Two must reads - what was there and the prior warning for the Japanese - http://avalon.law.yale.edu/20th_century/mp06.asphttp://avalon.law.yale.edu/20th_century/mp06.asp
https://www.cia.gov/library/center-for-the-study-of-inthttps://www.cia.gov/library/center-for-the-study-of-intelligence/csi-publications/csi-studies/studies/vol46no3/article07.htmlelligence/csi-publications/csi-studies/studies/vol46no3/article07.html
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There ain't anything there ...