All language subtitles for Cracking.The.Code.S01E03.720p.AMZN.WEB-DL.DDP2.0.H.264-Kitsune.[eng]

[bomb exploding]
[dramatic music]

- [Narrator] World War
II's war in the Pacific.

The battle for
supremacy will depend

on unraveling unbreakable
codes and ciphers.

- When they saw the
five number groups,

they were like, what is this?

- You don't know what it means.

And you've gotta find
a way of breaking it.

[propellors whirring]

- [Narrator] Two brilliant
minds go head to head.

Japan's most formidable
Naval strategist.

- Yamamoto's plan was to destroy
the American Pacific fleet.

- [Narrator] And a U.S. officer

with a penchant for crosswords.

- He was such a whiz at puzzles,

crossword puzzles,
number puzzles.

He could almost see
them intuitively.

- [Narrator] But can
codebreakers really stop

the Japanese onslaught

and turn the war
in America's favor?

- They need to crack JN-25.

[tense music]

- [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,

[gun firing]

and reveals enemies
in our midst.

Now we uncover how
they were decoded,

the genius minds
that broke them,

and the secrets they revealed.

[light music]

December 7th, 1941.

The Pacific islands of Hawaii.

[electronic beeping]
[ominous music]

Just after dawn, the
tranquility is shattered

as Japan launches
an all out attack

on the U.S. Naval
base at Pearl Harbor.

- Seven o'clock in the morning,
planes appeared overhead.

[propellors whirring]

Then the bombs exploded.

[bombs exploding]

[suspenseful music]

- The Japanese planes
sweep across the island,

strafing and bombing at will.

- There were eight
battleships in Pearl Harbor

on that morning.

Four were sunk outright,
four others badly damaged.

More than 2,400
Americans were killed

and many thousands more wounded.

[ominous music]

- [Narrator] The man
behind the surprise attack

is Japan's formidable
Admiral Yamamoto.

His aim, to clear the way for
Japan's Imperial expansion

throughout the Pacific region.

- The attack on Pearl Harbor

was not to conquer
the United States.

It was to knock the American
fleet out of the way

so they could gain
access to the resources

in the South Pacific.

- Japan is a heavily
industrialized nation,

but it's short on raw materials.

So by seizing these territories,

Japan is going to gain
the resources it needs

to build its military, to
build its industrial strength

in a way that would rival
that of even the greatest

of European nations.

[dramatic music]

- [Narrator] Four days
after the lethal strike,

America joins the war in Europe.

- This was completely unexpected
from the American side.

It was absolutely devastating.

This completely changed the
American mindset on the war.

- [Narrator] But on home soil,

concern is growing
that the attack

that crippled the U.S.
Navy is just the beginning.

Harvard graduate and master
poker player Yamamoto

knows his enemy and the
value of playing his cards

close to his chest.

- Might alone was not going
to defeat the Japanese.

Cryptographers working
in dusty offices

were gonna be just as crucial
to victory in the Pacific

as men and ships would be.

[propellors whirring]

- [Narrator] To make sure
his enemies stay in the dark,

Yamamoto has ensured all
military communication

is heavily encoded,

not once, but twice,

using a complex
and top secret code

known to Japan's
enemies as JN-25.

- All planning and
movement of operations

were done via JN-25.

That was the main
operational code.

Everybody had it.

- [Narrator] For months,

Allied intelligence
has been intercepting

Japanese JN-25 messages,

[electronic beeping]

but cracking the
complex super code

has so far proved impossible.

- The British had a
base in Singapore,

and they're listening
into the Japanese signals,

but they can't understand them.

- The Japanese Imperial
Navy thought JN-25

was utterly unbreakable.

[suspenseful music]

[cannon firing]

- [Narrator] Already
on the back foot

following Pearl Harbor,

unlocking Japan's secret code
is the only chance America has

of finding out what Admiral
Yamamoto's next move will be.

- They need to crack JN-25.

They need the crucial
strategic advantage

that being able to read
the Japanese coded signals

will give them.

