Pearl Harbor advance-knowledge debate

Pearl Harbor advance-knowledge debate

The Pearl Harbor advance-knowledge debate is a dispute over what, if any, advance knowledge American officials had of Japan's December 7, 1941 attack on Pearl Harbor.

Ever since the Japanese attack there has been debate as to how and why the United States had been caught off guard, and how much and when American officials knew of Japanese plans for an attack.

Several writers, including journalist Robert Stinnett and former United States Navy Rear Admiral Robert A. Theobald, have argued that various parties high in the U.S. and British governments knew of the attack in advance and may even have let it happen or encouraged it in order to force America into war "via" the "back door." Evidence supporting this view is taken from quotations and source documents from the time and the release of newer materials.

Examination of information released since the War has revealed there was considerable intelligence information available to US and other nations' officials. Rather than attribute the lack of preparedness at the base to failure to process, it has been argued that the U.S. must have had some degree of advanced knowledge of the attack.

Ten official US inquiries

The U.S. government has had ten official inquiries into the attack – the inquiry by Secretary of the Navy Frank Knox (1941), the Roberts Commission (1941–42), the Hart Inquiry (1944), the Army Pearl Harbor Board (1944), the Naval Court of Inquiry (1944), the Hewitt investigation, the Clarke investigation, the Congressional Inquiry (1945–46) and the top-secret inquiry by Secretary of War Henry L. Stimson, authorized by Congress and carried out by Henry Clausen (the Clausen Inquiry) (1946). The tenth inquiry, the Thurmond-Spence Hearing, took place in April 1995. The Dorn Report resulted from this tenth hearing. [Citation
title=Advancement of rear Admiral Kimmel andMajorGeneral Short on the Retired List
chapter=III. The Pearl Harbor Investigations
date=December 1, 1995
(Source: Office of the Under Secretary of Defense for Personnel and Readiness. Online page created 24 December, 1996, maintained by Larry W. Jewell.)

All ten reported incompetence, underestimation and misapprehension of Japanese capabilities & intentions, problems resulting from excessive secrecy about crypto, and lack of adequate manpower for intelligence (analysis, collection, processing, ...).Verify source|date=July 2008

It is important to note that investigators prior to Clausen did not have the security clearance necessary to receive the most sensitive information, and some of those questioned were put in a difficult spot of having to lie (even under oath) to protect secrets they were charged with. Clausen reported that even though he had a letter from Secretary Stimson informing witnesses he had the necessary clearances to require their cooperation, he was repeatedly lied to until he produced copies of top secret decrypts, thus proving he indeed had the proper clearance.

The Stimson report to Congress (based on Clausen's work) was limited due to secrecy concerns (largely about crypto); a more complete account was not publicly available until the mid-1980s and not published until 1992, with Clausen's own account of the investigation. Reaction to the 1991 publication has varied; some regard it as a valuable addition to understanding, others note that (a) he didn't speak to General Walter Short, Army commander at Pearl Harbor during the attack, and (somewhat prematurely) (b) his investigation was "notoriously unreliable" in several aspects. [Roberta Wohletter, Pearl Harbor - Warning and Decision, Stanford University Press, 1962, page 35.]

Assertions that Japanese codes had already been broken

US signals intelligence in 1941 was both impressively advanced and uneven. In the past, the US MI-8 cryptographic operation in New York City had been shut down by Henry Stimson (Hoover's newly appointed Secretary of State), citing "ethical considerations", which inspired its now broke former director, Herbert Yardley, to write a book, "The American Black Chamber", about its successes in breaking other nations' crypto traffic. Most countries responded promptly by changing (and generally improving) their ciphers and codes, forcing other nations to start over in reading their signals. The Japanese were no exception.

Nevertheless, U.S. cryptanalytic work continued after Stimson's action in two separate efforts: the Army's Signal Intelligence Service (SIS) and the Navy's Office of Naval Intelligence (ONI) crypto group, OP-20-G. Cryptanalytic work was kept secret to such an extent, however, commands such as the 14th Naval District at Pearl Harbor were prohibited from working on codebreaking by Admiral Kelly Turner as a consequence of the bureaucratic infighting in Washington.

By late 1941, those organizations had broken several Japanese ciphers, such as J19 and PA-K2, called "Tsu" and "Oite" respectively by the Japanese. [Kahn's "The Codebreakers" has the specifies on these lower-level codes, beginning with LA, beginning on p.14.] The highest security diplomatic code, dubbed PURPLE by the U.S., had been broken, but American cryptanalysts had made little progress against the IJN's current D code (called JN-25 by the U.S.)

In addition, there was a perennial shortage of manpower, thanks to penury on one hand and the perception of intelligence as a low-value career path on the other. Translators were over-worked, cryptanalysts in short supply, staff generally stressed. Furthermore, there were difficulties retaining good intelligence officers and trained linguists; most did not remain on the job for the extended periods necessary to become truly professional. For career reasons, nearly all wanted to return to more standard assignments. However, concerning the manning levels, "... just prior to World War II, we had some 700 people engaged in the effort and we were, in fact, obviously having some successes." [U,.S. Navy "Oral History Interview" conducted by Cdr. "Irv" Newman (USN Retired) on May 4,5, and 6, 1983 of Robert D. Ogg, SRH-255, declassified on 17 November 1983, p.23. Commander Laurence Safford, SRH-149, pp.6 and 19, shows 730.] Of these, 85% were tasked to decryption and 50% to translation efforts against IJN codes. [Safford, "loc. cit.".] The nature and degree of these successes has led to great confusion among non-specialists. Furthermore, OP-20-GY "analysts relied as much on summary reports as on the actual intercepted messages." [Parillo, "The United States in the Pacific", in Higham and Harris, p.290.]

The U.S. was also given decrypted messages by Dutch (NEI) intelligence, who like the others in the British-Dutch-U.S. agreement to share the cryptographic load, shared information with allies. The U.S. refused to do likewise. [C.H. Baker, "Nanyo" 1987.] This was, at least in part, due to fears of compromise; sharing even between Navy and Army was restricted.

In any case, the eventual flow of intercepted and decrypted information was tightly and capriciously controlled to the point at times even President Roosevelt did not receive information from code-breaking activities. (This was in part due to fears of compromise as a result of poor security, after a memo dealing with MAGIC was tossed in the wastebasket of Brigadier General Edwin M. (Pa) Watson, the President's military aide. [Kahn, "op. cit.", 1967, p.26.] )


The break into PURPLE was a considerable cryptographic triumph, and proved quite useful later in the War. It was the highest security Japanese Foreign Office system, but prior to Pearl Harbor carried little information about Japanese plans; the military, who were essentially determining foreign policy for Japan, distrusted the Foreign Office and left it "out of the loop". Unfortunately for the US, the two US crypto groups generally competed rather than cooperated, and distribution of intelligence from the military to US civilian policy-level officials was poorly done (eg, capriciously selected for distribution) by both the Army and Navy who handled the traffic on alternate days, and furthermore in a way preventing any of its recipients from developing a larger sense of the meaning of the decrypts. Along with the obsession with security, there was little or no analysis done for recipients. Decrypts were typically provided raw, completely without context, and without much taking into account the needs of the recipients. As well, recipients were not permitted to retain them, or notes made from them, again for security reasons.

Most unfortunately, to date not all PURPLE messages have been released. This was noted as long ago as the Joint Congressional Hearings during the "Magic" testimony. This known fact is often missed, as well as other curious items, for example, the Hearing's questions regarding the missing 25 pages from the Roberts Commission report. Blanket or un-qualified statements on what decoded "Magic" messages revealedare, therefore, pre-mature.


The JN-25 superencrypted code is one of the most debated portions of Pearl Harbor lore. JN-25 is the US Navy's final term for the cryptosystem the Imperial Japanese Navy sometimes referred to as Naval Code D. Other names used for it include five-numeral, 5Num, five-digit, five-figure, AN (JN-25 Able), and AN-1 (JN-25 Baker), and so on. [Some writers, notably Stinnett, have refused to recognize "5Num" as JN-25, despite years of research. See comprehensive end remarks with references to examples.] It was an example of the then state of the art in crypto systems and was quite different than modern forms of message encryption in being a code ("i.e.", battleship = 63982) and further being superenciphered with an additive cypher, taken from a large book. So, for example, 63982 + 12345 = 75227 (using modulo arithmetic, non-carrying addition and non-borrowing subtraction, also called Fibonacci or "Chinese arithmetic"), giving the actually transmitted group (75227); on receipt the additive was subtracted (75227 - 12345 = 63982 (modulo arithmetic again)) and the code group looked up in the current JN-25 code book. The worth of the additive step is that the next time anyone mentioned 'battleship', a different additive would be used. It was based upon the Japanese syllabary ("kana"), due to the difficulties in using Japanese "kanji" (ie, Chinese style characters) in telegraphy and the fact that electric teletype printers were more or less easily converted (eg, more characters in the syllabary) to "kana" from the Roman alphabet.

