Decoding Secret Japanese Messages | Secrets of War | Timeline

published on June 30, 2020



shortly after 1:30 am on the 7th of

December 1941 the naval intercept

station at Bainbridge Island Washington

intercepted a transmission from Tokyo

bound for the Japanese Embassy in

Washington DC the message was in purple

the most secret and complex of the

Japanese diplomatic ciphers as tensions

mounted in the Pacific the importance of

breaking the enigmatic cipher became all

the more pressing the message was the

last in a series that had been sent over

the past 18 hours it would become one of

the most infamous messages in history

the United States had been monitoring

the secret communications of Japan as

well as those at most of the other world

powers for more than two decades the

cipher Bureau on a joint undertaking of

the department's of State and War had

begun the work in 1919 it was headed by

Herbert o Yardley a former state

department code clerk who had been

instrumental in the development of the

code in cipher Section mi-8 in the first

world war it was the first time the

United States had a national

organization it's very significant that

it was a code-breaking organization it

worked against the diplomatic materials

of about two dozen foreign countries one

of the bureau's first challenges was the

diplomatic codes of Japan it would not

be an easy task in addition to the

complexities of the language itself the

Japanese employed nearly a dozen

different codes between 1919 and the

spring of 1920 in 1921 American

President Woodrow Wilson proposed an

arms limitation summit to be held in

Washington representatives of the United

States Great Britain France Italy and

Japan would negotiate a treaty to limit

the number and size of capital ships

allowed in their navies by the time the

negotiations commenced Yardley was

supplying the State Department with

daily decrypts of communications between

Japan and its negotiators in Washington

essentially as the message is given to

the Japanese delegation by their code

people Yardley is giving it to our

delegation so we know exactly what the

Japanese position is what Yardley

learned was that the Japanese had

secretly instructed their negotiators to

settle for much less than they were

asking for at the conference table armed

with this information the American

delegation pressed the point and the

Japanese conceded it was a major

diplomatic coup for the United States

and a major cryptological triumph for

Yardley and the cipher Bureau and it was

a classic act where prior intelligence

information paid off in very handsome

dividends in terms of the kind of treaty

and we were able to make the Japanese

sign yeardley claimed that from its

inception the cipher Bureau solved more

than 45,000 encrypted telegrams from

some 20 foreign governments but its

success did not guarantee its survival

in 1924 its appropriations were cut by

nearly half and in 1929 newly appointed

Secretary of State Henry Stimson

completely pulled State Department

funding of the covert agency there's a

legend that when Stimpson closed this

down he took a moralistic position he is

supposed to have said gentlemen don't

read other gentleman's mail I believe it

was strictly a budget decision

whatever the reason America's primary

cryptological effort was suddenly out of


yeardley disgruntled and shorted money

wrote the american black chamber an

expose of the exploits and successes of

the cipher Bureau the book was an

instant sensation and scandal the

Japanese translate the book and the

Japanese learn all about the breaking

down of the code this more or less

starts to lead toward tighter encryption

by the Japanese namely using machines

rather than the standard number codes

that had been broken the cipher bureaus

files some six thousand dollars in

leftover funds and the problems that

Yardley's book created were transferred

to the Army's Signal Corps the chief

cryptologist of the Signal Corps was

William Frederick Friedman who had been

studying codes and ciphers most of his

adult life Friedman whose parents had

emigrated to the United States from

Russia shortly after he was born studied

the relatively new field of genetics at

Cornell while in graduate school he was

offered a job by Colonel George phibian

a wealthy Illinois textile merchant

colonel george fabian was not a colonel

in the conventional military sense he

was an honorary title

he was an eccentric millionaire who had

a large estate outside Chicago and he

engaged in various things that

interested him he was trying to improve

the breeding of animals and various

kinds of crops and so forth and he then

got into other things it was whatever

interested him he had the money and the

inclination to pursue

among those employed at Fabian's

500-acre estate was Elizabeth Smith a 21

year old librarian on Fabian recruited

for one of his more obscure projects my

mother was hired by Fabian to help two

sisters the Gallup sisters who were

Baconian they believe that Sir Francis

Bacon wrote Shakespeare my mother had

