Book
Pearl Harbor: Warning and Decision
by Roberta Wohlstetter · 1962 · 1 reading card
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Pearl Harbor: Warning and Decision · 1962
The signal is lost not through too little information but through too much irrelevant information.
Roberta Wohlstetter's Bancroft Prize-winning study moved the Pearl Harbor question from who was asleep to why it was not seen. Her answer: the United States failed to anticipate the attack not for want of the relevant materials but because of a plethora of irrelevant ones. The signals were there, but they were few and faint, buried in a larger and louder mass of indications pointing elsewhere. In December 1941 there was ample evidence for all the wrong interpretations, and they looked wrong only after the event. The problem survives in the profession's vocabulary as the signal-to-noise ratio. For an analyst the lesson is practical. More collection does not solve the problem and can make it worse, because noise grows with volume. What helps is knowing in advance which signal you are listening for — explicit hypotheses and indicators defined before the crisis — and judging each clue in its own context rather than with hindsight. The typical trap is the retrospective verdict: it was obvious is almost always the illusion of someone who knows the ending. Her most uncomfortable conclusion: strategic warning cannot be counted on, so defences must be designed to work without it.
“Signals that are characterized today as absolutely unequivocal warnings of surprise air attack on Pearl Harbor become, on analysis in the context of December 1941, not merely ambiguous but occasionally inconsistent with such an attack.”