Superenciphered codes of this sort were widely used and were the state of the art in practical cryptography of the time. JN-25 was very similar in principle to the British "Naval Cypher No. 3", known to have been broken by Germany during WWII. ["Rhapsody in Purple: A New History of Pearl Harbor" in "Cryptologia", July (pages 193-229) and October (pages 346-467) issues of 1982.]

Once it was realized what sort of cryptosystem JN-25 was, the cryptanalytic approach was known. Stinnett, in fact, notes the existence of a USN handbook for attacks on such a system, produced by OP-20-G. Even so, breaking it was not easy in actual practice. It took much effort and time, not least in accumulating sufficient depth in intercepted messages prior to the outbreak of hostilities when IJN radio traffic increased abruptly and substantially; prior to December 7, 1941 IJN radio traffic was limited, since the IJN played only a minor role in the war against China and therefore was only rarely required to send radio messages in their highest level crypto system. (As well, interception of IJN traffic off China would have been at best spotty.) Rather oddly however, the official history of GYP-1 shows nearly 45,000 IJN messages intercepted during the period from 1 June 1941 until 4 December 1941. Thus, most Japanese encrypted broadcast military radio traffic was Army traffic associated with the land operations in China. [The chief approach is related to cryptanalytic attacks used as long ago as early in the 19th century; Scovell's analysis survives from Wellington's Peninsular Campaign). See Mark Urban, "The Man Who Broke Napoleon's Codes: The Story of George Scovell" (London: Faber), 2001.]

Breaking a superencrypted cipher like JN-25 was a three-step process: (a) determining the "indicator" method to establish the starting point within the additive cipher, (b) stripping away the superencryption to expose the bare code, and then (c) breaking the code itself. When JN-25 was first detected and recognized, such intercepted messages as were interceptable were collected (at assorted intercept stations around the Pacific by the Navy) in an attempt to accumulate sufficient depth to attempt to strip away the superencryption. Success at doing so was termed by the cryptographers a 'break' into the system. Such a break did not produce a cleartext version of the intercepted message. Only after breaking the underlying code (another difficult process) would the message be available, and even then its meaning — in an intelligence sense — might be less than fully clear.

When a new edition was released, the cryptographers were forced to start again. The original JN-25A system replaced the 'Blue' code (as Americans called it), and used five-digit numbers, each divisible by three (and so usable as a quick, and somewhat reliable, error check, as well as something of a 'crib' to cryptanalysts), giving a total of 33,334 legal code values. To make it harder to crack a code value, meaningless additives (from a large table or book of five-digit numbers) were added arithmetically to each five-digit cipher. JN-25B superseded the first release of JN-25 at the start of December 1940. JN-25B had 55,000 valid words, and while it initially used the same additive list, this was soon changed and the cryptanalysts found themselves entirely blacked out again.

Over the years, various claims have been made as to the progress made decrypting this system, and arguments made over when it was readable (in whole or part). Lt. "Honest John" Leitweiler, Commander of Station CAST, the Philippines, stated in November 1941 that his staff could “walk right across” the number columns of the coded messages. He is frequently quoted in support of claims JN-25 was then mostly readable. This comment, however, refers not to the message itself but to the superenciphering additives and referred to the ease of attacking the code using a new method for discovery of additive values.

The 16 November 1941 letter [Navy Department, Philippines Operations Summaries, 3200/1-NSRS.] to L.W. Parks (OP-20-GY) sent by Leitweiler states, "We have stopped work on the period 1 February to 31 July as we have all we can do to keep up with the current period. We are reading enough current traffic to keep two translators very busy." Another document, Exhibit No. 151 from the Hewitt Inquiry has a copy of the US Navy message OPNAV-242239 'Evaluation of Messages of 26 November 1941' which has in part: '1. Reference (a) advised that Com 16 intercepts were considered most reliable and requested Com 16 to evaluate reports on Japanese naval movements and send dispatch to OPNAV, info CINCPAC. Com 16's estimates were more reliable than Com 14's, not only because of better radio interception, but because Com 16 was currently reading messages in the Japanese Fleet Cryptographic System ("5-number code" or "JN25") and was exchanging technical information and translations with the British C. I. Unit at Singapore. Arthur McCollum knew this and gave it due consideration when he drafted the McCollum memo. Duane L. Whitlock, (traffic analyst at CAST [Quoted by Stinnett (note 8 to Chapter 2), Whitlock expressly contradicts Stinnett's thesis.] ), was not aware before the attack that IJN movement traffic code was being read. "Reading" in this context means being able to see the underlying code groups, not breaking out the messages into plaintext. [ [ Foreknowledge of Pearl Harbor? No!: The story of the U. S. Navy's efforts on JN-25B | Cryptologia | Find Articles at BNET ] at] The Hewitt Inquiry document also states, "The "5 numeral system" (JN-25B) yielded no information which would arouse even a suspicion of the Pearl Harbor raid, either before or afterward."

The claim that no pre-attack IJN message expressly mentioned Pearl Harbor is perhaps true. Similarly are the claims no PURPLE traffic likewise pointed to Pearl Harbor. To note, however, in both instances neither all traffic (IJN nor PURPLE) from these pre-attack intercepts have been declassified and released to the public domain. Hence, any such claims are now indeterminate, pending a fuller accounting.

Additionally, no decrypts have come to light of JN-25B traffic, and importantly identified as such, with any intelligence value prior to Pearl Harbor. Such breaks as recorded by authors W.J. Holmes and Clay Blair, Jr., were into the additive tables, which was a required first step of two.Fact|date=July 2007 The first 100 JN-25 decrypts from all sources in date/time order of translation have been released, and are available in the National Archives. The first JN-25B decrypt was in fact by HYPO (Hawaii) on 8 January 1942 (numbered #1 up JN-25B RG38 CNSG Library, Box 22, 3222/82 NA CP). The first 25 decrypts were very short messages or partial decrypts of marginal intelligence value. As Duane Whitlock stated, "The reason that not one single JN-25 decrypt made prior to Pearl Harbor has ever been found or declassified is not due to any insidious is due quite simply to the fact that no such decrypt ever existed. It simply was not within the realm of our combined cryptologic capability to produce a usable decrypt at that particular juncture." [The Truth About Pearl Harbor: A Debate Stephen Budiansky The Independent Institute 1/30/03]

Detailed month by month progress reports have shown no reason to believe any JN-25B messages were fully decrypted before the start of the war. Tallied results for September, October, and November reveal roughly 3,800 code groups (out of 55,000, about 7%) had been recovered by the time of the attack on Pearl Harbor.

Detection of Japanese transmissions

As the Japanese "Kido Butai" (Special Attack Force), led by Admiral Chuichi Nagumo, neared Hawaii, there is claimed to have been a flurry of radio traffic that begat warnings to US intelligence and even directly to those with White House connections. For instance, the Matson liner SS "Lurline", heading from San Francisco to Hawaii on its regular route, is said to have heard and plotted unusual radio traffic, noting that telegraph code used was very different from International Morse. That traffic, which is said to have persisted for several days, and noted as coming from a moving source and not shore stations, is further claimed by some to have been from the approaching Japanese fleet. There are several problems with this analysis. Surviving officers from Nagumo's ships state there was no radio traffic to have been overheard by anyone; their radio operators had been left in Japan to fake traffic for the benefit of listeners ("i.e.", military intelligence traffic analysts in other countries), and all radio transmitters aboard Nagumo's ships were physically disabled to prevent inadvertent broadcast and subsequent tracking of the attack force.