recently graduated from college as an

English major and she was hired to help

them in their studies a theory of the

time held that there was a code in the

original folios of Shakespeare's plays

that when deciphered would reveal their

true authorship Friedman and amateur

photographer was drafted into the

project to take pictures of the texts he

enlarged them so Fabian's cryptologists

could examine the letters more closely

the Shakespeare codes piqued his

interest and he began to read the scant

information on codes and cyphers than

available soon he became the head of

Fabian's riverbank Industries Department

of ciphers as well as its department of

genetics by the time he and Elizabeth

Smith were married in May of 1917 they

were well on their way to becoming

America's premier code breakers

initially they really got involved with

the government through Fabian's efforts

when he realized that he had two people

that knew probably more about codes and

ciphers than anybody around in the

United States at the time he let this be

known in Washington and the State

Department and the Army started sending

messages to riverbanks to be solved and

mother and dad would work on them and

solve them and send them back in

addition to his code breaking activities

Friedman tested and advised the

government on cipher machines and by the

fall of 1917 the Army was sending

officers to riverbank for freedmen to

Train as part of the lessons Friedman

wrote a series of pamphlets which Fabian

published and so became known as the

riverbank papers the seven booklets he

wrote from 1917 to 1918 became Seminole

Texas on cryptology as America entered

the war Friedman desperately wanted to

serve his country and to test what he'd

learned about cryptology in the field he

was inducted into the Army and sent to

Europe in the spring of 1918 just five

months before the war ended after the

war Friedman returned to riverbank where

government projects continued to come

his way in 1920 he wrote what would be

the most important text in the field of

crypt analysis the index of coincidence

and it's applications in cryptography

was a revolutionary treatise on the

statistical analysis of letter frequency

and distribution the paper applied

science to the alchemy of cryptology

in November of the same year the

Freedmen's accepted positions as

civilian cryptologists for the

government so eventually they got to

Washington and my father became the

chief cryptologist for the Army Signal

Corps mother went to work briefly for

the Navy and my father started to

develop more techniques in both

developing codes and ciphers and

deciphering codes and ciphers

despite the nature of their work the

Freedmen's life in Washington in the

1920s was by all accounts normal they

bought a house and started a family

William was working for the US Army

Signal Corps and Elizabeth began working


but soon prohibition would supply her

with new assignments and a new set of


Elizabeth Freedman was hired by the

Treasury Department in the mid 1920s to

work against code systems used by

smugglers who were violating the

prohibition laws and she also trained

other krypt analysts to carry on this


Elizabeth Friedman became not only the

treasury department's primary

cryptologist but also the government's

star witness in a number of high-profile

smuggling cases and when the Treasury

Department determined it needed a

full-time Cryptologic unit and she was

put in charge of it by the time

Secretary of State's Stimson closed the

cipher Bureau in 1929 William Friedman's

unit now renamed the signal intelligence

service consisted of only two people

Friedman himself and a typist in

response to the growing responsibilities

of his office Friedman hired three young

mathematicians Frank rollit Abrahamson

cough and Solomon Kovac he initiated

them into the secret world of cryptology

using techniques and principles that

he'd developed and refined over the past

decades Friedman instructed the young

men in the intricacies of codes and

cyphers how to recognize them how to

make them and how to break them they all

had a great aptitude for cryptology the

first thing he had him do once they got

involved and understood the business was

to start developing some stronger codes

for the United States and Friedman's

words the us codes were atrocious he

said once you're able to devise some

strong unbreakable codes then you'll be

able to break other nation's code soon

another member was added a young

linguist named John Hurt who had enact

for Japanese the signal intelligence

service or as is continued to grow but

this would be the core of the team that

would attack Japan's most secret and

mysterious cipher by the early 1930s

many Americans believed that war with

Japan was inevitable the Japanese

invasion Manchuria in 1931 seemed to

cast the die of expansionism that would

set the Land of the Rising Sun on a

collision course with the land of the

free in 1934 the Japanese introduced the

cipher machine type a as a system for

