Lt. Tony Nadal survived three days and three nights of vicious fighting at Landing Zone X-Ray, the first major battle of the Vietnam War. When it was over, 79 American soldiers, including some of Nadal’s closest friends, were dead.

While clearing a village on another mission, Nadal and his soldiers tossed a grenade into a tunnel that they suspected concealed enemy fighters. After the explosion they found the bodies of only a mother and her two small children, too frightened to come out when called.

“I’ve never gotten over that. I have tears in my eyes just telling you about it,” Nadal said in an interview a half century later. “But that was an act of war. In my view, it was a legitimate assumption that they were a threat.”

No casualties of war prepared Nadal for what he saw when he opened the Dec. 5, 1969, issue of Life magazine.

The glossy pages contained the first view for most Americans of an atrocity committed by U.S. soldiers 18 months before: photographs of scores of dead women, children and babies sprawled in a ditch at My Lai. Photos of terrified, huddled women holding babies, and grandmothers crying just before their murders.

Nadal was by then an instructor at the U.S. Military Academy. “I told the cadets how ashamed I was,” he said.

“I was ashamed for the Army. I was ashamed soldiers had done this and I was ashamed that nobody had stopped it.

“My Lai is a stain on the Army,” said Nadal, 82, a retired colonel. “It’s a stain on the judicial system of the U.S. military.”

The My Lai massacre — pronounced “mee leye” — is considered the nadir in modern Army history. More than 500 Vietnamese civilians were raped, tortured, stabbed and shot to death March 16, 1968, by three platoons of the boys next door.

A cover-up started that day would be dismantled bit by bit, leading to courts-martial and reprimands for a handful of officers.

But why it happened and who should be held responsible remained in dispute.

Should soldiers who said they were following orders be blamed or the superior officers in command? Was how America waged war in Vietnam responsible? Or was it something, however horrifying, that happens in all wars?

Fifty years and three U.S. wars later, there’s still no clear consensus. Rather than serving as a lasting warning for servicemembers, My Lai has been all but forgotten in the ranks of today’s armed forces.

Nadal blames the chain of command. Company C of the 1st Battalion, 20th Infantry Regiment, 11th Infantry Brigade (Light) of the 23rd (Americal) Division, he said, like other Army units in 1968, had officers unequipped for command, men not among the best and the brightest.

“Harvard wouldn’t fight,” Nadal said.

Badly trained, “shake-and-bake” non-commissioned officers added to the problem.

“Any NCO in that unit could have said, ‘This is bullshit,’ and stopped it,” Nadal said. “Not one of them had the intellect, courage, character or discipline to say, ‘Stop.’ ”

Atrocities have occurred in all wars, he said, but not in units commanded by competent leaders who troops respect and know will come down hard on abuse.

“It’s easy to stop atrocities from happening,” Nadal said. “If it happens in a unit, it happens because the chain of command blew it.”

Retired Brig. Gen. John Johns, who served on a Pentagon task force created after My Lai that found 320 other atrocities substantiated by military investigators, disagreed.

“I don’t believe it is preventable in these kinds of counterinsurgency wars,” Johns said. “There will be atrocities regardless of how well the troops are trained and led. The frustration from seeing one’s comrades led into ambushes ... can eat at discipline. And it goes back to the human instinct to demonize those outside our tribe,” Johns said.

“I blame the national leaders who put troops in situations that they have no business being in.”

Contributing factors

The first comprehensive review of how and why My Lai and its cover-up occurred was done by Lt. Gen. William Peers. He had been assigned the task in November 1969 by then-Army Chief of Staff Gen. William Westmoreland, just as news of the atrocity was breaking nationwide. At first, officials wondered whether the company had “an unusual number of men of inferior quality,” Peers wrote. They pulled the soldiers’ personnel files and test scores and found that the men of Charlie Company “were about average as compared with he other units of the Army.”

The Peers Inquiry listed 13 contributing factors.

Among them were lack of proper training, lack of discipline, racist attitudes toward Vietnamese people, the ambiguity between combatants and civilians and a poor command climate from the company to the division levels.

Leadership lapses continued long after the massacre, the report said.

“Within the Americal Division, at every command level from company to division, actions were taken or omitted which together effectively concealed the ... incident. Efforts ... deliberately to withhold information continue to this day,” the report said.

Historian Howard Jones, whose book “My Lai, Vietnam, 1968, and the Descent into Darkness” was published in June, said it was more than bad leadership in one division.

“Life is plentiful, life is cheap in the Orient,” Westmoreland had said, and Jones said the U.S. military seemed to take that to heart in prosecuting a brutal war of attrition.

Massive bombing indiscriminately killed Vietnamese civilians.

“Body counts, free-fire zones, search-and-destroy missions,” said Jones, a professor at the University of Alabama. “This is just a recipe for disaster.”

As Johns’ task force found, first reported by Deborah Nelson and Nick Turse in the Los Angeles Times in 2006, war crimes occurred throughout Vietnam.

