All language subtitles for Cracking.The.Code.S01E06.720p.AMZN.WEB-DL.DDP2.0.H.264-Kitsune.[eng]

- [Narrator] The race
for the ultimate weapon.

- Literally the
future of the world

was hanging in the balance.

- [Narrator] To stay
ahead of the Soviets,

American codebreakers
must do the impossible.

- All the computers
working for a billion years

would not be able to
break that cipher.

- [Narrator] What they achieve
reveals a shocking truth.

Soviet spies infiltrating
America's most top
secret project.

- The Soviets have
gained enough information

to build their own atom bomb.

- [Narrator] The US government.

- There is a leak at
the very highest level.

- [Narrator] And even
the upper echelons

of the British establishment.

- Were you, in
fact, the third man?

- It's a story that's
stranger than any spy thriller

and the stakes couldn't
possibly be higher.

- [Announcer] Two, one.

[bomb explodes]

- [Narrator] These are the
codes that changed our world.

Bizarre markings,

random letters,

and numbers,

words that make no sense,

but cracking them
unlocks military secrets,

decodes ancient civilizations,

and reveals enemies
in our midst.

Now we uncover how
they were decoded,

the genius minds
that broke them,

and the secrets they reveal.

1943.

In World War II,
the tide has turned.

The Nazis are
heading for defeat.

In November,

the Allies meet to discuss
the conflict's final stages,

but theirs is an
uneasy alliance.

- The Soviet Union and America
were allied in World War II,

but Stalin is known
for his brutality,

his mercilessness,

and the Americans have
no illusions about

what's gonna happen
when the war is over,

that it's all going
to be tra-la-la,

and rainbows, and happiness.

- [Narrator] Fearing the
Soviet Union may emerge

from World War II as a
superpower to rival America,

the US needs to know
what Stalin is planning

and stay one step ahead.

- This is just like
a game of poker.

If you know your opponent's
cards that he's holding,

well, it certainly gives
you a real advantage.

- [Narrator] But the Soviets
are keeping their cards

close to their chest.

So US intelligence chiefs
have little way of finding out

what they know.

In desperation,

they turn to an
ever growing pile

of encrypted Soviet telegrams

being collected in a back room

of the Army's Signal
Intelligence Service HQ

in Arlington, Virginia.

Thousands upon thousands
of pieces of paper

covered in strings of letters

arranged in seemingly
meaningless groups of five.

- So after Pearl Harbor,

as part of a massive
intelligence effort,

the US government requires
telegraph companies

to turn over to them

every single telegraphic message

sent by a foreign
power either to

or from the United States.

And one of the results is they
end up with this stockpile

of encrypted diplomatic messages

passing between Soviet
diplomats in America

and their counterparts
in Russia.

- [Narrator] In the hope
these diplomatic telegrams

contain information about
Stalin's post-war ambitions,

US intelligence sets up a
project to investigate them,

a project called Venona.

The operation is top secret,

but US intelligence is
playing a dangerous game.

If the Soviets discover
the US is spying on them

before Germany is defeated,

it could jeopardize
their alliance

and risk turning the
war in the Nazis' favor.

So no one can know that
Venona Project exists.

- Even the president
doesn't know about it.

Just the whole goal is that

you don't want to tip your hand.

You don't want the Soviets
who are your ostensible allies

to know that you're
spying on them.

- [Narrator] But the pile of
encrypted messages is growing

by at least 4,000 new
telegrams each week.

The Venona Project
urgently needs manpower,

but America's men are
away fighting the war.

So the Army turns to
the nation's women.

They'll make up 90% of
the Venona Project staff,

and almost all of them are new
to the art of code breaking.

- So they came to
Arlington Hall,

the messages keep on pouring in,

and they would look at these
and try to make sense of it,

but it was overwhelming.

- [Narrator] What secrets
do these telegrams conceal

and what can they reveal
about Stalin's ambitions?

The first step is easy.

The letters are actually numbers

and the codebreakers know this

because the messages only
ever feature 10 letters

rather than the full alphabet.

This is because the telegrams
have been sent as Morse code

via regular commercial
cable companies,

which require numbers to
be converted into letters.

Using a standard and widely
available conversion table,

the letters can be
quickly converted

into their original form.

