This document discusses the failure of U.S. Naval Intelligence to anticipate the Japanese attack on Pearl Harbor in 1941. Despite collecting intelligence on Japan for 40 years and conducting counterintelligence operations against Japanese officials, ONI was surprised by the attack. The document examines ONI's intelligence gathering efforts on Japan over time, including establishing a Japanese language program in the 1920s and the Army's early success in decrypting Japanese communications before World War 2, but how these efforts did little to prepare ONI for the Pearl Harbor attack.

1. PEARL HARBOR: THE FAILURE OF U.S.NAVAL INTELLIGENCE
By Pedro Loureiro
Copyright:Pedro Loureiro
Much has been written about the Japanese attack on PearlHarbor and American military
unpreparedness priorto the PacificWar inDecember 1941, but the importantroleofUnited States
Intelligence,particularlyNavalIntelligence,has been neglected. For almost fortyyears,the U.S.Navy
collected information on Japan'smilitaryintentionsand capabilities.The OfficeofNavalIntelligence
(ONI)became the most knowledgeable agency inthe United States on Japan and itsnavy. During
1940 and 1941, the agency carriedout many covert,and often illegal,counterintelligence operations
againstJapanese officialsand the various consulateson the West Coast and Hawaiiinan effortto
penetratethe secrecy surrounding Japan'sdiplomaticand militaryplans. By late1940, italso
benefittedgreatlyfrom the successfuldecoding ofJapan'stop-secretdiplomaticcom munications.
Yet,despiteallthese efforts,ONI was unprepared on 7 December 1941. Thisstudy seeks to
determine how American intelligence agencies and ONI inparticular,perceived Japan priorto the
PacificWar and to also explainwhy itwas taken by surprised.
Nearlyhalf-a-century before the attack on PearlHarbor the United States began seriouslyto
perceive Japan as a potentialenemy. Both countriessought to exerttheirdominance inthe Pacific
and in1897, clashed as a resultofeach other'sexpansionistpoliciesdirected toward the Hawaiian
Islands. To prevent Japanese controlover the islands,the United States annexed Hawaii. The
possibilityofwar with Japan was firstalluded to by the Board on Defenses at the U.S.NavalWar
College during thiscrisis.By 1898, as a resultofthe Spanish-American War, Guam and the
Philippineswere ceded to the United States. As America began to acquiremore territoryinthe
Pacific,itsfearofJapan increased. Itwas not,however,untilJapan'sstunning victoryinthe Russo-
Japanese War, which now threatened the balance ofpower inAsia,thatan American jointArmy-Navy
1

2. Board developed formalwar plans againsther. Potentialenemy nations were assigned colorcodes
and Japan was designated Orange. Known as War Plan Orange, itenvisioned a hypotheticalJapanese
attack on Guam, the Philippines,and Hawaii. The firstOrange Plan was vague and undefined but it
was expected thatthe United States would lose the Philippinesand possibleHawaii. By 1907, Japan
had become the only serious threatto American interestsinthe Pacificand thisbeliefcontinued to
dominate militaryplanning forthe next three decades. During a jointplanning meeting inDecember
1921, itwas stated that,"our most probable enemy isORANGE." War Plan Orange went through
much changes throughout the years but remained the basisofAmerican war planning againstJapan
untilthe late1930s.1
American militaryleadersbelieved thatany eventualconflictwith Japan would be primarilya
navalencounter,therefore,itwas the Department ofNavy thatbecame most concerned with
Japanese activities. The Navy required much accurate and up-to-date information forthe preparation
ofitswar plans. The task ofgathering thisdata fellupon the OfficeofNaval Intelligence. ONI'smain
functionwas to collect,evaluate,and disseminate information on foreign countries,especiallyon,but
not limited to,navalmatters.2
ONI did not begin to systematicallycollectintelligence on Japan untilthe eve ofthe
Washington Conference in1921. Although NavalIntelligence did not possess much information,itdid
provide the American delegation with statisticsand chartson the number ofwarships and strengths
ofthe ImperialJapanese Navy. One oftheirmain sources ofinformation was from the reportsofU.S.
navalattaches inJapan. ONI also managed to compilea biographicalfileon the Japanese delegates
although itconsisted oflittlemore than gossipcolumn types ofhearsay. Unlikethe Army's
cryptographicsuccesses againstJapanese diplomaticcodes,the contributionsofNaval Intelligence to
the conference were ratherlimited.3
Afterthe Washington Conference,ONI was stillunable to expand itscoverage ofJapanese
navalactivities. There was no information as to whether Japan was complying with treatyobligations
or whether itwas developing new weapons and fortificationsinthe Mandated Islands. The Directorof
Naval Intelligence (DNI),Capt.Luke McNamee, knew nothing about the constructionofJapanese
submarines in1923 and admitted thatONI was "unable to determine definitelyclasses,numbers in
each class,and characteristicsofJapanese submarines...."4
Things were not any betterforthe
navalattache inTokyo where he encountered a policestatewith extreme secrecy and security. His
2

3. job was made even more difficultwhen the government-controlledpress labelledhim a spy. Littleof
value was forwarded to ONI during thisperiod. What information Naval Intelligence did receive was
often falseand misleading. One attache dangerouslyunderestimated Japan'snavalaviationwhen he
reported that,"She [Japan]dreads aerialwarfare and seeks to limititsscope forshe willnot use itto
advantage aggressively." Another reportfrom a Marine Corps Major noted that,"Our advantage over
the enemy willbe those generallycom mon to the Nordicraces over the Oriental-higher individual
intelligence,physique and endurance."5
ONI was aware ofitsinabilityto obtainaccurate intelligence on Japan and had therefore
initiateda language studiesprogram foritsofficersin1921. Language officerswere regularly
assigned to the three-year course inTokyo and benefittedtremendously from the experience.
Although itwas stillalmost impossibleto penetrateJapanese militarysecrets,these officerswere
able to provide more realisticassessments ofJapanese capabilitiesand intentions. Unfortunately
seniorofficialsinWashington often ignored these reports. Inmid-1924, Lt.Cdr.EllisM. Zacharias,
one ofthe firstofficersto be sent to Japan in1921, returned from histhree-year assignment to find
thatONI was not even interested inwhat he had to reportabout hisexperiences and observations.
He complained bitterlythat:
The directorlistened to my reportwith gentlemanly boredom ...and
suddenly closed the discussion without any indicationofa follow-up job
forme. ...Ihad spent three years studying a forbidding language,
gathering data ofvitalimportance ...and now itwas my turn forsea
duty. To put itbluntly,Iwas to forgetallextraneous mattersand
refitmyselfintothe generalroutine ofa navalcareer.
Zachariasthen approached ONI'sFar Eastern Section thinking thatthey would surelybe
interested ifthe DNI was not. To hisfrustration,he found only "yawning indifference and
complacency" and hisreportswere "gratifyinglyacknowledged but completelyoverlooked."6
Despite
ONI'sunconcern,the successfullanguage program continued untildeterioratingrelationsbetween
the two countriesforced itto end inthe late1930s. Many ofthese officersbecame specialistson
Japan and went on to distinguished careersinintelligence inlateryears.7
Inthe fieldofcryptanalysisand com munications intelligence,itwas the Army's Military
Intelligence Division(MID) thatfirstmanaged to crack Japan'sdiplomaticcodes. Under HerbertO.
Yardley,and jointlyfunded by the State Department,the cryptographicbranch or the so-calledBlack
Chamber achieved itsfirstbreakthrough with Japanese diplomaticcom munications inFebruary 1920.
3