Nelson and Turse, who gained access to the Vietnam War Crimes Working Group files gathering dust in the National Archives, reported that among the substantiated cases in the archive were:

• Seven massacres from 1967 through 1971 in which at least 137 civilians died.

• 78 other attacks on noncombatants in which at least 57 were killed, 56 wounded and 15 sexually assaulted.

• 141 instances in which U.S. soldiers tortured civilian detainees or prisoners of war with fists, sticks, bats, water or electric shock.

The files contained 500 other alleged atrocities that Army investigators could not prove or that they discounted, Nelson and Turse reported.

Peers stressed that before My Lai, “there had been instances of mistreatment, rape and some unnecessary killings in Task Force Barker.”

Some troops engaged in contests of raping women, Jones said, with “extra points for killing them.”

Very few were prosecuted and almost none served jail time. “It helped form a pattern of behavior,” Jones said.

A sort of slide into evil wasn’t difficult in Vietnam, Philip Caputo wrote in his 1977 book, “A Rumor of War.”

“Everything rotted and corroded there: bodies, boot leather, canvas, metal, morals. Scorched by the sun, wracked by the wind and rain of the monsoon, fighting in alien swamps and jungles, our humanity rubbed off of us as the protective bluing rubbed off the barrels of our rifles.”

‘Flawed intelligence’

When Tony Nadal went to Vietnam in 1965, as the war’s escalation and the anti-war movement were just getting started, more than 60 percent of Americans supported sending troops to the country.

Three years later, support had plummeted.

During a supposed truce in observation of Tet, the Vietnamese lunar New Year, on Jan. 30, North Vietnam troops launched a huge surprise assault that took 10 U.S. battalions nearly a month to beat back.

After that, only a third of Americans agreed that progress was being made. Nearly half said the U.S. should never have intervened in Vietnam.

On Feb. 27, CBS News anchor Walter Cronkite, considered the nation’s most trusted newscaster, told his millions of viewers that the war could not be won.

Two weeks later, on March 16, Capt. Ernest Medina led Charlie Company, part of Task Force Barker, into the hamlet of My Lai.

The unit had lost 28 soldiers from snipers, landmines and booby traps, and hadn’t once seen the enemy, Jones said. The area was considered rife with Viet Cong fighters and civilian sympathizers.

“You’ve got all this fear and frustration. And then they got flawed intelligence, that up to 300 or 400 Viet Cong would be implanted in My Lai,” Jones said.

That there were no Viet Cong fighters became clear early in the mission. No shots were fired at the troops, no weapons were found.

Platoon leader Lt. William Calley and his men nonetheless went to work, burning huts, raping women and girls, and killing with knives, grenades and machine guns.

Some soldiers testified later that they’d understood their orders were to lay waste to the village and kill everyone there because they were Viet Cong sympathizers. Officers denied it; no such written orders were ever found, although it was acknowledged that the troops were ordered to kill the livestock, burn the huts and poison the wells, and that there was no order as there should have been addressing the safeguarding of civilians.

One soldier shot himself in the foot to avoid his orders, turning the quintessential action of a coward into something almost self-sacrificing. He, like the rest of the soldiers, kept quiet about what they’d seen and done.

“I just started killing any kind of way I could kill. It just came, I didn’t know I had it in me,” Varnardo Simpson said in a 1982 TV interview, 15 years before he killed himself. “From shooting them to cutting their throats to scalping them to cutting off their hands and cutting out their tongue. I did that. And I wasn’t the only one that did it, a lot of other people did it.”

The exception was Warrant Officer Hugh Thompson and his two-gunner helicopter crew. “Something ain’t right about this,” Thompson said over his radio as he flew overhead. “There’s bodies everywhere. There’s a ditch full of bodies that we saw.”

Thompson landed his helicopter repeatedly to confront and defy higher-ranking officers. He coaxed out a dozen villagers hiding in a bunker Calley and his solders were about to kill with grenades, and called in a gunship to evacuate them. “Y’all cover me,” Thompson told his gunners, Larry Colburn and Glenn Andreotta, as he faced off against the U.S. infantrymen.

“If those bastards open up on me or these people, you open up on them.”

Thompson officially reported the slaughter up the chain of command, which called off the rest of the operation and buried the report.

Battalion commander Lt. Col. Frank Barker called the operation in My Lai “well planned, well executed and successful” in his after-action report. He reported 128 “enemy” killed in action.

Brigade commander Col. Oran Henderson, informed by Thompson of all he’d seen, reported 20 noncombatants inadvertently killed in a crossfire between U.S. and Viet Cong forces.

Maj. Gen. Samuel Koster, Americal Division commander, insisted later to investigators that he’d reviewed and believed Henderson’s report, which, unfortunately had somehow gone missing.

But the truth would come out.

Undeniable evidence

Ron Ridenhour, a former gunner in another unit, sent registered letters to some 30 lawmakers and officials in March 1969, telling them what other soldiers had told him.