Then comes the hard part.

The novice codebreakers
must then scour

the strings of numbers
for a clue, however small,

that will help them
crack the Soviet code.

- They're looking for the
merest hint of a repetition,

the merest hint of
a shape or structure

that will allow them to
unravel the whole message.

- [Narrator] But
there's nothing,

because the Soviets have
hidden their secrets

behind not one,

but two layers of encryption.

- What the Russians
have done is, in effect,

locked the door once,

and they lock it again,

and then they
throw away the key.

So you can never break it.

- [Narrator] First, the
Soviets encode the messages

with a standard issue
intelligence service code book.

- A code is something
that involves meaning,

you take one word and
you substitute another.

- [Narrator] In the code book,

every word is assigned a
unique four digit number.

So for example,

the unique code word
or number "Moscow"

might be 3-2-1-4.

But then the Soviets
make it yet more complex

by adding a second
layer of security,

a cipher.

Unlike a code in which
entire words are replaced

by alternative words or numbers,

with a cipher,
individual characters,

whether they're
letters or numbers,

are changed.

In a commonly used cipher,

one might be
substituted for three,

three for five,

six for eight.

Each time the numbers have
been moved along two digits.

- We're looking a recipe,

an algorithm, a system,

and every recipe in every
system leads to a pattern.

And that's what codebreakers
are looking for.

- [Narrator] But
the Soviet messages

show no signs of a pattern

because they've been encrypted

using a far more
sophisticated cipher,

known as a one-time pad.

- The one-time pad is the
greatest encryption system

in the world ever,

forever,

because it doesn't give any
patterns in the resulting text.

- [Narrator] The
Soviet one-time pads

consist of sheets filled
with five digit numbers.

These have been
randomly generated,

meaning they contain no
trace of a pattern or system.

The random numbers are added to

the already encoded
number groups.

- See, if I'm adding
something that has no pattern,

then the result will
have no pattern.

And if the result
has no pattern,

there's no way I
can decipher it.

- [Narrator] The only way
to decrypt each message

is with a duplicate
of the same page

from an identical one-time pad.

- The strength of this
code relies entirely

on the fact that you and
I are the only two people

that have that
sequence of numbers.

And it relies on the fact that

we only ever use
that sequence once.

- [Narrator] To make the
message even more secure,

the page from the
one-time pad is destroyed

as soon as the message
has been encrypted.

And the only duplicate page

at the receiving
end is destroyed

as soon as the message
has been decrypted.

- And that's it.

If you don't have those
pieces of information,

you really can't break the code.

- [Narrator] Faced with a
seemingly uncrackable code,

US intelligence has no way
of knowing what secrets,

if any, these messages contain.

But the fact they've been
encrypted with a one-time pad

strongly suggests espionage,

because the one-time
pad was a key component

of Soviet spycraft.

- [Film Narrator] Perhaps
there is no better proof

of the steady intensity
of the Soviet offensive

against the security
of the United States.

- [Narrator] In 1953,

a similar single use
Soviet code surfaced

in the unlikely setting
of a Brooklyn sidewalk.

- [Film Narrator] A young
news boy had just finished

the weekly collections
from his paper route,

a five cent piece
slipped out of his hand

to the pavement.

He was astonished
at what he saw.

The nickel had split
into two equal segments.

- [Narrator] On
closer examination,

the FBI discovered
a minuscule hole

in the R of the word "trust,"

drilled so a fine
needle could be used

to force the nickel open.

- Somebody obviously
went to a lot of work

to engineer this nickel.

- [Narrator] Inside the coin
was a tiny piece of microfilm

covered with microscopic columns

of neatly typed
five digit numbers.

- This looks strikingly similar

to the one-time pad code

that was used by the
Soviets in the 1940s.

The evidence certainly
pointed to Soviet espionage.

- [Narrator] But with nothing
to compare the numbers with

the message proved
impossible to decode.

It would take another four years

to confirm the FBI's suspicions,

when a former Soviet spy,
called Reino Hayhanen,

defected to the west.

- Apparently, Hayhanen
had been given this coin

when he was first
deployed in New York,

but he showed himself to be
something less than a master spy

because he
accidentally spent it.

