AFTER A LONG day of decoding enemy intercepts, two U.S. military cryptanalysts rushed into the office of Pacific Fleet intelligence officer, Edwin Layton, and put a deciphered message in his hands. Layton’s eyes immediately lit-up. Grasping the implications of the message instantly, he leaped to his feet and darted down the hall to Admiral Chester Nimitz, Pacific Fleet Commander.
The message, received on April 14, 1943 as part of a series of radio-intercepts, was a Japanese naval communication encoded in the usual JN-25D cipher. Its contents were a potential bombshell for the U.S. war effort. Within the message were details of an upcoming flight by Admiral Isoroku Yamamoto to an airstrip on the island of Bougainville, New Guinea. Remarkably, the message contained a precise timetable of the flight, slated for April 18, indicating exactly when the admiral intended to land. It also revealed that Yamamoto and his staff would be traveling in two Betty bombers, that would be escorted by six Japanese Zero fighters. Since Bougainville was at the outer limit of the striking distance of the American airfield on Guadalcanal, the decoded report represented an intelligence jackpot.
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