For all you Crypto and or just plain History buffs, DoD declassified and released files on Magic - Communications Intelligence for the period leading up to December 7, 1941. Just after the War, President Truman issued an Executive Order prohibiting the release of this information - ever. True, a lot of material here, but a whole lot of insight, new to the public, if not new, confirmed to many that knew or thought that they knew. Do not "cherry pick" the information.
http://www.ibiblio.org/pha/magic/
http://www.ibiblio.org/pha/magic/