[upbeat music]

- [Narrator] The
seemingly impossible
task of breaking JN-25

begins in a smoky,
windowless basement

at the Naval base in Pearl
Harbor, known as the Dungeon.

This is the nerve
center for the U.S. Navy

Signals Monitoring and
Cryptographic Intelligence Unit,

or Station Hypo.

Heading up the crack
American code breaking team

is Joseph Rochefort,

a Naval officer with a
penchant for crosswords.

- Now Rochefort was not
a Naval Academy graduate,

which perhaps to some
made a difference,

but he had been recommended
for the code section

by a commanding officer
early in his career

because of his innate
ability to solve puzzles.

He was such a whiz at puzzles.

He could almost see
them intuitively.

- [Narrator] Rochefort isn't
just a crossword genius.

He has a second killer skill.

He's a gifted linguist and
has a passion for Japan,

spending years studying the
country's language and culture.

[energetic music]

- His cultural understanding
of Japanese society

allowed him to see
things in these messages

that few others
might have discerned.

- [Narrator] But
in December, 1941,

Rochefort is facing one
of the toughest challenges

of his Navy career.

He has hand picked
the Hypo team,

not only for their
codebreaking skills,

but because, for all of them,
cracking JN-25 is personal.

- The cryptoanalysts who worked

in those air-conditioned
basement rooms at Station Hypo

were driven, by a sense,

to break the Japanese
operational code.

They knew that if they had
done so prior to December 7th,

it might have been possible
for them to give warning

of the pending Japanese attack.

And they Flad
themselves almost daily

for the fact that they
had been unable to do. So.

- They'd been in the
thick of it, so to speak,

because you know,
they were in Hawaii.

They had suffered
friends had died.

[dramatic music]

- They work literally around
the clock trying to find pieces

of information that would
allow them to warn their bosses

of the next Japanese initiative.

[soft music]

- [Narrator] It's a
monumental challenge.

But thankfully,
Rochefort and his team

aren't starting
completely from scratch.

For the past two years,
British codebreakers,

based at the Government
Code and Cipher School

at Bletchley Park
just outside London

have been intercepting
Japanese Naval communications.

The result is pages and pages
of apparently random sequences

of five digit numbers.

[electronic beeping]

- When they saw the
five number groups,

they were like, what is this?

That's the hardest
thing in cryptoanalysis

is solving the system.

When you're faced
with nothing but pages

of five digit numeral groups.

[tense music]

- [Narrator] Hunting
for a way to understand

how the encryption worked,

British codebreakers
began the mammoth task

of gathering and
analyzing every message

that had been intercepted.

- The first requisite is to
accumulate enough traffic,

enough messages, where you
can start to see patterns.

Am I looking for
repeats and groups

that tells me that somehow
these things are related.

- [Narrator] Getting hold
of the JN-25 messages

was the easy part.

- All navies use
radio transmissions

to communicate with
their fleets at sea.

Radio messages sent by the
Imperial High Command in Tokyo

out to the fleet were
sent by telegraph messages

in Morse code.

- [Narrator] What was
proving almost impossible

was working out what the
Japanese were sending

in Morse code.

The internationally recognized
communication system

works by breaking up words
into their individual letters.

But the Japanese language
doesn't use letters.

It uses logograms
and characters,

unique images and symbols that
represent words and syllables

rather than letters.

Because there are no letters,

in theory, Morse
code shouldn't work.

Yet thousands of messages
were being sent and received

by the Japanese Navy.

So how did JN-25 work?

The first breakthrough
came from Britain,

and one of Bletchley Park's
most extraordinary codebreakers.

- The first person to make
inroads into the JN-25 code

was Brigadier John Tilman.

He was a Scottish officer.

He was known as the Brig,

and he wore his army uniform
with tartan trousers.

He was quite a character.

He was also
absolutely brilliant.

[light music]

- [Narrator] Tiltman
was convinced

that each five digit number
stood for a different word,

but he discovered no
message ever contained

the same sequence
of numbers twice.

Tiltman realized that the fact
there weren't any repetitions

meant JN-25 must contain a
second layer of encryption.