encrypting its secret diplomatic

communications US Army made the cracking

of this machine which they codenamed to

read a top priority

the Japanese transmitted their encrypted

messages in Morse code by breaking the

complex Japanese language into a series

of some 50 syllables with an additional

20 syllables used for punctuation and

emphasis each syllable was then in

ciphered and transmitted in the familiar

dots and dashes despite the complexity

of the new machine army cryptologists

were able to crack the red code by

applying these same principles of

statistical analysis that friedman had

set down in the index of coincidence the

signal intelligence service was able to

do a rather Swift job of breaking the

red code because it in ciphered vowels

and consonants differently and they were

able to apply statistical knowledge of

the frequency of letters in the japanese

language to both the vowels and the

consonants they became so adept at the

system that frank roll had designed a

code wheel to quickly decipher read

transmissions soon the Americans were

able to read all of the diplomatic

traffic it intercepted but this success

would be short-lived as tensions were

rising in the Far East

the Japanese introduced a new more

complex cipher the Japanese called the

new machine the 97 cheeky Obon in G key

the American code breakers called it

simply purple

purple was far more complex than its

predecessor but there were things

working in the allies favor while more

sophisticated purple was not entirely

unlike red like the previous machine

purple in ciphered vowels and consonants

separately making decryption more

manageable purple was also similar in

that keying sequences were changed daily

the Allies were fortunate that in the

transition between systems some messages

were sent in both they already

compromised red as well as the new

purple ciphers this duplication gave

Friedman's team considerable insight

into one day's messages in addition the

Japanese code clerks tended to follow a

strict protocol in the language of their

messages such repetition provided

valuable clues to the nature of the

entire system in a sense the Crypt

analyst didn't have to start from the

very beginning but rather the Crypt

analysts knew that you know if you you

have a an opening of a letter and a

closing of a letter you know those are

the parameters and you can start to

piece things together

besides the talent and ingenuity of the

cryptologists themselves perhaps the

biggest contributor to the success of

the sis in its attack on the purple

cypher was the introduction of

tabulating machines precursors to

computers in the process while working

on the red cypher

Friedman had been allowed to use an IBM

accounting machine that the

quartermaster Corps was phasing out the

machine proved so useful that Friedman

acquired a similar unit for the sole use

of the signal intelligence service the

punch card machines sorted and collated

the vast amounts of information that

until then had to be sorted by hand in

the spring and summer of 1940 the

traffic in purple increased dramatically

especially between Tokyo and the

Japanese embassies in Berlin and Rome

this was due to the impending tripartite

pact the treaty that would bind the Axis

powers the incredible influx of

information gave the harried

cryptologists more work but also more

clues they analyzed weeks and weeks

worth of messages statistically they

developed an appreciation for the subtle

patterns that the machine generated

figured out how the system would encrypt

using these on and off switching devices

and then the system was able to be read

by the Americans

the first major solution for a message

in ciphered with the purple machine came

on September 25th 1940 two days before

the tripartite pact was signed

Friedman's team had done the seemingly

impossible but their job was only half

done breaking the cypher was just the

first step being able to decipher the

messages quickly and accurately would

require another superhuman effort by

analyzing the substitution patterns

inherent in the cipher the Esaias

cryptologists were able to

reverse-engineer a device that would

duplicate the output of the Japanese

purple machine they designed a machine

which used a dozen standard telephone

stepping switches to scramble and

unscramble messages to keyboards were

used for input and output a plug board

determined the keying sequence in cipher

a message under that system you type a

letter on the first electric typewriter

goes through and the stepping switches

so forth out comes the in ciphered

version of it but when you go to

decipher it you have the message and

you've set up the wheels the same and

have the same matrix there's a plug

board and you have to get the plugs in

the right positions so then when you

type the in ciphered letter on the first

typewriter here comes the plain language

on the other side with the completion of

the purple analog the sis was able to

decipher messages as fast as the

Japanese code clerk's themselves short

