FDR knew the location of the Japanese fleet. UK & US crypto broke the Japanese codes. NSA released partial documents in the 80s.  " In 1979 the NSA released 2,413 JN-25 orders of the 26,581 intercepted by US between Sept 1 and Dec 4, 1941. The NSA says "We know now that they contained important details concerning the existence, organization, objective, and even the whereabouts of the Pearl Harbor Strike Force." (Parker p 21) Of the over thousand radio messages sent by Tokyo to the attack fleet, only 20 are in the National Archives. All messages to the attack fleet were sent several times, at least one message was sent every odd hour of the day and each had a special serial number. Starting in early November 1941 when the attack fleet assembled and started receiving radio messages, OP-20-G stayed open 24 hours a day and the "First Team" of codebreakers worked on JN-25. In November and early December 1941, OP-20-G spent 85 percent of its effort reading Japanese Navy traffic, 12 percent on Japanese diplomatic traffic and 3 percent on German naval codes. FDR was personally briefed twice a day on JN-25 traffic by his aide, Captain John Beardell, and demanded to see the original raw messages in English. The US Government refuses to identify or declassify any pre-Dec 7, 1941 decrypts of JN-25 on the basis of national security, a half-century after the war."  Read more: PEARL HARBOR - MOTHER OF ALL CONSPIRACIES | WHAT REALLY HAPPENED http://www.whatreallyhappened.com/WRHARTICLES/pearl.php#ixzz5jJ4Uh6Ih