And so this nickel with
microfilm inside of it

went into the
general circulation

and was passed from hand to
hand for who knows how long

before that news boy
happened to break it open.

- [Narrator] Heyhanen
revealed to US intelligence

how the coded message
was deciphered.

- The irony is the message
wasn't really that important.

It was basically
a welcome message

with a few basic instructions
for how to get started.

- [Narrator] A decade before

the news boy found
the hollow nickel,

the Venona codebreakers
aren't so lucky.

They have the coded
messages, thousands of them,

but no Soviet defector
to help unlock them.

And without the specific page
used to encrypt each message,

there's no math and no
technology in existence

that can unlock the value

of these randomly
generated numbers.

The only way for
the codebreakers to
crack the secret code

is if someone on the Soviet
side makes a mistake.

- A one-time pad can be broken

if it becomes a two time pad.

If you reuse one,

then things are
no longer random.

- [Narrator] The Venona
team has already analyzed

thousands of messages.

They haven't spotted
a single mistake,

but they have to keep looking

because it's becoming clear
there's far more at stake

than the balance of
power in postwar Europe.

The future of the world itself

may depend on unlocking
these numbers.

[bomb explodes]

A year before the
start of World War II,

German scientists Otto
Han and Fritz Strassmann

set in motion a chain of events

that will change
the world forever.

- They do something
that is going to

eventually make history.

They split the atom.

- [Narrator] The
splitting of one atom

produces around 200
million times more energy

than a traditional fuel
source, such as coal.

In theory, this vast
new source of power

could be harnessed to produce
a weapon unlike any other.

It's an idea that soon
attracts the attention

of both superpowers,

America and the Soviet Union.

- Everyone knew this
was the technology

that held power in
the post-war world.

And so the nuclear race was on.

- [Narrator] Eight months after
the attack on Pearl Harbor,

President Roosevelt tasks
his most brilliant scientists

with creating an atomic
bomb for America.

The Manhattan Project.

- Roosevelt authorizes
the single largest,

most expensive,

and most complex secret
scientific military project

in history.

- [Narrator] America and
Russia are still allies

in the fight against
Hitler and Japan.

But the US government
knows that an atom bomb

will give America the upper
hand in the post-war world.

And they know Stalin will
be thinking the same.

- The American
government considers it

a matter of highest urgency

to find out just how far
the Soviets have progressed,

just how much
knowledge they have,

and what their goals are.

- [Narrator] Knowing
what the Soviets know

will allow America to stay
one step ahead of Stalin

and potentially save the
world from nuclear war.

- It's hard to
think of anything,

any conflict where the
stakes have been higher.

Literally the
future of the world

was hanging in the balance.

- [Narrator] While
the top secret

Manhattan Project
scientists conduct tests

in the New Mexico desert,

pressure is mounting on the
equally top secret Venona team

to find out whether there's a
similar Soviet atomic project.

A clue comes not from
Moscow or Washington,

but from the distant past.

Two and a half
thousand years ago

in the ancient city of
Persepolis in modern day Iran,

royal scribes developed
a fiendishly complex

written language known
as old Persian cuneiform.

Archaeologist, and now
Venona codebreaker,

Richard Hallock,

has spent years decoding
these ancient inscriptions,

searching for patterns
and repetitions.

This gives him an eye for detail

and an idea.

- The diplomatic military
messages that were conveyed

during the Persian empire,

it had a particular form,

there was a salutation at
the beginning of the message

and a sign off signaling
the end of the message.

- [Narrator] Hallock
wonders if the Soviets,

just like the ancient Persians,

are using a standard phrase
to start their messages.

- If that was true, that
would give them a big leg up.

- [Narrator] In an age
before digital computing,

comparing the opening
numbers of all the messages

in search of repetitions
will take years,

perhaps even decades,

with no guarantee
of finding anything.

So the team turned to one of
the few pieces of technology

at their disposal.

- They put all the pages,
thousands of pages,

into a primitive IBM computer.

- [Narrator] These mechanical
punch card data processors

are widely used in
government and business

to collate and sift information.

Each machine can process at
least 250 cards per minute,

which makes them perfect
for testing Hallock's hunch.

If the one-time pad protocol
has been followed correctly,

then no five digit number will
occur in the same position

in two messages.

