Original subtitles

Tonight on "Secrets Declassified,"

the top secret tech built to outwit, outgun,

and outmaneuver the enemy,

from the nuke so small it's nicknamed

the atomic watermelon.

It's the smallest nuclear bomb ever built,

and it can be fired from a bazooka.

To the spy plane so extraordinary,

it seems out of this world.

This is actually responsible

for more than half of all reported

UFO sightings in the 1950s.

And the World War II aircraft carrier

that's made of solid ice.

This will be the largest naval vessel ever built.

These are the astonishing and sometimes terrible

inventions designed by governments

and the people who work for them.

It's time to bring them to light.

In 1943, the world is at war,

and the U.S. is looking for a way for their spies

to move underwater undetected.

The solution isn't born out of a top secret government lab.

It comes from the mind of a medical student

on summer break.

At the start of World War II,

America launches a brand-new intelligence agency,

the Office of Strategic Services.

The OSS is the first version of the CIA,

and its job is to find creative ways

to gather intelligence and sabotage Axis forces.

And one of its biggest obsessions

is finding ways to put spies underwater.

If you can keep spies undetected underwater,

you could slip into enemy harbors,

sabotage vessels, and disrupt entire naval operations.

There's just one problem.

At this time, breathing underwater

is anything but stealthy.

There's one device called the aqualung,

but it releases air bubbles.

This is a problem for covert operations.

You might as well send up a signal flare.

The solution comes from an unlikely source--

a young student at the University of Pennsylvania.

Christian Lambertsen is an undergraduate student,

and he's studying physiology.

He's absolutely fascinated about breathing underwater.

Every summer, Christian Lambertsen

heads down to the New Jersey coast.

But he's not chilling on the beach.

He's in the water experimenting

with breathing contraptions.

One day, Lambertsen has a breakthrough.

The equipment that helps patients breathe in hospitals

could be modified to help divers breathe underwater

without producing bubbles.

Anesthesia equipment contain absorbent materials

that remove carbon dioxide from the air

that patients breathe while they're unconscious.

Lambertsen figures, he can use similar materials

to remove the carbon dioxide from the air

that a diver exhales.

That way, a diver's air can be rebreathed,

rather than being breathed back out into the water

and creating bubbles.

After years of trial and error,

Lambertsen perfects his idea.

Lambertsen builds a prototype.

He calls it the Lambertsen Amphibious Respirator Unit,

LARU for short.

LARU funnels exhaled air

through a canister lined with soda lime,

so oxygen can be rebreathed over and over.

It's pretty remarkable.

It's silent, doesn't weigh much,

and best of all, no bubbles.

So Lambertsen shows this prototype

to his professor, who immediately understands

the possible implications.

He realizes this is a potential tool for spies.

Seeing the possibilities,

Lambertsen's professor makes some calls,

and eventually, the OSS hear about this invention.

They ask Lambertsen down to Washington D.C.

for a demonstration.

He straps it on, drops into the pool, and stays under.

No bubbles, no noise.

Just smooth movement beneath the water's surface.

Needless to say, the OSS are absolutely fascinated

by what this prototype could do,

so they hire Lambertsen.

A dip in the pool is one thing.

What the OSS really wants to know

is whether this homemade spy gadget can perform

in a real combat mission.

Lambertsen is given the job of training

the very first unit of combat swimmers for a live test.

The OSS want Lambertsen and his team

to infiltrate a heavily defended harbor

and plant dummy explosives on a target ship

and then get out of there undetected.

It has underwater sound detection systems,

patrol boats, and security nets.

This place is locked down.

It's essentially a make-or-break

high-stakes underwater heist.

They're trailblazers.

This hasn't been done before, so they're having

to invent the tactics and procedures

and the technology at the same time

to enable this kind of operation.

The test mission is given the name

Operation Cincinnati.

The training is absolutely brutal.

The divers have to learn how to operate in freezing-cold waters

and in complete darkness.

After a year and a half's training,

Lambertsen's new team are ready.

Under cover of night, the divers slip into the water.

They're armed only with the LARUs, waterproof compasses,

and dummy explosive charges.

They glide past the patrol boats

and navigate around the underwater nets.

