Home > News
  print button email button

Saturday, Dec. 8, 2001


U.S. code said cracked in '41

Staff writer

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.

Toshihiro Minohara, an assistant professor at Kobe University, and Satoshi Hattori, a lecturer, announced that documents discovered in the Foreign Ministry's archives show clearly that the Japanese government had broken secret codes used not only by the United States but also Britain, China and Canada.

"The findings by Minohara and Hattori defy the conventional belief that Japan only decoded clerical matters and that Japan was behind in the information war against the U.S.," Makoto Iokibe, a professor at Kobe University who supervised the research, said at a conference to announce the results Wednesday.

The path to discovery began earlier this year when Minohara was doing research on the Manchurian Incident of 1931 in the U.S.

While digging through declassified CIA documents at the National Archives in Washington D.C., he came upon a letter, written by the CIA in 1967 and classified until 1996, that revealed Japan had cracked U.S. codes prior to the Pearl Harbor attack.

"As soon as I read this, I got hold of Hattori. A search through the Foreign Ministry archives revealed that messages from the U.S. Embassy to Washington from about May to early December 1941 had been decoded by the Japanese a few days after they were sent," Minohara said.

In one set of documents, dated Sept. 22, 1941, and apparently decoded by Japan on Sept. 25, Joseph Grew, then the U.S. ambassador to Japan, notes a nine-point settlement for China that was then being discussed by the Japanese government.

The discussions called for Japanese troops to be withdrawn from China unless they were needed to prevent "communistic and other subversive activities which may constitute a menace to both countries."

In addition, Minohara and Hattori noted that Japan had by Dec. 2, 1941, just five days before the Pearl Harbor attack, decoded a document sent from Washington to the U.S. Embassy in Tokyo on Nov. 28. In the document, Grew was told that a proposed peace plan that the U.S. was considering would be dropped.

The significance of that particular proposal was that it called for an additional three-month period of negotiations, during which the U.S. would consider a slight relaxation of the trade embargo on Japan, as well as allowing Japan to keep some troops in French Indochina.

But Grew received the telegram only two days after Secretary of State Cordell Hull sent Tokyo a note demanding that Japan withdraw all its military forces from China and French Indochina. Japan interpreted the Hull note as a final ultimatum that was impossible to meet and the Pearl Harbor attack went forward.

Minohara added that it was his belief that the late Emperor Showa was aware of the information contained in the decoded messages between Grew and Hull, as he received regular briefings and updates on the negotiations with the U.S. during autumn 1941.

"Emperor (Showa) was probably not told where, exactly, the information came from, but it certainly would have been made available to him," Minohara said.

Proof of what the emperor knew at the time, he said, would probably only be gained if his long-rumored diaries are ever brought to light. While Imperial Household Agency officials claim the diaries do not exist, Minohara does not believe them.

"There's no doubt that Emperor Showa kept a diary. All educated people at the time did," Minohara said.

We welcome your opinions. Click to send a message to the editor.

The Japan Times

Article 8 of 17 in National news

Previous Next

Back to Top

About us |  Work for us |  Contact us |  Privacy policy |  Link policy |  Registration FAQ
Advertise in japantimes.co.jp.
This site has been optimized for modern browsers. Please make sure that Javascript is enabled in your browser's preferences.
The Japan Times Ltd. All rights reserved.