According to a 1942 Japanese after action report [ "Dai Toa Senso Senkun [Koku] [Hawai Kaisen no Bu] Dai Ichi Hen, Battle Lesson of Hawaii (a 1942 document) appendix in volume, Senshi Sosho: Hawai Sakusen, Tokyo: Boeicho Kenshujo Senshishitsu; 1967] "In order to keep strict radio silence, through steps such as taking off fuses in the circuit, holding and sealing the keys were taken. During the operation, the strict radio silence was perfectly carried out.... The "Kido Butai" used the radio instruments for the first time on the day of the attack since they had been fixed at the base approximately twenty days before and proved they worked well. Paper flaps had been inserted between key points of some transmitters on board "Akagi" to keep the strictest radio silence..." Commander Genda, who helped plan the attack stated, "We kept absolute Radio Silence". For about two weeks before the attack, 31 ships "used flag and light signals" (semaphore and blinker), perfectly usable with task force ships remaining in line of sight. Kazuiyoshi Koichi, the Communications Officer for "Hiei", dismantled vital transmitter parts and kept them in a box that he used as a pillow to prevent "Hiei" from making any radio transmissions until the attack on Pearl Harbor had commenced. [David Kahn, "The Codebreakers", p.33] Former Lieutenant Commander Chuichi Yoshoka, communications officer aboard the flagship, "Akagi", said he did not recall any ship dispatching a radio message before the attack. [Layton, E. T., 1985, "And I was there", p.547n15.] Furthermore, Captain Kijiro, in charge of the three "Kido Butai" submarines, stated nothing of interest occurred during the transit to Hawaiian waters. [Jacobsen, P. H. (Burke, C. editor) (2007), p.227.] Vice Admiral Ryunosuke Kusaka stated, "It is needless to say that the strictest radio silence was ordered to be maintained in every ship of the Task Force. To keep radio silence was easy to say, but not so easy to maintain." There is nothing in the Japanese logs or after action report that shows that radio silence was broken until after the attack. Which Kusaka worried about when briefly broken on the way home. [Goldstein and Dillon, "The Pearl Harbor Papers", pp.136 and 143.]

An often debated subject is also the appendix to the war-initiating operational order. The message of 25 November 41 from CinCCombined sent to All Flagships from Admiral Yamamoto stated, "Ships of the Combined Fleet will observe radio communications procedure as follows: 1. Except in extreme emergency the Main Force and its attached force will cease communicating. 2. Other forces are at the discretion of their respective commanders. 3. Supply ships, repair ships, hospital ships, etc., will report directly to parties concerned." Furthermore, [Goldstein and Dillon, eds. "The Pearl Harbor Papers: Inside the Japanese Plans", p.149, "Operational Plan Given to Whole Fleet at Hitokappu Bay".] "In accordance with this Imperial Operational Order, the CinC of the Combined Fleet issued his operational order, ... The Task Force "then drew up its own operational order," which was given for the first time to the whole force at Hitokappu Bay. ..." However also stated is under the appendix to that document, paragraph four where the especially secret Strike Force was specifically directed to "maintain strict radio silence from the time of their departure from the Inland Sea. Their communications will be handled entirely on the general broadcast communications net." [ P. Jacobsen pg 14 "Pearl Harbor: Who Deceived Who" letter section Naval History 2/05]

Since to disobey the radio silence orders would mean the location of the entire attack force would have been exposed, the personnel reports fit well with the requirements of the objective. Unfortunately, the current whereabouts of either "Lurline"'s log, or the reports delivered to the Navy or Coast Guard by "Lurline"'s radio operator Leslie Grogan in Hawaii, are not known, so contemporaneously written evidence of what was recorded aboard "Lurline" is not now available - the original logs "Lurline", surrendered to Lt. Cmdr. George W. Pease, 14th Naval District in Honolulu, have disappeared. Grogan commented on a signal source "moving" eastward in the North Pacific over several days as shown "via" "relative bearings" which then "bunched up" and stopped moving. ["The Broken Seal: OPERATION MAGIC and the Secret Road to Pearl Harbor" written by Ladislas Farago, Bantam Books edition 1968, "POSTSCRIPT - New Lights on the Pearl Harbor Attack," pp. 379-389.] ["Warning at Pearl Harbor: Leslie Grogan and the Tracking of the "Kido Butai" by Brian Villa and Timothy Wilford, "The Northern Mariners/Le Marin du nord, Volume 11, Number 2 (April 2001), pages 1-17.] Generally, however, the directions given by Grogan in a recreation of the logbook for the Matson Line are consistent with locations used for radio deception by the Japanese (from the homeland) at the time. A recently discovered missing report by Grogan, dated 10 December 1941 and titled "Record for Posterity", also does not support claims of "Kido Butai" broadcasting.Fact|date=October 2007

Another technique confirmed to be used by the Japanese was the practice of radio deception. Susumu Ishiguru, intelligence and communications officer for Carrier Division Two, stated, "Every day false communications emanated from Kyushu at the same time and same wavelength as during the training period." This gave Rochefort the idea First Air Fleet remained in Home Waters for routine training. The ships left their own regular wireless operators to carry on "routine" radio traffic. Captain Sadatoshi Tomioka stated, "The main force in the Inland Sea and the land-based air units carried out deceptive communications to indicate the carriers were training in the Kyushu area." The main Japanese naval bases (Yokosuka, Kure, and Sasebo) all engaged in considerable radio deception. By analyzing DF bearings (when such bearings were obtained) from Navy directional finder stations, claimed breaks of radio silence can be accounted for, and by plotting the bearings directions, they match up with the various locations previously mentioned, instead of the actual locations of those ships on the relevant dates. [Jacobsen, "Pearl Harbor: Who Deceived Whom?", "Naval History Magazine" December 2003.]

Rochefort claims there were no dummy messages used anytime throughout 1941 and that there was no effort by the Japanese to use serious deception. He also stated, when asked after the attack just how he knew where "Akagi" was, he recognized her "same ham-fisted" radio operators. However, the critical DF tracked radio transmissions have clearly shown bearings that could have not come from the strike force. Emissions monitored from CAST [Wilford, T. (2001) "Pearl Harbor Redefined: USN Radio Intelligence in 1941", pp.68-69] or CAST's report "Akagi" was off Okinawa on 8 December 1941, are examples, though some transmissions continue to be debated. [Jacobsen, P. H. Burke C. (2007) "Radio Silence of the Pearl Harbor Strike Force Confirmed Again: The Saga of Secret Message Serial (SMS) Numbers", p.226]

One suggested example of a "Kido Butai" transmission is the November 30, 1941 COMSUM14 report in which Commander Joseph Rochefort, commanding HYPO, mentioned a "tactical" circuit heard calling "maru"s". [SRN-116476] (a term often used for commercial vessels or non-combat units). Further, the perspective of U.S. naval intelligence at the time was, "... The significance of the term, 'tactical circuit' is that the vessel itself, that is AKAGI, was using its own radio to call up and work directly the other vessels rather than work them through shore stations via the broadcast method which was the common practice in Japanese communications. The working of the AKAGI with the Marus, indicated that she was making arrangements for fuel or some administrative function, since a carrier would rarely address a maru." [Proceedings of the Hewitt Inquiry, p.515.]

Statements by high-ranking officials

One perspective is given by Vice Admiral Frank E. Beatty, who at the time of the Pearl Harbor attack was an aide to the Secretary of the Navy Frank Knox and was very close to President Franklin D. Roosevelt's inner circle, with perspicuous remarks as, "Prior to December 7, it was evident even to me... that we were pushing Japan into a corner. I believed that it was the desire of President Roosevelt, and Prime Minister Churchill that we get into the war, as they felt the Allies could not win without us and all our efforts to cause the Germans to declare war on us failed; the conditions we imposed upon Japan — to get out of China, for example — were so severe that we knew that nation could not accept them. We were forcing her so severely that we could have known that she would react toward the United States. All her preparations in a military way — and we knew their over-all import — pointed that way." [Vice Admiral Frank E. Beatty, "Another Version of What Started the War with Japan," "U. S. News and World Report", May 28, 1954, p. 48.]

Another "eye witness viewpoint" akin to Beatty's is provided by Roosevelt's administrative assistant at the time of Pearl Harbor, Jonathan Daniels; it is the telling comment about FDR's reaction to the attack - "The blow was heavier than he had hoped it would necessarily be. ... But the risks paid off; even the loss was worth the price. ..." ["1941: Pearl Harbor Sunday: The End of an Era," in "The Aspirin Age - 1919-1941," edited by Isabel Leighton, Simon and Schuster, New York, 1949, page 490.]

