SIXTY-FOUR YEARS AGO, Japan stunned our nation with a daring raid on Pearl Harbor, killing 2,400 Americans and crippling the Pacific fleet. That same day, Japan also attacked U.S. forces in Manila, Midway and Wake Islands, and Guam, as well as British forces throughout East Asia. American leaders had anticipated attacks on the latter targets, but not on Pearl Harbor.

In the years following, fierce debates raged--in congressional hearings and among historians--over how the United States could have been so completely surprised. But it was not until the publication of Pearl Harbor: Warning and Decision, historian Roberta Morgan Wohlstetter's 1962 Bancroft Prize-winning study, that the dimensions of this national tragedy came to be fully understood.

Through her painstaking review of the events and decisions preceding Pearl Harbor, Wohlstetter found that the United States had failed to foresee the attack "not for want of the relevant materials, but because of a plethora of irrelevant ones." That is, decision-makers and intelligence analysts--the latter of whom were then decentralized and dispersed among the military services--collectively failed to distinguish the small, faint signals warning of military disaster from the larger, louder mass of background noise suggesting anything but.

Only in retrospect, Wohlstetter stressed, did the warning signals become obvious and discernible. "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," she wrote. "Indeed, at the time 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."

This perennial problem of intelligence analysis--of finding and pulling actionable warning signals from the vast morass of irrelevant background noise--is now known as "the Roberta Wohlstetter problem." The 9/11 attacks renewed public awareness of this problem. Indeed, Wohlstetter's study was referenced by, and served as an intellectual model for, the 9/11 Commission's final report.

But another problem that concerned her deeply has received less attention--namely, what she termed "slow Pearl Harbors." Wohlstetter developed this concept in a 1979 essay in the Washington Quarterly, "The Pleasures of Self-Deception," and in a later, unpublished manuscript. Unlike the dramatic surprises of December 7, 1941, and September 11, 2001, slow Pearl Harbors unfold when "the change at any given time seems innocent enough," but, over time, "the changes add up and can ultimately spell disaster." Here, she elaborated, "the problem is that after each small change even hindsight is not very clear. In fact, one can sometimes argue interminably even about the cumulative disaster."

Wohlstetter saw a slow Pearl Harbor in Britain's reluctance during the 1930s to recognize that Nazi Germany was using arms control agreements not to avoid what Hitler had called "an unlimited arms race," but to slow Britain's rearmament while using ambiguous violations of these agreements to accelerate its own.

Today, the problems posed by nuclear proliferation may be best understood as potential slow Pearl Harbors. Despite prolonged negotiations in the 1990s--in particular, the establishment of the Agreed Framework in 1994--North Korea successfully used a series of ambiguous violations to test American, Western, and international resolve while accumulating plutonium for several nuclear explosives. Lingering uncertainty about North Korea's intentions dissipated in 2003, when Pyongyang withdrew from the Nuclear Nonproliferation Treaty and declared its possession of nuclear weapons.

In 2003, Mohamed ElBaradei, director of the International Atomic Energy Agency, became aware of undeclared Iranian nuclear activities. But today Iran--claiming an intention to comply with IAEA safeguards while nevertheless reasserting its "inalienable right" to practically any nuclear activity short of inserting fissile material into a nuclear explosive's core--is repeatedly testing American, Western, and international resolve.

Last week, ElBaradei agreed with Western assessments that, once Iran's underground uranium enrichment complex at Natanz resumes operation, Iran will be within "a few months" of building a nuclear explosive. Still, he warned against attempts to use non-diplomatic--yet less-than-military--responses to Iranian intransigence. Such responses, the Nobel Peace laureate claimed, would "open a Pandora's box. There would be efforts to isolate Iran; Iran would retaliate; and at the end of the day you have to go back to the negotiating table to find the solution."

But to deal with potential slow Pearl Harbors, Wohlstetter stressed, we must prepare proportional but firm responses to such less dramatic--but nonetheless serious--developments. "Our own counter-strategy first of all must be to take these small changes seriously, even when they seem trivial," she explained. "It is important to make proportionate counter-moves, sometimes to offset the opponent's gains, or to induce him to withdraw."

"There are always a multitude of reasons for turning a blind eye to infractions," she cautioned, "but one essential that runs through many examples is the desire to keep an existing agreement intact, or to keep relations calm, if not actually pleasant, in order to write a new agreement."

If nothing else, Roberta Wohlstetter's writings on Pearl Harbor and "slow Pearl Harbors" should remind us that, in using negotiations as a means to the end of disarming nascent nuclear-armed nations, or preventing nations from building nuclear explosives, we should be careful not to give up our end in order to obtain our means. For disasters, both foreseeable and unforeseeable, may follow.

James Johnson and Robert Zarate are writing a biography of the strategist Albert Wohlstetter, Roberta Wohlstetter's late husband.

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