Secrets Declassified with David Duchovny

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 front line 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.