"Ten days before the Attack on Pearl Harbor", Henry L. Stimson, United States Secretary of War at the time "entered in his diary the famous and much-argued statement - that he had met with President Roosevelt to discuss the evidence of impending hostilities with Japan, and the question was 'how we should maneuver them [the Japanese] into the position of firing the first shot without allowing too much danger to ourselves.'" [ Cumings, Bruce: "Parallax Visions: Making Sense of American-East Asian Relations" Duke 1999 p. 47; Text above from Wikipedia's Henry L. Stimson] "

Mark Parillo, in his essay "The United States in the Pacific", wrote that " [t] hese theories tend to founder on the logic of the situation. Had Roosevelt and other members of his administration known of the attack in advance, they would have been foolish to sacrifice one of the major instruments needed to win the war just to get the United States into it." [Parillo, Mark, "The United States in the Pacific", in Higham, Robin, and Harris, Stephen, "Why Air Forces Fail: The Anatomy of Defeat" (Lexington: University Pres of Kentucky, 2006), p.289.]

One quote is often used to add legitimacy to the notion the British Government knew in advance the attack was coming. Oliver Lyttelton, the British Minister of War Production, said, "... Japan was provoked into attacking the Americans at Pearl Harbor. It is a travesty of history ever to say that America was forced into the war. Everyone knows where American sympathies were. It is incorrect to say that America was truly neutral even before America came into the war on an all-out basis." [Gordon Prange, "Pearl Harbor: The Verdict of History", p.35.] If Britain, did, indeed know and chose to conceal, "withholding this vital intelligence only ran the risk of losing American trust", [Parillo, in Higham and Harris, p.289.] and with it any further American aid, which would be reduced after the attack in any event.

When considering information like this as a point for or against, the reader must keep in mind questions such as: was this official privy to information about the U.S. government? Did he have communications with high-level administration figures such as President Roosevelt or Ambassador Joseph Grew? Is this just a strongly held personal opinion? Or were there measures justifying this view?

Lend-Lease, enacted in March 1941, informally declared the end of American neutrality in favor of the Allies by agreeing to supply Allied nations with war materials. The signing of the bill into existence, because the materials would be used to combat the Axis powers, made the United States a "de facto" hostile and opened her to future attack.

In addition, Roosevelt authorized U.S. destroyers to report U-boats, then later authorized "shoot on sight". Neither is the act of a disinterested neutral.

Furthermore, one position discussed in author Robert Stinnett's "Day of Deceit" suggests a memorandum prepared by Office of Naval Intelligence Lieutenant Commander Arthur McCollum was central to U.S. policy in the immediate pre-war period. The memo suggests only a direct attack on U.S. interests would sway the American public (or Congress) to favor direct involvement in the European war, specifically in support of the British. An attack "by Japan" would not, could not, do that, as history would prove.

Although the memo was passed to Captains Walter Anderson and Dudley Knox, two of Roosevelt's military advisors, on October 7, 1940, there is no evidence available to suggest Roosevelt ever saw it, nor any he did not. Moreover, although Anderson and Knox offered eight specific plans to aggrieve the Japanese Empire and added, "If by these means Japan could be led to commit an overt act of war, so much the better," of the eight "plans" (actions to be taken) offered in the memo only one was ever implemented in any fashion, and there is considerable doubt the memo was the inspiration. Nonetheless, as shown in "Day of Deceit" [Notes for Chapter Two, paperback edition, pp.321-322, notes 7, 8, and 11.] Stinnett claims all action items were implemented.

ONI is further said to have been aware of Japanese carrier movements. First publicly reported in John Toland’s "Infamy" was a Dutch Rear Admiral's claim to have been present at ONI not long before the 7th. According to Toland, entries in J.E. Meijer Ranneft’s diary made on December 2nd and on December 6th, show that ONI informed Ranneft about two Japanese carriers. Toland claims the diary places these ships northwest of Honolulu. Later, Toland claims the diary states the ships were north. However the diary clearly states "beW" meaning “Westerly" of Honolulu, Hawaii. So the documentary evidence cuts Toland's own ground from under him. Also none of the witnesses present on those dates support Ranneft’s claims, clouding their actual significance considerably. David Kahn's review of Toland's book (The NY Review of Books May 27, 1982) and Zimmerman (IaNS Vol. 17, No 2) suggested the diary could have been reference to carriers near the Marshall Islands. Toland has also made other conflicting and incorrect claims about the diary as well during lectures at IHR.

The diary states at 02:00 (6-12-41) Turner fears a sudden Japanese attack on Manila. At 14:00 the diary states "Everyone present on O.N.I. I speak to Director Admiral Wilkinson, Captain MacCollum, Lt. Cdr. Kramer...They show me – on my request – the place of the 2 carriers (see 2–12–41) West of Honolulu. I ask what the idea is of these carriers on that place. The answer was: ‘perhaps in connection with Japanese rapports [sic] on eventual American actions’. There is not one of ours who speaks about a possible air attack on Honolulu. I myself did not think of it because I believed everyone on Honolulu to be 100% on the alert, as everyone here on O.N.I. There prevails a tense state of mind at O.N.I." These diary entries are provided (in Dutch) in the photo section in George Victor's "The Pearl Harbor Myth: Rethinking the Unthinkable". [photograph section following page 178.]

The McCollum Memo

"Main article : McCollum memo"

On October 7, 1940, Lieutenant Commander Arthur McCollum of the Office of Naval Intelligence submitted a memo to Navy Captains Walter Anderson and Dudley Knox, which details eight actions which might have the effect of provoking Japan into attacking the United States. The memo remained classified until 1994. Sections 9 and 10 of the memo are cited as the "Smoking Gun", and a primary thesis of an influential book (Stinnett's, see further reading) suggests that it was central to the high level conspiracy to lure the Japanese into an attack. Evidence that the memo or derivative works actually reached President Roosevelt, senior administration officials, or the highest levels of US Navy command, is largely conjectural.

From section 10 of the memo:

cquote|If by these means Japan could be led to commit an overt act of war, so much the better. At all events we must be fullyprepared to accept the threat of war. -- A. H. McCollum

Japanese intelligence

Japanese intelligence (espionage) efforts against Pearl Harbor included at least two "Abwehr" agents. One of them, Otto Kuhn, was a sleeper agent living in Hawaii with his family; he and they were essentially incompetent. The other, Dusko Popov, a Yugoslavian businessman, was thought quite effective by "Abwehr", but was actually a double agent whose loyalty was to the British. He worked for the XX Committee of MI5. In August 1941, he was tasked by "Abwehr" with specific questions about Pearl (Masterman's "The Double-Cross System" and Prange's "Verdict" both reproduce it), but the FBI seems to have evaluated the effort as of negligible importance. There has been no report its existence, or even Popov's availability as a double agent, was passed on to U.S. military intelligence or to civilian policy officials. J. Edgar Hoover dismissed Popov's importance, noting (without basis) his British codename, Tricycle, was connected with his sexual tastes. In any case, he was not allowed to continue to Hawaii and to develop more intelligence for the UK and U.S. Regardless, Prange demonstrates Popov's claim to have provided warning is overblown, and makes a case the notorious questionnaire was a product of "Abwehr" thoroughness.

More to the point, the Japanese did not need "Abwehr" assistance, having an active consulate in Hawaii which eventually included on its staff an undercover IJN intelligence officer, Takeo Yoshikawa. [Stinnett insists on using his covername, for reasons that are not clear. ] The consulate had been making reports to IJN Intelligence for years, and Yoshikawa increased the rate of reports after his arrival from Japan. (Sometimes called a "master spy", he was in fact quite young, and his reports not infrequently contained errors.) Pearl Harbor base security was so lax that Yoshikawa, indeed anyone, had no difficulty obtaining access to it, even taking the Navy's own harbor tourboat. (Even had he not, hills overlooking the Harbor were perfect for observation or photography, and were not off-limits.) Gossip with taxi drivers is supposed to have been one of his sources. Some of his information, and presumably other material from the Consulate, was hand-delivered to IJN intelligence officers aboard Japanese commercial vessels calling at Hawaii prior to the War; at least one is known to have been deliberately routed to Hawaii for this purpose during the summer. Most, however, seem to have been transmitted to Tokyo, almost certainly "via" cable (the usual communication method to/from Tokyo). Many of those messages were intercepted and decrypted by the U.S.; most were evaluated as the sort of intelligence gathering all nations routinely do about potential opponents, and not as evidence of an active attack plan. None of those currently known, including those decrypted after the attack when there was finally time to return to those remaining undecrypted, explicitly stated anything about an attack on Pearl; the only exception was a message sent from the Hawaiian Consulate on 6 December, which was not decrypted until after the 7th and was thus moot with regard to questions of U.S. foreknowledge. No cable traffic was intercepted in Hawaii until after David Sarnoff of RCA agreed to assist during a visit to Hawaii immediately before the 7th; such interception was illegal under U.S. law, though it had been going on "sub rosa" in New York for some time. Farago's postscript [Bantam paperback edition] offers a viewpoint from RCA personnel. In the final analysis, illegal co-operation of American cable companies likely changed little or nothing, since radio intercept stations were picking up some of the consular traffic anyway, and American intelligence failed to make optimum use of their information in any case.