The LARU allows a diver to stay submerged at a depth

of 50 feet for up to 90 minutes.

The navy's state-of-the-art sound detection equipment

hears nothing.

They reach their target, plant the charges,

and get away without a sound

or a single ripple on the surface.

The operation is a stunning success.

The OSS immediately deploys a new unit of combat swimmers

equipped with the LARU on covert missions

all around the globe.

Lambertsen's device opens the ocean to millions

of recreational divers, but its covert military origins

and its make-or-break test remain buried

in classified files for another 40 years.

In 1995, the CIA declassifies the files

that reveal the LARU's origins as a cutting-edge spy gadget,

and we get to learn how a medical student on summer break

invented a device that changed underwater espionage forever.

The LARU was the brainchild of a single

talented medical student.

But when the U.S. government wants to build the world's

smallest nuclear bomb, it enlists an army

of highly trained scientists.

The device they create is known as the atomic watermelon.

In the late 1950s, in Europe,

Soviet forces outnumbered NATO forces 10 to 1,

and as a result, the United States are terrified

of a Soviet invasion.

They especially fear the Soviets

sending thousands of tanks across

what is known as the Fulda Gap.

The Fulda Gap is a geographical feature

right along the border in Germany--

two open-plain areas that would make it easy

for Communist bloc nations

to stream from east toward the west.

If Russian tanks roll through the Fulda Gap,

there won't be enough time for America

to scramble its strategic nuclear bombers.

U.S. military planners know,

if they wanna protect the free world,

they need to find a way to defend the Fulda Gap.

For that, they decide they need a brand-new weapon.

What the U.S. Army needs is a tactical,

low-yield nuclear weapon.

It needs to be scary enough to make the Soviets think twice

about invading, but small enough

to race along the West German frontline at a moment's notice.

In 1959, Los Alamos National Laboratory engineers

begin work to design the smallest

ever nuclear weapon.

Engineers use a new form

of highly enriched plutonium 239.

This new, miniaturized device has an explosive yield

equivalent to about 20 tons of TNT.

That's similar to the largest conventional bombs

ever constructed.

And it weighs only around 50 pounds.

That's less than 1% the weight of the Hiroshima bomb,

and this is a device that's less than 11 inches in width.

Its size and shape inspire a nickname:

the atomic watermelon.

Now the military needs to see if this melon

can deliver the destruction they're hoping for.

There's a test detonation of the warhead

at the Nevada test site in July 1962.

This is designed to prove that the weapon system

is capable of functioning.

There's a bit of theater associated with this test.

There are bleachers that are built.

Those who are invited

to attend the test and observe it,

they're given special goggles so that they won't be blinded

by the blast once it occurs.

There's a VIP seating area.

Robert F. Kennedy is there.

It's being proven not just to the American military,

but to American political leadership.

And it's also a rollout, if you will,

to prove we're capable of using this on the battlefield.

The target is a point in the dry desert basin

nearly 3,000 meters away.

At 10:00 a.m., the weapon is fired.

And it works.

The round was set for a low height of burst.

It detonated perfectly,

releasing its lethal radiation.

The launcher, the delivery system,

the warhead all work flawlessly,

exactly as designed.

And tests at the delivery site show radiation levels

that confirm that anyone within 200 meters

would have been killed instantly.

The atomic watermelon is a success.

It's loaded into Jeeps across West Germany,

ready to race to the frontline.

Over 2,000 atomic watermelons are manufactured

and distributed across Europe to face the Soviet threat.

Each weapon is handled by a five-man team,

who are only to use the weapon if they are faced

with an imminent threat of being overrun.

Shooting a nuke from a short-range

rocket launcher comes with one very real risk.

That five-man team will move forward

at high speed using the vehicle.

They'll fire the weapon.

And then, immediately upon releasing it,

they will move as fast as possible

out of the fallout range of the weapon

so that they themselves do not become irradiation casualties.

Despite the danger, the atomic watermelon

is judged such an effective deterrent

that it's deployed to other vulnerable outposts,

including Korea, Guam, and Hawaii.

The atomic watermelon is a key part

of American defense for the better part of a decade,

but by the late 1960s, it still hasn't been used in combat.

