[Cryptography] Pearl Harbor

[Hersey, Darren]

I have a link to a google drive provided by the US Cryptological Museum  that contains intelligence reports from back in that time.  There are a lot of documents, and nothing about US non-intel info, but it shows what the US intercepted and decoded at the time in a couple of documents.  There are also other interesting documents about other stuff, the list can easily steal large amounts of time from the curious.

https://drive.google.com/drive/folders/1jQ64F-fsqBCZDV6_ErtQ4zCiVqw_VXWy

Darren Hersey
703-621-4016

From: cryptography <cryptography-bounces+dhersey=akamai.com at metzdowd.com> on behalf of Steven M. Bellovin <smb at cs.columbia.edu>
Date: Thursday, June 19, 2025 at 10:12 PM
To: John Levine <johnl at iecc.com>
Cc: cryptography at metzdowd.com <cryptography at metzdowd.com>, hbaker1 at pipeline.com <hbaker1 at pipeline.com>
Subject: Re: [Cryptography] Pearl Harbor
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You may want to look at page number 37 of https://urldefense.com/v3/__https://www.nsa.gov/portals/75/documents/news-features/declassified-documents/friedman-documents/pearl-harbor/FOLDER_494/41782679082173.pdf__;!!GjvTz_vk!RztMFsWRdXqsP-5qx59xThYr7Ej4AoWkZHGl52qyJON51IiZt_VdNuZFEwvgQITwbWDW6DETa9uRDwg$<https://urldefense.com/v3/__https:/www.nsa.gov/portals/75/documents/news-features/declassified-documents/friedman-documents/pearl-harbor/FOLDER_494/41782679082173.pdf__;!!GjvTz_vk!RztMFsWRdXqsP-5qx59xThYr7Ej4AoWkZHGl52qyJON51IiZt_VdNuZFEwvgQITwbWDW6DETa9uRDwg$>  — it's a declassified document from the Friedman Collection, released by the NSA about 10 years ago. Another document from the Friedman collection, which I can't find at the moment, noted that in May 1941 the US actually wargamed a Japanese carrier-based attack on Pearl Harbor—but forgot about it. Add to that a non-trivial amount of anti-Japanese racism, and you had the makings of a disaster.

From everything I've read, the US had known for quite some time that war was coming, with the tip-off that war was imminent just before Pearl Harbor, but they didn't know just where Japan would strike—attacks much closer to home and to the south were seen as far more likely. Japan had excellent operational security and didn't leak anything. (I once asked an expert why the crack of the Purple machine, used for Japanese diplomatic communications, didn't give any clues—the Allies learned a lot from communications between Tokyo and Berlin (https://urldefense.com/v3/__https://en.wikipedia.org/wiki/Hiroshi_**Ashima__;xYw!!GjvTz_vk!RztMFsWRdXqsP-5qx59xThYr7Ej4AoWkZHGl52qyJON51IiZt_VdNuZFEwvgQITwbWDW6DEThk_i1PY$ ). The answer, I was told, was that the Japanese ambassador had been a general in the Japanese Army, whereas the strike on Pearl Harbor was a Navy operation, and interservice rivalry meant that he and the Army were never told.)

        --Steve Bellovin, https://urldefense.com/v3/__https://www.cs.columbia.edu/*smb__;fg!!GjvTz_vk!RztMFsWRdXqsP-5qx59xThYr7Ej4AoWkZHGl52qyJON51IiZt_VdNuZFEwvgQITwbWDW6DETw3Y-6Tc$<https://urldefense.com/v3/__https:/www.cs.columbia.edu/*smb__;fg!!GjvTz_vk!RztMFsWRdXqsP-5qx59xThYr7Ej4AoWkZHGl52qyJON51IiZt_VdNuZFEwvgQITwbWDW6DETw3Y-6Tc$>
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