Allied intelligence

Locally, Naval Intelligence in Hawaii had been tapping telephones at the Japanese Consulate before the 7th, and, among much routine traffic, overheard a most peculiar discussion of flowers in a call to Tokyo (the significance of which is still publicly opaque and which was discounted in Hawaii at the time), but the Navy's tap was discovered and was disconnected in the first week of December. The local FBI field office was informed of neither the tap nor its removal; the local FBI Agent in Charge later claimed he would have had installed one of his own, had he known the Navy's had been disconnected.

Throughout 1941, the U.S., Britain, and the Netherlands collected a considerable range of evidence suggesting Japan was planning some additional military adventure. The Japanese attack on the U.S. in December was essentially a side operation to the main Japanese thrust to the South against Malaya and the Philippines—many more resources, especially Imperial Army resources, were devoted to these attacks as compared to Pearl Harbor. Many in the Japanese military (both Army and Navy) had disagreed with Admiral Isoroku Yamamoto's idea of attacking the U.S. Fleet at Pearl Harbor when it was first proposed in early 1941, and remained reluctant after the Navy approved planning and training for an attack beginning in spring 1941, and through the highest level Imperial Conferences in September and November which first approved it as policy (allocation of resources, preparation for execution), and then authorized the attack. The Japanese focus on South-East Asia was quite accurately reflected in U.S. intelligence assessments; there were warnings of attacks against Thailand (the Kra Peninsula), Malaya, French Indochina, the Dutch East Indies (Davao-Weigo Line), the Philippines, even Russia. Pearl Harbor was not mentioned.

The U.S. Navy was aware of the traditional planning of the Imperial Japanese Navy for a war with the U.S., as maintained throughout the 1930s and into the 1940s. The Japanese made no secret of it, and in the 1930s American radio intelligence gave U.S. war planners considerable insight in Japanese naval exercises. [Prados, "Combined Fleet Decoded", pp.61 and 87.] These plans presumed there would be a large "decisive battle" between Japanese and U.S. battleships, but this would be fought near Japan, after the numerical superiority of the U.S. Pacific Fleet (assured by the Washington Naval Treaty, and still taken as given) was whittled down by primarily night attacks by light forces, such as destroyers and submarines. [Evans and Peattie, "Kaigun", pp.286-291] This strategy expected the Japanese fleet to take a defensive posture, awaiting US attack, and it was confirmed by the Japanese Navy staff only three weeks before Pearl Harbour . [Evans and Peattie, "Kaigun", p.482.] In the 1920s, the decisive battle was supposed to happen near the Ryukyu islands; in 1940 it was expected to occur in the central Pacific, near the Marshall islands. War Plan Orange reflected this in its own planning for an advance across the Pacific. [Prados, "Combined Fleet Decoded", p.87.] Yamamoto's decision to shift the focus of the confrontation with the U.S. as far east as Pearl Harbour, and to use his aircraft carriers to cripple the American battleships, was a radical enough departure from previous doctrine to leave analysts in the dark.

There had been a specific claim of a plan for an attack on Pearl Harbor from the Peruvian Ambassador to Japan in early 1941. (The source for this bit of intelligence has been traced to the Ambassador's Chinese cook. It was treated with skepticism, and properly so, given the now known nascent state of planning for the attack at the time.) Since Yamamoto had not yet then decided to even argue for an attack on Pearl Harbor, discounting US Ambassador Grew's report to Washington in early 1941, was quite sensible. Later reports from a Korean labor organization also seem to have been regarded as unlikely, though they may have had better grounding in actual IJN events. There has been uncovered no record of a serious belief or conviction by anyone in US or UK military intelligence (in Hawaii or DC or elsewhere), or among US civilian policy officials, prior to the attack, that Pearl Harbor or the US West Coast was on a target list.

Notices to Japanese foreign stations -- the Winds Code message

The "Winds Code" announcing the direction of new hostilities "via" a broadcast weather 'forecast', remains a curious and confusing episode, demonstrating the uncertain meaning inherent in most raw intelligence information, and its handling/mis-handling - and in this case, even uncertainty about the existence of some intelligence information, or of its active removal from official records, especially some years after the event. At most, however, the Winds system was to be implemented only if the communications between Japan and Washington were cut, and since this never obtained prior to the attack, there was no need for it. Given this, any talk of intercepted "Winds" messages would appear to be specious. Note, however, in Safford's testimony on this topic he states very clearly London (not Washington) was the addressee of this message.

There are two problems with this evaluation. First, there is Admiral King's endorsement of the Navy Court of Inquiry, page 344, reading in part, " ... (3) Admiral Kimmel was not informed of the implementation of the "Winds Message". Admiral Stark says he never got this information himself, but it is clear that it did reach Admiral Stark's office. This, together with the handling of other matters of information, indicates some lack of efficiency in Admiral Stark's organization. ..." Second, there exists more documentation for the "Winds Execute" [Briggs' Special Research History - SRH-051, still a very heavily censored document, in the U.S. National Archives] which relates an account of interception of the "Winds Execute", passing the message to ONI, and later, his direct order from Captain Harper [Briggs, SRH-051, p.16.] not to testify in support of Safford at one of the Pearl Harbor hearings. Also see RG457 SRH-255 Archives II College Park MD where Ogg's statements during an interview by Captain Irwin G. Newman were considerably different from Toland's attributions and amplified by authors Stinnett and Wilford, and where neither Ogg or Newman ever mention the Winds code topic.

Official US war warnings

Despite all these fumbles and confusions, in late November 1941, both the US Navy and Army sent explicit war with Japan warnings to all Pacific commands. Although these plainly stated the high probability of imminent war with Japan, and instructed recipients to be accordingly on alert for war, they did not mention the likelihood of an attack on Pearl Harbor itself, instead focusing on the Far East. Washington forwarded none of the raw intelligence it had, and little of its intelligence estimates (after analysis), to Hawaiian commanders, Admiral Husband E. Kimmel and General Walter C. Short. Washington did not solicit their views about likelihood of war or Hawaiian special concerns. Washington's war warning messages have also been criticised by some (e.g., the US Army Pearl Harbor Board - "Do/Don't Messages") as containing "conflicting and imprecise" language.

Since the Army was officially responsible for the security of the Pearl Harbor facilities and Hawaiian defense generally, and so of the Navy's ships while in port, Army actions are of particular interest. Short reported to Washington he had increased his alert level (but his earlier change in meaning for those levels was not understood in Washington and led to misunderstanding there about what he was really doing). In addition, Short's main concern was sabotage from fifth columnists, which accounts for his orders that Army Air Corps planes be parked close together near the center of the airfields. There seems to have been no increased Army urgency about getting its existing radar equipment properly integrated with the local command and control in the year it had been available and operational in Hawaii before the Attack. Leisurely radar training continued and the recently organized early warning center was left minimally staffed. Anti-aircraft guns remained in a state of low readiness, with ammunition in secured lockers. Neither Army long range bombers nor Navy PBYs were used effectively, remaining on a peacetime maintenance and use schedule. In Short's defense, it should be noted he had training responsibilities to meet, and the best patrol aircraft, B-17s and B-24s, were in demand in the Philippines and Britain, both of which had higher priority.

The mistakes made by both Hawaii and Washington meant little was done to prepare for air attack. Inter-service rivalries between Kimmel and Short did not improve the situation. Particularly, most intelligence information was sent to Kimmel, assuming he would relay it to Short, and "vice versa"; this assumption was honored mostly in the breach. Hawaii did not have a PURPLE cipher machine (although, by agreement at the highest levels between US and UK cryptographic establishments, four had been delivered to the British by October 1941), so Hawaii remained dependent on Washington for intelligence from that (militarily limited) source. However, since Short had no liaison with Kimmel's intelligence staff, he was usually left out of the loop. Henry Clausen reported the war warnings could not be more precise because Washington could not risk Japan guessing the U.S. was reading important parts of their traffic ("i.e.", most importantly PURPLE, despite the fact there was no known tactical or strategic info in that traffic).

