Friday, April 3, 2009


Adam Larson / Caustic Logic
The 12/7-9/11 Treadmill and Beyond
April 3 2009

JN-25 is the name given by US cryptanalysts to the Imperial Japanese Navy’s main operational code in 1941. More precisely, it was JN-25B, the second incarnation introduced in Dec 1940 (it was called “AN’ code at the time, and has also been referred to as “5-numeral” code, or variants thereof). A sophisticated code-and-cipher system, JN-25 was based on 5-number groups directly representing words, enciphered with random additives to scramble the number groups. It effectively concealed hundreds of thousands of intercepted IJN messages with among the most vital clues available to Japanese intentions. They believed it unbreakable, but it was finally cracked in spring 1942, helping turn the tide of the Pacific War from the Battle of Midway onward

JN-25-encoded messages include the November 1941 transmission of plans for the Pearl Harbor attack – actually a three-week-long string of communications outlining all the details multiple times in different ways. Whether these messages ever were transmitted by radio is itself an unanswered question, to my knowledge. Most sources, reputable and otherwise, seem to presume it was, but with surprisingly little reason given (I’ll try to settle this at another time). If it were sent on radio waves it would be open to interception, which would put it at the mercy of the cryptographers and code-breakers and offered every clue one would need to fully prepare for the battle of Pearl Harbor

How well the secrets would hold up at that level is a matter of some controversy – the body of evidence supports the general accepted stance that the code was at least partly recoverable, and some 10-15% of this was readable as of November 1941 (different aspects of it changed frequently, including at the end and beginning of that month). Some revisionists have suspected the code may have been completely broken by US analysts prior to December 7, and a few have gone so far as to claim to have proven this – that the intent of the Japanese force was openly available to the top levels of power but withheld from those who were to be sacrificed. I've seen two different clue tracks said to lead to this stance, offered by two different theorists. Both are absolutely worthless (the evidence tracks). [ETA: There are other allegations of pre-12/7 JN-25 penetration by either the British or the Dutch, but these, and their proponents, will be covered later]

The prime champion of JN-25 revisionism is the eminent Robert B. Stinnett, who explains his case in the afterword to the second edition of Day of Deceit, too late a discovery to make it to the first cut in 1999. The main text covering this is a remarkably slim two-and-a-half pages with scant detail, considering the truly massive implications if it were true. In May 2000 he claims to have received over 4,000 never-before-seen documents that revealed to him the “unambiguous truth” that “by mid-November 1941, as Japanese naval forces headed for Hawaii, America’s radio cryptographers had solved the principal Japanese naval codes” [1] Station CAST on Corregidor in the Philippines were the geniuses he credits with the feat. They pierced the "5-num code" as he calls it, by no later than November 16, when CAST’s commanding officer, Lieutenant John M. Lietwiler, wrote to a colleague in Washington:
“we are reading enough current traffic (messages) to keep two translators very busy.” [2]

After spending so much time in the quote mine, that's not much of a nugget to haul back. But thanks to Lietwiler’s historic “admission,” Stinnett can say with no hyperbole “the major secrets of Pearl Harbor are at last out in the open.”

The next few pages highlight some of the new finds, and elaborates on the letter that “notifies naval headquarters” about CAST’s hinted-at breakthrough. “Lietwiler bragged that his crypto yeoman, Albert E. Myers, Jr., had initiated a new technique that allowed the cryppies to “walk right across” the Japanese messages.” A further explanatory note attached to this explains Myers and another guy named Hess were transferred to CAST in September 1941 and brought a new machine, the Jeep IV “for recovering the 5 NUM code.” This wondrous device “enabled the cryppies to recover current (July to December 4, 1941) additives and subtractors for the 5-Num code.” [3]

David Kahn, author of The Codebreakers panned Stinnett's interpretation; he decided the letter "expresses discontent," not joy, over the Jeep IV, and "whatever Lietwiler is discussing, it is clearly not the Imperial Japanese Navy's main, currently used naval cryptosystem, JN 25 B." [4] He offers a fuller excerpt of the letter (parts not shown by Stinnett bolded):
"We are reading enough current traffic to keep two translators very busy, with their code recovery efforts, etc. included. In this connection, I certainly wish you could see your way clear to drop the ancient history of this cipher and work with us on each current system as it comes up."

