Title: Pearl Harbor Warning and Decision
Author: Roberta Wohlstetter
Wohlstetter, Roberta (1962). Pearl Harbor: Warning and Decision. Palo Alto, CA: Stanford University Press
Date Updated: June 14, 2016
Reviewed by L. B. Kirkpatrick for the CIA Historical Review Program (Sep 22, 1993)
“If our intelligence systems and all our other channels of information failed to produce an accurate image of Japanese intentions and capabilities, it was not for want of the relevant materials. Never before have we had so complete an intelligence picture of the enemy.”
Thus does Roberta Wohlstetter start the seventh and last chapter of her magnificent analysis of the circumstances leading to the disaster of 7 December 1941. Winner of the Bancroft Prize for 1963 and now in its third printing, her book is the most objective examination of the intelligence failure culminated at Pearl Harbor yet published. She makes extensive use of the 39-volume Report of the congressional Joint Committee on the Investigation of the Pearl Harbor Attack as basic source material, but works out her own exceptionally fine study of the intelligence reporting, processing, and estimating.
After her sweeping initial statement in Chapter Seven, Mrs. Wohlstetter qualifies it. She points out that “no single person or agency ever had at any given moment all the signals existing.” And while the decision-makers had at hand an impressive amount of information on the enemy, “they did not have the complete list of targets [estimated to be the objectives of an evidently imminent seaborne attack), since none of the last-minute estimates included Pearl Harbor. They did not know the exact hour and date for opening the attack. They did not have an accurate knowledge of Japanese capabilities or of Japanese ability to accept very high risks…. If we could enumerate accurately the British and Dutch targets … [of] a Japanese attack … either on November 30 or December 7, why were we not expecting a specific danger to ourselves?”
Several reasons are offered. “It is much easier after the event to sort the relevant from the irrelevant signals … Before the event [a signal] is obscure and pregnant with conflicting meanings . . . In Washington, Pearl Harbor signals were competing with a vast number of signals from the European theater … In short, we failed to anticipate Pearl Harbor not for want of the relevant materials, but because of a plethora of irrelevant ones.”
Examples are cited which “illustrate … the very human tendency to pay attention to signals that support current expectations about enemy behavior.” There were other problems for the analysts: there had been previous alert situations and false alarms; the enemy tried to keep relevant signals quiet and conducted an elaborate deception program; there was such careful control over the most important information that “only a very few key individuals saw these secret [MAGIC] messages, and they saw them only briefly. They had no opportunity or time to make a critical review of the material, and each one assumed that others who had seen it would arrive at identical interpretations.”
There were interservice and interservice rivalries and a general disregard for intelligence. “The most glaring example of rivalry in the Pearl Harbor case was that between Naval War Plans and Naval Intelligence. A general prejudice against intellectuals and specialists, not confined to the military but unfortunately widely held in America, also made it difficult for intelligence experts to be heard … Low budgets for American intelligence departments reflected the low prestige of this activity, whereas in England, Germany, and Japan, 1941 budgets reached a height that was regarded by the American Congress as quite beyond reason.”
The doctrinal conclusions the author arrives at in her study are not optimistic. These include:
“The fact that intelligence predictions must be based on moves that are almost always reversible makes understandable the reluctance of the intelligence analyst to make bold assertions.”
“In spite of the vast increase in expenditures for collecting and analyzing intelligence data and in spite of advances in the art of machine decoding and machine translation, the balance of the advantage seems clearly to have shifted since Pearl Harbor in favor of a surprise attacker. The benefits to be expected from achieving surprise have increased enormously and the penalties for losing the initiative in an all-out war have grown correspondingly.”
“If the study of Pearl Harbor has anything to offer for the future, it is this: We have to accept the fact of uncertainty and learn to live with it. No magic, in code or otherwise, will provide certainty. Our plans must work without it.”
While such disturbing conclusions are justified by the history of the Pearl Harbor catastrophe, in which the lack of any capability for systematic analysis and unified estimates loomed large, they are perhaps less fully applicable today than Mrs. Wohlstetter believes. Nothing, to be sure, will “provide certainty,” but the postwar development of the U.S. intelligence effort has substantially eliminated many of the problems and weaknesses, horrendous to contemplate in the brilliance of our 20-20 hindsight, which she describes.