Additionally, Clausen claims military men of Kimmel and Short's seniority and background should have understood the significance of the warnings, and should have been more vigilant than they were, as for instance in scouting plane flights from Hawaii, which were partial at best in the period just before the attack. All other Pacific commands took appropriate measures for their situations.

Like most commentators, Clausen ignores what the "war warnings" (and their context) explicitly warn, though indistinctly, against. Washington, with more complete intelligence than any field command, expected an attack anywhere on a list of possible locations (Pearl Harbor not among them), and since the Japanese were already committed to Thailand, it seems to have been expected another major operation by them was impossible. Clausen, like most, also ignores what actions Kimmel, Short, and Admiral Claude C. Bloch (Commander, Fourteenth Naval District, responsible for Naval facilities in Hawaii) actually took. They took precautions against sabotage, widely expected as a precursor to war, and reported their preparations. The Hawaiian commanders did not anticipate an air attack, despite good reason to have done so;Fact|date=October 2007 no one did so explicitly.

One major point often omitted from the debate (though Costello covers it thoroughly) is the Philippines where MacArthur, unlike Kimmel or Short, had complete access to decrypted PURPLE traffic (indeed, Stinnet quotes Whitlock to that effect), and was nonetheless caught unprepared and with all planes on the ground nevertheless, nine hours after the Pearl Harbor attack. Caidin and Blair also raise the issue.

Although it has been argued that there was sufficient intelligence at the time to give commanders at Pearl Harbor a greater level of alert, some factors may take on unambiguous meaning not clear at the time, lost in what Roberta Wohlstetter in her masterful examination of the situation called "noise", [Wohlstetter, "Pearl Harbor: Warning and Decision".] "scattered amid the dross of many thousands of other intelligence bits, some of which just as convincingly pointed to a Japanese attack on the Panama Canal." [Parillo, in Higham and Harris, p.289.]

"Inherent invulnerability" of Pearl Harbor

One of the main considerations making an attack against Pearl Harbor unimaginable to many was the depth of Pearl Harbor — generally less than convert|40|ft|m. Depths of less than convert|150|ft|m had been (in the US Navy and others) widely believed insufficient for torpedo attack; at the time, torpedoes dropped from planes dove deeply before attaining running depth and in water that was not deep enough (like Pearl Harbor) would contact the bottom, detonating or embedding themselves in harbor mud.

Not all in the US Navy shared this opinion. A mock air attack on Pearl Harbor during war games in the 1930s was judged to have been a success. Shortly after taking office, Navy Secretary Knox wrote an overview memo which specifically noted the possibility of an attack at Pearl Harbor. Neither observation led to formal policy recommendations to forestall such an attack, however.

The British proved torpedoes, modified for shallow water, could be effective in their attack on the "Regia Marina" at Taranto on November 11, 1940. The US Navy discussed this new development [ as can be seen in a June 1941 memo] , as Taranto was about convert|75|ft|m deep and Pearl less than 40. It was not considered the British attack method was relevant to a torpedo attack at Pearl.

The Royal Navy had used Swordfish torpedo planes, and their low speed was part of the reason the Taranto attack succeeded. The Imperial Japanese Navy no longer had any similar planes, so they had to develop other methods, both hardware and delivery technique. They independently developed shallow water torpedo modifications (called "Thunder Fish") during the planning and training for the attack in 1941. Wooden fins were added to the tail and anti-roll "flippers" kept the torpedo upright once in the water. The fins kept the torpedo's nose level in the air and broke off on entering the water. The flatter "flight" trajectory helped keep them from diving so deeply as to encounter bottom mud (but, despite these modifications, some Japanese torpedoes did indeed reach the bottom and several remain unaccounted for). These simple modifications were not anticipated by the USN, and Admiral Bloch (commander of the Pearl Harbor Naval District) didn't push to install torpedo nets or baffles at Pearl. Nor, it seems, did anyone else. Practical considerations also were an influence. Due to the shallow anchorage (which continues to require regular dredging), installation of torpedo nets would have severely restricted the mobility of vessels entering, leaving, and maneuvering in the harbor.

Kimmel and his staff testified regarding torpedo nets, booms, ...: "(m) Fact XV ... The decision not to install baffles appears to have been made by the Navy Department." ["The Statement of Facts", Part 39, and Navy Court of Inquiry Parts 32 and 33.] . That is, in Washington, DC, rather than in Hawaii.

Role of American carriers

None of the three US Pacific Fleet aircraft carriers were in Pearl Harbor when the attack came. This has been alleged by some to be evidence of advance knowledge of the attack by those in charge of their disposition; the carriers were supposedly away so as to save them (the most valuable ships) from attack.

In fact, the two carriers then operating with the Pacific Fleet, "Enterprise" and "Lexington", were on missions to deliver fighters to Wake and Midway Islands, which were intended in part to protect the route used by planes (including B-17s) bound for the Philippines. (The third, "Saratoga", was in routine refit in Puget Sound, at the Bremerton shipyard.) At the time of the attack, "Enterprise" was about 200 miles west of Pearl Harbor, heading back. In fact, "Enterprise" had been scheduled to be back on December 6th, but was delayed by weather. A new arrival estimate, put her arrival at Pearl around 7:00AM, almost an hour before the attack, but she was also unable to make this schedule.

Furthermore, at the time, aircraft carriers were classified as fleet scouting elements, and hence relatively expendable. [Wilmott, "Empires in the Balance" & "Barrier & the Javelin" (USNIPress, 1982 & 1983); Peattie & Evans, "Kaigun" (USNIPress, 1997); Holmes, "Undersea Victory" (1966); Miller, "War Plan Orange" (USNIPress, 1991); Humble, "Japanese High Seas Fleet" (Ballantine, 1973); Mahan, "Influence of Sea Power on History" (Little Brown, n.d.); Blair, "Silent Victory" (Lipincott, 1975)?; Morison's 14 volume history of USN ops in WW2.] They were not capital ships. The most important vessels in naval planning even as late as Pearl Harbor were battleships ("per" the Mahan doctrine followed by both the U.S. and Japanese navies at the time). [Wilmott, "Empires in the Balance" & "Barrier & the Javelin" (USNIPress, 1982 & 1983); Peattie & Evans, "Kaigun" (USNIPress, 1997); Holmes, "Undersea Victory" (1966); Miller, "War Plan Orange" (USNIPress, 1991); Humble, "Japanese High Seas Fleet" (Ballantine, 1973); Mahan, "Influence of Sea Power on History" (Little Brown, n.d.); Blair, "Silent Victory" (Lipincott, 1975)?; Morison's 14 volume history of USN ops in WW2.] However, as the only major strike power remaining available in the Pacific fleet, carriers became the Navy's most important ships only following the attack.

One question to consider here is that, at the time, naval establishments all over the world regarded battleships, not carriers, as the most powerful and significant elements naval power. So, had the US wanted to preserve its key assets from an invited attack, it would almost certainly have focused on protecting battleships, not carriers.

American response to attack

Closer to the moment of the attack, the attacking planes were detected and tracked as they approached by an Army radar installation being operated that morning as a mostly unofficial training exercise. The Opana Point radar station, operated by two enlisted men (Pvts. Lockard and Elliot) plotted the approaching force, and their relief team plotted them returning to the carriers. Elliott called in the reading to the information center. The call was received by Pvt. Joseph McDonald. McDonald found Lt Kermit Tyler indicating that a large number of planes were coming in from the north and he never received a call like this before. Tyler told McDonald that it's nothing. McDonald called back the Opana radar when he reached Pvt. Joseph Lockard. Lockard told McDonald that the radar return was the largest that he had ever seen. McDonald insisted that Tyler speak directly to Lockard. Lockard was told "Well don't worry about it." McDonald asked Tyler if he should call back the plotters and warn Wheeler Field. Tyler indicated that it was not necessary. The initial radar returns were thought, by the ill-trained junior officer (Lt. Kermit A. Tyler) in charge at the barely operational warning information center at Pearl Harbor, to be a flight of American bombers expected from the mainland. In fact those bombers did arrive, from a somewhat different bearing in the middle of the attack. Additionally, Japanese submarines were sighted and attacked (by USS "Ward") outside the harbor entrance a few hours before the attack commenced, and at least one was sunk—all before the planes came within even radar range. This might have provided enough notice to disperse aircraft and fly off reconnaissance, except, yet again, reactions of the duty officers were tardy. It has been argued failure to follow up on DF bearings saved USS "Enterprise". If she had been correctly directed, she might have run into the six carrier Japanese strike force.