- Tiltman works out it's
been additionally scrambled

with what called
additive numbers.

So groups of extra
numbers just put in

to confuse any
codebreaking attempts.

- [Narrator] That meant decoding
any message sent as JN-25

needed two books,

each one containing a
different set of numbers.

- One is a code book, which
translates words into numbers.

And one is a cipher book,

which is full of streams
of random numbers.

- [Narrator] Creating
a code in JN-25

was a two step process.

Firstly, the sender
would use the code book

to replace every word

with a corresponding
five digit number.

Then they would use the
cipher book to choose another

sequence of five digit numbers,

this time completely
random ones.

The random numbers
would then be added

to the original number to
superencipher the code.

And it's these numbers
that are then sent

by Japanese Morse code.

Although Tiltman had
discovered how the code worked

two years before the
attack on Pearl Harbor,

without a Japanese cipher book

to at least unscramble the
first layer of encryption,

it was impossible to make
sense of the messages.

[tense music]

In Hawaii in 1941,

John Tiltman's discovery
has given Joseph Rochefort

and his team a small head start
in the race to crack JN-25.

The other advantage
the U.S. codebreakers

have over their
British counterparts

is the sheer amount of
data now available to them,

because a surge in
Japanese military activity

means JN-25 coded messages
are now pouring in.

- The Japanese were
running almost rampant

in the Western Pacific.

[soldiers shouting]

- [Narrator] The fear
is that Admiral Yamamoto

is gearing up for
another big attack.

- Another devastating
unexpected loss

on the part of the
U.S. is very real.

- The Japanese were gobbling
up those resource bases

in the South Pacific,

and there was great fear in
America that they might extend

this even further,

that Australia might in
fact become a target,

that Hawaii itself
might be targeted.

[suspenseful music]
[gun firing]

- [Narrator] The
Japanese advance

is beginning to
look unstoppable.

The clock is ticking and
the pressure is on Rochefort

and is small team
of codebreakers

to find out what Yamamoto
is planning next.

[light music]

By early 1942, the team
in Hawaii is stuck.

They know how JN-25 works

and they have thousands
of messages to analyze.

But without the Japanese
Navy cipher book

to unlock the super code,

all they have are random
strings of numbers.

- You don't have the code book.

You don't have the cipher book.

You're starting with nothing.

- [Narrator] In desperation.

Rochefort decides to try to
reverse engineer the code.

[energetic music]

It makes sense the person
receiving the message

will need to know
how to first decrypt,

then decode the numbers.

[electronic beeping]

The codebreakers figure there
must be a clue in each message

guiding the receiver to the
correct numbers to start with.

But with so many
messages to analyze,

it's not humanly
possible to identify

which five digit number
is the all-important key.

- The Japanese saw how
complicated this was

and believed it all but
impossible for any eavesdropper

to break that code.

[cannon firing]
[dramatic music]

- While Rochefort and his
team battled to unlock JN-25,

the Japanese offensive
in the Pacific

continues to be relentless.

In the weeks since the
attack on Pearl Harbor,

Hong Kong and the American
controlled Philippines

have been invaded.

Singapore has fallen,

and the Japanese have taken
the U.S. Pacific Islands

of Wake and Guam.

The daunting result of
this aggressive offensive

is yet more encrypted messages
for Rochefort and his team

to work with.

- After the operations
on 7 December, 1941,

the volume of radio traffic
increases dramatically,

probably three, fourfold.

- The number of messages
sent down into the Dungeon

for analysis was staggering.

At least 500, sometimes
a thousand per day.

- [Narrator] The deluge of data
means Rochefort's small team

is now having to work
around the clock.

In desperation,

they turn to technology to
help process the information.

It's a decision that will give
them their first major break.

- The card sorting machines
were designed to find patterns

in the Japanese messages.

They didn't really
try to solve a problem

the way a computer
would solve a problem,

but they were a shortcut
for the cryptoanalysts

in trying to discern
patterns or repetitions.

- [Narrator] Using the sorting
machine is a game changer.