on funds Friedman arranged to have the

Navy build five of the machines since

personnel were instructed to completely

destroy them when abandoning an embassy

no Japanese purple machine was ever

captured still pieces of one recovered

in Berlin after the war so how

incredibly accurate their deductions and

design had been

the intense pressure Friedman was under

began to take a toll in January of 1941

he was admitted to the neuropsychiatric

ward of the Army's Walter Reed Hospital

in Bethesda Maryland

it was extremely stressful and my father

wound up in the hospital with what in

those days was called a nervous

breakdown with the situation in the

Pacific worsening Friedman was given

little time to recover

he returned to full-time duty the first

of April by the autumn of 1941 it had

become apparent that relations with

Japan were nearing a breaking point

twice purple decrypts indicated that the

Japanese considered negotiations at an

impasse traffic analysis in Hawaii had

warned repeatedly of the formation of a

Japanese attack fleet so the messages

that were intercepted on the 6th and 7th

of December were not entirely a surprise

the 14th part of the long message

reached Washington around five o'clock

the morning of December 7th

cryptologists quickly deciphered the

message and by 8 am and had been

translated from the Japanese it would be

hours before Japanese code clerks could

even begin to work on it

hours before Japanese planes would lift

off from the decks of aircraft carriers

thousands of miles away five hours

before the first bombs were dropped on

Pearl Harbor

the 14th part says essentially

diplomatic negotiations are at an end

it does not say that the Japanese are

going to attack Pearl Harbor on Sunday

morning December the 7th but everyone

who's working with Japanese American

relations knows that a diplomatic brink

is coming in very soon probably

immediately and that this will

ultimately lead to war when Pearl Harbor

wasn't warned of the impending attack

and the subject of speculation for more

than half a century based on this 14

part message the American military

indeed sent warning messages to their

overseas posts however there was no

specific warning about Pearl Harbor and

Cole Harbour was not singled out so a

routine message was sent turns out when

they got into comm center equipted the

message up or went to send it out the

army circuits were busy said well let's

send it out on the Navy surfaces no no

we'll send it by RCA and Western Union

not as a high precedence either we want

to pay for a high precedence message so

that's the message the war warning and

got out there the general short Wow

Pearl Harbor was the


precisely at 1:00 pm the Japanese

ambassador in Washington was to

officially inform the American Secretary

of State that negotiations between the

two nations had broken down but the

Ambassador himself didn't get the

deciphered message in time to deliver it

before the attack had commenced also

hindering Hawaii's ability to anticipate

the danger was the fact that none of the

American built purple analog machines

had been sent to the radio intelligence

unit based in Honolulu the machine that

had been earmarked for Honolulu had been

sent to London as part of an exchange of

krypt illogical information with Great

Britain but the war had just begun and

the Americans had made great strides

toward learning the secrets of their foe

in the Pacific from the earliest war

plans it was foreseen that a war with

Japan would be a war of navies armies

would still be needed but it would be

the battleships cruisers and aircraft

carriers they capital ships that twenty

years earlier the washington arms

limitation treaty had sought to limit

that would now determine victory


once war was declared in the Pacific the

emphasis shifted from the intentions of

diplomats to the plans of generals the

Cryptologic alone is shifted from

William Friedman in the army signal

intelligence service to naval code

breakers before 1917 the United States

had given little thought to the idea of

signal intelligence no significant plans

had been made to either secure its own

communications or intercept and decrypt

those of the enemy during the first

world war the Navy's primary signal

intelligence effort was in setting up a

series of Direction finding stations in

the Atlantic to track German shipping

and submarines

it wasn't until 1924 that the Navy

established a permanent communications

intelligence organization unlike the

Army's sis which always had trouble

finding Japanese translators the Navy

had a number of officers who served in

Japan and were fluent in the language

they did not however have a surplus of

radio operators experienced in Japanese

kana the language of their coded

transmissions in 1923 a group of Navy

and Marine radio men stationed in the

Pacific were unofficially studying the

Japanese kana and the Morse code in

which they transmitted their wireless


four of those original Connor radio men

became instructors when the Navy began

