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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 were in short supply, and staffs were 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, " Furthermore, OPGY "analysts relied as much on summary reports as on the actual intercepted messages.
However, the U. At times, even President Roosevelt did not receive all information from code-breaking activities.
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Pa Watson , the President's military aide. The Japanese code dubbed " Purple ", which was used by the Foreign Office and only for diplomatic but not for military messages, was broken by Army cryptographers in A part message using this code, sent from Japan to its embassy in Washington, was decoded in Washington on 6 and 7 December.
The message, which made plain the Japanese intention to break off diplomatic relations with the United States, was to be delivered by the Japanese ambassador at 1 p. Washington time dawn in the Pacific. Colonel Rufus S. Bratton , then serving as an aide to Marshall, took this to mean that the Japanese intended to attack at dawn somewhere in the Pacific.
Marshall ordered a warning message sent to American bases in the area, including Hawaii. Due to atmospheric transmission conditions the message was sent out via Western Union rather than the usual signal channels and was not received until the attack was already underway. The claims that no Purple traffic pointed to Pearl Harbor may also be true, as the Foreign Office was not well thought of by the military and, during this period was routinely excluded from sensitive or secret material including war planning. It is also possible any such intercepts were not translated until after the attack, or indeed, after the war ended; some messages were not.
Hence, any such claims are now indeterminate, pending a fuller accounting.
Additionally, no decrypts have come to light of JNB traffic with any intelligence value prior to Pearl Harbor, and certainly no such has been identified. Such breaks as recorded by authors W. Holmes and Clay Blair Jr. The first 25 decrypts were very short messages or partial decrypts of marginal intelligence value. As Whitlock stated, "The reason that not one single JN decrypt made prior to Pearl Harbor has ever been found or declassified is not due to any insidious cover-up It simply was not within the realm of our combined cryptologic capability to produce a usable decrypt at that particular juncture.
The JN superencrypted code, and its cryptanalysis by the US, is one of the most debated portions of Pearl Harbor lore. JN is the U. Navy's last of several names for the cryptosystem of the Imperial Japanese Navy , sometimes referred to as Naval Code D. Superenciphered codes of this sort were widely used and were the state of the art in practical cryptography at the time.
Once it was realized what sort of cryptosystem JN was, how to attempt breaking into it was known. It took much effort and time, not least in accumulating sufficient 'cryptanalytic depth' in intercepted messages prior to the outbreak of hostilities when IJN radio traffic increased abruptly and substantially; prior to 7 December , 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 whatever the highest level crypto system might have been.
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, IJN messages intercepted during the period from 1 June until 4 December Breaking a superencrypted cipher like JN 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 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 always produce a cleartext version of the intercepted message; only a break in the third phase could do so.
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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 JNA 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, 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 element.wordpress-11600-25562-61098.cloudwaysapps.com/the-papers-of-william-thomas.php
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JNB had 55, valid words, and while it initially used the same additive list, this was soon changed and the cryptanalysts found themselves entirely locked 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. 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 letter  to L. Parks OPGY sent by Leitwiler 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. Safford from the Hewitt Inquiry  has a copy of the U. 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 Japanese-to-English translations  with the British unit the Far East Combined Bureau then at Singapore.
Memories of 1941 Pearl Harbor attack continue to affect U.S., Japan in Asia
Arthur H. McCollum was aware of this, and it may have been part of his thinking when he drafted the McCollum memo. Duane L. Detailed month by month progress reports have shown no reason to believe any JNB messages were fully decrypted before the start of the war.
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In all, the U. So convinced were U. Navy planners Japan could only stage a single operation at a time,  after intercepts indicated a Japanese buildup for operations in the Dutch East Indies, for more than two weeks between 1 November and 17 November , no JN message not relating to that expected operation was even examined for intelligence value.
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Japanese espionage against Pearl Harbor involved at least two Abwehr agents. One of them, Otto Kuhn , was a sleeper agent living in Hawaii with his family. Kuhn was incompetent and there is no evidence he provided information of value. In August , he was sent by the Abwehr to the U. It is possible that previous propaganda and forged or unreliable intelligence from the British contributed to J.
Edgar Hoover 's dismissing Popov's interest in Pearl Harbor as unimportant. Popov later asserted his list was a clear warning of the attack, ignored by the bungling FBI. The questions in his list were rambling and general, and in no way pointed to air attack on Pearl Harbor. Prange considered Popov's claim overblown, and argued the notorious questionnaire was a product of Abwehr thoroughness.
Furthermore, the Japanese did not need Abwehr assistance, having a consulate in Hawaii which had on its staff an undercover IJN intelligence officer, Takeo Yoshikawa.
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 Yoshikawa had no difficulty obtaining access, even taking the Navy's own harbor tourboat. Even had he not, hills overlooking the Harbor were perfect for observation or photography, and were freely accessible. 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 with Tokyo. Many of those messages were intercepted and decrypted by the U. 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 Harbor. In November , advertisements for a new board game called "The Deadly Double" appeared in American magazines.
These ads later drew suspicion for possibly containing coded messages, for unknown agents, giving advance notice of the Pearl Harbor attack. The ads were headlined "Achtung, Warning, Alerte! It was suggested that these could possibly be interpreted as giving warning of an air raid on day "7" of month "12" at approximate latitude coordinate "20" Roman numeral "XX". There are claims that, as the Kido Butai the Striking Force steamed toward Hawaii, radio signals were detected that alerted U.