Surprise attacks, conceived as intelligence failures, have received significant scholarly attention in the half century since Roberta Wohlstetter's (1962) Pearl Harbor: Warning and Decision. The subject also has become, in the hands of politicians and pundits and not just academics, drenched in conventional wisdom. Erik Dahl has written a valuable corrective to much of what is mistaken and misguided in previous commentary and analysis on this subject. His book deftly applies the historical record of relevant cases to the question concerning why the targets of surprise attacks are surprised. In so doing, he convincingly demonstrates that some of the major tenets of the conventional wisdom are wrong.

Dahl comes at this topic with the practical experience of a military intelligence officer, although he states that the conclusions he reached are not what he expected when he began the study. That this is so is a tribute to the thoroughness and objectivity of the study itself. Dahl's command of the applicable literature is strong, and his representation of different strands of thinking within it is fair. The introductory chapter of the book would be useful as a primer on schools of thought about what explains intelligence failures.

The most distinctive aspect of Dahl's methodology, setting it apart from most of what has been written about surprise attack, is to examine successes (i.e., in preventing a surprise attack) as well as failures. This approach minimizes the problems that inevitably follow from selecting on a dependent variable. It also permits pairwise comparisons between otherwise similar historical cases. Regarding conventional attacks, Dahl contrasts failure at Pearl Harbor with success at the subsequent Battle of Midway. As for terrorism, the book compares 9/11 and the earlier attacks on U.S. embassies in Africa with the successful foiling of a plot in 1993 to bomb several landmarks in New York City.

The book supplements detailed examination of these major cases with shorter looks at several other prominent instances of surprise attack, from North Korea's invasion of South Korea in 1950 to Iraq's swallowing of Kuwait in 1990. The author also uses his own database of failed terrorist plots over the past 25 years, making as much of a determination as he can from unclassified sources as to why each plot failed. The use of these different methods—a large-n study, in-depth scrutiny of a few case studies, and something in between—exploits the relative advantages of each. The parallel nature of the conclusions suggested by each method bolsters the persuasiveness of book's overall conclusions.

Dahl's main conclusion is that success in thwarting any adversary's plans for surprise attack depends primarily on two things: the acquisition of detailed, tactical intelligence about those plans—detailed and specific enough to roll up the plot or to take whatever other tactical action is required to defeat the planned attack—and what he calls the receptivity of policymakers to warning information. Receptivity depends, in turn, largely on the policymakers' own prior belief in a looming threat and on their confidence in intelligence. Dahl labels his conclusions a “theory of preventive action,” which is not a self-explanatory term but which is consistent with the important principle that success or failure in warding off surprise attack is a function not just of an intelligence service making a call but of interaction between those who warn and those who must decide whether and how to take any action on the warning.

The conventional wisdom about failures involving surprise attacks is much different from these conclusions. The conventional wisdom errs for several reasons, a couple of which Dahl notes: the focus on failures but not successes, and the heavy role that hindsight habitually plays in looking at failures. The well-known signal-to-noise problem that Wohlstetter highlighted can be a factor, but Dahl shows that with the Pearl Harbor attack as well as other cases, the main difficulty has been that the only available signals were not specific enough about the time, place, and method of the impending attack, not that signals were overwhelmed by noise. An even larger part of conventional wisdom—fostered in particular by the enormously influential 9/11 Commission and the uncritical public acceptance of its views—is that a deficiency in strategic analysis of threats is most often to blame, as is deficient analysis of the sort described by the cliché about “connecting the dots.” Dahl's analysis helps to show that more often with failures there are not enough good dots to connect; that without hindsight, whatever dots that are available can be connected in many plausible ways; and that no matter how good strategic analysis may be, it does not provide the specific information needed to roll up plots or foil attacks. The author’s treatment of the 9/11 case also shows that the commission was factually wrong in asserting that there was inadequate strategic analysis about the threat posed by Al Qaeda.

The book elucidates several implications of Dahl's conclusions concerning how the intelligence agencies or other governmental components might improve their anticipation of impending attacks. The author explains why another of the popular notions that the 9/11 Commission promoted—about a “failure of imagination”—is not helpful. It is easy to imagine many different ways in which an adversary could attack us; what is difficult is getting needed information about the particular way (and time and place) that the adversary will use. Most efforts at organizational reform have also been misdirected because they are based on the conventional wisdom. None of this lets intelligence services off the hook, because one of Dahl's central implications is the need for collection of more and better tactical intelligence.

Intelligence and Surprise Attack could have benefited from a further exploration of the reasons for what is often low receptivity among policymakers for warning intelligence. Sheer inbox-filling decision-making overload is one of them; the attention of senior policymakers is a scarce and precious commodity. Another reason is the preference of policymakers for certain types of action (or inaction) in response. Dahl does touch on this regarding an episode commonly regarded as a “success”: an intelligence prediction that the 1967 Middle East War would result in a swift Israeli victory. Lyndon Johnson was receptive to the intelligence partly because he did not want to rush any aid to Israel anyway.

Limited resources in responding to threats is perennially a reason for what may look retrospectively as an inappropriate lack of responsiveness. Dangers lurk in many places, and governments cannot safeguard themselves preemptively against all of them. Dahl devotes considerable attention to unanswered calls by the U.S. ambassador in Nairobi to beef up security for her embassy before it was bombed in 1998. Might there be some hindsight involved in dwelling on this particular episode, given that other U.S. ambassadors probably could have made comparably justified demands on whatever embassy security resources were available at the time?

This book is an important, cogent, and insightful contribution to the literature on surprise attack. While bearing in mind that warning of such attacks is only one of several intelligence functions, it also would be a useful addition to any curriculum that addresses the ingredients of intelligence success and failure.