To Americans of a certain generation, the news this weekend must have seemed dreadfully familiar: an endless war, whose rationale is ever harder to understand, and where "victory" is gradually drained of meaning; a group of soldiers enraged by the loss of a comrade to an invisible enemy, running amok and exacting revenge on civilians, whose only crime was to have been in the wrong place at the wrong time.
Today, the name that threatens to besmirch an entire war is Haditha, a town on the Euphrates river, north-west of Baghdad, deep in the "Sunni Triangle". A generation and a half ago, the place was My Lai, a hamlet in South Vietnam.
At Haditha, it is US Marines who are under accusation, soldiers from K or Kilo Company of the 3rd Battalion of the 1st Marine Division. In Vietnam, the troops who carried out the massacre at My Lai were from C, or Charlie Company, of the 11th Brigade of the Americal Division. But though separated by 37 years, the similarities abound.
No one disputes that what happened at Haditha on 19 November 2005, when as many as 24 civilians, including families complete with women and children, may have been shot by rampaging US soldiers, was provoked by the death of the 20-year-old Marine Lance Corporal Miguel Terrazas, killed in a roadside bomb. In Vietnam, dozens of members of Charlie company had been killed and wounded by insurgents in the weeks before the atrocity in the hamlet of My Lai 4 (then known in military jargon as Pinkville).
A couple of days earlier, on 14 March, a Vietnamese version of the IED (Improvised Explosive Device) of the variety that took L/Cpl Terrazas's life had killed one C Company sergeant and wounded others. Military intelligence concluded that a crack unit of the Viet Cong was holed up in My Lai, and C Company was ordered to destroy them. Three platoons were assigned to the operation, one led by a lieutenant named William Calley, an unemployed college drop-out who had been rushed through officer training before being sent to lead soldiers in a full-scale guerrilla war.
Lt Calley's platoon entered the hamlet with guns blazing at around 8am on the morning of 16 March. There was no hostile fire and the men found only 700 residents: old men, women, and children ("we never saw a male of military age," one participant later confessed).
Over the next three hours, the men ran amok. Villagers were bayoneted, women and children were shot in the back of their heads as they prayed, at least one girl was raped and murdered. Lt Calley himself is said to have personally slaughtered dozens of villagers whom he rounded up and ordered into ditch, mowing them down with a machine-gun. By 11am it was all over. The exact number of victims is unknown to this day, anywhere from 300 to over 500. A monument at the site lists the names of 504 people, their ages ranging from 1 to 82.
My Lai, in fact, was far from the sole example of such barbarity in Vietnam. During 1967 a unit called the Tiger Force is said to have murdered hundreds of Vietnamese men, women and children in the Quang Ngai province of the former South Vietnam, that country's equivalent of the Sunni Triangle, where guerrillas melted into the local population, as indistinguishable to the unqualified eye of the ordinary American soldier then as Iraqi insurgents in Haditha today.
An initial investigation was quietly put to rest some 30 years ago. The full story was laid bare by the Toledo Blade newspaper in several articles in October 2003. Published at a moment when public support for the Iraq war was still strong, they attracted relatively little attention. But, apparently just like Haditha now, My Lai was proof of the ghastly things that can happen in wars fought by young troops who have lost close friends to an enemy they cannot see, in another skirmish in a conflict seemingly with no end, where every victory is fleeting, which unfolds amid a civilian population whose language the young soldiers cannot speak, whose true sympathies they cannot fathom.
Part of the blame undoubtedly attaches to commanders who failed to impress upon trained soldiers the difference between right and wrong, even under such pressure. But should we be surprised that this group of US Marines seems to have snapped? Can we all put our hands on our hearts and say that under such appalling stress, when a fighting man's greatest loyalty is not to his country or his commander-in-chief, but to his buddies alongside him in the heat and the dust and the carnage, we could not have done something similar?
Rarely, alas, do such considerations cross the minds of the presidents and prime ministers who send their armies into war. Delivering the commencement speech at West Point military academy this weekend, George Bush invoked the Cold War as the comparison for the "war on terror", of which the White House has long proclaimed that Iraq is the central front. But more clearly with every passing day, the war that Iraq resembles is Vietnam.