After the attack, the search for the attack force was concentrated south of Pearl Harbor, continuing the confusion and ineffectiveness of the American response.

Roosevelt's desire for war with Germany

Theorists challenging the traditional view that Pearl Harbor was a surprise repeatedly note Roosevelt wanted (though did not say so officially) the United States to intervene in the war against Germany. A basic understanding of the political situation of 1941 precludes such an understanding as reasonable evidence Roosevelt knew of, allowed, or even invited, the Pearl Harbor attack.

First, no attack by Japan on the U.S. was a guarantee the U.S. would declare war on Germany. In such a case, American public anger would be directed at Japan, not Germany, just as happened. The Tripartite Pact (Germany, Italy, Japan) called for each to aid another in case of attack; Japan could not reasonably claim America had attacked Japan if it attacked first. For instance, Germany had been at war with the UK since 1939, and with the U.S.S.R. since June 1941 without Japanese assistance. There was a serious, if low-level, naval war going on in the Atlantic between Germany and the U.S. Navy in the summer of 1941, in any case. Nevertheless, it was only Hitler's declaration of war, unforced by the Axis treaty, several days after the Pearl Harbor attack, that brought the U.S. into the European war.

Clausen and Lee's "Pearl Harbor: Final Judgement" contains some interesting information on the intelligence available to Roosevelt and Churchill prior to the Attack. On page 367 in the Appendix is a PURPLE message, dated 29 November 1941, from the Japanese Ambassador in Berlin to Tokyo. A closing paragraph reads, " ... He (Ribbentrop) also said that if Japan were to go to war with America, Germany would, of course, join in immediately, and Hitler's intention was that there should be absolutely no question of Germany making a separate peace with England. ..." According to David Irving, Churchill (having full access to PURPLE traffic) was well aware of this message, noting it in red ink. [David Irving, "Churchill's War", Volume Two, p.220.] While theorists challenging the conventional view that the Attack on Pearl Harbor was a surprise treat this as a guarantee to join after Japan's attack, it can as easily be taken as a guarantee to come to Japan's aid, as Germany had done for Italy in Libya.

Release of information -- delays and problems with declassification

Conflicting stories regarding FOIA (Freedom of Information Act) requests for the source materials used, e.g., Sheet Number 94644, or materials available at the National Archives are also common among the debate. However, much information has been said to have been automatically destroyed under a destruction of classified information policy during the war itself. Note various authors have nevertheless continued to bring classified Pearl Harbor materials to light "via" FOIA.

For instance, Sheet No. 94644 derives from its reference in the FOIA-released Japanese Navy Movement Reports of Station H in November 1941. Entries for 28 November 1941 have several more items of interest, each being a "movement code" message (indicating ship movements or movement orders), with specific details given by associated Sheet Numbers. Examples are: Sheet No. 94069 has information on "KASUGA MARU" - this being hand-written ("Kasuga Maru" was later converted to CVE "Taiyo"); Sheet No. 94630 is associated with IJN oiler "Shiriya"; and finally for Sheet No. 94644 there is another hand-written remark "FAF using Akagi xtmr" (First Air Fleet using "Akagi"'s transmitter). It is known the movement reports were largely readable at the time. [Pelletier, "Cryptolog", Summer 1992, p.5.]

These three documents (Sheet Numbers 94069, 94630, and 94644) are examples of materials which yet, even after decades and numerous specific FOIA requests, have not been declassified fully and made available to the public. Sheet Number 94644, for example, noted as coming from "Akagi"'s transmitter and as being a "movement code" report, would have likely contained a reported position.Fact|date=July 2007 [For an FOIA-released copy of this 28 November 1941 document, see Timothy Wilford's MA Thesis in History, University of Ottawa, "Pearl Harbor Redefined: USN Radio Intelligence in 1941", copyright Canada 2001, Appendix II, p.154.]

Another issue in the debate is the fact neither Admiral Kimmel nor General Short ever faced court martial. It is alleged this was to avoid disclosing information showing the U.S. had advanced knowledge of the attack. When asked, "Will historians know more later?", Kimmel replied, "' ... I'll tell you what I believe. I think that most of the incriminating records have been destroyed. ... I doubt if the truth will ever emerge.' ..." [Brownlow, "op. cit.", pp.178-179.] It is equally, probably more, likely this was done to avoid disclosing the fact Japanese codes were being read, given there was a war on.

Unreleased classified information

Part of the controversy of the debate centers on the state of documents pertaining to the attack. There are some related to Pearl Harbor which have not been made public. Others may no longer exist, as many documents were destroyed early during the war due to fears of an impending Japanese invasion of the Hawaiian Islands, still others are partial and crudely mutilated. ["Conclusions" Section, from "Signals Intelligence and Pearl Harbor: The State of the Question" appearing in "Intelligence and National Security", Prof. Villa and Dr. Wilford, Volume 21, Number 4, August 2006, pp.520-556.]

* All trans-oceanic telephone conversations (transcripts and recordings) between President Roosevelt and Churchill during November (of interest is especially November 26th) and December 1941 (the first week in particular). Much of this is based on fictional documents with an often claimed location of "Roll T-175" at the National Archives. There is no Roll T-175; NARA does not use that terminology. Also see [ [ / THE CHURCHILL-ROOSEVELT FORGERIES] at]

* Full and "true copy" RDF (Radio Direction Finder) records from all of the US Navy's Pacific facilities as well as those of Allies, for November 1941 and December 1941.

* Complete and "true copy" of all raw intercepts of IJN Operations traffic for 1941, including all communications information (eg, Frequencies Used, Call Signs, TOI, Originator, Action/Information, ..., etc.). SRN-115376 and SRN-116643 are of particular interest for some.

