Today is the 70th anniversary of the attack on Pearl Harbor. In our chapter on foreign policy and national security, we cite the most influential book on the attack, Roberta Wohltstetter's Pearl Harbor: Warning and Decision. At the History News Network, historian Robert Divine summarized:
Relying on the 39 volumes of the 1945-46 congressional hearings, as well as the extensive secondary literature, Wohlstetter set out to explain what had gone wrong in 1941. The primary difficulty, she argued, was separating"signals" (intelligence data that pointed to what actually happened) from"noise" (the flood of conflicting reports and assessments that pointed toward other possible outcomes)."To understand the fact of surprise," she wrote,"it is necessary to examine the characteristics of the noise as well as the signals that after the event are clearly seen to herald the attack." (p. 3)
Wohlstetter explored the range of contingencies facing American intelligence analysts in the months prior to the Pearl Harbor attack in 1941. Several times warnings were sent to Pacific commanders referring to the likelihood of a Japanese move to the north - an invasion of the Pacific maritime provinces of the Soviet Union. Other warnings dealt with the oil-rich Dutch East Indies, the Philippines, and most often, the Panama Canal, vital to American defense in the Pacific. As it turned out, the Japanese did attack the Dutch East Indies and the Philippines, as well as Hawaii, but not Siberia or Panama. But only after the attack on Pearl Harbor did the signals become clear -- only then could an investigator focus on the data pointing to the likelihood of an attack on the American fleet and dismiss information suggesting moves against the Panama Canal as"noise."
Roberta Wohlstetter's conclusions about the Pearl Harbor attack bear directly on the question of an intelligence failure on September 11, 2001. She points out the folly of 20-20 hindsight by observing that"it is much easier after the event to sort out the relevant from the irrelevant signals.""After the event," she continues,"of course, a signal is always crystal clear; we can now see what disaster it was signaling, since the disaster has occurred." (p. 387) In the case of Pearl Harbor, she contends,"there was a good deal of evidence available to support all the wrong interpretations of last-minute signals, and the interpretations appeared wrong only after the event." (p. 392)