4. By the sum mer of1921, 813 telegrams addressed to Tokyo by the Japanese ambassador inLondon
had been solved. MID'sabilityto interceptand read these messages provided the Americans with a
greatadvantage during the Washington Conference of1921. The Conference was convened largely
because the United States wanted to maintainitsnavalsupremacy by limitingthe constructionof
capitalwarships,especiallyJapan's. When the Naval Conference began inNovember,Yardley'steam
was reading the most secretmessages ofthe Japanese delegation. Knowledge ofTokyo'sinstructions
to itsambassador enabled the United States to press Japan intoaccepting a considerablylower
number ofcapitalships than had hoped for.8
Yardley'sspectacularsuccesses,however,were not to be repeated afterthe Washington
Conference. For the restofthe decade,the Black Chamber produced littleofvalue. An investigation
by the Army in1929 found many deficiencieswithinthe organizationand decided to dismiss Yardley.
Itwas also at thistime thatthe new SecretaryofState Henry L Stimson was shown several
intercepted Japanese messages. Stimson reacted furiouslywhen he realizedthatthe U.S.
government was unethicallyinterceptingthe com munications ofother nations and he immediately
ordered the Black Chamber to cease alloperations.9
Severalyears later,HerbertYardley,broke and
unemployed,sold the storyabout the Black Chamber and itsoperationsto a publisher. The book,
titledThe American Black Chamber,was published in1931 and revealed how the United States had
managed to out-negotiatethe Japanese during the Washington Conference because ithad
eavesdropped on Japan'sdiplomaticcom munications. The book was published inJapan the next year
and was widelyread. Yardley'srevelationsnot only embarrassed the Japanese government and
strained relationsbetween the two countries,but worstofall,was thatitresulted inJapan'schanging
ofallitscodes and cipher systems and also a greatertightening ofsecurity. Years ofhard work by
American cryptanalystshad been wasted.10
With the closing ofthe Black Chamber, the Army established itsown cryptographic
organizationin1930. Known as the SignalIntelligence Service(SIS),itwas headed by the brilliant
cryptanalyst,William F.Friedman. For the firstseveralyears,Friedman concentrated on training
competent codebreakers and also the settingup ofinterceptfacilities.While the Navy was
responsibleforJapanese navalcom munications,SIS focused on Japan'sdiplomatictrafficand also on
Japanese army codes to a lesserdegree. But SIS faced an extremely difficulttask because Japan had
improved itsenciphering capabilitiesinthe early1930s. And in1937, the Japanese Foreign Ministry
4

5. furthercomplicated Friedman's task by introducing highlysophisticated machines to encipher its
messages. Thisnew process was designated "Purple"by the Americans.11
By early1939 SIS had made littleprogress,therefore,the Navy began to assistby taking over
allJapanese diplomatictrafficother than Purple. Thisfreed Friedman to concentrateon Purpleand he
finallymanaged to solve severalmessages by August 1940. As a result,"the interception,decryption
and translation,on a currentbasis,ofsecretJapanese world-wide diplomaticmessages then began.
The information...derived from thissource [was] designated MAGIC."12
Since Magic included
despatches from Tokyo to allitsdiplomats throughout the world,the volume oftrafficthatwas
intercepted grew tremendously withinweeks. SIS was unable to handle the huge volume of
information because ofa lack ofcryptanalystsand translators. Therefore,they turned again to the
Navy forassistance. But even with Navalassistance,many ofthe Magic interceptswhich were
judged subjectivelyto be unimportant,were never translated. There were severalgrades of
encipherment and the policywas thatinterceptswhich came through the lower grade systems were
considered unimportantand were processed months afterreceipt. Thus,only messages which came
through the high prioritysystem were translated immediately. Trafficcoming through the other
systems which did carrysome importantmessages were,therefore,unknown to American officials
untilafterthe PacificWar began.13
The Navy'scryptographicwork did not begin untilthe early1920s and was directed mainly at
Japan,itstraditionalenemy.14
Itwas inthe spring of1920 thatthe OfficeofNavalIntelligence
discovered thata copy ofthe Japanese Navy'sfleetcode book was kept at the consulateinNew York.
Counterintelligence operativesmanaged to break intothe Japanese consulateand secretlyacquired a
photocopy ofthe Japanese Navy'sfleetcodes. The newly acquired copy was designated JN-1 because
itwas the firstJapanese code book to fallintoAmerican hands. ONI'sfirstcovert,though illegal,
mission againstJapan had been highlysuccessfuland contributed immensely to the basicdeciphering
ofJapanese codes inlateryears.15
In1924, the Navy decided to setup a permanent code and ciphersection withinthe Officeof
Naval Com m unications. Headed by Lt.Laurence F.Safford,the unitwas given the titleof"Research
Desk" to mask itscovertoperations. As Saffordtestifiedat the PearlHarbor Hearings,hisunit's
primary mission was to furnishintelligence "on foreign nations,particularlyJapan -infact,almost
exclusivelyJapan ..."16
Inorder forcodebreakers to operate effectively,itisnecessary to acquirea
5

6. large number ofsignals. Safford'simmediate task,therefore,was to collectradiotrafficforanalysis
by settingup interceptstationsinthe Pacificarea. Stationswere established inShanghai,Oahu,
Peking,Guam, Manila,Bar Harbor (Maine),Astoria(Oregon),and Washington,D.C.17
The Research
Desk made tremendous progress on Japanese Navalmessages during the 1920s because ofthe JN-1
code book thatONI had stolen from the New York consulate. The Japanese used the same codes until
1930 thereby providing the U.S.Navy with a complete pictureoftheirwar plans and training
methods. But these achievements came to a haltafter1930. Frequent code changes by the Imperial
Japanese Navy severelyhindered the progress ofAmerican codebreakers. By 1940, Safford'sunitwas
working on JN-25b which meant thatthiswas the b or second editionofthe twenty-fifthcode thatthe
Japanese had adopted since JN-1 was stolen from the consulatein1920. Itwas not until1942 that
the United States was able to read bitsand pieces ofJapanese navalmessages.18
The next step was the trainingofa regulargroup ofcryptanalystsand translators. Thiswas
especiallydifficultforJapanese radiotrafficbecause allmessages were transmitted phonetically.For
someone working on Japanese com munications,they not only had to be competent codebreakers,but
they also had to know the language extremely well. Until1942, there were only a handfulof
proficienttranslatorsinthe Navy. The problem was apparent as earlyas the 1920s when the Director
ofWar Plans wrote in1926 that"there isa need to provide sufficientcompetent translatorsincase of
an Orange War." At the same time,the navalattache inPeiping [Peking/Beijing],China,could not
findanyone who was able to translatecertainJapanese messages which he had obtained. By 1936,
the ChiefofNaval Operations (CNO) found thatthe language officerswho had returned from their
studiesinJapan were only capable oftranslatingwritten Japanese and were not conversantinthe
language. And as lateas 1940, there were only twelve officerswho were qualifiedas interpretersor
translators. Itwas not until1941 thatthe Navy decided to institutea speciallanguage program to
trainJapanese linguists.19
In1941, ONI'sspecialunitthatwas responsiblefortranslatingMagic had sixtranslatorsand
only three ofthem were experienced enough to work independently. Japanese isa difficultlanguage
to translateintoEnglish,especiallywhen allthe intercepted messages were transmitted as phonetic
characters. Each word could have many differentmeanings. Even seasoned Japanese translators
were required to have "considerableexperience inthisparticularfieldbefore they could be trusted to
come through with a correctinterpretation...." And diplomaticcom munications made the
6

