After the United States understood the code, it was possible to study messages from the Japanese ambassador to Germany and to his supervisors in Japan.
Understanding these messages helped the United States prepare for a possible war in the Pacific with Japan. Yet, the United States was surprised by the Japanese attack on Pearl Harbor, Hawaii. The Japanese military did not send coded military information to the country’s diplomats. Military messages used different codes.
After the attack on Pearl Harbor, an American Naval officer named Joseph Rochefort struggled to understand the Japanese navy code. He worked on the American base at Pearl Harbor. It was early in 1942. The American naval commander in the Pacific Ocean was Chester Nimitz. His forces were much smaller than the Japanese Naval forces. And the Japanese had been winning many victories.
Joseph Rochefort had worked for several months to read the secret Japanese Naval code called JN-25. If he could understand enough of the code, he would be able to give Admiral Nimitz very valuable information. The admiral could use this information to plan for battle. By the early part of the year, Mr. Rochefort and the men who worked with him could read a little less than 20 percent of the Japanese JN-25 code.
From the beginning of 1942, the Japanese code discussed a place called “AF.” Joseph Rochefort felt the Japanese were planning an important battle aimed at “AF.” But where was “AF”? After several weeks, he and other naval experts told Admiral Nimitz that their best idea was that the “AF” in the Japanese code was the American-held island of Midway. Admiral Nimitz said he must have more information to prepare for such an attack.
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2013-11-25
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