But that's not what the
punch card machines reveal.

The machines sift
through the cards,

finding messages with
the same initial digit,

then the same two digits,

three digits,

until pairs of messages remain,

each pair beginning with the
exact same five digit number.

- They crunch the
numbers on this

and they decide that
it's something like

a billion to one chance
that this is just random.

They're onto something here.

- [Narrator] Hallock's
hunch is correct.

The Soviets begin each message

with the first five digit
number from a one-time pad page.

This tells the recipient
who has an identical pad,

which page to use to
decode the message.

Because it comes from
a unique one-time pad,

which is destroyed after use,

this number should
never appear again.

But the Venona
team has discovered

the same number
appears more than once.

There's only one explanation.

The same one-time pad
page has been used

to encrypt two
different messages.

Someone on the Soviet
side has broken protocol

and made a mistake.

- The factory in
the Soviet Union

who made the one-time pads,

for whatever reason,

made a whole set with the
same groups of numbers.

So instead of just having two
duplicate pads being used,

a number of messages come
using the same sets of numbers.

- Often it's little mistakes
that give codebreakers

that chink in the armor
that gets them in,

that gets them started.

- [Narrator] The Venona
team runs more cards

through the machines
and gets more hits.

A lot more hits.

In total, more than 35,000
messages have been created

with duplicate one-time pads.

It's the human error the Venona
team has been hoping for.

- An impossible mission has
suddenly become possible.

We can crack this code.

We can get rid of
the encipherment.

- [Narrator] Now the
Venona team can try

one of the most
reliable techniques

in the codebreaking arsenal,

a brute force attack.

- The brute force attack
means you just try everything.

So imagine you've got a bicycle
padlock with three wheels

and each wheel runs
from zero to nine.

You could create all the
numbers from 0-0-0 to 9-9-9.

So you've got a thousand
combinations there.

Sooner or later you'll
find the right combination.

So a brute force attack
would be trying out

every single one of those
thousand combinations.

- [Narrator] Find the
correct combination

and the bicycle lock will open.

But if the Venona
codebreakers do stumble across

the correct numbers,

how will they know
they found them?

- A codebreaker is
faced with gobbledegook

and apparently random
series of letters

or symbols or numbers.

And what they're looking for

is some clue to the
underlying structure

or some clue to the
underlying meaning.

- [Narrator] The
different messages

enciphered with the same
pad could contain that clue.

If the original messages
contain some of the same words,

for example, "Moscow,"

then a brute force attack
on the cipher layer

should reveal the matching
code number for "Moscow."

The codebreakers won't
know these numbers

represent that specific word,

but the more often
these numbers appear

in a brute force attack,

the greater the chance

they're the correct
Soviet code numbers.

- They can start finding
repetitions, patterns,

and start narrowing down the
range of options in the code.

- You can take the encipherment
apart brick by brick.

It's no longer an
impossible wall to scale.

- [Narrator] Through
trial, error,

and educated guesswork,

the codebreakers
remove fragments

of the one-time pad cipher,

only to find another
wall behind it.

- They've gotten to
the underlying code,

but that's still a code
they need to break.

They know those numbers
represent words,

but to figure out
what those words are,

they really need a code book.

- [Narrator] Without
a Soviet code book

all the Venona team's hard
work will be for nothing

and Stalin's atomic research
will remain a mystery,

which is a major problem

because America is about
to raise the stakes.

On August 6th, 1945,

America detonates an atomic bomb

in the skies above the
Japanese city of Hiroshima.

- The first bomb
kills 140,000 people.

Many of them
vaporized instantly,

others dying lingering deaths
from radiation sickness.

- [Narrator] In a split
second of devastation,

America has proved it's capable
of making an atomic bomb.

- The dropping of the atom bomb

showed that America
was going to be

the world dominating power.

It had this weapon
that made them

immediately the most
powerful nation on earth.

- [Narrator] The war is over,

but without a common cause to
bind the superpowers together,

the former Allies are
rapidly becoming enemies,

opponents in a new Cold War.

Now more than ever,

the IS needs to know
the Soviets' game plan.

And the Venona team
believes it may have

the final piece of the puzzle

to crack Stalin's secret code.

It's come from the enemy
both countries were fighting

just months earlier.