7. translatorstask even more difficultbecause ofthe many subtlemeanings and significance ofits
language.20
The American abilityto interceptJapanese com munications was exceptionallygood. Of the
227 messages sent between Tokyo and Washington which dealtwith U.S.-Japan negotiationsduring
1941, allbut fourwere intercepted. Laurence Saffordexplained proudly,"...there were very few
purplekeys which we failedto solve,maybe two or three per cent,and ...maybe ten or fifteen
[percentoflower grade codes],which we failedto solve due to insufficienttrafficor extremely bad
luck...."21
The Navy and Army were capable ofdecoding messages promptly,the only problem was
the length oftime ittook to process the intercepts. At times,Magic was translated withinhours or on
the same day ofreceipt;on other occasions,ittook up to a month forprocessing. The longestittook
was fifty-nine days to translatean interceptthatoriginated from the Japanese consulateinLos
Angeles to the Foreign MinistryinTokyo. Although Magic was given top-priority,many messages
were not translated untilafterthe Japanese attack on PearlHarbor.22
No figuresare availableforthe SIS,the AssistantDirectorofNavalCom munications during
1941, Rear Adm. Joseph R. Redman, however,stated thatthe number ofintercepted Japanese
messages was manageable inearly1941, but increased considerablyfrom month to month until7
December. Redman estimated thatinNovember,which happened to have been the busiestmonth,
there were about 700 Magic despatches which were intercepted. Com menting on the volume of
Magic trafficduring the PearlHarbor Hearings,AdmiralRedman stated,"September and October
[1941] were also heavy,but itincreased inNovember.... Itwas beyond the capacityofthe staffwe
had to handle allthose translationsexpeditiously...." There was always a backlog ofundecoded
and untranslated materials.23
Despitethe securitytaken to concealthe existence ofMagic,American Intelligence was
horrifiedwhen they intercepted a message dated 5 May 1941 from Japan'sForeign Ministerto its
ambassador inWashington. Translated on the same day,itread,"According to a fairlyreliable
source ofinformation itappears almost certainthatthe United States government isreading your
code messages." Ambassador Kichisaburo Nomura was asked to verifythe warning and on 20 May
reported,"Though Ido not know which ones,Ihave discovered thatthe United States isreading some
ofour codes. As forhow Igot the intelligence,Iwillinform you by courieror another safe way." The
source ofthe leak has never been determined but itwas the Germans who notifiedJapan thatits
7

8. agents inthe United States found out thatJapanese diplomaticcodes had been compromised.24
Because ofJapanese suspicions,the United States expected Japan to change allitscodes and
thus,years ofhard work would have gone down the drain. Incredibly,as the weeks went by,the
Japanese were stillusing the same codes and no action was taken to secure theirdiplomatic
com munications. American Intelligence continued to obtainvitalinformation through Magic. The
only feasibleexplanation was thatthe Japanese simply could not believe thatthe Americans were
capable ofbreaking theirextremely complicated enciphering system and then stillmanage to
translatecomplex Japanese textsintoEnglish.
Relationsbetween the United States and Japan did not begin to deteriorateuntilthe outbreak
ofthe Mukden Incidentin1931. When PresidentRoosevelttook officein1933, there was genuine
fearabout the danger ofwar with Japan. Rooseveltsaw Japan as an aggressiveand dangerous nation
which was strivingto establisha vastempire inAsia. The possibilityofwar seemed very realwhen it
was brought up fordiscussion as earlyas 7 March 1933, during the president'sfirstworking cabinet
meeting.25
Naval Intelligence also became alarmed over the situationinAsia and the DNI,Capt.Hayne
Ellis,warning ofa surpriseattack by Japan,cautioned the CNO not to divide the fleetbetween the
Atlanticand Pacificbecause "the movement ofthe Fleet,or any large portionofit,to the Atlantic,
might affordthe Japanese the opportunitythey are seeking -a sudden blow thatwould place us at an
initialdisadvantage." Indeed,during the Navy'sFleetProblem XIV war games in1933, itwas
determined thatitwas technicallyfeasibleforJapan to carryout an airattack againstOahu.26
The Far
Eastern Section ofONI responded by preparing periodicsum maries ofthe Sino-Japanese conflict,
estimates ofJapan'smilitaryintentionsand navalstrengths forWar Plans,and monographic studies
on Japan. These monographs dealtwith topicssuch as the kinds ofraw materialswhich were vitalto
Japan,Japanese shipping routes,movements ofmerchant vessels,and Japanese aviation.27
Although American navalofficerswere allowed to visitnavalinstallationsand factoriesin
Japan during the 1930s,confidentialmilitarydata was not easilyobtainable.28
The navalattache in
Tokyo was able to occasionallyprovide importantand usefulinformation but ONI made histask more
difficultby refusing to setup an espionage network ofinformants and agents inJapan. Much ofthe
intelligence thatONI received came from reconnaissance tripsby squadrons ofthe AsiaticFleetand
from navalattaches and observersinJapan and China. NavalIntelligence also began increasinglyto
8

