Everybody knows today what
was very secret in 1941. We had broken
the Japanese code. So how could the
attack on Pearl Harbor have been a surprise?
I believe it should not have been
a total surprise, but it was. We had broken the Japanese diplomatic code, which
was based on the Purple Machine variant of the German Enigma machine. That
said, we had not developed methods to distribute top secret cryptographic
intelligence in a secure way. As a result, Washington gave commanders a general
war warning based on the intercepts, but withheld details in order not to
reveal that we had broken the Japanese code. We also had not broken the
Japanese Naval codes, so we had no detailed knowledge of what was coming and
when. When we broke the diplomatic message we intercepted on December 7
announcing the attack, we did not notify combat commanders because there was no
safe communication channel to do so. Later in the war, there was a whole
specialized structure built to handle the distribution of "Ultra"
source intelligence, as intercepted decoded messages were called. Part of the reason the structure was built was the
breakdown at Pearl Harbor.
The best book I have
found on this subject is "Pearl Harbor Final Judgement" by Henry
Clausen and Bruce Lee. Mr. Clausen was appointed by Secretary of War Stimson as
the official investigator to find out why we were surprised at Pearl Harbor. Here's
a link to a review of the book:
http://www.amgot.org/phclausn.htm
The book I read about how "Ultra" intelligence was distributed is "The Ultra Secret" by F W Winterbotham. A review of the book which includes a warning of the book's inaccuracies and exaggerations is here:
https://www.cia.gov/library/center-for-the-study-of-intelligence/kent-csi/vol19no3/html/v19i3a05p_0001.htm
http://www.amgot.org/phclausn.htm
The book I read about how "Ultra" intelligence was distributed is "The Ultra Secret" by F W Winterbotham. A review of the book which includes a warning of the book's inaccuracies and exaggerations is here:
https://www.cia.gov/library/center-for-the-study-of-intelligence/kent-csi/vol19no3/html/v19i3a05p_0001.htm
This is a link to my LinkedIn discussion of this topic. It has further elaboration.