“I asked ‘Butch’ several times if all the people were killed. He said that he thought they were — men, women and children,” Ridenhour’s letter said. “He recalled seeing a small boy, about 3 or 4 years old, standing by the trail with a gunshot wound in one arm. ... He just stood there with big eyes staring around like he didn’t understand. ... Then the captain’s RTO (radio operator) put a burst of 16 (M-16 rifle) fire into him.”

The public didn’t hear about it for another eight months until journalist Seymour Hersh, who’d gotten wind of Calley’s upcoming court-martial, broke the story. The Army photographer who’d been on the My Lai mission, Sgt. Ronald Haeberle, provided the photos to the Cleveland Plain Dealer, which was the first to publish them. Haeberle then sold his photographs to Life magazine.

About 30 men were charged with crimes connected to the massacre or the cover-up. About half of them were officers, most of them charged with dereliction of duty.

But charges were dropped or military juries acquitted. Only Calley, against whom there was overwhelming evidence, was convicted of a crime. In 1971 he was sentenced to life in prison for the murder, although he served only three years under house arrest before being freed.

Many of those who were at My Lai had left the service by the time the story broke. At the time, federal law provided no widely accepted way to prosecute former enlisted soldiers for crimes committed overseas while in uniform, although the Army’s general counsel, Robert E. Jordan III, recommended in 1969 that the My Lai participants be tried before a special war crimes tribunal.

Eighty percent of Americans objected to Calley’s prosecution, according to a contemporary Gallup poll.

Twenty percent said Calley was executing his superiors’ lawful orders on the battlefield.

Jimmy Carter, then Georgia governor, urged constituents to “honor the flag” as Calley had done, and to leave their headlights on to show their support. A song lauding him played on the radio.

Others considered Calley a scapegoat.

“We only want this country to realize that it cannot try a Calley for something which generals and Presidents and our way of life encouraged him to do,” Vietnam vet and future Secretary of State John Kerry said at an anti-war protest.

“And if you try him, then at the same time you must try all those generals and Presidents and soldiers who have part of the responsibility. You must in fact try this country.”

“If you were against the war, Calley was a war criminal writ large — but a dupe,” said Ted Thomas, who served in Vietnam and teaches a class on the war at the Army Command and Staff College at Ft. Leavenworth, Kan. “If you were on the right, he was just a soldier doing the best he could.”

Setting standards

The Hague Conventions in the early 1900s set out the laws of war that required safeguarding the fundamental human rights of prisoners of war, wounded troops and civilians.

Later, the Nuremberg Principles stated that a soldier “just following orders,’’ as numerous Nazi war criminals had claimed, was not an excuse: Illegal orders must not be obeyed.

Likewise “command responsibility” — the idea that higher-ranking officers are responsible for atrocities committed by their troops — has been codified since the American Civil War.

After the execution of Japanese Gen. Tomoyuki Yamashita for war crimes committed by troops in the Philippines in 1944 — despite there being no evidence that he approved or even knew of them -- the doctrine was refined and given his name: the “Yamashita standard.”

It said that officers who knew about — or should have known about — atrocities and failed either to prevent or stop them could be criminally prosecuted.

My Lai resulted in another standard: the “Medina standard,” named for Capt. Ernest Medina, which clarified U.S. law to make command responsibility applicable not only to foreign officers but U.S. officers.

Calley testified he’d been following Medina’s orders, and other witnesses testified to seeing Medina kill a woman lying injured. The Peers Inquiry found he’d possibly killed three people and that although aware of the massacre had done nothing to stop it.

Medina was acquitted of all charges.

“At least they tried,” said Stjepan Mestrovich, a war crimes expert and sociology professor at Texas A&M University in College Station.

Since then, the Army has failed to even attempt to hold officers accountable for war crimes, he said, instead, scapegoating low-ranking troops.

The sexual humiliation and physical abuse of detainees at Abu Ghraib in Iraq, for instance, was an “isolated incident” caused by “a few bad apples,” then-Defense Sec. Donald Rumsfeld said in 2004.

But in fact, harsh treatment and torture of detainees had been sanctioned at the highest government levels and occurred at a number of military prisons and “black sites.’’

“It’s not just a bunch of bad apples. It’s a whole orchard,” Mestrovich said. “The Army protects high-ranking officers, it’s that simple.”

Lessons forgotten?

Historians say My Lai damaged military morale and increased revulsion to the war at home.

The “lessons of My Lai” also provided a model for future soldiers of what not to do.

Yet most enlisted troops have never heard of it, Nadal said.

Even West Point graduates, considered among the Army’s best and brightest, struggle to recall it.

“It was an atrocity. … It was a unit that was taking casualties, and they took it out on the village and committed atrocities,” answered a lieutenant colonel recently asked what he knew about My Lai.

My Lai had been discussed in his philosophy class at West Point about just and unjust war, he said. But that was a couple of decades ago. His memory was hazy.

“I can’t remember the name of the platoon leader,” he said.