9. approach Americans who were travellingor livinginJapan to reporttheirobservations.29
Despitelimitations,a greatdealofinformation was obtained by militaryand navalattaches in
Japan and China who often provided detailedand accurate reportson Japanese capabilities.In1937,
Capt.MerrittB. Booth who spent ten days with the Japanese Army's 38th InfantryRegiment at Nara
was given an opportunityto testfirea new automaticrifleand wrote,"Ifired12 rounds and hitall
targetsmany times. Inoted also thatexcellentresultswere being obtained by allengaged inthis
exercise." AfterNara,Booth was attached to the 27th InfantryRegiment on Hokkaido forthree and a
halfmonths,he took partinfieldexercisesand maneuvers,and was allowed to firelightand heavy
machine guns. He submitted long and detailedreportswhich included accurate drawings ofJapanese
machine guns. Booth did not limithimselfto technicaldetails,he was also able to witness and count
the number oftroops at the railstationswho were preparing to go to China. Another Army observer
who was attached to a differentunit,photographed many Japanese weapons and included them inhis
reports. Between 1939 and 1941, hundreds ofmilitaryreports,often totallingseventy pages or more,
poured intoArmy HeadquartersinWashington.30
The Navy was especiallyinterested inthe development ofJapanese navalaviationand when
EllisZachariasbecame head ofONI'sFar Eastern Section in1934, he revised earlierinaccurate
estimates about Japanese inabilityto launch aircraftfrom carriersat sea. Others studieswere also
carriedout by the Far Eastern Section. The DNI,Capt.William D. Puleston,was thus able to inform
the Navy thatJapanese navalpilotswere well-trained and quitecapable oflaunching predawn air
strikesfrom carriers. He warned the CNO inlate1934 thatJapanese pilotswere "as good and
probably betterthan U.S.aviatorsininstruments and nightflying."31
But untilthe Marco Polo Bridge
IncidentinJuly1937, accurate reportson Japanese aviationwere infrequent and went unnoticed. The
extensive fightinginChina provided ONI and MID with a seemingly unlimited opportunityto collect
militaryinformation on Japan and thus,American intelligence diligentlyfollowed the airwar.
Inadditionto occasionalreportson aerialdevelopments from itsattache,Col.Joseph W.
Stilwell,MID also received reportsfrom ClaireL.Chennaultand other Americans who worked forthe
Chinese government. MID's branch inthe Philippinescollected much information from theirofficers
who visitedChina and also conducted numerous interviews inManilawith many Americans who were
connected with China'sciviland militaryaviation. The Army received quitea bitofinformation on the
latesttechnicaldevelopments. InJanuary 1938, assistantmilitaryattache at Canton,Capt.F.N.
9

10. Robertsinformed Washington thatCharlesDay, an engineer ina Chinese aircraftfactory,had
observed a aerialdogfightbetween Chinese planes and Japan'snew MitsubishiType 96 fighters. Day
wrote,"Iwas most astonished at the performance ofthe Japanese pursuits,as they completely
outclassed the Hawks [CurtisHawk-2 biplanes]inspeed,climb and maneuverabilityand were quite
differentfrom any Japanese pursuitsthatIhave ever heard about." Chennaultconfirmed these
assessments fourmonths laterand informed Washington about it.He noted,"the most striking
significance about the Japanese Type 96 Pursuitairplane [isthatthey]are made inJapan eitherunder
license or from theirown designs. Japan isself-supportingand independent offoreign suppliesin
buildingairplanes." He furtherconcluded thatflighttestsconfirmed thatthe Mitsubishiwas "one of
the best up-to-date pursuitairplanes inthe world."32
Naval Intelligence also followed the fightinginChina and managed to obtaina wealth of
information on Japanese aviation. Cmdr. ArthurMcCollum, head ofONI'sFar Eastern Section,claimed
that"an entireshipload ofwar junk from the Far East arrived during the firstyear offighting."
OfficersinChina collected a wide range ofusefulmaterialsfrom the battlefields. Lieutenant Kemp
Tolleyrecovered partsofa Japanese bomb dropped near Shiukuan,another officerwas able to
examine a nearlyundamaged Zero pursuitplane downed near Chungking,and the AsiaticFleet
intelligence officercollected empty Japanese shellsfrom Shanghai. The most talented was assistant
navalattache,Capt.James M. McHugh, USMC, who frequentlyaccompanied Chinese forces into
combat. He was able to not only recover bomb fragments and aircraftpartsbut he also managed to
obtaina top-secretradiocode book from the body ofa dead Japanese pilotwho was discovered ina
remote region by hisChinese contacts.33
InSeptember 1939, McHugh reported to ONI thatChennaulthad informed him thatafter
examining a captured Nakajima Type 97 fighter,Chennaultconsidered it"the best ofitskinds he has
ever seen and which he believes can beat anything incombat which we can produce inthe U.S.A." A
year later,the Japanese introduced an even betterfighter,the MitsubishiZero which managed to
destroy much ofthe Chinese airforce. By November 1940, ONI received itsfirstreportson the Zero
which the Chinese had provided afterthey shot down a Japanese bomber and interrogated the pilot.
A Zero was finallybrought down by the Chinese inMay 1941 and afterexamining the relativelyintact
plane,they prepared a reporton theirfindings. The reportconfirmed earlyestimates ofthe Zero and
itwas forwarded to Washington by Captain McHugh.34
10

11. Although American intelligence agencies possessed much technicaldata about Japanese
militarycapabilities,especiallyaerial,most ofthe information was simply filedaway or justforwarded
to other departments without any assessments. SeveralONI officerscomplained thatno one inthe
Bureau ofOrdnance ever read the reportson Japanese guns,aircraft,and many other departments
remained ignorantofthe Zero'ssuperiorperformance. American officialsmade relativelylittleuse of
militaryintelligence. The question ofwhether Japan "had 10 carriersor 20 ...[was]not even raised
when policy-makers examined the basicissues ofstrategy."35
Ingeneral,U.S.militaryand civilian
officialshad a poor understanding ofJapan which led eventuallyto a fatalunderestimation of
Japanese capabilitiesand intentions. Despitethe availabilityofnumerous accurate and perceptive
reports,erroneous and confusing information about Japan permeated American intelligence and
seniorofficialsinWashington. Itwas generallybelieved thatthe Japanese soldierand sailorcould
barelysee straight. Japanese pilotsinparticularwere often discounted by both intelligence services.
The Com mander ofthe 20th PursuitSquadron com mented, "Iremember thatitwas generallythought
thatallJapanese pilotshad such poor eyesightthatthey could not flyhigh performance aircraftbut
could only flyplanes thatwere inferiorinperformance to those we flew."36
The prevailingopinion
was thatJapanese aircraftwere second rate and shoddilybuilt.An Australianpilotwho participated
inthe Malaya campaign remembered thatWestern intelligence expertsassured them that"A mere
match ought to be able to ignitethe Japanese toys,ifonly the Buffalocould get up to or above the
Zero."37
Even Captain Puleston,the former DNI who warned the CNO in1934 thatJapanese pilots
were as good as the Americans,wrote later,"Japan has been energeticinher effortsto create naval
aviation,but she isusuallya phase behind. She cannot match innumbers the planes carriedon
American carriers,and what isequallyimportant,her personnelcannot send planes aloftor take
them aboard as rapidlyas American personnel."38
Pilotswho read the reportsby Chennaultand
McHugh refused to believe the information and remained skepticalabout Japanese capabilities.One
ofthem recalled,"Someone said those attaches inTokyo must have had too much Saki[sic]."39
Japanese airsuccesses at the outbreak ofthe PacificWar astonished the world. Yet,afterthe
war,American analystswith the U.S.StrategicBombing Survey were stillunconvinced by the quality
ofJapanese planes thatattacked PearlHarbor. They stated,"Inretrospect,itisremarkable thatthis
most spectacularand successfulattack should have been carriedout with dive bombers and torpedo
planes having littleor no armor plate,no self-sealingtanks." Intheirview, "Only the Japanese
11