offering classes in Japanese Morse code

in 1928 they chose radium and second

class or the Marine Corps equivalent

from the fleet to go to this school in

Washington DC actually the room was a

converted room that was built on the top

of the roof of the Navy building in

Washington DC and these people would

come there for a class and they were

taught this katakana code somewhere

along the line someone dubbed this group

of people as the on the roof game be on

the roof gang graduates became part of

an ever-growing intelligence

organization that by June of 1940

included a hundred and forty-seven

officers enlisted men and civilians

employed in all aspects of signal

intelligence they were designated simply

as up 20 G while up 20 G also worked on

the Japanese diplomatic ciphers their

primary focus was on the codes employed

by the Japanese military in 1922 naval

operatives had quietly broken into the

Japanese consul general's office in New

York they cracked the safe and

photographed some pages of a Japanese

naval codebook the code was nicknamed

the red book referring to the cover of

the binder in which the photocopies were

kept despite regular changes to the code

naval cryptologists continued their

mastery of the system and soon were

reading virtually all of the traffic

encoded in it

the hard work of the naval spies and

cryptologists paid off handsomely in the

spring of 1930 when Japan held its grand

maneuvers I'm studying the war games we

were able to learn a great deal about

the Japanese order of battle about their

state of armaments and about their

intentions should war breakout

intercepted and decoded messages sent

during the japanese grand maneuvers of

1930 revealed not only their war plans

the Japanese had correctly anticipated

the Americans plans for fighting in the

Pacific this traffic also disclosed

procedures for mobilizing the Japanese

fleet as well and the extent of their

land-based defenses the red book was

supplanted in December of 1930 by a code

that became known as the Blue Book

similar in execution to its predecessor

Navy code breakers were able to read

more than half of the messages encoded

in the blue book

when Japan once again held war games in

1933 but in addition to the blue book

the Japanese employed three fleet codes

and nine cipher systems during the

exercises it would take the small

research desk staff three years to

decrypt all of the messages that had

been intercepted the Japanese continued

to change their codes regularly and in

the summer of 1939 issued what would be

the most important code of the war in

the Pacific the sophisticated high-level

naval operational code would be used

throughout the war to encrypt Japan's

most sensitive and secret military

communications the Americans called it

jn-25 jn-25

was a Japanese naval general-purpose

code jn-25 is the American name for it

I'm not sure that we knew what the

Japanese themselves called it jnt merely

means Japanese Navy 25 meant that it was

the 25th system that we knew about

the jn-25 codebook similar to this

Japanese army codebook listed more than

33,000 words and phrases that were each

given a five digit numerical value to

this was added a changing five digit key

number so that the numeric value that

was transmitted it would not be repeated

in addition variations on the code were

regularly introduced the naval code

breakers of op 20g would work for more

than a year on the intricate code with

little success jn-25 was extremely

difficult to crack and by the time Pearl

Harbor comes along we were reading

probably no more than 10% of jn-25

and that's clearly not enough to know

that the Japanese are coming towards

Pearl Harbor

one of the enduring rumors of the Second

World War is that British cryptologists

at Bletchley Park had secretly broken


and had known about the impending attack

on Pearl Harbor but withheld the

information to force America into the

war that's not true the British and the

United States had been cooperating

somewhat on the attempts to break jn-25

before Pearl Harbor we knew and know the

extent of their successes before Pearl

Harbor and they had not broken that


it wouldn't be until late in January

1942 that Navy cryptologists would make

any significant progress on jn-25 more

than a month too late to avoid the

disaster of Pearl Harbor but in time to

change the course of the war in the


in the months following the attack on

Pearl Harbor Japan went on an

unprecedented spree of expansion and

naval conquest from the first week of

December of 1941 through the spring of

1942 Japan recorded a stunning string of

victories capturing Bangkok Guam Wake

Island Hong Kong Manila Bataan

Corregidor Singapore and Burma in less

than six months the first American

victory in the Pacific was scored not

over territory it was scored over access

to information quietly by the naval code

breakers in January of 42 they finally

succeeded in breaking the Japanese naval

code jn-25 this was broken through trial

and error the Americans had to do first

of all mathematical analysis examining

