Um, the "Magic" intercepts were almost entirely diplomatic in nature. You can read them here: The "Magic" Background To Pearl Harbor I put up the HTML and PDF copies of the "Magic" so folks could see that we knew at the time. We were aware that Japan was keeping an eye on Pearl Harbor, just as they were eyeing Cavite, San Diego, Seattle, the Canal Zone, etc. In case you're referring to the "Bomb Plot" messages, remember that the Japanese never called them that and they weren't considered tactical information then, as they weren't. The pilots didn't need that information, they would just have to look out their canopies.