12. fightersapproached the performance standards ofa modern airforce."40
Much ofthe prewar information on Japan was provided to American intelligence agencies by
attaches and observersinJapan and China. The second most importantsource ofinformation was
from com munications intelligence. By 1941, both intelligence servicesand the State Department
came to relyincreasinglyon Magic forinformation on Japanese intentions. Intercepted messages in
1941 conveyed an image thatJapan was preparing fora militarythrusttowards eitherthe south,at
Malaya,and the Dutch East Indies,or towards the north at the SovietUnion. InJuly,an intercept
dated 2 Julywhich was from Tokyo to itsambassador to Berlin,stated,"Japan ispreparing forall
possibleeventualitiesas regards the U.S.S.R.inorder to joinforces with Germany inactively
combating the com munistmenace." The cable emphasized thatJapan was making military
preparationsforan attack towards Siberiaand was "determined to destroy the com munistsystem
established there."41
Based on thismessage, Com mander McCollum prepared a reportentitled,
"PossibilityofEarlyAggressive Action by Japan." He concluded thatJapan would not attack the Soviet
Union immediatelyand that:
ifany sudden aggressive action at allisplanned,such action would be
inthe direction...againstthe South China coast...or French
Indo-China....the possibilityofJapanese action againstRussia
though stillconsidered unlikely,cannot be ruled out entirely....42
Another cable dated 14 Julyfrom Canton,China to Tokyo confirmed McCollum's estimates.
The interceptmentioned Japan'splans forIndochina and stressed thatthe next move would be:
sending [an]ultimatum to Netherlands Indies...inthe seizing of
Singapore the Navy willplay the principalpart...Army willneed
only one divisionto seize Singapore and two divisionsto seize
Netherlands Indies...with airforces...we willcrush British-
American militarypower...43
By lateNovember, more information from Magic indicated thatJapan would ultimatelymove
againstSoutheastAsia ratherthan Siberia. Ina me morandum to the DNI,McCollum reported that
Japan was making extensive preparationsfor"an eventualcontrolor occupation ofThailand followed
almost immediatelyby an attack againstBritishpossessions,possiblyBurma and Singapore."44
On 1
December,Com mander McCollum orallypresented thisme mo to allthe seniorNavy officersand
added thatinhisown opinion,"war or a rupture ofdiplomaticrelationswas imminent,"and enquired
"whether or not the fleetsinthe Pacifichad been adequatelyalerted." The CNO and DirectorofWar
Plans,Adm. Richmond Turner assured him thatthey had already sent out warnings "fullyalertingthe
12

13. fleetsand placing them on a war basis."45
The warnings thatthe two admiralswere referringto was a
me morandum dated 27 November and sent to the com manders ofthe Asiaticand PacificFleetswhich
stated:
Thisdespatch isto be considered a war warning. Negotiationswith
Japan ...have ceased and an aggressive move by Japan isexpected
withinthe next few days. the number and equipment ofJapanese troops
and the organizationofnavaltask forces indicatesan amphibious
expeditionagainsteitherthe PhilippinesThaior Kra peninsulaor
Borneo. Execute an appropriatedefensive deployment preparatoryto
carrying out the tasks assigned inWPL46 [Navy'sbasicwar plan].46
Even though Cmdr. Arthur McCollum was head ofthe Far Eastern Section,he had not seen
the 27 November war warning and decided to drafta condensed version ofhisme mo fortransmission
to the fleetswhich now included the com ment "thatwe felteverything pointed to an imminent
outbreak ofhostilitiesbetween Japan and the United States." Despitethese alerts,there was stillno
specificwarning or notion ofa possibleJapanese attack on the Hawaiian Islands. McCollum brought
hisdraftto AdmiralTurner forapprovalbut the Admiraldeleted most ofthe importantinformation.
Turner then showed the Com mander the 27 November warning -the firsttime thatMcCollum had
seen it.McCollum responded,"Well,good gosh,you put inthe words 'warwarning.' Ido not know
what could be plainerthan that,but,nevertheless,Iwould liketo see mine go too."47
Turner insisted
thatthe me morandum be sent the way he had corrected itor itwould not be sent at all.The me mo
was never sent.
ONI'sperceptions ofJapanese intentionswere increasinglyinfluenced by Magic during the last
months of1941. Allofthe Magic messages pointed irrefutablyto an imminent Japanese move
againstSoutheastAsia and these proved to be accurate. Not one ofthe intercepts,however,referred
specificallyto an attack on Hawaii. The DNI,Adm. Theodore Wilkinson testifiedrepeatedlythat
"Every evidence indicated theirmovement was down towards those areas [SoutheastAsia]."48
When
asked at the PearlHarbor Hearings whether the possibilityofa Japanese move againstOahu was
even discussed inONI during the month priorto 7 December,the DNI replied,"Unfortunately,no."49
It
seemed thatNavalIntelligence had become so overawed with Magic thatthey had forgotten thatonly
Japan'sdiplomaticcom munications were available. There would obviouslybe no reference to the
Japanese Navy'stop-secretplans on the PearlHarbor operationamongst the Magic messages. Like
Japan'srefusalto believe thatthe Americans were capable ofbreaking theirsecretcodes,the United
States never imagined thatthe ImperialJapanese Navy would dare to initiatean assaulton itsheavily
13

14. fortifiednavalbase nor thata task force could possiblycross the PacificOcean without being
detected. As Col.Rufus Bratton explained at the PearlHarbor Hearings,"itwas always emphasized
by the latter[Navy] thattheirforces inthe Pacificwere alertand so stationed as to make such a
Japanese attack impracticableor suicidaland we thereforerelegated such an attack to the realm of
remote possibility."50
PearlHarbor had itsown com munications intelligence which was calledthe Combat
Intelligence Unitand was supervised by Cmdr. Joseph J.Rochefort.51
The unit'sprimary mission was
radiointelligence which was also known as trafficanalysiswhereby the locationand movements of
the Japanese fleetwas determined by analyzing the ships'radiocallpatternsand frequencies. They
did not have Magic;neitherwere they provided with the interceptsfrom ONI. Rochefortreported
directlyto the com mandant on Oahu and also maintained close tieswith the PacificFleet's
Intelligence Officer,Cmdr. Edwin T.Layton.52
In1941, com munications intelligence was "the only source ofinformation on the current
strength ofthe Japanese Navy, the organizationofitsfleet,the movements ofitsships and units,and
itsplans and operations."53
Rochefort'sCombat Intelligence Unithad to identifyradiosignalcalls
from more than 15,000 originatorsand on 1 May 1941, found itstask complicated by the Japanese
Navy'ssemi-annualcallchanges. Although Rochefort'steam managed to identifymany ofthe naval
unitswithintwo months,they could not locatethe importantcarrierdivisionswhich had maintained
strictradiosilence inorder to keep theirwhereabouts secret.54
By July,the Combat Intelligence Unitrealizedthatthe Japanese fleetwas undergoing a major
reorganization. Rochefortnoted thata new airfleethad been created under the com mand ofAdm.
ChuichiNagumo. Nagumo's FirstAirFleetwas to be the task force thatwould carryout the Pearl
Harbor operation. Intelligence knew thatthisairfleetconsisted ofeightaircraftcarrierswith support
vesselsand an escortofat leastsixteen destroyers. Thiswas a formidable task force thatshould
have also indicated Japan'semphasis on navalairpower. But as Layton writingafterthe war,"Its
significance,however,was not appreciated untilearly1942."55
Instead ofrecognizing Japan'snew
focus on navalaviation,ONI mistakenlyconcluded that,"inconformitywith our knowledge oftheir
currentnavaldoctrineand thinking,the FirstAirFleetwould play a supporting roleinoperationswith
the battlefleets." The U.S.Navy was unable to comprehend thatthe ImperialJapanese Navy no
longer subscribed to the outdated notion thatcarrierswere thought ofas primarilysupportvessels
14