hundreds thousands perhaps tens of

thousands of Japanese messages until

they discerned a pattern in the numbers

and were able to strip away the numbers

from the Edit of table once they did

that they had the underlying code book


the breaking of the Japanese code came

just in time to alert the us to

Japanese plans to invade the tiny

Australian outpost of Port Moresby on

the island of Papua New Guinea capturing

this tiny outpost would secure Japan's

stranglehold on the western Pacific in

early April of 1942 traffic analysis and

direction finders of the naval

intelligence station in Hawaii

codenamed hypo warned of a Japanese

strike force gathering in Ramallah in

the first week of May

intercepted messages revealed that the

Japanese fleet would be in position and

ready to strike on the morning of May

the 7th armed with this information

American Admiral Chester Nimitz finally

had a chance to take the offensive

accordingly Nimitz was able to send two

of our very few carriers the Lexington

Yorktown down to Coral Sea to try to

stop the Japanese he was also able to

send a land-based aircraft increased the

number that were available in Port

Moresby again to seek out the Japanese

and to attack the American Armada

intercepted the larger Japanese task

force northeast of Australia it was the

first battle in naval history in which

the two fleets never got within sight of

each other for two long days aircraft

from the opposing fleets waged a bitter

battle over the deep waters of the Coral



so this is the military case of where

pre-warned through intelligence you can

move your forces on the chess board if

you will so that you're able to counter

them at the right spot at the right

moment both sides sustained heavy losses

the American carrier Lexington was sunk

and the Yorktown was damaged the

Japanese lost the light carrier Shah and

had to send two carriers back to Japan

for repairs well it wasn't a clear

victory for the Allies the superior

Japanese fleet had been turned back Port

Moresby had been saved this outcome

would have serious repercussions in the

upcoming Japanese offensives even before

the Battle of Coral Sea American

intelligence intercepted messages in the

Imperial Japanese fleets jn-25 code

about another massive carrier strike

planned against a US base but the main

attack was intended to destroy the

American aircraft carriers that had been

out to sea in December the previous year

and thus had avoided the tragedy of

Pearl Harbor virtually the entire

Japanese fleet would be involved in the

operation which would consist of a

diversionary attack on US bases in

Aleutians and a small task force that

would raid a vital American outpost in

the western Pacific when the us fleet

responded another larger strike force

would ambush the allied Armada from the

broken jn-25 he was able to determine

the location of the Japanese operation

the forces the Japanese intended to

deploy and indeed the starting date for

the operation itself almost everything a

commander would want to know about his

enemy armed with his knowledge the Navy

rushed repairs in the Yorktown and

prepared to set up a trap of its own but

there was a disagreement as to the point

of the Japanese attack June 25 messages

always referred to the area only with

the two-letter designator af Midway was

suspected as the target

the Americans were wrong the result

would be disastrous Naval Intelligence

in Hawaii came up with a brilliant

deception a message was sent saying that

Midway was short of fresh water a day or

two later we intercept a Japanese

message that says there is a shortage of

water on and they used the two letters

which then identified Midway as the

objective and all the other message

traffic that we've been able to


the Japanese task force heading for

Midway greatly outnumbered the American

fleet but due to losses in the Battle of

the Coral Sea it would contain only four

aircraft carriers on the 3rd of June

1942 the Japanese began their attack on

the Aleutians just south of Alaska but

decrypts had told the American

commanders that this was just a feint

the real battle was scheduled to begin

in the following morning while the

smaller Japanese strike force pounded

Midway American carrier based aircraft

pumped on the main Japanese fleet

three of the Japanese couriers were sunk

within four minutes by the end of the

first day all four were destroyed the

battle raged for three days

the Japanese losses included four

aircraft carriers 275 planes a heavy

cruiser three destroyers and 3,500 men

by comparison 307 American servicemen

lost their lives the us lost one

carrier 150 planes and a destroyer

it was the most stunning defeat that the

Japanese Navy had ever suffered


shortly after the Battle of Midway a

story appeared in the Chicago Tribune

stating that the Allies had known the

Japanese plans implying that the

Americans had broken their codes in the

investigation that followed the Navy

found that the former executive officer

of the Yorktown had shared a cabin with