Rochefort's team begins
to spot the same sequence

of numbers appearing
time and again.

They suspect it's the
code that pinpoints

the start of the column of
numbers in the cipher book

used in the second
level of encryption.

Even better, it seems the
people coding the messages

are creatures of habit.

- Hypo starts to see a tendency

among Japanese radio operators

to begin their use of
additives in the same spot

on the same page very often.

For example, they would go
to the upper left hand corner

and begin with that
over and over again.

- The same sequence of
numbers from the cipher book

is being used repeatedly
to encrypt the numbers

from the code book.

[electronic beeping]

But frustratingly,

because they don't have
the all important code book

that converts
numbers into words,

they can only guess at
the original content
of the messages.

- You know what sort of
things might be there,

but you don't know
what's in that message.

[propellors whirring]

[dramatic music]

- [Narrator] By
late January, 1942,

the Japanese have taken Rabaul,

a vital natural
harbor in New Guinea.

The Australian mainland is
now under a very real threat

of attack.

But Rochefort's codebreakers
are still a long way

from cracking JN-25

and delivering the much
needed intelligence

that could stop the
Japanese offensive.

All they've got is
a set of numbers

that means nothing without
the right code book

to decode them.

- The JN-25 code book had 33,000

different possible
entries in it.

Putting that back together
was an immense task.

- It's now that
Joseph Rochefort,

linguist, crossword enthusiast,

and lover of Japanese
language and culture

comes into his own.

- The Japanese had a
very formal approach

to sending messages, and
very, very respectful.

[dramatic music]

- [Narrator] Rochefort
reckons this formal way

of communicating means
the same words and phrases

will be used time and again

in all naval communications.

[electronic beeping]

These presumed words,
also known as cribs,

can then be used as
a way of starting

the decryption process.

Using Rochefort's
intimate knowledge

of the Japanese language,

the codebreakers begin to
tentatively replace numbers

with words for the first time.

- John Rochefort could
look at set of code groups

and see some words
and he said, well,

this is what you would fit in,

here because it's
a naval context.

- If you can work out
what the context is,

then you can begin
to guess the content.

And then you begin to
rebuild the code book.

- [Narrator] After weeks
of painfully slow analysis

and guesswork,
Rochefort and his team

are beginning to
achieve the impossible.

[ominous music]
[soldiers shouting]

But they're struggling to keep
up with a Japanese onslaught.

By March, 1942,

the Japanese are advancing
relentlessly through Burma,

and Darwin in Northern Australia

has suffered a major airstrike.

As mainland Australia
begins to look

under serious
threat of invasion,

Rochefort scores his
first significant hit.

- In April, Hypo partially
decodes a message

indicating the Japanese have
dispatched a carrier group

to the South Pacific.

And a British intercept
reveals the Japanese

are moving two fleet carriers.

- [Narrator] The
messages reveal elements

of Admiral Yamamoto's next step

in his plan to conquer
the entire Pacific region.

He's calling it Operation MO,

and Rochefort's increasing
understanding of the super code

provides his team with
a possible target.

Rochefort is
convinced Operation MO

is the Japanese code
name for Port Moresby,

an allied controlled base north
of Australia on New Guinea.

- The Japanese used a
two letter indicator

for all geographical locations.

Then Rochefort kept
a careful record

of these geographical locators.

- [Narrator] Yamamoto's
intentions are
immediately clear.

Port Moresby is the
perfect launchpad

for a Japanese invasion
of Northeastern Australia.

- Port Moresby is a seaport

on the southern
edge of new Guinea.

- It has an airstrip.

It has a repair station.

It has sub docking facilities.

So it holds crucial
strategic importance.

- [Narrator] Taking the
poorly equipped garrison

at Port Moresby
should be a cakewalk

for the might of
the Imperial Navy.

But Yamamoto has no
idea that Rochefort

and his team of
Codebreakers are onto him.

- The Americans had found a way

to break into those
various layers of secrecy

and figure out what was
inside those messages.