Plus, advances in missile guidance

have essentially rendered it obsolete,

so it's retired in 1971.

The story of the atomic watermelon

remains buried in classified archives for decades.

remains buried in classified archives for decades.

Only after the end of the Cold War

are the full details revealed to the world.

When aerospace manufacturer Lockheed Martin designs

the ultimate Cold War spy plane,

the CIA will do anything to keep the top secret tech

under wraps, even if it means igniting

one of history's greatest conspiracy theories.

This plane is cutting-edge technology,

but it's kind of weird.

It uses advanced materials like titanium

that's strong and lightweight,

but it also has these strange features.

Like, it's gangly, and the landing gear

is lined up like bicycle wheels.

This is a curious-looking bird.

This plane has 130-foot-long wings that droop

at their length, to the point that

they actually will hit the ground

when the plane is grounded.

Most unusually, though, for a plane produced by

a fighter jet company, this aircraft isn't going

to carry a single weapon.

The reason for this plane's extreme design

is its extreme mission.

It's being made for the U.S. government

to fly at record-breaking altitudes

on top secret reconnaissance missions

over Soviet territory.

In the 1950s, the Americans are worried

about the technology that the Soviets have.

The rumor at the time is that the Soviets

had developed a bomber capable of flying from Moscow

to the United States.

So the CIA comes up with this ingenious plan

to find out if it was true.

We don't have much of a spy network operating

in the Soviet Union in the 1950s.

The Soviets are protected behind an Iron Curtain.

If you can't go through the Iron Curtain

or sneak behind it,

you might have to fly over it.

To avoid detection, the CIA decides to build

a state-of-the-art spy plane.

Any aircraft that are flying over Soviet territory

might be susceptible to air defense,

including sophisticated missiles.

And they might be accused of violating international law.

The solution is to create an aircraft

that flies twice as high as the Himalayan peaks.

70,000 feet and above.

No plane has flown so high for so long.

To achieve it means developing brand-new technology.

So the government tasked Lockheed

to build this spy plane.

And their solution is essentially

to make a giant glider and to stick a jet engine on it.

Flying at the altitude that it is

presents all sorts of new challenges.

For instance, traditional jet fuel just won't work.

They need to invent an entirely

new type of kerosene fuel that doesn't

boil off at low pressure.

Lockheed's engineers

call its new creation the Angel,

as it flies so close to heaven.

The government designates it Utility Aircraft 2,

or the U-2.

But building this incredible plane

is only half the battle.

When the U-2 is complete,

the government needs to figure out how to test it

and, most importantly, where to test it.

Building a plane in secret,

that's doable because it's done inside of a hangar.

But testing a plane in secret, that's a lot more difficult.

For decades, the location of the U-2's

testing site remains one of the government's

most closely guarded secrets.

But conducting so many flights of this classified plane

has a strange side effect.

When they start testing the U-2,

UFO sightings go up tremendously.

The public sees it.

They have no idea what they're looking at.

Air traffic controllers and professional pilots,

they don't know either.

They see the shimmering in the sky.

They don't know what it is. It's really high up there.

Therefore, they think it's a UFO.

Rather than confess that they're testing

a top secret new plane,

which might alert the Soviets to their plan,

the CIA launch a cover-up.

They claim the sightings are due to natural phenomena,

so understandably, the conspiracy theories go nuts.

There are some people who argue that the U-2,

in its early stages of development

is actually responsible for more than half of all

reported UFO sightings in the 1950s.

In 2013, the U.S. admits for the first time

what many have long suspected.

The name of the U-2's secret test base is Area 51.

One of the reasons that Area 51 is so important

and so secret is that it's near the Nevada proving grounds.

And no one in their right mind is

gonna wanna go into an area where

they're testing nuclear bombs.

They specifically purchased

the land for testing the U-2.

Were it not for the U-2, there would be no Area 51,

and we would have lost our most iconic

UFO conspiracy location.

While Area 51 becomes the most notorious

UFO site in the world,

the U-2 plane becomes one of America's

most vital intelligence tools.

Between 1956, the first operational flight,

July 4th, through May 1st of 1960,

the U-2 program dispelled

the missile gap and the bomber gap.