- The Americans hear rumors that

there is a castle in Germany

that had been used
by Nazi intelligence,

where they've been listening
in to Soviet messages.

- [Narrator] Knowing this
could be a treasure trove

of intelligence,

in the waning months of the war,

America sent a top secret
team to investigate.

- The Germans lead them
down into the cellar

and they see boxes and boxes
and boxes of information

the Germans have
gathered during the war

in trying to break
Russian codes.

- It's a treasure trove,

including one of the things
that they wanted most of all.

- [Narrator] There among
the chaos is the holy grail.

The missing piece of the puzzle

that the Venona team
has been hoping for,

a Soviet code book.

But when the book arrives
at Arlington hall,

it's been badly burnt and worse,

it's out of date.

- So what does Venona
have at this point?

They have a code book,

but they're really still
at the base of the mountain

they have to climb.

- It doesn't give
any real answers.

It gives a sense of how
the Russian code book

would be assembled.

- [Narrator] After
two and a half years,

the Venona Project,
now 600 strong,

is still nowhere near decoding

the hundreds of thousands
of Soviet messages.

They have the charred code book,

but they're out of ideas.

- Once you've got rid
of the enciphering,

you still have to get
rid of the encoding.

And that's where a man
of true genius steps in.

His name is Meredith Gardner.

- [Narrator] In early 1946,

linguist Meredith Gardner
joins the Venona Project

and changes everything.

- Meredith Gardner was a loner.

He had grown up in a
boarding house in Texas

and started reading
foreign newspapers

the travelers would bring
into the boarding house.

He then goes on to the
University of Wisconsin

and gets his
doctorate in German.

By the time he's 23,

he's talking German, Russian,

Yiddish, Spanish,

he teaches himself Japanese,

he knows Sanskrit,

and he's recruited
to Arlington hall.

- [Narrator] Gardner
proposes something

seemingly impossible,

to reconstruct the
current Soviet code book

based on the charred,
out of date version.

- It's as if you had
a copy of Moby Dick

and you say, well, this is
what a novel looks like.

Now go write a novel.

- [Narrator] The
talented linguist

decides to start from scratch

and begins to work through the
partially deciphered messages

to see if something
has been missed.

Within weeks, he spots something

none of the Venona team
has noticed before.

- Gardner recognizes that
in a lot of these messages,

a five digit number
will appear in the text,

and then the same five
digit number will appear

a little bit later.

And this happens
over and over again.

What do these numbers represent?

- [Narrator] He suspects
the five digit numbers

are a signal to the reader
to do something different

when decoding the message.

- Since these messages
involve the United States,

there might be English words

that don't have an easy
Russian equivalent,

maybe names and places
and things like that.

Is it possible that this
five digit repetition

is some bit of code that says

we're switching to English now,

or, you know, switching
out of English now?

That's his hunch.

- [Narrator] As a linguist,

Gardner realizes the Russians
won't have an equivalent

for many English names.

So the chances are they
won't have a code number

for those names either.

- So they have to break
down English words

into something simpler,

some system of substituting
certain numbers

for certain letters

in order to spell out the words

that aren't in their code book.

So that's a chink in the armor.

That's a way to
get into the code

without having the
code book in hand.

- [Narrator] Letter
by painstaking letter,

the Venona team
concentrates on identifying

the English words spelled
out within the messages.

- And if they could
find a familiar word

or maybe a noun
followed by a verb,

they could start
making educated guesses

as to what those
things might be.

The odds are if it's
a diplomatic cable,

you might have a word
like Washington DC,

or President Truman,

or other phrases
that you would think

the Soviets would
be concerned about.

They're probably not talking
about the latest Broadway play.

- [Narrator] It's a
process of guesswork,

trial, and error.

- It's an incredibly
complex kind of

linguistic crossword puzzle

that requires a deep
understanding of language

and how it works

as well as the
principles of encryption.

- [Narrator] Three years after
the Venona Project began,

Meredith Gardner is
finally able to decode

fragments of a Soviet telegram.

Against all the odds,

the Venona Project has achieved

its seemingly impossible goal.

And what the code
breaking team uncovers

from this first
telegram is disturbing.

The telegram had been
sent two years earlier

from New York to Moscow.

