Roosevelt and Churchill clearly knew that Japan was readying an attack of some kind. Beginning in the 1920s, U.S. cryptologists cracked a series of Japanese codes revealing the country’s war preparations. In 1940, an American named Genevieve Grotjan broke the most secret Japanese diplomatic cypher, code-named PURPLE. A wealth of information about Japan’s intentions followed–even though the most sensitive military cypher remained unbroken. On the night of Dec. 6, 1941, Roosevelt read an intercept ordering the Japanese Embassy in Washington to burn code books and commented: “This means war.”
But war where? Assemble the evidence one way, and a conspiracy seems all too plausible. A British double agent acquired Japanese battle plans describing an attack on Pearl Harbor. U.S. experts decoded a Japanese message ordering that individual ship positions in Pearl Harbor be plotted. A Dutch diplomat warned Washington specifically about an impending attack on the base. Finally, U.S. military officials picked up a coded radio broadcast to Japanese worldwide three days before the attack: Higashi no kazeame (East Wind Rain). It was the “Go” code. Why wasn’t it relayed to Hawaii?
Convinced? Author John Toland was. An extensive review led him to conclude that Roosevelt “had known.” But another interpretation of the available information is arguable. Critics say the truth was buried in a din of intelligence “noise.” The cracked codes revealed Japanese intentions only in a general way. Historian Fred Parker says that messages pinpointing the attack were intercepted. But they were written in a new undeciphered code, “JN-25 Baker.’ Most U.S. analysts expected the Japanese to strike closer to home, like the Philippines (which was in fact attacked). “Though war with Japan was indeed expected,” writes reporter David Kahn in Foreign Affairs, “it is impossible in logic to leap from a general belief to a specific prediction.”
The latest twist on the theory is that Churchill knew, but kept Roosevelt in the dark. This analysis, by British author James Rusbridger, is based on secret war documents he has unearthed and the recollections of Australian cryptographer Eric Nave, who served with Britain during the war and coauthored the new book “Betrayal at Pearl Harbor.” Rusbridger and Nave make a convincing case that while U.S. cryptographers failed to crack Japan’s military code before Dec. 7, British experts had been reading a version of it. Some intercepts pointed to Hawaii. “Although Pearl Harbor was never mentioned by name, all the clues were there,” they write.
But clues aren’t conclusive. Neither is the suggestion that British authorities demonstrated they have something to hide by trying to block the book’s publication there–and refusing to open relevant World War II files. The prevailing belief, Kahn writes, is that “the intelligence, good though it was in certain areas, was not good enough.” But as long as there still are secrets about Pearl Harbor, the conspiracy theory will thrive.