[dramatic music]

- [Narrator] On the
basis of the intelligence

provided by Rochefort's team,

Admiral Nimitz, Commander in
Chief of the U.S. Pacific fleet

dispatches a battle
group of 26 vessels,

including the aircraft
carriers Lexington and Yorktown

towards Port Moresby
in the Coral Sea.

- It was a significant
risk for Nimitz to say,

I'm gonna send my two
carriers into the Coral Sea

to stop the Japanese.

And he wouldn't
have done it at all

but for the codebreaking
effort of Station Hypo.

- [Narrator] On May 3rd, 1942,

Yamamoto orders the
start of the operation

to take Port Moresby.

[propellors whirring]
[suspenseful music]

But the Americans
are waiting for him.

- The Battle of the Coral Sea

is a really crucial
naval engagement.

It's a carrier on carrier battle

fought largely by the
planes being launched

from those carriers.

[propellors whirring]

- Each carrier force sends an
airstrike to attack the other,

170 miles away roughly.

So the two fleets never
actually see one another.

[bombs exploding]

- [Narrator] During
the two day battle,

Japanese torpedoes and bombs

cripple the Lexington
beyond repair,

and they drop an
armor piercing bomb

deep in the Yorktown.

- The Japanese pilots
came back reporting

that they had sunk not
only the Lexington,

but also the Yorktown.

And the Yorktown
was badly damaged,

but it was not sunk.

It continued to be operational,

and was able to withdraw
under its own power

back to Pearl Harbor.

- [Narrator] The U.S.
may have taken a hit,

but Yamamoto's Imperial Navy
doesn't get off scott free.

[plane exploding]

He also loses a carrier.

And the fleet carrier
Shokaku is so badly damaged,

it's forced to limp
away from the battle.

[soft music]

Both sides retire to
lick their wounds.

But crucially, Port
Moresby is safe, for now.

- Technically it's a stalemate,

since both sides are
forced to withdraw

and neither can claim
decisive victory.

But it's kind of a morale
victory for the Americans

'cause it's the first
time they're able

to successfully resist an
incursion by the Japanese.

[somber music]

- [Narrator] The U.S. Navy was
only able to stop the attack

on Port Moresby thanks to
the codebreaking efforts

of Rochefort's team
back on Hawaii.

- This is the first
moment that the Japanese

were prevented from
doing something that
they wanted to do.

It's the turning point
in the Pacific War.

- [Narrator] Although
Rochefort and his team

are directly responsible for
slowing down Yamamoto's plans,

trouble is looming.

[tense music]

In Washington, DC.

the new head of Naval
intelligence, John Redman,

believes Rochefort
is a loose cannon

who ignores the
chain of command.

- Joe Rochefort was supposed
to send his information

to John Redman,

who would then come up with
operational suggestions

for Nimitz.

Instead of that,

Rochefort went straight
to Nimitz's headquarters.

And that left Redman
out of the loop.

- [Narrator] Rochefort's
unorthodox approach

is making enemies at home that
will come back to haunt him.

But right now he has a
bigger problem on his hands.

[foreboding music]

His team has intercepted
JN-25 messages

which seem to indicate
Yamamoto is gearing up again.

- As the Battle of the
Coral Sea was being fought,

Hypo, back in Hawaii, was
beginning to get messages

that suggested there
was going to be another

Japanese offensive, an even
bigger Japanese offensive.

- [Narrator] Rochefort's
team has spotted

another two letter location code

cropping up in
Japanese Navy messages

with increasing regularity.

- They begin to see
the references to AF,

that this engineering
unit is going to go to AF,

that this seaplane
reconnaissance unit

is going to be
transferred to AF.

And so they begin to see
this and they say, well,

where is this AF going to be?

- [Narrator] Worse, from
the sections of the messages

Rochefort and his team
are now able to decode,

there is the suggestion
that Admiral Yamamoto

is planning to hit
this mystery location

with one of the most deadly
naval assaults in history.

The problem is that AF
could be almost anywhere

in the Pacific.

- Is it going to be another
attack on Pearl Harbor?

Or perhaps even an assault
on the American west coast?