the Chicago Tribune reporter on a

transport returning to the States the

reporter was allowed to read classified

documents that detailed covert

operations relating to the battle

fortunately at that time although the

Japanese had still had people in Mexico

and some other places they seemed to be

more interested in the New York Times in

the Washington Post and some of the West

Coast newspapers to avoid further

publicity the Navy officer was not

prosecuted but he was secretly barred

from further promotions the Japanese

continued to use the jn-25 code for

their high-level naval communications on

the 14th of April 1943 the radio

intelligent Durand in Hawaii intercepted

a message detailing the plans for an

inspection tour of Japanese bases in the

Solomon Islands the inspection was to be

conducted by Admiral Isoroku Yamamoto

Japan's most highly regarded naval

strategist the message was quickly

deciphered and translated Yama motors

nearest approach to American forces

would be the island of Bougainville some

400 miles from the US base on

Guadalcanal the information was

forwarded to the US commander Admiral

Nimitz who now had a tantalizing

decision to make use the information and

attempt to assassinate Yamamoto and risk

alerting the Japanese to American

success in breaking their codes or pass

on what might be a golden opportunity

it was determined that the new Lockheed

p-38 aircraft equipped with extra gas

tanks could make the long flight but

there would be a very small window of

opportunity to assassinate the Japanese

Admiral if the p-38s were to make it

back to Guadalcanal they could stay in

the area less than 10 minutes the

mission would require a near

split-second timing but yamamoto was

known to be punctual to a fault on the

morning of April 18th 1943 18 p38 lifted

off from Henderson Field on Guadalcanal

heading Northwest

they food just above the waves to avoid

raid outer the squadron made the 435

miles flight in just over two hours they

got there ten seconds off their

estimated time of arrival and as they

peeled in over the island they looked

over and here came two petty bombers

escorted by zeroes on a landing approach

and they knew they had to man

Yamamoto his plane was shot down over

the jungle as it approached for a

landing all aboard were killed


but had Nimitz's gamble paid off or had

the Americans tipped their hand did the

Japanese know that the Americans were

reading their mail in fact after the

shoot-down of Admiral Yamamoto the

Japanese guessed that we had intercepted

his aircraft based on decrypt

information but fortunately for the

United States they guessed wrong as to

which code we had broken nearly 40 years

would pass before many in Japan learned

the truth that their greatest military

leader of the Second World War had been

the explicit target of American fighters

and despite whatever strategic or

tactical advantage Yamamoto's death may

have given the Allies it was perhaps

fitting that American aviators and naval

code breakers had been responsible for

the demise of the man who led the attack

on Pearl Harbor code breaking had played

a vital role in some of the most

decisive Allied victories in the Pacific

but the war wasn't over yet

navel cryptologists recorded an

impressive string of accomplishments

beyond the work on the Japanese naval

code jn-25

and their work paid significant

dividends throughout the war I think

it's very interesting that the Japanese

merchant shipping in Pacific that was

out there supply their military used the

water transport code that the Navy had

broken of course unknown to the Japanese

and they had to transmit daily their

position to a higher headquarters at

noon every day

with this detailed information American

submarines were dispatched to the area

to await their prize I just choked off

the Japanese supply and through this

breaking of the maru code and the

communications is with the submarine

force they were able to affect this

tremendous damage on the Japanese

shipping hundreds of thousands of tons

of supplies bound for the Japanese war

machine were destroyed in this matter

the army signal intelligence services

worked on the purple cypher continued to

be a valuable asset even after the

Japanese Embassy in Washington was

closed Japanese diplomats in other

countries continued to use purple and

much of this communication proved highly

valuable not only in the war in the

Pacific but also in the war against

Hitler in Europe the Japanese ambassador

to Berlin Baron Hiroshi Oshima was a

three-star general and an avid proponent

of Nazi ideals he was given

unprecedented access to sensitive areas

and updates on the German war effort

Hitler saw to it that he was invited to

Nazi Party functions saw to it that he

had briefings by the high command and

frontline tours being a good soldier

Oshima wrote detailed reports and

ciphered them in the purple system and

broadcast them to tokyo Oshima's reports

on the success or failure of bombing

raids and german cities and different