There was none.

We were still ahead of the Soviets,

even though they were saying they were ahead of us.

Over the next four years, 30 flights

photograph almost 15% of the USSR.

This provides 90% of the CIA's hard intelligence

on its fiercest rival.

The CIA thought it had a shelf life

of two to four years.

Well, other than the B-52, the U-2 spy plane

is the longest flying airplane

in the U.S. Air Force's arsenal.

And it's still flying today.

In World War II, Hitler's U-boats

are hunting British ships relentlessly.

So Britain gambles on a radical new innovation,

an unsinkable ship built not from steel, but from ice.

By 1942, Britain feels like it's against the ropes.

U-boats hunting in the mid-Atlantic

are sinking 650,000 tons of shipping every month.

The killing zone is called U-boat Alley.

It's a stretch of the mid-Atlantic

where Allied ships are unprotected.

Air Force planes can't reach that far from land bases,

and the British can't send aircraft carriers to help

because they would be sunk by the U-boats too.

What they need is an aircraft carrier that can't be sunk.

Enter Geoffrey Pyke,

an eccentric adventurer and inventor

now working for Allied HQ.

Geoffrey Pyke comes up with the realization

that nature already produces giant, unsinkable platforms

in the ocean.

They're called icebergs.

So he comes up with the idea that

you could flatten one

and tow it wherever you wanted it to be.

You can use it as an unsinkable aircraft carrier,

and it can close the mid-Atlantic gap.

But Pyke soon realizes icebergs won't work.

They have this nasty tendency to flip,

which would put your aircraft and your crew

in the cold Atlantic waters.

So no, not a good solution.

Pyke won't be stopped so easily.

He begins to design an artificial iceberg.

Pyke's idea is to create

a giant aircraft carrier not from steel,

but from blocks of carved ice.

He could have a system of cooling pipes

throughout the ice to keep it frozen

and also use diesel engines to propel it forward.

At a secret lab

hidden in a refrigerated storage unit

at London's Smithfield Meat Market,

Pyke's team starts experimenting.

There's one big shortcoming with ice:

it is extremely brittle.

If it came under enemy attack, it will fracture.

So as Pyke considers this problem,

he takes some inspiration from reinforced concrete

and the idea that perhaps combining

water with another element

would produce a harder ice product.

Pyke's team searches

for potential additives

to increase the durability of ice.

They find a research paper

from scientists in Brooklyn, New York,

testing cotton as a reinforcer.

But this makes a slushy, uneven ice block.

Finally, after lots of experimentation,

they come up with just the right recipe,

and that is 4% wood pulp and 96% water.

This combination creates an incredibly durable

block of ice.

Pyke's new ice behaves

like nothing else on Earth.

It's strong as concrete and almost bulletproof

but can be cast like metal and cut like wood.

They name this new miracle material Pykrete,

after its inventor.

British Prime Minister Winston Churchill

is the kind of guy who likes unusual, bold, daring ideas.

So he says, yeah, let's do this.

Pyke's project is given the code name Habakkuk.

Habakkuk is an Old Testament prophet

who records God's promise to the doubtful.

"I am going to do something in your days

that you would not believe, even if you were told."

Pyke chooses the name to fit his impossibly ambitious

ice ship.

Now he needs to construct a prototype.

But Britain is too warm to build it,

so the entire project moves to Canada.

They turn the frozen surface of Patricia Lake

into a giant laboratory and build a 1,000-ton,

60-foot-long scale model.

The Habakkuk team starts experimenting,

and they find that, in order to keep the ice stable,

the ship's refrigerators need to keep it

at a frosty 5 degrees.

They also discover that, to stop a torpedo,

the hull has to be at least 30 feet thick.

When they complete their design,

it is an absolute behemoth.

Pyke wanted an ice ship with a runway

2,000 feet long and 300 feet wide.

It has 40-foot-thick walls,

and it can carry over 150 bombers at one time.

This will be the largest naval vessel ever built.

Project Habakkuk is now becoming hugely expensive,

so it needs American backing.

In August 1943, at the Allied conference in Quebec,

the Brits make their pitch.

