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Just curious, if the U.S. had broken the Japanese Naval codes, why didn't we know that Pearl Harbor was coming?

IIRC we had broken the diplomatic codes, but not the IJN codes. Until 1942 that is.

funny you should ask..i am reading about that right now....before pearl we knew a attack was coming but not alot of details (ofcourse my grandfather would argue that. on DEC 5th he was hurried from San Fran to PH. ) We did not really "break" the code till just before Midway.....and then it was only about 30 - 40% of the traffic

Remember also Pearl Harbor was placed on Alert on DECEMBER 1st.

They had the right target just the wrong time.

as stated earlier we had not broken the naval code. the japanese changed their call signs on 01nov41 which was normal (every 6 months) but changed them again on 01dec41 which was unusual. the japanese strike force (kito butai) was under strict radio silence to the extent the crystals were removed from all tranismitters. they took a northern route outsid eof normal shipping lanes to avoid detection. also, as late as 01dec41, we thought the the japanese carriers were in home waters. additionally the war warning messages did not mention hawaii as a possible target. and, like terrorists flying airliners into skyscrapers, folks back then could not conceive of an attack on pearl harbor. (that doesn't mean they did not think it was possible, just from a geopolitical outlook it made no sense)

i am in final edit on a paper that is an alternate history story of the attack on pearl harbor. it addresses what the commanders did and did not do and why, makes some realistic changes in command decisions and then shows how these changes altered the outcome of the battle. the japanese plan is not changed.