It contained thoughts
on the potential success

of President Roosevelt in the
1944 presidential election.

- What's shocking to Gardner is

this message isn't about trade,

it's about American politics,

and it seems to have been
sent by an English speaker.

Is there a spy or spies working
in the American government

and using this
Soviet code system

to send messages back to Moscow?

- [Narrator] The first
telegram is just the beginning,

as Gardner and the team
slowly tease out words

from one telegram after another,

their findings are explosive.

- By focusing on the English
components of these messages,

Gardner is coming up with lists
of English names and phrases

that are appearing multiple
times in these messages.

- [Narrator] Many of these
names belong to the scientists

working on America's top
secret atomic bomb program,

the Manhattan Project.

- Their identities
were classified.

They were all closely
watched and supervised.

They did not communicate
anything about their project

to the outside world.

They didn't even tell
their own families

what they were working on.

- [Narrator] There's only one
way the Soviets could know

the scientists' names.

They must have been leaked

from within the
Manhattan Project.

- The United States
government realized

that the Soviets have
spies working in America

and these spies have
not only discovered

the existence of the
Manhattan Project,

this program to manufacture
an atomic weapon,

but they've penetrated it,

and they've stolen secrets.

- [Narrator] Stalin is the
last person on the planet

who should have
access to information

from inside the top
secret Manhattan Project.

But if Gardner's
decoding is correct,

he's been receiving reports

about America's atomic bomb
program since at least 1942.

- It becomes clear that
the Soviets have gained

enough information to
build their own atom bomb.

[bomb explodes]

- [Narrator] But what
kind of atom bomb?

- The Americans were hard at
work at nuclear weapon 2.0,

the big boom.

The hydrogen fusion bomb,

an exponential scale up in
the power of these weapons.

- If Stalin were able to get
his hands on a hydrogen bomb

before the US,

it would be a
complete game changer.

Even if the weapon
was never used,

if Stalin was able
to threaten the west

with the potential
of a hydrogen bomb,

the Cold War would
effectively be over

and the Soviet
Union would've won.

- [Narrator] The only way to
discover what the Russians know

is to identify the spies
who leaked the information

from inside the
Manhattan Project.

- As Gardner begins to
unbutton the messages,

he enters into a whole
new world of intrigue.

He sees references to
various Soviet agents.

Their names are not revealed,

but their code names are.

He uncovers names like "Rest,"

or "Goose,"

or "Antenna,"

or "Liberal,"

and then Gardner has to try
to identify who is Rest,

who is Liberal,

who is Antenna.

- [Narrator] No longer just
a fact finding mission,

the Venona Project
becomes a man hunt.

- Now, the FBI working
with the codebreakers

at Arlington Hall,

have to form a team to track
down these Russian agents

already embedded and
hiding in America.

- [Narrator] By 1949,

it becomes clear that one
Soviet agent in particular

has given critically important
secrets to the Soviets,

a spy known as Rest,

and in later
messages, as Charles.

- This code name
will start appearing

again and again in
these transmissions.

And many of them associated
with the research

that's going on in Los Alamos.

- [Narrator] But these
code names only appear

in messages sent up to 1945.

After that, the
Soviets stopped using

the duplicate one-time pads

and the messages become
unreadable once again.

In the intervening four years,

the spy could have
continued to share

America's most closely
guarded secrets,

including research into
the next generation

of atomic weapons.

The race is on to find
Rest and stop him,

if it's not already too late.

- Gardner's team decrypts
a partial telegram

that reveals that he is
a resident of the island,

which is the code for Britain.

So that narrows the
field considerably.

- [Narrator] Rest, AKA Charles,

must be one of the
15 British scientists

employed in key positions
within the Manhattan Project.

- Bit by bit,

they're able to figure
out from other messages

that Rest had a sister

who was here in America,
in Massachusetts.

So now they know it's
a British scientist

who has a sister
in Massachusetts.

- [Narrator] Only one of the
Manhattan Project scientists

ticks both these boxes,

senior theoretical
physicist Klaus Fuchs.

- It turns out that Fuchs
has been feeding the Soviets

all kinds of information

from how much plutonium
they'll need for the project,

to various design specs,

technical information.