Are they gonna go for the
Aleutian Islands in Alaska?

There's a lot of ocean
and a lot of territory.

- [Narrator] But Rochefort
knows he's seen AF before.

- For months before
they even found it

in the message traffic,

he had a list of
geographical designators,

MO for Port Moresby,
RR for Rabaul,

so that when he
found one in a code,

he could understand probably
what it referred to.

- Rochefort is convinced
Yamamoto's next target, AF,

Is Midway Atoll.

[dramatic music]

Two tiny islands in the
middle of the Pacific ocean.

- On the map, it
doesn't look like much,

tiny fly speck in the middle
of the vast Pacific ocean.

But there's some crucial
facilities there.

- Those two islands post an
airfield and an anchorage.

So it had a certain
operational value.

So it is, as its name suggests,

kind of a midway stopping point
for transpacific airlines.

- [Narrator] Rochefort
immediately sees
how Midway Atoll

could be of strategic interest

to the Japanese Imperial Navy.

Despite previous warnings from
his new boss in Washington,

Rochefort once again
ignores the chain of command

and goes straight to the top.

- Rochefort reported to Nimitz

that the Japanese were
planning a major offensive

against Midway Atoll sometime
toward the end of May

or the beginning of June,
that it would have four,

possibly five carriers
plus battleships.

This was going to
be a major effort.

- [Narrator] Rochefort's
prediction is once
again the result

of JN-25 decrypts,
radio traffic data,

ship movements, and
his own gut instinct.

But in Washington, Rochefort's
new boss John Redman

is far from convinced
that AF is Midway Atoll.

- There was concern
that the Japanese

might try something else.

They might retry to
take Port Moresby.

They might try a second
attack on Pearl Harbor.

There were some who even
suspected that the target

might be the west coast
of the United States,

or even the Panama Canal.

- [Narrator] Redman thinks that
acting on Rochefort's hunch

is too big a gamble for the U.S.

If he's wrong,

diverting ships and manpower
to the middle of the Pacific

will leave other key U.S.
sites wide open to attack.

- Rochefort is thinking,
hey, Midway is the target.

It's that simple.

And Redmond says, well,

you don't have enough
evidence to convince me

that Midway is the target.

The Japanese could
be deceiving us.

- [Narrator] America
cannot afford

to get this decision wrong.

The clock is ticking on
another major Japanese attack,

and neither Rochefort nor
Redman will back down.

Then one of Rochefort's team
has a light bulb moment,

a bluff to flush out
more information.

- Why don't we send
a message to Midway

using the submarine cable,

so that it's not
intercepted by the Japanese,

to have Midway tell us by radio

that their salt water
evaporator has broken down

and that they're short
of fresh drinking water.

- [Narrator] If Japan is
planning on taking over Midway,

they'll know a working
desalination plant

to produce drinking water
from seawater is crucial.

Without it,

the base would be unable to
support an invading force.

- If you're gonna station
a Japanese force on Midway

and you don't have a
desalinization machine,

those people are all
going to die of thirst.

- [Narrator] If AF is Midway,

Rochefort knows
Japanese intelligence

will immediately
understand the problem

and will begin sending
out encrypted messages

warning Yamamoto's fleet
about the broken water plant.

And if that happens,

then intercepting and
decoding those messages

will confirm Rochefort's theory.

It's a devious plan, but
Admiral Nimitz likes it.

- The message goes
out into the air.

Then he waits.

[suspenseful music]

- [Narrator] It's 24 hours
before a response is picked up.

[dramatic music]

- Sure enough, the Japanese
intercept that radio message

and report back to Tokyo

that AF

is short of water.

There you are, smoking gun.

That proves to the skeptics
that AF is indeed Midway.

- [Narrator] It's
vindication for Rochefort.

But more importantly,

the decrypted messages
reveal yet more

of Admiral Yamamoto's
master plan

for control of the Pacific.

Midway isn't the main target.

It's a stepping stone
to a far bigger goal.

- Yamamoto's plan wasn't
so much to seize Midway,

although that was
part of the operation.

