Forum: Intelligence
Topic: Japanese penetrated us codes...pre-wwii
started by: David Aiken

Posted by David Aiken on Mar. 25 2003,4:40
Aloha All,

Prior to 7 Dec 1941, there were penetrations of several Allied codes primarily due to break-ins of consulates in Japan.

The State Department's Gray [Japanese called it AF-2] code was penetrated prior to Pearl Harbor...knowing it was broken the State Dept used it to send verbatum text [newspaper accounts or official statements]. FDR even said to send the 6 Dec message to Hirohito in the gray code [he knew it was broken]...the State Dept's two part Brown code was thought to be better, but the Japanese had rifled an American consul office in 1938...it was called AF-6 by the Japanese.

The US Naval attache' in Peiping, China used WIFE code to the chief of Naval Operations. A copy in Tokyo was obtained by burglary.

The British INTERDEPARTMENTAL code was designated BF-2. The code book was lifted by a Japanese clerk typist working in the British Consul in 1935. They similarly pilfered the British merchant ship code in 1936.

There was a [pre war] two digit US Navy code: AN-2 which the Japanese was able to read.

The source for much of this is from, Kazuko Kamaga: "Dai toa senso ni okeru angosen to gendai angosen" [code battle in greater east asia war and the code battle today] in the book by Dodai kurabu koenkai (eds): Showa Gunji Hisshi [confidential stories of the military during Showa].

HTH,
Posted by pjacobsen on Mar. 28 2003,7:54
For a more com plete listing of pre-war Allied codes broken by the Japanese see, Gerhard Krebs, "Signal Intelligence in the Pacific War" in the "Journal of Intelligence History" Vol. 1 No. 2 (Winter 2001) pp. 163-168. However, he only lists one U.S. Army Air Force air code used in China as an Allied WWII military or naval code that was broken. He gives many citations, with a large number being Japanese.  

There is also an SRH in the RG457 series at the National Archives about Japanese code breaking. As I recall, the main codes broken by the Japanese listed there were diplomatic.

Thus, it still appears that the Japanese had little success against Allied naval and military codes during WWII in spite of Professor Krebs' claims of Japanese code breaking successes.

Phil Jacobsen
Posted by David Aiken on Mar. 28 2003,8:48
Wow Phil,
Thanx for a good source! From what I could see the Japanese had more success in consulate-breaking [in] than code-breaking!
Cheers,
David
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