factories for example supplied the

Allies with detailed information that

was extraordinarily beneficial to the

war effort

Oceania would tour these bombed out

sites or you know radio back reports of

how bad the RF or the American army air

corps pounded raised in Lubec or hun /

or some other german city the night

before and he said well you know they

missed this plant in this plant in that

plant but then you know the next night

they didn't because the ocean was leaked

in November of 1943 Oshima was taken on

an extensive tour of the Atlantic Wall

the system of concrete barbed wire

machine guns and artillery that was to

be Germany's first line of defense

against an Allied invasion Oshima's 20

page report and what he saw during this

tour was intercepted deciphered and sent

to the planners of the d-day invasion

general Marshall and the American army

chief of staff in the Second World War

he said that that Oshima Hiroshi the

Japanese ambassador in Berlin was our

key source of information concerning

Hitler's intentions even as the war was

coming to a close

purple continued to supply the Allies

with insight into what the enemy was

thinking in the months before the

planned invasion of Japan decrypted

traffic showed that Japanese ambassadors

were looking for an avenue to discuss

peace unfortunately the military leaders

who by then controlled the Japanese

government were of a different mind they

hoped to inflict enough casualties and

the Americans that they could dictate

peace terms

the interception of this information

helped Sea of Japan is faked

cryptologists don't win battles soldiers

sailors pilots do but the achievements

of American Army and Navy code breakers

ensure that many more of those warriors

that were sent to defend democracy in

the Pacific would return home when the

fighting had ended the Japanese

throughout the war were very much of the

mind that their coats were unbreakable

and it's a good thing because we believe

that breaking the Japanese codes in

world war ii probably shortened that

conflict by about two years saved

millions of lives

the signal intelligence and

cryptological organizations that were

built by the United States military were

not dismantled when hostilities ceased

as they had been after the first world

war leaders of world war ii became the

military and civilian leaders of the

post-war world they very clearly

understood the value that code making

and code breaking had given them in

World War two the advantage it had

provided they were determined to protect

this capability in the post-war world

and they knew the value of holding your

hand close nobody should know your

secrets so we kept not only a capability

going of looking at other nations codes

and getting intelligence from them but

we kept the effort going to develop

secure systems for United States in 1952

president harry s truman consolidated

many of the country's cryptological

responsibilities and resources with the

establishment of the National Security

Agency William F Friedman became its

chief technical consultant and two years

later he became special assistant to the

director when he retired he was replaced

by Frank Rowland his first student at

the Army Signal Corps

Elizabeth Friedman also contributed to

post-war security in the United States

setting up the cryptology Bureau of the

OSS the predecessor to the CIA after

they retired Elizabeth and William

Friedman revisited the subject that's at

them both on the road to lifelong

careers in cryptology in 1954 I think it

was after my father retired they said

about writing a paper for a contest at

the Folger Shakespeare Library their

monograph was called the cryptologist

looks at Shakespeare and then it was

adopted by Cambridge University Press

and renamed and published under the

title Shakespearean ciphers examined

which annoyed them greatly because it

implied there were ciphers in the

Shakespeare plays and their whole book

was to show that there weren't any real

ciphers there

even though their search for secret

codes in the works of Shakespeare was in

vain their search for secrets in the

messages of hostile Nations helped to

win a world war when looking back at

cryptology in the 20th century the codes

and ciphers the countries that used them

and the men of women who created and

broke them a few things become apparent

nations will always endeavor to keep

secrets and other nations will endeavor

to learn those secrets today computers

shroud communications in a veil of

complexity undreamed-of by Herbert

Yardley but the lessons of his work hold

true in his book the American black

chamber he hardly said if no attempt is

made to decipher messages during quiet

periods when there seems no likelihood

of important issues arising the true

aims and intentions of a government

cannot possibly be ascertained one never

knows at what moment another government

will start a movement prejudicial to our



perhaps the best lesson is that

gentlemen do read each other's mail

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