A lot of the essential
pieces of the puzzle

they'll need to
assemble their own bomb.

- [Narrator] Confronted
with the accusation,

Fuchs confesses and spends
nine years in prison.

But he wasn't acting alone.

Letter by letter,

message by message,

the Venona codebreakers
untangle an entire web of spies

centered on the
Manhattan Project.

Caliber is David Greenglass,

a machinist at Los Alamos.

Liberal and Antenna
are code names

for Greenglass' brother-in-law,
Julius Rosenberg.

Goose is chemist Harry Gold.

MLAD, physicist Theodore Hall.

Many of the spies are motivated

not by an ideological
attachment to communism,

but by a belief that
the world will be safer

if both superpowers
have an atomic bomb.

And most of them
never face justice.

- Because Venona
was still so secret,

they have no evidence
they can offer in court.

They couldn't afford to
let the Russians know

that they were unraveling
all their secrets.

That would've been
immensely compromising

for ongoing intelligence.

- [Narrator] Around
200 other spies

mentioned in the Soviet cables

remain unidentified to this day.

The only spies to face
the most severe punishment

are perhaps two of
the least significant,

Julius Rosenberg
and his wife, Ethel.

- Julius was a recruiter and
also a courier for information.

His wife, Ethel,

she was nowhere near as involved

and probably really only
typed up information.

But regardless,

they were both convicted
of treason and executed.

- [Narrator] After six
years of painstaking work

against overwhelming odds,

Venona's codebreakers
have fixed the leak

in the Manhattan Project.

Only to find a deeper,
more dangerous leak.

And this one comes direct
from the heart of power

in Washington, DC.

- Among the messages
that Venona uncovers

is a verbatim
record of a telegram

that's gone directly
from Churchill

to the American president.

- [Narrator] The telegram had
been sent in September, 1944,

at a time when communication
between the wartime leaders

was more closely
guarded than ever.

And yet here, deep inside
the corridors of power,

a Soviet agent saw and
copied the message.

- What it shows is
that there is a leak

at the very highest levels

in either the British or
the American establishment,

or in both.

- [Narrator] That leak was
an agent code named Homer,

and he was a prolific
and committed spy.

The Venona
codebreakers discovered

that between 1944 and 1945,

he sent at least 12
messages to Moscow,

all revealing highly classified,

politically sensitive
information.

- If this spy is still active,

information might
still be leaked

about the highest
level of activity

in the scientific and military
establishment to the Soviets.

And worst of all,

specific technical information

about this devastating
new weapon,

the hydrogen bomb,

might fall into Soviet hands.

- [Narrator] As the
Venona team decodes

more of Homer's messages,

it becomes clear that when
the telegrams were sent

five years earlier,

the spy was working
inside the British embassy

in Washington, DC.

- The FBI narrowed down
the possible people

who might have
seen this telegram

to about 6,000 people.

Then they start to think

who might have
communist sympathies,

who might be the
likeliest suspects

to have had a motive

to want to send this top
secret document back to Moscow?

- [Narrator] Enter the man
trusted with finding the spy.

In September, 1949,

high ranking British
diplomat, Kim Philby,

arrives in Washington.

To identify Homer,

Philby gains the confidence
of his colleagues

in the British embassy,

the Venona Project,

and the FBI.

- Philby is very charming,
very well dressed,

a marvelous storyteller.

Everyone liked him.

Everyone trusted him.

- [Narrator] And
that is a disaster

for British and
American intelligence,

because unknown to his
employers and colleagues

on either side of the Atlantic,

Kim Philby is the Soviet agent.

- He is actually
protecting the very people

he's meant to be exposing in
the British establishment.

- [Narrator] In Washington's
British embassy,

Philby finds himself
walking a fine line.

On the one hand,

he has to be seen to
be hunting for the spy.

On the other,

he's working to protect
that same spy's identity.

Philby is above suspicion.

He has unrestricted access to
Washington's political elite,

to the FBI investigation,

and to the Venona Project.

- He's walking their halls.

He's sitting in meetings
with Meredith Gardner.

He's learning everything about
what they're discovering.

And so, in a sense,

the fox is really
in the henhouse,

but no one knows he's a Fox.

- [Narrator] But this fox
is about to run out of luck.