To prove the properties of pykrete to the Americans,

one of the UK's top commanders, Lord Mountbatten,

stages a demo.

Mountbatten gives U.S. General Hap Arnold an ax

and asks him to smash a block of pykrete.

Arnold swings at the pykrete with all his might.

The ax bounces off.

Then Mountbatten draws his pistol

and fires it at the pykrete.

The bullet ricochets off,

sending the generals diving for cover.

The room erupts, but the point is made.

The Americans are on board for Habakkuk.

Before production can begin,

the tides turn in the Atlantic.

Long-range aircraft and new anti-submarine tactics

blunt the U-boat threat.

With the crisis over, the ice ship is no longer needed.

In January 1944, Project Habakkuk is canceled.

The prototype ship they built on Patricia Lake

is allowed to melt away.

Soon the war comes to an end,

but the British military keeps details of pykrete

on ice for the next 30 years.

We only learn the full details

through declassified documents that are discovered in 1973.

They speak to an hour of desperation

when England faced an existential threat

as a result of the U-boat.

Some new technology lands with a bang,

others barely a sound.

To help end the Vietnam War,

the CIA needs a helicopter so stealthy,

the enemy will never even know it's there.

It's 1971, and the Vietnam War

has been going on full tilt for six years.

The American public is now putting pressure

on the government to end the war,

and troops are actually starting to come home.

Peace talks are underway,

but President Nixon finds himself in the middle

of a diplomatic deadlock that is just so absurd that--

and this is no joke-- after 10 weeks,

the only thing negotiators have agreed on

is the shape of the conference table.

Henry Kissinger is Richard Nixon's

national security advisor.

Kissinger feels a concern that the North Vietnamese

are not negotiating in good faith.

He turns to the CIA in the interests of developing

a more accurate intelligence picture.

The CIA has learned that about 15 miles

from the city of Vinh, a single phone line

carries the North Vietnamese military's

most senior communications.

Laying a tap on this line

could hand Nixon Hanoi's playbook in real-time.

But there's a catch.

The phone line runs about 150 miles into enemy territory.

Reaching it means flying a helicopter

deep behind enemy lines.

And this is further than any covert flight of the war.

Very little about a helicopter is stealthy.

A conventional helicopter can be heard for several miles.

Using one will blow the mission's cover

and also get the team shot down.

Somehow, the team need to source a helicopter

that the enemy won't hear coming.

Enter the Quiet One, a stealth helicopter

in the works at the Pentagon's top research lab.

Instead of four rotor blades, it runs five.

It cuts down on the thump

that these rotor blades tend to make.

They also use oversized mufflers, which soften

the entire exhaust signature.

At 400 feet, it registers just 71 decibels,

earning its title as the world's

quietest helicopter.

But quiet isn't the same as combat-ready.

Landing in North Vietnam would be catastrophic,

so the Quiet One needs to make a 300-mile

round trip without stopping.

The CIA modifies it with a 500 horsepower engine,

twice the standard, so it can fly

long haul without refueling.

They also give the aircrew forward-looking

infrared screens, allowing these crews

to fly in complete darkness.

To top it off, the whole chopper is

coated head to toe in experimental

radar-absorbing black paint.

By October of 1971, two prototypes are ready

and shipped to a secret air base in Taiwan.

Now Kissinger just needs the right team

to fly his new machine.

The CIA wants to keep this mission deniable

for the U.S. government, so they send in two

American helicopter pilots to train Taiwanese

on how to fly the stealth helicopter.

Training turns out to be a disaster.

The Taiwanese pilots are told to push the aircraft

beyond what they're capable of.

One of the helicopters crashes and is damaged beyond repair.

Down to their last Quiet One,

the CIA upends its original plan.

By late 1972, the CIA has no choice.

The U.S. pilots will have to fly the mission themselves.

So on December 6, they give the green light

for the most covert flight of the entire Vietnam War.

The aircraft delivers the team to the bluff.

The team scramble off of it.

The aircraft then quietly returned to the air.

Placing the wiretap should be the easy part,

but there's a problem.

The telegraph poles are not made of wood,

like they expected, but they're concrete.