In this electronic age, of course, everything in war is speeded up, including cover-ups. The first official version of My Lai spoke of a signal victory, in which the Americans had killed 128 insurgents and suffered only one casualty. But, in March 1969, an ex-soldier who had heard eyewitness accounts of what had really happened sent letters detailing what he had heard to President Nixon, the top commanders at the Pentagon, and members of Congress.
Slowly the military was prodded into action, but only on 5 September 1969, almost 18 months after the massacre, was Lt Calley charged with premeditated murder. The wider public knew none of the details until the story was broken by Seymour Hersh, the same investigative journalist who, in April 2004, first disclosed the prison abuse at Abu Ghraib - which was, at least until Haditha, the greatest single blot on America's reputation left by the Iraq War.
A cover-up was attempted at Haditha too, but it has unravelled far more quickly. Within two months, Time magazine was informing the military of allegations of an atrocity and, in mid-March, published the first details.
The criminal investigation should be wrapped up by late June; some Marines are already reported to be in custody, likely to face murder charges that could carry the death penalty. General Michael Hagee, commander of the US Marine Corps, is already in Iraq, impressing upon his men the overriding need to observe the rules of war. But it may already be too late.
If the worst accounts are true, Haditha could be devastating on three separate scores. It can only further erode the trust of ordinary Iraqis in the invaders who were supposed to bring them peace, democracy and human decency. Second, it could eat into public affection for the troops - one of the most pernicious legacies of the Vietnam war and of incidents like My Lai, where returning veterans found little honour even in their own land. Today, whatever his or her view of the war, no American will speak ill of soldiers at the sharp end in Iraq. But now, who knows? Most important, Haditha could affect the US prosecution of the war. The death toll may not be on the scale of My Lai. But the incident has occurred when public opinion here has already turned against the war, far more decisively than when details of the slaughter at "Pinkville" became public knowledge.
Even before the latter, opinion was shifting, evidenced a fortnight earlier, on 6 March 1968, when the CBS anchorman Walter Cronkite had broken the reporters' code of neutrality and spoken out on air against the war. "If I've lost Cronkite," President Lyndon Johnson mused, "I've lost the American people." And so it would ultimately prove.
But not until after Hersh published his account of My Lai did polls first reveal a majority against the Vietnam war. Today, six out of 10 Americans already believe the 2003 invasion of Iraq was a mistake - a disillusion that even that peddler of illusions George Bush had to acknowledge at his rather downbeat press conference with Tony Blair last Thursday.
Conceivably, Haditha could be the stone than unleashes an avalanche of clamour for a speedy American exit from Iraq, not matter what. It is no co-incidence that the congressman who has spoken out most loudly about the affair is John Murtha, a normally hawkish Pennsylvania republican, highly respected and with close ties to the Pentagon. Last November, he created a sensation by demanding a swift US withdrawal from Iraq, arguing that the war was doing America more harm than good.
Haditha has only strengthened that conviction. "This will be very, very bad for America," the former Marine and combat veteran from Vietnam noted earlier this month as he reported that his Pentagon contacts had told him that the incident was even more savage and inexcusable than first thought.
"This is the kind of war when you have to win the hearts and minds of the people," Mr Murtha told ABC's This Week programme yesterday. "And we're set back every time something like this happens. This is worse than Abu Ghraib."
For Mr Murtha, what happened was murder, pure and simple. "This investigation should have been over two or three weeks afterwards, and it should have been made public and people should have been held responsible for it." And that perhaps will be the final acid test of Haditha. Who will be held responsible? Will it be like My Lai, where Lt Calley was the only person of consequence to be convicted (and then released on parole a few years later)? Or will heads roll higher up, among commanders who did not sufficiently impress upon their men the need to obey the law? The precedents of My Lai and Abu Ghraib, for which no senior officer has yet faced charges, is not encouraging. But My Lai helped destroy a country's faith in its military and the judgement of its leaders. Thirty-seven years later, Haditha may do the same.