His main objective
was to destroy

the American Pacific fleet.

And specifically the
aircraft carriers.

- Yamamoto wanted to
get those carriers.

He never felt that he
could really control

the Western Pacific until
he could put those carriers

on the bottom of the ocean.

- [Narrator] Yamamoto is
gambling that Midway Atoll

is too important
for America to lose.

And once he's taken it,

he's banking on a swift
retaliation from the U.S. Navy.

- Midway had an anchorage,
it had an airfield.

It was a stopping off point
for American submarines

on their way to the
Western Pacific.

And Yamamoto hoped
that the Americans

would consider that it
had enough strategic value

to warrant their sending out
their carriers to fight for it.

- [Narrator] Yamamotos
plan is to ambush

the cream of the U.S. Navy,

taking it out of
action for good.

But its success relies
on total surprise.

He has no idea that
Rochefort's team

has begun to unravel JN-25.

They are now able to decrypt
up to 30% of every message.

Slowly but surely,

more and more words from
the Japanese code book

are being revealed.

But Rochefort and his
team can't afford to rest.

- Some of those who
receive the radio messages

sometimes work 12
hours on, 12 hours off.

The cryptoanalyst
down in the Dungeon

worked even longer
hours than that.

And if they were in
the middle of a message

that looked promising, they
might just continue working.

- [Narrator] Rochefort's
intelligence allows
the U.S. Navy

to prepare for Yamamoto's
surprise invasion.

But the codebreakers know
the inroads they've made

could disappear in a heartbeat

if the Imperial Navy decides
to change the JN-25 code book.

- If the new code book came in,

they would've had to
start from nothing again.

- [Narrator] But
Rochefort's team

is about to catch a lucky break.

The Japanese are about
to become victims

of their own
successful battle plan.

- The problem was
for the Japanese,

they had gone so far
with their assault,

they could not deliver the
code books to all the new sites

because they were too far away.

[dramatic music]

- [Narrator] The speed
and success of the
Japanese incursion

in the Pacific means the
release of the new code book

has been delayed.

And this buys
Rochefort more time

to decode yet more of JN-25.

By late spring, 1942,

Rochefort and his team
have pieced together

almost all of
Yamamoto's battle plan

for the occupation of Midway.

- In his briefing to
Nimitz on the 25th of May,

he told Nimitz that Japanese
were coming with four carriers.

Now he was pretty
sure of that by now.

Probably two
battleships as well,

some cruisers, some destroyers.

So that was the strength
of the Japanese fleet.

[ominous music]

- [Narrator] The
decoded messages reveal

Yamamoto is planning to
have significant air support

and naval firepower in place
to ambush the U.S. carriers

as soon as they
arrive at Midway.

Little does he know that
Rochefort has given Nimitz

everything he needs
for the Americans

to scupper Yamamoto's
ambush plans.

- Nimitz sent almost everything
he could get his hands on

that would fly out
to Midway's airfield.

His hope was that as the
Japanese approached Midway

in order to bomb it, neutralize
it for their invasion,

he could then launch
an attack on them

where they would
least expect it.

[dramatic music]

- [Narrator] And Admiral Nimitz

has another significant
advantage over his enemy.

Yamamoto believes he
will only be taking on

two U.S. aircraft carriers.

- The Japanese believed they
had sunk two American carriers

in the Coral Sea.

That meant the Americans
had only two left.

So the fact that the Japanese
were sending four carriers

out to take care of them,
should be an easy walkover.

- [Narrator] But
master strategist and
poker player Yamamoto

has for the first time
badly overplayed his hand.

- There weren't two
American carriers.

There were three,

because the Yorktown did
not sink in the Coral Sea.

And Nimitz made sure that
its repairs were rushed

to get her back out to sea in
time to join the other two.

[solemn music]

- [Narrator] Rochefort's
advanced warning

means the U.S. carriers
will be at Midway

long before Yamamoto's
attack force.

They'll have 360 aircraft
already lying in wait

for Japan's 248 planes.