The special climbing gear they brought won't bite.

The commandos muscle their way up the pole

by hand, which wastes precious time.

Undeterred, they reach that spot,

install the wiretap, scramble back down.

The Quiet One descends in silence,

the commandos climb back aboard, and they head for base.

A few weeks later, the Vietnam War

comes to an end when the Paris Peace Accords are signed.

Many believe that the intercept by the Quiet One

gave Kissinger the leverage that he needed

to close the deal.

While Kissinger takes the spotlight,

the Quiet One disappears into CIA silence.

And its Black Ops mission is buried.

Then, in 1982, historians Ken Conboy and James Morrison

start to piece together the truth

through hundreds of interviews with those involved.

Over a decade later, they reveal

the full story to the world.

In a remote desert, military engineers test a cutting-edge

piece of spy tech so unusual and classified,

some will claim it's out of this world.

This is a very technologically advanced program,

so secret that the individuals working on it

don't know what they're working on.

Nearly everyone on this program are told

that they're working on meteorological equipment.

Even the code name, Mogul, is classified.

Project Mogul is being built

to keep the U.S. in the lead of the nuclear arms race.

As far as the Americans know, the Soviets don't have

the technology to build the atomic bomb,

but they also know that it's only a matter of time

before they do.

The Soviet Union is filled

with these vast wildernesses.

The Americans are concerned that they're gonna be able

to test these weapons in total secrecy.

This is in an age where we can't get over the Soviet Union

undetected, so they have to come up

with an idea on how to monitor the Soviets

as they test nuclear weapons.

The answer comes from a renowned

U.S. geophysicist and oceanographer who claims

he can make tech that can listen for the Soviet tests.

Dr. W. Maurice Ewing is convinced

sound channels exist at high altitudes

which could be used to detect nuclear explosions.

His idea gets the attention of U.S. Air Force officials,

who authorize a top secret research effort

called Project Mogul.

The concept is simple-- to place microphones

8 1/2 miles in the air in the aerial sound channel

to listen for nuclear detonations.

The idea may be simple,

but the execution is not.

The Americans have to figure out how to get

these microphones up to altitude, 70,000, 100,000 feet,

and stay up there for a very long time.

Dr. Ewing thinks the answer is to float them,

using helium balloons.

Helium balloons don't make any sound,

they can stay aloft for days at a time,

and they don't need any fuel or a crew.

They're basically the perfect autonomous vehicle.

In 1947, the Mogul team head into the desert

to begin the secret testing of these balloons

and the cutting-edge audio spy tech they will carry.

The payload equipment--

sound monitors, ballast, and batteries--

they all hung below.

This stretches up to 600 feet from tip to tail,

which is twice as tall as the Statue of Liberty.

Rising to 45,000 feet, balloons can withstand

temperature fluctuations of up to 160 degrees Fahrenheit

and winds of over 30 miles per hour.

It takes just one accident

for this top secret program to ignite an enduring mystery.

There's one problem.

These balloons can not always be controlled.

They don't always go where you want them to,

and sometimes they crash.

In June 1947, a rancher stumbles

upon strange, mangled, high-tech metallic debris.

The rancher brings a sample of the wreckage

to a nearby army airfield.

When the airfield public affairs officer releases

a statement about the debris, he has no idea

about the Air Force's Mogul Program.

He says there is a flying disk among the debris

now being analyzed at a nearby airfield

that is called Roswell.

Headlines around the world appear--

UFO, Roswell, New Mexico.

The air force is thrilled.

It needs a cover for these balloons,

and alien spacecraft are as good a cover as any.

As a result, Roswell, New Mexico,

has become synonymous with UFOs, and still is today.

No one connects the dots for nearly five decades.

The truth is only revealed in 1995,

when an investigation into the Roswell UFO incident

makes the link to the top secret balloon program.

For the military, the alien invasion cover story

is a huge success, but the project is not.

Mogul's use of balloons to detect bombs proves a failure.

Spies use tech to eavesdrop on the enemy,

to secretly photograph them, and even to kill them.

But what about smell them?

When the U.S. needs to find enemy troops

in the Vietnam jungle,

they build a machine to do just that--

hunt soldiers by their scent.

