Shortly before 3 a.m. on January 31, 1968, a squad of Vietcong guerrillas blasted a hole in the outer wall of the U.S. Embassy compound in Saigon, gunned down two American military policemen who tried to stop them, and laid siege to the lightly defended headquarters building where the flag of the United States was officially planted in South Vietnam.

As part of a nationwide wave of surprise attacks by the Communists during the Lunar New Year—the Tet holiday—the resulting six-hour battle was militarily inconsequential. In fact, in strictly military terms, the two-month struggle known as the Tet Offensive was a disaster for the attackers. It ended with the expulsion of the North Vietnamese Army and the southern-based insurgent troops, known in the West as Vietcong, from each place they invaded.

In the theater of public opinion in the United States, however, the attacks were a great success for the North Vietnamese. Brought into the living rooms of Americans by new communications satellites over the Pacific, scenes of the carnage, particularly at the embassy, severely damaged national confidence in the war policies of President Lyndon Johnson, who was already under fire from a frustrated citizenry in a presidential election year. The dramatic developments set in train during Tet led eventually to the withdrawal of American forces and the collapse of South Vietnam.

Tet was a historical anomaly: a battlefield defeat that ultimately yielded victory. This remarkable result accounts for Tet's resonance whenever U.S. military forces meet even temporary reverses. In the 12 months after Baghdad fell in April 2003, for example, more than 200 stories in major English-language newspapers referred to the Tet Offensive. And faced with a flare-up of attacks in Iraq this past June, Secretary of Defense Donald Rumsfeld told a radio interviewer that he had no doubt the insurgents had "read about Tet and the fact that if they make a big enough splash, even though they get a lot of people killed and we pound them, they end up winning psychologically."

Nearly four decades after the battle, Tet still provokes sharp debate. Why did the attack come as such a surprise? Did the American press misreport a U.S. victory as a defeat? Such questions drew more than three dozen historians, some unborn when the battle took place, to reassess the Tet Offensive at this year's meeting of the Society for Military History in Bethesda, Maryland. (As a correspondent for the Knight newspapers during Tet and author of a book on the subject, I was invited to participate.)

At the time of the Tet Offensive, I had been covering the Vietnam War for three years, ever since Johnson dramatically raised the U.S. stake in the war by sending in ground combat troops. After arriving in Saigon on January 1, 1968, for my third extended visit to the war zone, I made plans to go at the end of the month to neighboring Laos in order to escape the journalistic void that would likely envelop Vietnam during Tet, the Lunar New Year and by far the most important national and family holiday for Vietnamese. But when I got to Laos, a British doctor told me that "the Vietcong have taken over the U.S. Embassy in Saigon" (news that was a gross exaggeration). Commercial flights to Vietnam were shut down, but I was able to reach a silent and demoralized Saigon on a U.S. military aircraft three days after the battle began. By then, the city was filled with the odor of rotting garbage and, here and there, the stench of the dead.

During the weeks that followed, I traveled widely. In the former imperial capital of Hue, I covered the bloody fighting of U.S. Marines and South Vietnamese troops and the North Vietnamese regulars who held the citadel of the former Nguyen emperors for 25 days before being driven out. It was in Ben Tre, a provincial capital in the Mekong Delta I visited on February 7, that an unnamed U.S. major famously told Peter Arnett of the Associated Press that "it became necessary to destroy the town to save it." Nearly everywhere I went, the lack of preparedness for the extraordinary attacks was an important part of the story.

We did not know then—and only learned with publication in 1988 of historical documents in Hanoi—that the North Vietnamese Politburo had decided as early as June 1967 to aim for a decisive battlefield victory in 1968, a U.S. presidential election year. The following month the Politburo approved a plan for simultaneous surprise attacks on Saigon and other urban areas of the South. In October 1967, according to the official history published in Hanoi, the Politburo decided that the attacks would begin during the Tet holiday, then only three months away.