15. forscouting and reconnaissance. The FirstAirFleetwas created forthe purpose ofoffensive
operationsand was now preparing forthe attack on PearlHarbor. As Layton lamented later,
"battleshipsailors[U.S.]stillruled the waves" inthe sum mer of1941.56
As a result,the U.S.Navy
tragicallyunderestimated the Japanese.
On 1 November,the Japanese Navy routinelychanged itscallsignalsagain. Combat
Intelligence was thoroughly confused because the Japanese also began to send many falseradio
messages inorder to hide the whereabouts oftheircarriers. The U.S.Navy was aware ofthese
deceptions,and Rochefortsensed thatsomething very out-of-the-ordinary was going on but could not
figureitout. There were a lotofcallsbut none originated from the carriers. Layton explained,"When
carriersare not heard from, ifthey do not originatetraffic,they are most likelyinport...itisonly
when they originatetrafficthemselves at sea thatdirectionfinderbearing can be taken ..."57
So,
with no signalsfrom the carriershaving been detected,NavalIntelligence reported on 13 November
that,"Carriersremain relativelyinactive." Severaldays later,Nagumo's task force lefttheirbases to
assemble at Hitokappu Bay where they waited fororders from the Navy GeneralStaff. Combat
Intelligence failedto detectthe departure ofthe strikeforce from itsvarious home bases and the
sum mary of18 November read,"No movement from home waters has been noted ..."58
The task
force'stripacross the Pacificwas unknown to Rochefort'steam because the Japanese Navy
maintained strictradiosilence throughout itsvoyage. An officialreportprepared by the Japanese
Navy inthe sum mer of1942 attributed theirsuccess to a number offactorswhich included radio
silence. The reportstated,"Inorder to keep strictradiosilence,thorough steps such as taking off
fuses inthe circuit,holding and sealingthe keys were taken. During the operation,the strictestradio
silence was perfectlycarriedout." Combat Intelligence would have certainlylocked inon Nagumo's
fleetifithad broken radiosilence.59
Surprisingly,the Japanese Navy did not make any realeffortsto concealtheirextensive
preparationsforitssouthern operations. Radio intelligence intercepted at PearlHarbor indicated
clearlythatseveralJapanese task forces were about to embark on a major militaryoperation aimed
at Malaya and the Dutch Indies. Reportsfrom American attaches and observersalong the China
coastand Britishintelligence also confirmed the massing oftroops and equipment and the movement
ofships.60
Japan must have intentionallywanted the United States to focus on these preparationsin
order to divertattentionfrom itsPearlHarbor task force. Thisploy apparentlysucceeded as indeed,
15

16. ONI believed thatany hostilemove by Japan would certainlyoccur inSoutheastAsia.
Com mander Rochefortand histeam continued theirattempts to track the Japanese fleetbut
on 1 December,alltheircallsignalssuddenly changed again.61
Thistime itwas very unusualas the
signalshad been changed only very recently. Rochefortsuspected thatsomething was up because
he feltthatthe change inradiocalls"indicated an additionalprogressivestep inpreparing foractive
operationson a large scale."62
But he lateradmitted thathe did not connect the information "in
terms ofPearlHarbor at the time."63
Until7 December,ONI believed thatmost ofJapan'saircraft
carrierswere stillinhome waters.
Com mander Layton recounted laterthaton 2 December,inreference to the locationofthe
carriers,he wrote,"Homeland waters?"on the intelligence report. When Adm. Husband E.Kimmel,
Com mander-in-Chiefofthe PacificFleet,read it,he was furiousand surprised thathisfleet
intelligence officerdid not know where the Japanese aircraftcarrierswere located. He asked Layton,
"You mean they could be coming around Diamond Head, and you wouldn'tknow it?" And Layton
replied,"Yes,sir,but Ihope they'dhave been sighted before now."64
Unfortunately,the Japanese
strikeforce was never detected and completelysurprised the Americans at PearlHarbor.
Inthe fieldofcom munications intelligence,the Magic breakthrough in1940 was a great asset
to American intelligence. Not since the Yardley successes did the United States manage to attain
such a tremendous advantage againstan enemy. Magic was extremely usefulduring the Cordell
Hull-Nomura talksand enabled the U.S.to learn more about the Japanese Foreign Ministry'strue
intentionsthan even itsown ambassador was aware of. And indeed,italso proved to be very
accurate about Japan'sinvasion ofSoutheastAsia. But inthe excitement over thisnew secret
weapon, American officialsreliedtoo heavilyupon itformilitaryinformation forgettingthatMagic
carriedonly Japan'sdiplomatictraffic.Another problem thatplagued the Americans was the difficulty
intranslatingJapanese. Ittook years ofdedicationto master Japanese,and itrequired even more
skillsto understand the complexitiesofdiplomaticlanguage. With a handfuloftranslators,American
intelligence was able to produce spectacularresultsthateven the Japanese refused to believe was
possible. But a lack ofqualifiedtranslatorsresulted ina constantbacklog ofuntranslated messages.
Not untilOctober 1941 did the Navy decide to setup speciallanguage schoolsat Berkeley and
Harvard. Yet,despitethismanpower shortage,no Nisei,though highlyqualified,were recruited
because they were considered a securityrisk. Because ofthe vastquantitiesofintercepts,
16