By the mid 1960s, the United States

is struggling to monitor enemy troop movements in Vietnam.

The Viet Cong are masters of hide-and-seek.

They have tunnels, spider holes, jungle camouflage.

The enemy has become so masterful

in the use of concealment that there are cases where

GIs are 3 feet away from the enemy,

and they don't even know that they're there.

You can't fight an enemy that you can't find.

The thick jungle canopy

makes aerial reconnaissance useless,

so the U.S. needs a new type of technology

to pinpoint the invisible enemy.

Their incredible solution is a device that will

sniff them out, literally.

The natural process of producing sweat

releases ammonia.

A large formation of troops will

consist of men who are releasing

invisible ammonia gas.

If you have the ability to detect that,

you can fix the exact position of the enemy force.

To seek out the enemy's sweat,

the army approaches General Electric.

They're already building chemical detectors

to trace the exhaust fumes of enemy submarines.

Now they're given this new mission.

Technicians at General Electric come up

with a scent sensor they call

the XM-2 Man Packed Personnel Detector.

The troops will call it something simpler--

the People Sniffer.

The XM-2 is meant to be carried

on a GI's back like a backpack.

It has a tube that attaches to the muzzle

of a soldier's weapon with a probe that sucks in air.

The air passes over hydrochloric acid.

If there's ammonia present, the acid reacts with it.

This will be turned into a beeping sound

in the operator's earphones.

The gadget is basically an alarm bell that tells you,

hey, just so you know, I can smell that the enemy

is pretty close right now.

In August 1965, 200 People Sniffers are sent

to Vietnam for field testing.

But the jungle is a big leap from the laboratory.

The field results are mixed at best.

The XM-2 does work sometimes.

But it doesn't have much range, 300 yards at most.

And even worse, if the wind shifts

and blows back at you...

You'll get a false positive from your own sweat.

But the U.S. Army doesn't shut down

the People Sniffer project.

Instead, they double down on the technology,

only this time, they send it into the sky.

The army realizes that ammonia

is lighter than air, and it always rises,

so they decide to put the sniffer on a helicopter.

The result is the Airborne Personnel Detector.

They lengthen the probe so it hangs

outside the aircraft.

Plus, they put two XM-3s in each aircraft

so they can double their sniff power.

This sniffer bird flies low and fast,

maybe 50 feet over the trees.

When it gets a hit, the operator

radios in the location, then they call in the cavalry.

In the fall of 1967,

this unusual new gadget

suddenly faces a make-or-break test.

U.S. intelligence reports rumors

of an ominous buildup of North Vietnamese troops

near a strategic outpost called Dak To.

Dak To is home to a critical camp

where the CIA train civilian militias.

The U.S. suspects that a major offensive on Dak To is coming.

They need to confirm whether this force of VC

is really hiding in the jungle.

This crucial mission is given

to the Airborne People Sniffer.

So the Sniffer helicopter is flying

perpendicular to the wind, just above the tree tops.

You have an operator.

He detects at first a faint beep.

The beep continues to get louder.

The aircraft sweeps back around to the area

where they detected the beep to begin with,

and it gets louder and louder and louder,

and they finally realize, we're on to something here.

It's ammonia. This must be thousands of men.

This is exactly the confirmation

Command has been waiting for.

Thanks to the People Sniffer,

the U.S. launches a massive preemptive strike

on Viet Cong positions outside Dak To...

Safeguarding their critical base.

But this battle will be the Sniffer's high point.

The enemy soon learns how to deceive it.

The North Vietnamese come up with a way

to mislead that flying Sniffer, by hanging buckets of mud

and urine in the trees to create false positives,

ultimately sending the Americans on wild goose chases

to empty patches of jungle.

Outwitted by buckets of waste,

the People Sniffer fades from use.

Its full story remains a secret for decades,

until 2000, when a review of the project

is declassified, finally revealing the strange history

of a gadget that used classroom chemistry

to fight jungle warfare.

From aircraft carriers made from solid ice

to helicopters that don't make a sound.

When it comes to governments' battle for supremacy,

no technology is off-limits.

But even their most closely guarded inventions

can't stay hidden forever.