the snorkel improved the odds,

improvements in detection technology,

combined with the development of specialist ships

to hunt and destroy you boats,

meant that they were no longer

the supreme stealth weapon they had been.

In fact, by 1945, U-boat losses were routinely 30 per month.

And in April of that year, they exceeded 50.

Not so long ago, the Battle of the Atlantic

was the most critical factor in the war.

Now convoy after convoy, all strongly escorted,

crosses the Western ocean virtually unmolested

in comparison with those days of crisis.

When U-boats appear, it's they who are hunted now.

But the end of the war

and the birth of the nuclear age

unlocked a power source that would redefine submarines

and restore their place as perhaps the most feared

of all stealth weapons on the planet.

After World War II, the British put

most of their effort into commercial nuclear development.

But in 1947, Westinghouse were authorized

by the U.S. government to develop a nuclear reactor

which was capable of being fitted into a submarine.

That reactor was fitted

to a submarine named the USS Nautilus.

And it was revolutionary.

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Launched in 1955, the Nautilus was able to achieve

a submerged speed of 23 knots

and her hull could withstand pressures

at depths over 200 meters.

The important thing about the nuclear submarine

is it can remain submerged really

for a very long period of time.

And the submarine's endurance is really determined,

not by the fuel or the battery capacity,

but by the amount of food you can carry

and the endurance of the crew.

And that was a major evolution in submarine design.

From 1955 to 1957,

the Nautilus was put through a series of trials.

Trials which showed her revolutionary teardrop shaped hull

would allow her to match speed with those on the surface.

No longer would the submarine

be a fast surface ship that temporarily submerged,

but a fast submersible ship.

I think the most important thing about Nautilus,

is that she proved the value of nuclear power in submarines.

By the mid 1950s, the United States had stopped building

conventional diesel electric submarines.

To prove the supremacy of nuclear power,

on the 1st of August, 1958,

the Nautilus submerged near Alaska

and surfaced 96 hours later, Northeast of Greenland

having completed the first

submerged voyage under the North Pole.

And all went without a hitch.

Nautilus passed safely on her route right under the pole.

A tremendous achievement and the moment of relief

I should think for all on board when she surfaced.

The Nautilus had demonstrated

that she was at the cutting edge of stealth technology.

But during the Cold War,

as the Soviets developed their own nuclear submarines,

the U.S. was compelled to stay ahead.

62 Los Angeles-class Submarines.

The largest group of vessels constructed

for the United States Navy during the Cold War,

were specifically designed to counter the Soviet submarines

that the Americans believed would,

in the event of hostilities, target the heart of their navy,

the carrier groups.

Much of the information

about the Los Angeles-class is classified.

We know that it is capable of 20 knots on the surface.

And its reported top speed while submerged is 33 knots.

If continuously operated, it's propulsion plant

requires refueling just once every nine years.

The Los Angeles-class submarines

are armed with a mix of both land attack

and anti-ship versions of the Tomahawk missile.

Complimented by 25 torpedo tube launched missiles,

including the Harpoon anti-ship missile.

Submarines, of course, are a pressure vessel.

They consist of several major components.

The most principle one, of course, is the pressure hull.

And the more cylindrical that is,

the better it withstands pressure.

The deeper you go,

the more difficult you are to detect

and depth means pressure.

Increased power from nuclear reactors

allow submarine hulls to be thicker.

But a hull's strength is also measured

by how elastic it can be under pressure.

And this yield strength requires special steel alloys.

Although the operating depths of submarines are secret,

they're crush depth can be calculated

if you know what they're made from.

The Los Angeles-class have pressure hulls

made with HY-80, a nickel-chrome alloy

with incredible strength and elasticity.

This puts their crush depth somewhere around 600 meters.

Deep and stealthy.

But stealth at sea is no longer

the sole domain of the submarine.

At almost 183 meters, the largest destroyer

ever commissioned for the U.S. Navy,

the Zumwalt-class guided missile destroyer,

is as close as any ship has come to being invisible.

They're big ships, they're something like 15,000 tons.

So to call them a destroyer is something of a misnomer.

But it's a very stealthy ship,

which is difficult to find with radar.

To make a ship of this size difficult to detect

has required a complete shift in naval design thinking

and the application of lessons learned

from aviation stealth technology, beginning with the shape.

The structure is designed with a lot of tumblehome,

so that the upper deck is narrower than at the waterline.

The opposite to that of traditional vessels.

Resulting in a significant reduction

in its radar cross-section.

Like the F-22, the weapon systems are discreet.

The decks are clear with virtually no sharp lines

that could return a radar signal to its source.

On a typical warship,

you see an arrangement of spinning dishes and antennas

sitting atop a high profile mast.

The Zumwalt's deck house is a clean angled structure

straight out of the F117 design book.

It's array of radar sensors and communications hardware

is integrated directly into the deck house skin,

which is built of composites much like the B-2.

By incorporating these lessons,

designers have managed to give the Zumwalt,

on almost 15,000 ton heavily armed warship,

capable of 36 knots,

a radar cross-section the size of a fishing boat.

Improvements in stealth design

are continually being counterbalanced

by the ongoing development of detection methods.

The Zumwalt represents another beginning

in the race to appear invisible

and science continues to push the boundaries

of what seems possible.

Current studies involve cloaking aircraft in plasma shields,

fields of ionized gases that absorb all radar signals

and experiments with technologies that bend light waves

to render objects, or even people,

invisible to the naked eye.

It seems that, if science fiction can think of it,

militaries will try to make it a reality.

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