Another researcher named Timothy Wilford assembled a detailed article on JN-25, and seems to agree with Stinnett's take. However, he offers an even fuller look at the letter, allowing me to see more context for this strangely vague discovery without doing a ton of original research. [5] (This time Stinnett quotes bolded, [...] edits by me):
"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, i.e., with their code recovery efforts, etc. included. In this connection, I certainly wish you could see your way clear to drop the ancient history side of this cipher and work with us on each current system as it comes up. With Singapore, we have adopted a system of exchanging block numbers to prevent duplication. We have more or less given them a free hand in selecting the cipher blocks they tackle on account of their more limited traffic.
Using the 400 high frequency groups we have compiled a table of 24,000
differences. When we are stuck on a column now we take any likely looking group and subtract it from every other group in the column from the master group. […] reference to the table […] reciprocals […] Two days ago I saw MYERS walk right across the first 20 columns of a sheet using this method almost exclusively. In view of this I do not believe we want a new Jeep IV."

“We are reading […] current traffic” is the operative phrase – it does seem to mean understanding the underlying code, but also could mean ‘trying to read,’ or ‘reading for, ‘reading at,’ the difference between looking and seeing just vague enough I’d need more verification than Stinnett provides (which is zero, for the record). It looks like Myers was "walking right across" columns of additives in a manual process, since the Jeep IV was a pain in the arse, rather than across the actual code. All in all, the request seems to be to get help with "work" on "cipher blocks" for the "current system," not the kind of thing you'd ask for if it was already solved.

The second clue track I'd like to look at is one cited by right-wing revisionist Mark Willey, presumably in his book Pearl Harbor: Mother of all Conspiracies, as found on one of his websites. His tip-off reads "the first paragraph of the Congressional Report Exhibit 151 says the US was "currently" (instantly) reading JN-25B and exchanging the "translations" with the British prior to Pearl Harbor." [6] I was able to locate this exhibit in its entirety online. [7] It's a years-later memorandum (May 1945) from Lt. Laurence Safford, a founding member of the US cryptologic community, aka the "Winds execute" guy. Safford lists as references "Com 14-260110 (Nov. 1941), Com 16-261331 (Nov. 1941)," whatever these mean, he seems to be referring to November 1941, and Station HYPO (Pearl Harbor, 14th Naval District or COM 14), and station CAST (Corregidor, Philippines, 16th naval district). The letter reads, in part:
"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. […] some large scale movement involving most if not all of the Japanese Navy was about to take place. […] this estimate * was based entirely on "radio intelligence," the Com 14 C. I. Unit being unable to read anything except the Weather Ciphers and other minor systems of the Japanese Navy at that particular time. This fact was known in the Navy Department, and the Director of Naval Communications and the Director of Naval Intelligence were so informed by me."
* This being "strong force may be preparing to operate in Southeastern Asia while component parts may operate from Palao and Marshalls."

Again we see the ambiguous word "reading." Further passages give context to how that word is meant here; if he meant it was readable as Japanese text, he probably wouldn't say this:
"[T]he current code (JN25B) had been in effect since 1 December 1940, remained in effect until 27-31 May, 1942, and was partially readable in November 1941. A new system of keys was introduced on 4 December 1941 and reported by Com 16_041502, but the carry over of the old code made their solution quite simple, and we were reading messages again by Christmas, Corregidor getting the "initial break" on 8 December 1941."

Reading again, partially as before... nothing new here. The question is just how much, and there has been nothing aside from conjecture to support any more than 10% or so. The next question from there is "which 10%?" Mysteries upon mysteries...

[1] Stinnett, Robert. Day of Deceit: The Truth About FDR and Pearl Harbor. First Touchstone edition, 2001. p. 261
[2] Ibid. p. 262.
[3] Ibid. p. 269.
[4] Kahn, David. Remember Pearl Harbor: Response to Robert Stinnett. The New York Review of Books. February 8 2001.
[5] Wilford, Timothy. Decoding Pearl Harbor: USN Cryptanalysis and the Challenge of JN-25B in 1941. The Northern Mariner/Le marin du nord, XII, No. 1 (January 2002), p. 17 - 37. PDF download link.
[6] Willey, Mark. Pearl Harbor: Mother of All Conspiracies.
[7] Joint Congressional Committe on Investigation of he Pearl harbor Attacks. Exhibit no. 151. Memoranda prepared by Captain Safford. Originally for the Hewitt inquiry.

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