KOBE — In mid-1941, as tensions between Japan and the United States mounted, Washington took extreme precautions to protect coded diplomatic messages between the U.S. Embassy in Tokyo and the State Department from being intercepted by the Japanese.

The conventional wisdom after the war was that U.S. efforts had been successful. But a chance discovery by two young scholars at Kobe University earlier this year shows that Japan was decoding messages sent during the crucial months before the attack on Pearl Harbor, and experts now say that history will have to be rewritten.

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