17. translatorsoften worked under tremendous pressure. Under such circumstances errorsintranslation
did occur.
Japan'shighlysuccessfulairattack againstthe U.S.PacificFleeton 7 December 1941, was
largelya failureofintelligence. ONI must take most ofthe blame as war planning againstJapan was
primarilythe concern ofthe Navy. For almost fortyyears,the Navy had been continuously
developing war plans againstan eventualconflictwith itsonly potentialenemy inthe Pacific,Japan.
And from 1933 on,every major war game included a hypotheticalsurpriseairattack on Pearl
Harbor.65
War Plans and ONI reportsoften stressed thatpast experience had shown thatJapan
always preceded a declarationofwar with a surpriseattack. By earlyDecember 1941, ONI knew that
itwould only be a matter ofdays before Japan com menced hostilitiesagainstthe United States. An
ONI counterintelligence reportprepared during the firstweek ofDecember stated:
During the firstweek inDecember, large scaleshiftsinkey diplomatic
personnelfrom Canada and the United States to Mexico and LatinAmerica
have taken place,and a mass exodus ofJapanese residentsisunder way.
On December 1,1941, the ConsulateGeneralon the West Coast began to
destroy itsrecords,as did the Consulate General,the Japanese Chamber
ofCom merce and the Japan InstituteinNew York City.Secretcodes and
ciphers at the Japanese Embassy were burned on the nightofDecember 5,
1941.66
The reportalso stated thatallmajor Japanese businesses and banks planned to close by 6
December and thattheirpersonnelwere scheduled to leave forJapan the following week. Yet,
counterintelligence did not realizethatthese actionssignalleda definitebreak inU.S.-Japan relations.
Instead,they weakly concluded that"CurrentU.S.-Japanese relationsare not clearlydefined."67
Although the reportwas disseminated throughout the Navy Department,no action was taken.
ONI'spoor performance can be linked to problems withinthe organization. The importance of
intelligence was not fullyappreciated by many traditional-minded seniorofficialsduring the prewar
years. Not only was an intelligence schoolnot established untilthe PacificWar began, but the
subjectwas never taught at the Academy or War College. Allprewar intelligence officershad no
formal trainingintheirarea. Even the DNI,AdmiralWilkinson,when questioned about his
background during the PearlHarbor Hearings,admitted thathe had absolutelyno experience in
intelligence,"None other than attendance at two internationalconferences forlimitationor
armaments in1933 and 1934."68
The Navy'spolicyofroutinelytransferringofficersto sea duty often
deprived ONI ofsome ofitsmost experienced personnel. Inearly1940, Naval Intelligence lostfourof
17

18. itsseasoned section heads to sea duty.69
Itisextremely difficultto operate an effectiveintelligence
agency with inexperienced officers. Morale was furtherdemoralized in1941, when the agency went
through three differentdirectorsthatyear.
The main reason forAmerican unpreparedness on 7 December 1941, was the widespread
disregard forintelligence. Alltoo often seniormilitaryand navalofficerschose to ignore accurate
reportson Japanese capabilities.Culturalbiases also clouded theirestimates ofJapanese intentions.
There was a genuine disbeliefthatJapan would dare to initiatean assaulton PearlHarbor,where the
mighty PacificFleethad been based as a deterrenton Japanese aggression. Itwas also feltthatno
strikeforce would be capable ofcrossing the Pacifictoward Hawaiiwithout being detected. ONI
tragicallyunderestimated the Japanese. Although there were studiesand reportswhich indicated
Japan'sabilityto attack PearlHarbor without warning,seniorofficersignored these. The rootofthe
problem forthe United States was thatits"deeply ingrained myths about Japanese inferiorityproved
too pervasive."70
18

19. 1.AkiraIriye,PacificEstrangement:Japanese and American Expansion,1897-1911 (Cambridge,Mass.:
Harvard UniversityPress,1972),pp. 49-51; MichaelVlahos,"The Naval War College and the Originsof
War-Planning AgainstJapan,"Naval War College Review 33 (July-August 1980):24, 34; LouisMorton,
"War Plan Orange:Evolutionofa Strategy,"World Politics11 (January 1959):222, 228.
2.James RobertGreen,"The FirstSixtyYears ofthe OfficeofNavalIntelligence,"(M.A.thesis,The
American University,1963),pp. 1-2.
3.JefferyM. Dorwart,ConflictofDuty:The U.S.Navy'sIntelligence Dilemma, 1919-1945 (Annapolis,MD:
Naval InstitutePress,1983),pp. 20-21; EllisM. Zacharias,SecretMissions:The Story ofan Intelligence
Officer(New York:G. P.Putnam's Sons,1946),pp. 12-13.
4.Dorwart,p.26.
5.Ibid.,pp. 28-29.
6.Zacharias,pp. 71-72.
7.Some ofthe outstanding graduates ofthe language program included men like:Joseph Rochefortwho
became one ofthe most effectivecryptanalystagainstJapanese codes; EllisZachariasheaded ONI'sFar
Eastern Section and then went on to become AssistantDirectorofONI; Edwin T.Layton became Fleet
Intelligence Officerto the PacificFleet(1940-1946) and was postwar Directorofthe NavalIntelligence
School; Alwin Kramer served inONI'sFar Eastern Section from 1941 on; Arthur McCollum was head of
the Far Eastern Section (1939-1942) and was a major consultantto Roberta Wohlstetter'sbook on Pearl
Harbor; Alva Lasswell'scryptanalyticskillsbrought about the death ofAdmiralIsoroku Yama moto;
RedfieldMason played a key roleinthe Navy'sSignalIntelligence Unit; Eddie Pearce was partofa
SignalIntelligence team thatoperated inAustraliaduring the war; DanielMcCallum spent eightmonths
on Guadalcanallistening to Japanese militarycom munications; Rufus L.Taylorbecame DirectorofNaval
Intelligence and laterDeputy Directorofthe CIA; HenriSmith-Hutton was FleetIntelligence Officerof
the AsiaticFleetand returned to Japan as NavalAttache in1939; Joseph Wenger ran the Signal
Intelligence Unitinthe Philippinesand Washington,D.C.and eventuallybecame Deputy Directorof
Naval Com m unications; and Stephen Jurikabriefed the Doolittleairmen before theirraidon Tokyo and is
currentlyProfessorofInternationalRelationsat the NavalPostgraduate SchoolinMonterey,California.
Ronald Lewin,The American Magic:Codes,Ciphers and the Defeat ofJapan (New York:FarrarStraus
Giroux,1982),pp. 25, 29-32.
8.HerbertO. Yardley,The American Black Chamber (New York:BallantineBooks,1981),pp. 187-211.
9.Lewin,pp. 31-33.
10.David Kahn, "A New Source forHistorians:Yardley'sSeized Manuscript,"Cryptologia6 (April1982):
115.
11.U.S.,Department ofthe Army, The Originand Development ofthe Army SecurityAgency,1917-
1947 (Laguna Hills,CA: Aegean Park Press,1978),p.5; Ronald Clark,The Man Who Broke Purple:The
LifeofColonelWilliam F.Friedman, Who Deciphered the Japanese Code inWorld War II(Boston,MA:
Little,Brown and Co.,1977),pp. 117-145.
12.U.S.,Department ofDefense,The "Magic"Background ofPearlHarbor 5 vols.+3 app. (Washington
D.C.:Government PrintingOffice,1977),vol.1 preface.(hereafterMagic Background)
13.Ronald Clark,pp. 145-146.
14.William F.Clarke,"Government Code and Cypher SchoolitsFoundation and Development with
SpecialReference to itsNavalSide,"Cryptologia11 (October 1987):221.
15.Cipher A. Deavours and LouisKruh,Machine Cryptography and Modern Cryptanalysis(Cambridge,
MA: Artech House, 1985),pp. 212, 249 n.1; LadislasFarago,The Broken Seal:Operation Magic and the
PearlHarbor Disaster(New York:Random House, 1967),pp. 35-37; Edwin T.Layton,with Roger Pineau
and John Costello,And IWas There:PearlHarbor and Midway -Breaking the Secrets(New York:William
Morrow, 1985),p.31.

