IN mid-November 1945, three months after the guns fell silent in the Pacific, a joint committee of Congress began a months-long probe to explain the unexplainable: why the United States was caught by surprise at Pearl Harbor.
The circumstances surrounding the devastating Japanese attack that began in the dawn hours of Dec. 7, 1941, absorbed the interest of a nation finally at peace. The event has captivated professional and amateur historians ever since and given rise to one of the most durable conspiracy theories in American history: that President Roosevelt knew of Japanese plans to attack and withheld warnings that might have spared US lives, ships, and aircraft.
Half a century later, most historians have a different view: that Pearl Harbor was the result of what Harvard University scholar Thomas Schelling calls a "supremely ordinary blunder" stemming from military unpreparedness, faulty intelligence analysis, and a failure by policymakers to anticipate Japan's next move in the tense weeks that preceded the attack.
"Pearl Harbor provides a dramatic and well-documented example of an attack presaged by a mass and variety of signals, which nevertheless achieved complete and overwhelming surprise," writes historian Roberta Wohlstetter.
Waves of carrier-based Japanese planes destroyed hundreds of aircraft, immobilized the heart of the US Pacific fleet, and inflicted 3,600 casualties.
Even before the war ended, the national unity produced by the attack gave way to charges by New Deal opponents and diehard isolationists that Washington, not Tokyo, bore most of the blame.
According to the theory advanced by his critics, Roosevelt was determined to find a way to get the US into the war over the objections of an isolationist public and Congress. The result was a cynical plot to place the US Pacific fleet in harm's way and maneuver the Japanese into attacking it.
"It was a costly solution," wrote Roosevelt critic John Flynn in the 1950s. "But it got [Roosevelt] out of a hole and into the one he maneuvered to get into - the war."
The notion of a conspiracy was given credence by Roosevelt's own words, uttered in private to senior military advisers Nov. 25, 1941, and reported later in memoirs by Secretary of War Henry Stimson.
"We are likely to be attacked, perhaps next Monday," FDR said. The question is, "How should we maneuver [the Japanese] into the position of firing the first shot without much danger to ourselves?"
Conspiracy theorists also note that Roosevelt left the expansion-minded rulers of Japan few options. Secretary of State Cordell Hull delivered FDR's ultimatum to Tokyo on Nov. 26 - following protracted negotiations and the imposition of a US embargo on Japan - to withdraw all its armed forces from China and Indochina.
Moreover, as one adviser put it, Roosevelt was indeed "rescued" by the Japanese attack from an agonizing quandary: how to convince America to enter the war before it was too late to save Britain and halt the Nazi advance in Europe.
That said, few historians believe that the desirability of an attack to draw the US into the war meant any foreknowledge by Roosevelt of specific Japanese plans to strike.
The same general conclusion was reached by three major investigations, the last of which (that of the joint congressional committee, issued in 1946) was based on 39 volumes of documents and testimony. In the end, all three suggest the failure to anticipate the attack was the result of mundane factors.
One was the inability of FDR and his advisers to anticipate the illogic of Japan's move. They expected an attack on the Dutch East Indies, Singapore, or even the Philippines - blows that would have expanded Japan's empire without seriously risking war with the US. Instead, Japan hit the one target guaranteed to galvanize support in Congress for a declaration of war.
Another important factor was the failure of US analysts to divine Japan's intentions after breaking its diplomatic code in 1940.
The "MAGIC" intercepts were part of a mass of intelligence that poured into Washington in the months before the war. But while the data was useful for gauging the level of tension in Japanese-American relations, it was less helpful in discovering Japan's intentions.
One reason was that the "signals" contained in the intelligence were often ambiguous or conflicting. Resources and procedures used to evaluate and disseminate intelligence were also inadequate. And, as Ms. Wohlstetter notes, after the event it was much easier to distinguish the relevant signals the information held.
"We failed to anticipate Pearl Harbor not for want of the relevant materials," she writes, "but because of a plethora of irrelevant ones.... If no one is listening for signals of an attack against a highly improbable target, then it is very difficult for the signals to be heard."
What information Washington did have, the congressional investigation concluded, it did not impart adequately to commanders in the field.
"The war taught us this lesson - that we had to collect intelligence in a manner that would make the information available where it was needed and when it was wanted, in an intelligent and understandable form," President Harry Truman wrote later.
Weeks after the attack, the commanding officers at Pearl Harbor - Navy Adm. Husband Kimmel and Army Lt. Gen. Walter Short - were charged with dereliction of duty, demoted, and forced to retire.
"It did not excuse them that Washington did not anticipate that they would be attacked," Mr. Stimson wrote.
Many historians are convinced that the administration made scapegoats of the officers to cover its own mishandling of the events leading up to Japan's attack.
"There's a feeling that 'We have to explain how this debacle could have taken place. We have to put the blame on somebody,' " says Capt. Edward Beach, explaining what he believes was the thinking in the Roosevelt administration.
Curiously, Gen. Douglas MacArthur, commander of US forces in the Philippines, was not demoted, though he also was unprepared for an attack - which came seven hours after Pearl Harbor.
Captain Beach has just published a book that seeks to exonerate the Pearl Harbor commanders. He says if Washington had sent a more explicit warning, Kimmel and Short would have been better prepared.
Admiral Kimmel's family has appealed to have the ranks of the two officers restored posthumously. The results of a Pentagon review will be announced next month.
*Other articles ran Jan. 30, Feb. 13, March 6, April 10, May 5, June 12, July 17, Aug. 4, 8, 14, 21, Sept. 1, and Oct. 16.