In the spring of 1951,

cryptological genius,
Meredith Gardner,

uncovers the clue that
finally unmasks Homer.

- The words he decodes are
"Homer will be visiting tyre,"

which was the code for New York,

"monthly to visit
his pregnant wife."

- [Narrator] The authorities
narrow their list of suspects

to embassy employees
who had a pregnant wife

in New York in 1945.

- The list is a very short one.

Donald Maclean,

who had been the first secretary
to the British ambassador.

- Donald Maclean is the
high flying diplomat

of his generation.

When he goes to Washington,
he's only 31 years old,

and yet he's a first secretary
in the Washington embassy,

the biggest embassy of all.

So he's very much
going to the top.

- [Narrator] Maclean operates

at the highest level
of security clearance.

- He is the British
representative

on the most secret
committee of all,

which is the Atomic Energy
Authorities Committee.

- [Narrator] But Philby
already knew all of this.

In fact, he knew
Homer's identity

from the moment he was
assigned to unmask him.

- Kim Philby recruited
Maclean in 1933

when they both left Cambridge.

- [Narrator] At
Cambridge University,

both men had developed
a deep seated belief

in the communist cause.

- So as soon as Philby
is shown the paperwork

that says Homer is
one of these spies,

it doesn't take
him long to realize

that Maclean is the spy
they're looking for.

Kim Philby is the
instigator of everything

that's happened to Maclean.

- [Narrator] Before Maclean
can be interrogated,

Philby tips him off.

Maclean defects to Moscow

along with another
British diplomat,

his friend from Cambridge
and fellow Soviet spy,

Guy Burgess.

- It becomes front page news.

The diplomats are missing
and all hell breaks loose.

- Were you in fact,
the third man?

- No, I was not.

- [Narrator] The finger
points at Philby,

but because he wasn't
stationed in the US

when the Venona
messages were sent,

there's no evidence against him.

But his close association
with Maclean and Burgess

leaves him disgraced.

He's forced to resign from
the British foreign office

and no longer able to
spy for the Soviets.

The Venona Project
codebreakers have succeeded

in neutralizing perhaps
the most dangerous spies

ever to threaten
the United States.

Without their painstaking work,

Maclean, Philby, and
their associates,

together with the atomic spies
of the Manhattan Project,

would have continued
to share America's

most closely guarded secrets

and Stalin may have
won the Cold War.

Instead, on November 1st, 1952,

on a remote Pacific atoll,

America detonates the
world's first hydrogen bomb.

[bomb explodes]

Stalin loses the race to
develop the hydrogen bomb.

He dies four months later

and under his successor,
Nikita Khrushchev,

US-Soviet relations
begin to thaw.

- A lot of US atomic secrets
did leak to the Soviets,

but the Venona Project
helped throw a wrench

in that process

and prevented Stalin
from getting his hands

on a hydrogen bomb before
the US had developed its own.

- If Stalin had had
the hydrogen bomb,

would it have made
it more war likely?

Who knows.

But the world would've
been a less stable place,

that's for sure.

- [Narrator] The Venona
Project continues until 1980,

when US intelligence
officials decide

there's nothing
more to be gleaned

from the Soviets wartime cables.

- The files were all
packed away and stored

at the National
Security Agency's
headquarters in Maryland.

And everyone involved
maintained this vow of secrecy

that they'd been working
under their whole lives

at that point.

- [Narrator] It's not until 1995

that a handful of
documents are declassified.

- This information
was so important,

deadly important,

that it's only today
we are beginning

to piece together this story.

- [Narrator] The Venona Project
reshaped the post-war world.

Its codebreakers,
mathematicians, linguists,

and administrators,
most of them women,

most of them unknown and unsung,

made the world a safer place.

- In the wars of
the 20th century,

and especially the Cold War,

some of the most important
battles were fought

behind the scenes by
these codebreakers

and much of their work,

work that, in some ways, was
pivotal in saving civilization,

was never acknowledged
in their time.

These secrets were so deep that
they were kept for decades.

- [Narrator] Even today,

nearly 80 years after the
first novice codebreakers

began work at Arlington Hall,

the true significance
of their work

is still shrouded in mystery

because much of the
Venona Projects work

remains classified.

[exciting music]