20. 16.U.S.,Congress,House, JointCom mittee on the Investigationofthe PearlHarbor Attack,PearlHarbor
Attack:Hearings Before the JointCom mittee on the
Investigationofthe PearlHarbor Attack,79th Cong.,1st sess.,1946, 39 vols(Washington,D.C.:
Government PrintingOffice,1946),pt.36, p.60. (hereafterPearlHarbor Attack)
17.Laurence F.Safford,"A BriefHistoryofCom munications Intelligence inthe United States,"inRonald
H. Spector,ed.,Listening to the Enemy: Key Documents on the Role ofCom m unications Intelligence in
the War with Japan (Wilmington,Del:ScholarlyResources,1988),pp. 4-5.
18
.Safford,p.6; David Kahn, "Codebreaking inWorld Wars Iand II:The Major Successes and Failures,
TheirCauses and TheirEffects,"The HistoricalJournal23 (1980):625.
19.U.S.,Department ofthe Navy, United States NavalAdministrationinWorld War II,The Officeof
Naval Intelligence (Washington,D.C.:Navy HistoricalDivision,1959),pp. 598-599. (hereafterU.S.Naval
Administration,ONI)
20.PearlHarbor Attack,pt.8,pp. 3400-3401, 3895.
21.Ibid.,pt.36, p.314; David Kahn, The Codebreakers:The Story ofSecretWriting (New York:
Macmillan,1967),pp. 353-354.
22.Diane T.Putney,ed.,Ultraand the Army AirForce inWorld War II:An Interview with Associate
Justiceofthe U.S.Supreme CourtLewis F.Powell,Jr.(Washington,D.C.:OfficeofAirForce History,
United States AirForce,1987),p.68; Roberta Wohlstetter,PearlHarbor:Warning and Decision
(Stanford,CA: Stanford UniversityPress,1962),p.173.
23.PearlHarbor Attack,pt.33, p.915.
24.Magic Background,vol.1,pp. A-52 to A-53.
25.Stephen E.Pelz,Race to PearlHarbor:The Failureofthe Second London NavalConference and the
Onset ofWorld War II(Cambridge,MA: Harvard UniversityPress,1974),pp. 75-76.
26.JefferyM. Dorwart,ConflictofDuty:The U.S.Navy'sIntelligence Dilemma, 1919-1945 (Annapolis,
MD: Naval InstitutePress,1983),p.87, 179.
27.U.S.NavalAdministration,ONI,p.595.
28.Hayne Ellis[DNI]to allnavaldistricts,3 March 1934, inRecords ofthe ChiefofNavalOperations,
OfficeofNavalIntelligence,Record Group 38, FileA8-5/EF37,NationalArchives.
29.U.S.NavalAdministration,ONI,pp. 595-596.
30.David Kahn, "The United States Views ofGermany and Japan in1941,"inErnestR. May, ed.,
Knowing One's Enemies:Intelligence Assessment Before the Two World Wars (Princeton,NJ:Princeton
UniversityPress,1986),pp. 480-482.
31.Dorwart,p.62.
32.William M. Leary,"Assessing the Japanese Threat:AirIntelligence Priorto PearlHarbor,"Aerospace
Historian(December 1987):273-274.
33
.Dorwart,pp. 90-91.
34.Leary,pp. 275-276.
35.Kahn, "U.S.Views ofGermany and Japan,"p.478.

21. 36.Leary,p.276.
37.AlvinD. Coox, "AllGo Sleep:AlliedMilitaryPerceptions ofthe Japanese and the Effecton
OperationalThinking inthe PacificTheaterinWorld War II,"Paper presented at the ThirdU.S.Army War
College Conference on Intelligence and MilitaryOperations,17-19 May 1988.
38.Kahn, "U.S.Views ofGermany and Japan,"p.477.
39.Leary,p.276.
40.Coox, "AllGo Sleep."
41.CarlBoyd, "Significance ofMagic and the Japanese Ambassador to Berlin:(1)The Formative Months
before PearlHarbor,"Intelligence and NationalSecurity2 (January 1987):154.
42.PearlHarbor Attack,pt.15, p.1852.
43.Lewin,p.60.
44.PearlHarbor Attack,pt.15, p.1839.
45.Ibid.,pt.8,p.3385.
46.Ibid.,pt.14, p.1406.
47.Ibid.,pt.8,p.3388.
48.Ibid.,pt.4,p.1757.
49.Ibid.,pt.36, p.233.
50.Ibid.,pt.34, p.19.
51.Wilfred J.Holmes, Double-Edged Secrets:U.S.NavalIntelligence Operations inthe Pacificduring
World War II(Annapolis,MD: NavalInstitutePress,1979),pp. 9-11.
52.PearlHarbor Attack,pt.36, pp. 31-32.
53.Wilfred J.Holmes, "NavalIntelligence inthe War AgainstJapan 1941-45: The View from Pearl
Harbor,"inCraig L.Seymonds, ed.,New Aspects ofNaval History:Selected Papers Presented at the
Fourth NavalHistorySymposium, United States NavalAcademy, 25-26 October 1979 (Annapolis,MD:
Naval InstitutePress,1981),p.351.
54.Layton,p.125.
55.Ibid.
56.Ibid.,p.126.
57.PearlHarbor Attack,pt.23, pp. 659, 664.
58.Ibid.,p.660; Gordon W. Prange,incollaborationwith Donald M. Goldsteinand Katherine V. Dillon,
At Dawn We Slept:The Untold Story ofPearlHarbor (New York:McGraw-Hill,1981),p.362.
59.Gordon W. Prange,incollaborationwith Donald M. Goldsteinand Katherine V. Dillon,PearlHarbor:
The VerdictofHistory(New York:McGraw-Hill,1981),p.60.

22. 60.PearlHarbor Attack,pt.23, p.658.
61.Holmes, "NavalIntelligence inthe War AgainstJapan,"p.353.
62.PearlHarbor Attack,pt.36, p.35.
63.Prange,At Dawn We Slept,p.362.
64.Layton,p.18.
65.PearlHarbor Attack,pt.36, p.45.
66.ONI report,"Japanese Intelligence and Propaganda inthe United States During 1941,"4 December
1941, inRecords ofthe Army Staff,MilitaryIntelligence Division,File000.24 Japanese Activities,National
Archives.
67.Ibid.
68.PearlHarbor Attack,pt.4,p.1725.
69.Dorwart,p.150.
70.Leary,p.277.