As Japan prepared to enter World War II, the government drew up codes disguised as weather bulletins, to be broadcast on public radio to relay the course of developments to officials and Japanese expatriates in the know.
A crisis in relations with the United States was to be described as "east wind, rainy"; with Britain, "west wind, sunny"; and with the Soviet Union, "northerly wind, cloudy."
Japanese military codes used around the time of the attack on Pearl Harbor in 1941 are already well known: "Climb Mount Niitaka" was an order to launch the surprise raid, and "tora tora tora," was a message indicating its success. But such codes were for military units; the newly revealed codes were for broadcast on open radio for the benefit of government officials and informed Japanese citizens listening overseas.
The United States first learned of the "weather forecast" codes when it intercepted and deciphered a Foreign Ministry telegram on Nov. 19, 1941, being sent to Japanese missions overseas. It read: "If you hear 'east wind, rainy' on the radio, this indicates a crisis in relations between Japan and the United States. Burn encrypted documents."
After the war, a ministry official told U.S. occupation forces of the codes during interrogation. Some details were later reported in official American documents and by other sources, but only now have the codes been confirmed semi-officially, with the release of diplomatic archives on March 7 that show how the codes were used.
The documents are Japanese records of interviews with Kazuji Kameyama, who headed the telegram division of the Foreign Ministry at the start of the war, and with other individuals. The questioning was conducted in November 1945 by an officer of the U.S. occupation forces.
The U.S. interrogator asked Kameyama how the code had been broadcast and when, and about the chain of command behind its release, and about who had thought up the codes.
Kameyama said the staffer in charge of telegrams at the time had already died, "from overwork." He said he had "heard" that the department was doing coded broadcasts and replied that the timing of the message's broadcast was on or before the day of the 1941 assault on Pearl Harbor, "on Dec. 7 or 8." (Because Japan is on the other side of the international dateline, the attack occurred on Dec. 8 in Japan.)
The newly released papers also show that senior officials, including those at the level of Foreign Ministry director-general, took the decision to issue the message. And they quote other ministerial personnel describing the broadcast as "a measure to protect Japanese expatriates."
Another record that refers to this is "20 Seiki Hososhi" (The History of Broadcasting in Japan in the 20th century), a book published by Japan Broadcasting Corp., which quotes a former official as remembering the code's actual broadcast.
Shortly before 4 a.m. on Dec. 8 in Japan, the staffer recalled, a radio announcer suddenly said, "Now, here is the weather forecast."
He followed by saying "west wind, sunny," repeatedly. The attack on Pearl Harbor began at 3:19 a.m.
But the newly released papers suggest a discrepancy here.
The telegram the Americans had intercepted gave "west wind, sunny" as the code referring to a crisis in relations with Britain. It is unclear why it would have been broadcast in reference to the surprise attack on the United States, and the newly released diplomatic documents offer no insight on this point.
By RYOTA ENMAN/ Staff Writer
Applied witchcraft: American communications intelligence satellites during the 1960s
Canadair CL-13 "Sabre" jet fighter and proposed derivatives