Although the Communists tried to keep the offensive a secret, such an audacious project—67,000 troops attacking more than 100 targets—was bound to leak out. In mid-November, U.S. forces captured an early version of the attack plan, which declared that on an unspecified date, "troops should flood the lowlands" including Saigon and other urban areas in coordination with uprisings of the local population. The U.S. Embassy in Saigon actually distributed a translation of the Vietnamese document 25 days before the embassy was attacked; it was widely discounted. On the copy I picked out of a bin at the embassy press office, I expressed my own skepticism in longhand: "moonshine." Though the U.S. military command had ordered American forces on "maximum alert" on the eve of the holiday, many officers did not take the threat seriously. In fact, the very night the Tet attacks began, some 200 U.S. colonels, all assigned to the intelligence branch of the U.S. command, went to a party in downtown Saigon.

As the Communists prepared their attacks, the White House was setting itself up for a political disaster with a misguided "success offensive," claiming that victory was in sight. From the flight deck of the aircraft carrier USS Enterprise, President Johnson declared that the war would continue "not many more nights." Most tellingly, Gen. William Westmoreland, the handsome, square-jawed commander of U.S. forces in Vietnam, said before the National Press Club in Washington, D.C.: "With 1968, a new phase is now starting. We have reached an important point when the end begins to come into view."

In this context, the Tet attacks came as a particular shock. James J. Wirtz, a historian at the Naval War College who has closely studied the 1968 offensive, declared at the Bethesda conference that Tet was "an earth-shattering, mind-shattering event that changed the course of the war." Though the Politburo in Hanoi achieved neither the decisive victory on the battlefields nor the uprising by the Vietnamese people they had hoped for, they were able, as North Vietnamese Communist Party chief Le Duan had forecast in a letter to his southern fighters, to "shake the aggressive will of U.S. imperialism, compel it to change its strategy and de-escalate the war."

My friend and former Washington Post colleague, the late Peter Braestrup, blamed misreporting by the American press for the impact of Tet on the American public, citing "a portrait of defeat for the allies" that emerged from journalistic accounts. Many high-level military officials shared Braestrup's view, stimulating efforts by the post-Vietnam Pentagon to restrict press coverage of military operations.

I disagree. Unquestionably, there was misreporting of Tet, especially in the confusing and uncertain days following the attacks. In retrospect, some of my own reporting was too pessimistic, partly because I was misled by a CIA official who was trying to claim control of the delta for his agency.

But press reports were not the fundamental cause of the loss of domestic support for the war. In my view, the story of the Vietnam War can be summed up in an observation made by North Vietnamese premier Pham Van Dong, Ho Chi Minh's close aide and successor, to French war historian Bernard Fall in 1962, three years before the massive U.S. intervention and nearly six years before Tet: "Americans do not like long, inconclusive wars—and this is going to be a long, inconclusive war. Thus we are sure to win in the end." The North Vietnamese and their southern comrades were willing to fight to the death against the United States and the government it had installed, just as they did against the colonial French, who had tired of fighting and sued for peace. And this time, China, which had pushed the Vietnamese Communists to partition their country into North and South to end the first Indochina War in 1954, was fully on their side, as was the Soviet Union.

Despite the heavy Communist losses, Tet dramatically reinforced the view that there was no end in sight. When LBJ continued to insist, after Tet, that the war effort was still on track, his message was undercut by a leak of General Westmoreland's request for 206,000 more U.S. troops. This news, just two days before the March 12 presidential election primary in New Hampshire, further eroded Johnson's already dwindling credibility. Not long after his poor showing in New Hampshire, the president announced that he would not seek a second full term. And, he said, he had stopped the bombing of most of North Vietnam in a bid for peace talks. Richard Nixon, Johnson's successor, won the election by promising "peace with honor." Once in office, Nixon was able to sustain support for the war only by withdrawing increments of American troops every few months, and then negotiating a peace agreement that required full U.S. withdrawal. Seven years after the ill-fated Vietnamese sappers attacked the U.S. Embassy on Tet, the last Americans, and some of their Vietnamese allies, departed Saigon by helicopter from the building's roof on April 30, 1975.