ee also

*McCollum memo
*Day of Deceit
*Conspiracy theories
*Pacific war


Further reading

* Roberta Wohlstetter, "Pearl Harbor: Warning and Decision" (Stanford Univ Press, 1962). A book published early in the debate saying Pearl Harbor was a failure of strategic analysis and ineffective anticipation. In particular, she suggests that inter-Service friction accounted for much of the poor liaison in Hawaii. ISBN 0-8047-0598-4
* John Toland, "Infamy: Pearl Harbor and Its Aftermath" (Berkley Reissue edition, 1986) Some of his sources later claimed his interpretation of their experiences is incorrect. ISBN 0-425-09040-X
* George Victor, "The Pearl Harbor Myth: Rethinking the Unthinkable" (Potomac Books, 2007) openly confronts the level of denial about Washington's advanced knowledge of the Pearl Harbor attack, its "whys and wherefores" and vindicates Kimmel and Short and indicts FDR and his cabal. Offers no "moral" judgments but makes clear a sixty-five year plus cover-up.
* Donald G. Brownlow, "The Accused: The Ordeal of Rear Admiral Husband Edward Kimmel, USN" (Vantage Press, 1968). One of the earliest independent Pearl Harbor accounts. Contains materials based on extensive interviews and personal letters.
*James Rusbridger and Eric Nave, "Betrayal at Pearl Harbor: How Churchill Lured Roosevelt into WWII" (Summit, 1991). This book claims the British intercepted JN-25 and deliberately withheld warning the US because the UK needed their help. There is some question about Rusbridger's reliance on Nave's diaries; some entries don't match his account. ISBN 0-671-70805-8
* Henry C. Clausen and Bruce Lee, "Pearl Harbor: Final Judgement", (HarperCollins, 2001), an account of the secret "Clausen Inquiry" undertaken late in the war by order of Congress to Secretary of War Stimson. Clausen carried a vest bomb to protect the copies of decrypts he was allowed to carry with him. Background notes: (A) Clausen was the assistant recorder for the APHB (Army Pearl Harbor Board) and (B) Bruce Lee was the editor for Prange's "At Dawn We Slept" (See Layton, pages 508-509).
* Martin V. Melosi, "The Shadow of Pearl Harbor: Political Controversy of the Surprise Attack, 1941-1946" (Texas A&M University Press, 1977). Central focus is on the political motivations and partisanship during the war years which delayed public disclosure of the details surrounding this attack, and forced the decision not to court martial Kimmel or Short.
* Ladislas Farago, "The Broken Seal: The Story of Operation Magic and the Pearl Harbor Disaster" (Random House, 1967). Bantam paperback edition Postscript contains an account of "Lurline"'s "interception" and the "disappearing logbook".
* Edwin T. Layton (with Pineau and Costello), "And I Was There - Pearl Harbor and Midway - Breaking the Secrets" (William Morrow and Company, 1985) Layton was Kimmel's Intelligence Officer.
* Robert Stinnett, "" (Free Press, 1999) A study of the Freedom of Information Act documents that led Congress to direct the military to clear Kimmel and Short's records. ISBN 0-7432-0129-9
* L. S. Howeth, USN (Retired), "History of Communications - Electronics in the United States Navy", GPO (Government Printing Office), Washington, DC, 1963. A very good source of material, especially on equipment and capabilities. Chapter XV comments on identifying transmitters by their unique "tone" and a Navy radio operator's court-martial, resulting in conviction.
* Frederick D. Parker, "Pearl Harbor Revisited - United States Navy Communications Intelligence 1924-1941" from the Center for Cryptologic History, National Security Agency, 1944 -now available online [] . Of note are the SRNs given, and there to especially highlight are, for example: (a) the clear distinction the IJN made between shortware versus longwave radio transmissions (see SRN-115397 on page 59), (b) missing paragraphs: "2. Other forces at the discretion of their respective commanders." and "3. Supply ships, repair ships, hospital ships, etc., will report directly to parties concerned." (see SRN-116866 on page 62).
* Mark Emerson Willey, "Pearl Harbor - Mother of All Conspiracies" (self-published in 1999, now available in paperback). Has a detailed timeline of events leading to Pearl Harbor, discusses codebreaking and radio silence, with Appendix A highlighting the many contextural differences as evidenced in SRH-406 - "Pre-Pearl Harbor Japanese Naval Dispatches". Known for having some of the more outlandish claims. Chapter Two "Japanese Navy Codes" provides an excellent tutorial on "hatted" codes, especially JN25. [SRH-406 had several titles, an original non-censored version exits in private hands. A number of "GZ" comments have been removed from today's public version. FOIA requests for this original document have been denied.]
* A. J. Barker, "Pearl Harbor - Battle Book No. 10" (Ballantine's Illustrated History of World War II from 1969). An interesting approach to the sequence of events, rare photographs, having as military consultant/historian the well-known Captain Sir Basil Liddell-Hart. Claims others are mistaken as the belief of "Lurline"'s radioman, based on an inadequate grasp of naval communications.
* Stephen Budiansky, "Battle of Wits - The Complete Story of Codebreaking in World War II", (Free Press, 2000). An account of cryptography and cryptanalysis during World War II. Uncovered a vast amount of detailed information regarding JN-25.
* Michael V. Gannon, "Pearl Harbor Betrayed - The True Story of a Man and a Nation under Attack" (Henry Holt and Company, 2001). Includes letter addressed to Admiral Stark by Admiral Kimmel but never sent - "You betrayed the officers and men of the Fleet by not giving them a fighting chance for their lives and you betrayed the Navy in not taking responsibility for your actions; you ..." Also of note, critiques claims made by R. Stinnett regarding the McCollum memo.
* Gordon W. Prange, with Donald W. Goldstein and Katherine V. Dillon, "At Dawn We Slept (1981)", "Verdict of History", "Pearl Harbor Papers", "Miracle at Midway" The semi-official account of Pearl Harbor by MacArthur's historian during the Occupation. Prange had considerable official access to the Japanese immediately after the war. Regarded by some as error prone. See Layton, pages 495-526, for a critique of Prange (and associates) approach, and Gannon, page 323, note 56.
* John Prados, "Combined Fleet Decoded - The Secret History of American Intelligence and the Japanese Navy in World War II" (Random House, 1995). Quite a lot of new information on Janapese cryptography during the War. Pages 167-172 has more on the "Winds" Message, and on pages 698-699 is a recounting the recovery of the "Nichi" papers by US Navy divers from the "Chanticleer" in Manila Bay (last two photographs prior to page 423).
*David Kahn, "The Codebreakers - The Story of Secret Writing" (The MacMillian Company, 1967). An early, comprehensive account of cryptography. Includes much material on Pearl Harbor issues.
*Fred B. Wrixon, "" (Black Dog and Leventhal Publishers, 1998). An introductory account with many examples - and on page 104 and page 114, are descriptions of the 1943 BRUSA Agreement and 1947 UKUSA Agreement respectively.
*Timothy Wilford, "", (University Press of America, 2001); from his award winning Masters thesis in History from the University of Ottawa - the thesis is available online (ProQuest) with additional materials not included in the book, e.g., the Appendix materials, appendices begin on page 143. Provided on page 143 is a still censored letter from Fabian to Safford from 30 Aug 41. Presented are also other newer materials recently declassified on radio silence, codebreaking, RFP (Radio Finger-Printing), and "Fundamental Ripple" displays.
* Philip H. Jacobsen "Pearl Harbor: Radio Officer Leslie Grogan of the SS Lurline and his Misidentified Signals" (Cryptologia April 2005) Details errors, and conflicting stories within the works of Villa, Wilford, Stinnett, Toland, and Farago. Also covers the missing report of Leslie Grogan dated Dec. 10 1941 titled "Record for Posterity" and compares this with the 26 year old "remembrances" within Farago's "The Broken Seal". Jacobsen concludes what Grogan heard were Japanese commercial ships sending routine plain language radio messages in their specialized Kata Kana telegraphic code.
* Philip H. Jacobsen "Radio Silence and Radio Deception: Secrecy Insurance for the Pearl Harbor Strike Force" (Intelligence and National Security, Vol. 19, No.4 Winter 2004) Author reviews and refutes various claims of Robert Stinnett and most notably the works of Timothy Wilford regarding radio silence.
* John C. Zimmerman "" (Intelligence and National Security, Vol 17, No.2 Summer 2002) Various claims examined and refuted. Of special note: Toland and Stinnett claims of radio silence violations.
*History of GYP-1 General History of OP-20-3-GYP; Activities and Accomplishments of GY-1 During 1941, 1942 and 1943, RG38 CNSG Library, Box 115, 570/197 NA CP "JN-25 has no part to play in the story of Pearl Harbor".
*Duane L. Whitlock, "The Silent War Against the Japanese Navy" available online from the Corregidor Historical Society. Between June 1939 and December 1941 Washington did decrypt a few JN-25 messages, but they provided little insight into the current operational or intelligence picture.
*Costello, John. "Days of Infamy". Pocket Books hardback, 1994. Covers the issue of why MacArthur was unprepared in detail, including mention of access to intelligence.
*Ed., Colin Burke editing. (Posthumously published article, by Phillip H. Jacobsen) "Radio Silence of the Pearl Harbor Strike Force Confirmed Again: The Saga of Secret Message Serial (SMS) Numbers." "Cryptologia" 31, no. 3 (Jul. 2007): 223-232 Abstract: "By analyzing all the available Secret Message Serial (SMS) numbers originated by the Japanese CinC 1st Air Fleet, it is clear that no messages were sent by radio during the formation of the Strike Force or during its transit to Hawaii."

External links

* [ "Did Roosevelt know in advance about the attack on Pearl Harbor yet say nothing?"] — The Straight Dope, Straight Dope Science Advisory Board, February 28, 2001
* [ The Independent Institute: Pearl Harbor Archive] — Mostly a Stinnett site, but also has Pearl Harbor articles, debates, interviews, transcripts, book reviews, books, and Pearl Harbor documents
* [ The National Defense Authorization Act] (where it is noted that available intelligence regarding an impending attack was not conveyed to the American commanders at Pearl Harbor; page 121, section 546).
* [ Closing the Book on Pearl Harbor] — Stephen Budiansky on OP-20-G's progress breaking JN-25 from its appearance in 1939 to 12.7.41. In part a response to Stinnett's (and others') claims of major JN-25 breaks prior to the Attack.
* [ Communism at Pearl Harbor] — An article proposing that the Russians maneuvered the US into war
* [ An Interview with Robert Stinnett and WWII Vet O'Kelly McCluskey.]
* [ Foreknowledge of Pearl Harbor? No!: The story of the U. S. Navy's efforts on JN-25B] — Excellent in depth article illustrating the problems with Stinnett and Wilford's claims regarding JN-25.
* [ The Myths of Pearl Harbor] — Extensive site debunking claims of advance knowledge of the attack.
* [ The Great Pacific War] — 16 years before Pearl Harbor attack, an English naval writer Hector Bywater uncannily prophesied in detail the war in the Pacific.
* [ Pearl Harbor In the Wake of the Prophet] — It prophesied the Pacific War in detail.
* [ Freedom Daily. Sheldon Richman. December 1991. "Pearl Harbor: The Controversy Continues"] Article on foreknowledge as well as steps that might have provoked Japan

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