You are being lied to
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     One of the beliefs revisionists expouse is that the US was reading Japanese code prior to the attack on Pearl Harbor and thus would have known in advance that the Japanese were planning to attack, where, and when. There were several different codes that the Japanese were using at the time. One of them was code-named "Purple" by the allies and was the code used by Japan's diplomats. This code had been broken and was being read by the US, but this is not the code used by the Japanese Navy.

     The Imperial Japanese Navy used a system they called Code Book D. The US Navy originally called it AN but reclassifed it as JN-25 in April of 1942. For those that want a deeper understanding of JN-25, we have a fact sheet available that goes more in-depth. So the question is, was the US Navy reading messages encyphered in the AN-1/JN-25 system? To answer that, we need to look at historical documents from the National Archives. The following copies of these documents were provided by author Stephen Budiansky, author of "Battle of Wits: The Complete Story of Codebreaking in World War II" and I'd like to thank him for doing so and recommend his book.

     As we can see by Stephen's note above, the total number of messages read by year. Note that not only were no messages read in 1941, but even in early 1942 the messages that were read were not current, meaning that they had been intercepted in the past and only read when enough parts of the code had been successfully retrieved that the message was readable.





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