The preceding chapters of the book make a careful analysis of the intelligence organization at Pearl Harbor and a much more penetrating study of Washington intelligence. Particular attention is devoted to signals intelligence, notably to MAGIC intercepts, the “Winds” messages, Japanese espionage reporting, and frequency analysis. There is a look at the three earlier alerts in 1941-June 17, July 25, and October 16-and the effect these had on reactions in December, and careful consideration is given both to diplomatic reporting and to the able press coverage of the deterioration of Japanese-American relations. Finally there is a good study of the Japanese planning which highlights the fact that the Pearl Harbor attack was not finally settled upon until the last minute, a circumstance that did not make the problem any easier for U.S. intelligence.
This is a required textbook for intelligence officers—a little slow-going in spots, but on the whole exceedingly well done.
Reviewed by George C. Constantinides
Much praise has been rightfully heaped on this work. It has been called the most complete study of events leading to the surprise attack, an excellent study of strategic warning, and a most valuable analysis of the questions of indicators, warning systems, estimates, and alerts. Thomas Schelling in the foreword used the adjective “superb.” One writer called it the “vade-mecum for any serious student of the subject.” It is an outstanding analysis of the Pearl Harbor hearings evidence done by a first-class mind and with a sensitive feel for an understanding of the human, organizational, geographic, bureaucratic, and other factors that influence perception in intelligence estimating. She presents them as affecting the identification of critical warning indicators. Wohlstetter provided the terms “signals” and “noise” borrowed from communications theory to denote the type of information analysts and decision makers must deal with. Her treatment of the methods of collection and the interplay of methods, information, and decisions is classic.
Critiques of her analysis have tried to show that it was not complete. Whaley, who called it a brilliant analysis and the “first explicit statement of a systematic hypothesis about the nature and cause of strategic surprise,” pointed out in Codeword Barbarossa that Wohlstetter’s model was useful but only when deception was not practiced. Others concerned with deception and surprise have also argued that Wohstetter did not give it sufficient weight or attention. William Harris, one of that school, in his bibliography Intelligence and National Security, added that she was prevented from analyzing the Japanese side because of language difficulties and her work must be considered incomplete until Japanese records are exhausted and the deception factor is adequately weighed. The reader should not miss other facts and observations she brings forth on intelligence and counterintelligence. As examples we are told (in 1962) that a copy of a PURPLE cryptographic machine was given to Great Britain in 1941 in return for keys and machines needed to decode German codes and ciphers and of the violation of legal norms by the U.S. Navy and the FBI in their prewar counterintelligence work in Hawaii. For one disagreement with her principal conclusion on the attacker’s advantage, consult Michael Howard in the July 1963 issue of World Politics.
This is a review by the Defense Intelligence School.
Case study of a major intelligence failure. One of the most valuable books, not just on the historical event, but also on vital questions of intelligence estimates, alerts, and indications and warning systems.
Reviewed by Paul W. Blackstock and Frank L. Schaf
A well-documented study of the events leading to Pearl Harbor, with sane emphasis .on communications intelligence, its organization and interfaces with the decision makers in government. Also valuable as an insight into indications intelligence and the relationships between communications intelligence and indicators of hostilities.
 Constantinides, George C. (1983). Intelligence and Espionage: An Analytical Bibliography. Boulder, CO: Westview Press, pp. 497-498
 Harris, William R. (1968). Intelligence And National Security: A Bibliography With Selected Annotations. rev. ed. Cambridge, MA: Harvard Univ., Center for International Affairs
 Defense Intelligence School (1981). Bibliography of Intelligence Literature: A Critical And Annotated Bibliography of Open-Source Literature (7th ed, rev.). Washington, DC: Defense Intelligence School, p. 74
 Blackstock, Paul W. (1978) and Frank L. Schaf, Jr. Intelligence, Espionage, Counterespionage, And Covert Operations: A Guide to Information Sources. Detroit: Gale Research Co., p. 127