Toshihiro Minohara made a startling discovery while digging through the U.S. National Archives in College Park, Md., last summer. While researching secret codes used prior to the attack on Pearl Harbor 60 years ago, the young Japanese American professor stumbled upon a document, declassified by the CIA about five years ago, that proved that Tokyo had succeeded in breaking the U.S. and British diplomatic codes. A few microfilmed documents, showing the Japanese translations of the telegrams, were attached.
Minohara knew he was on to something important: For decades it was widely believed that Japan, then a developing country with a fierce rivalry between its army and navy, hadn't been up to measure when it came to code-breaking, particularly the documents of the Americans.
"We are so . . . arrogant," said Donald Goldstein, a professor at the University of Pittsburgh and co-author of "At Dawn We Slept: The Untold Story of Pearl Harbor." "It's very possible they could have broken our code, so why shouldn't they have?"
Research in Tokyo Confirms Findings
Further research by a colleague in Japan confirmed the findings--and may shed light on the mind-set that caused Japan's last holdouts for peace to opt for war just weeks before the attack, Minohara said this week.
When Minohara sent fellow Kobe University teacher Satoshi Hattori to check Japan's diplomatic archives in Tokyo, he wasn't optimistic: Most top-secret documents were burned after being read in wartime Japan. Those that remained were confiscated by the U.S. during the occupation that followed Japan's 1945 defeat; they are now housed in U.S. archives.
But Hattori unearthed a folder marked "Special Documents," containing 34 communiques that would have been easy to overlook--and apparently have been by other Japanese researchers numerous times. They are simple typed pages, written primarily in English, of U.S. and British diplomatic discussions and telegrams, many from U.S. Secretary of State Cordell Hull to various U.S. ambassadors.
The contents of the documents have long been known to historians the world over, and some even pop up on the Internet. But their appearance in the Japanese archives reveals that Tokyo knew what was going on in Washington in the weeks before Dec. 7, 1941, when the Japanese attacked Pearl Harbor, killing more than 2,000 people.
Minohara says his findings may shed light on why the few doves in the Japanese Cabinet--in particular, Foreign Minister Shigenori Togo--dropped their opposition to war.
Japan Stunned by Hard-Line U.S. Edict
The U.S., alarmed by the march of Japan's Imperial Army through Asia, had imposed an oil embargo on the nation and told it to get out of China, among other things. Togo had sent a conciliatory rebuttal, known as the "Five Points Plan," offering some concessions and seeking to continue discussions.
Japan knew from the decoded cables that the U.S. had been seriously considering some of the compromises. But on Nov. 26, 1941, the Americans stunned Japan with a hard-line edict essentially ordering Tokyo's troops to get out of China and Indochina or face the consequences. This apparently convinced even Togo that the U.S. had decided on war.
Many historians have speculated that President Franklin D. Roosevelt was looking for an excuse to get into the war in Europe; they posit that he knew Japan would attack but thought the target might be American forces in the Philippines or instead perhaps Malaya, then a British colony, which would prompt the U.S. to come to the aid of its ally.
The newly revealed documents raise an interesting question, Minohara says. Had the American side accepted the compromises it was considering--lifting the oil embargo for three months, permitting Japanese troops to remain in Indochina and continuing discussions on Japan's occupation of Manchuria--would Tokyo have still gone through with the surprise attack on Pearl Harbor?
Japan's war vessels had long before set sail for the Pacific, and the command "Climb Mt. Itaka" meant for Japanese troops to go forward with the attack on Pearl Harbor; but there was also a lesser-known command, "Climb Mt. Tsukuba," which meant return.
"The big question is why the U.S. dropped the offer," says Minohara, 30, who did undergraduate work at UC Davis before moving to Japan for graduate school at Kobe University, where he now teaches.
Togo wrote in his memoirs that, when he read the edict from the U.S., "I was shocked to the point of dizziness. At this point, we had no choice but to take action."
Historians often wondered why he was so shocked. Minohara says Togo's raised expectations that a deal was in the offing led to his anger.
Thomas G. Mahnken, a strategy professor at the U.S. Naval War College in Rhode Island who recently completed a book on U.S. intelligence on Japan in the years before World War II, says the knowledge that Japan was breaking the codes is "significant."
Then again, Mahnken notes, the U.S. diplomatic telegrams "were not tremendously sophisticated," and a number of countries had even broken those used by military attaches.
Neither Japan nor the U.S. had broken the other's military codes prior to Pearl Harbor, Minohara says.
Japanese historians often claim that the U.S. misinterpreted some of the country's telegrams--for instance, that Togo's "Five Points Plan" was translated as a "final offer" when Togo never said that.
Minohara says the Japanese "were doing the same thing. Even though there was no error in the translations, they were still misinterpreting the U.S.' intentions."