Nimitz is going to
ambush Yamamoto's ambush.

- Midway is without a doubt

one of the most significant
naval engagements

in the history of
modern warfare,

and probably the single
most important naval battle

of the Second World War.

- [Narrator] The outcome
for the U.S. stands or falls

on whether Rochefort's
code cracking is correct.

[propellors whirring]

[suspenseful music]
[guns firing]

On June 4th, 1942,

America launches its
own surprise attack

on Yamamoto's Japanese fleet.

- The Americans
launch early enough

so they catch the Japanese
at sixes and sevens.

All these dive bombers arrive
over the Japanese carriers

at about the same time.

The Japanese barely
have a chance to react.

The American dive bombers
scream down on them

at a 70 degree angle
and drop their bombs.

[bombs exploding]

[solemn music]

- By midday, three of the
four Japanese carriers

are on fire and sinking.

By morning the next day, the
fourth one will also have sunk.

- That changes the balance
of power in the Pacific.

- Midway is a disaster
for the Imperial Navy.

- [Narrator] The
U.S. codebreakers,

headed up by Joseph Rochefort,

have been fundamental in
the victory against Yamamoto

and the Japanese
Imperial Navy at Midway.

- Without the breaking
of the JN-25 code,

the outcome could have
been very different.

[suspenseful music]

- [Narrator] After Midway,

the war in the Pacific turns
increasingly America's way.

[somber music]

Yet, despite suffering
such a humiliating defeat,

Japan fails to believe
that its super code

has been compromised.

Almost a year after
the battle of Midway,

the same JN-25 code
is still in use.

But now the complex code
that helped the Japanese

plan their full scale invasion

will become the downfall of
one of its key architects,

Admiral Yamamoto.

On April 14th, 1943,

U.S. codebreakers decode
another vital Japanese message.

- It was the travel itinerary
of Admiral Yamamoto,

who was flying down from
Rabaul to Bougainville

to talk to some of
the Japanese outposts

and boost their morale.

[dramatic music]

Ridding the Imperial
Japanese Navy

of their most talented commander

would be a great
strategic success.

[propellors whirring]

- [Narrator] Yamamoto is warned
against taking the flight

because of the risk
of a targeted attack.

But the Admiral is still so
convinced JN-25 is uncrackable,

he boards the plane anyway.

- Nimitz authorized
a squadron of P-38s

with extended belly tanks
to get them to the location,

to fly out to Bougainville and
shoot down Admiral Yamamoto,

which they did.

[solemn music]

- [Narrator] Admiral
Yamamoto dies instantly

when his plane crashes into
the jungles of New Guinea.

The head of the Imperial Navy

is the highest profile victim
of the cracking of JN-25.

- The Japanese were
totally confident

in the security of JN-25,
that it couldn't be broken.

It was a misplaced arrogance
to believe that any system

would withstand
cryptoanalytic attacks

for as long as it did.

- All of it was a product
of the contributions

made by the cryptoanalysts
at Station Hypo

led by Joe Rochefort.

[light music]

- [Narrator] Despite his work
being directly responsible

for turning the war in the
Pacific in America's favor,

Rochefort's maverick attitude
and willingness to bypass

his boss in Washington, DC,
finally catches up with him.

- Redmond gave Rochefort a sort
of take it or leave it order

with the reorganization of
the Naval intelligence effort

out in the Pacific.

- [Narrator] Joseph Rochefort
is reassigned from the Dungeon

in Pearl Harbor and
sent to San Francisco.

His new role has nothing
to do with codebreaking.

- He's in charge of
a floating dry dock.

He never was put in a position

to be the intelligence analyst
that he was ever again.

[dramatic music]

- [Narrator] After the war,

Rochefort is finally honored
with the Legion of Merit

for his work cracking
the code of JN-25.

He does eventually
return to his roots,

heading up the Pacific
Strategic Intelligence Group

in Washington DC.

Today he's remembered
as the orchestrator

of a phenomenal code
breaking operation,

without which the Japanese
offensive in the Pacific

may never have been stopped.

[energetic music]

[light music]