Washington (CNN) -- More than 42 years after Air Force Chief Master Sgt. Richard L. Etchberger died on a Laotian mountaintop, President Barack Obama on Tuesday awarded him the Medal of Honor, saying, "It's never too late to do the right thing. It's never too late to pay tribute to our Vietnam veterans and their families."
Etchenberg's three sons were at the White House for the ceremony. For decades they didn't know about their father's heroism.
Cory Etchberger was in third grade in 1968, when he was told that his father had died in a helicopter accident in Southeast Asia. At age 29 he learned the truth, when the U.S. Air Force declassified his father's story.
"I was stunned," he told CNN during a visit to his hometown of Hamburg, Pennsylvania.
During the Vietnam War, U.S. troops weren't supposed to be in neutral Laos, so Richard Etchberger and a handful of colleagues shed their uniforms and posed as civilians to run a top secret radar installation high on a Laotian cliff. Called Lima Site 85, it guided U.S. bombers to sites in North Vietnam and parts of Laos under communist control.
"Dick and his crew believed they could help turn the tide of the war, perhaps even end it," said Obama.
The North Vietnamese wanted to eliminate the installation, and early on the morning of March 11, 1968, its soldiers succeeded in scaling the 3,000-foot precipice and launching an attack.
Timothy Castle, of the CIA's Center for the Study of Intelligence, wrote the book "One Day Too Long: Top Secret Site 85 and the Bombing of North Vietnam." He calls Etchberger "a hero."
Castle said Etchberger, a technician, picked up an M-16 rifle, which he barely knew how to use, and ferociously protected his colleagues.
One of them was Stanley Sliz.
"I got hit in both legs," Sliz remembered, "and everybody was screaming and hollering, but they weren't able to get close because of Etch firing at them."
John Daniel still has scars from the shrapnel wounds he got that day.
"He (Etchberger) was the only one that didn't get injured in the firefight," Daniel recalled. "They kept throwing grenades and shooting, and we kept picking up hand grenades and throwing them, or kicking them to the other side of the mountain."
When a helicopter flown by CIA-affiliated Air America arrived to evacuate them, Etchberger braved enemy fire to load three wounded comrades, including Daniel and Sliz, onto hoists.
"Thank God for Dick Etchberger. If it wasn't for him, I would not be alive today," Daniel told CNN.
Etchberger made it onto the chopper alive and unwounded. But as it began to pull away, enemy shots rang out.
Sliz said he saw a splotch of red, and realized the man who had saved his life had lost his own. One round had hit Etchberger and killed him.
"I live it every day," said Sliz. "I live it every day. It haunts me."
President Obama said Etchberger "lived the airmen's creed -- to never leave an airman behind, to never falter, to never fail."
Shortly after Etchberger's death, he was secretly awarded the Air Force Cross for bravery. He was recommended for the Medal of Honor, but then-President Lyndon Johnson rejected the idea, fearing it would expose the U.S. military's activities in Laos.
A few years ago an airman who had never even known Etchberger wrote his congressman asking that the matter be reconsidered.
Said Obama, "The greatest memorial of all to Dick Etchberger is the spirit that we feel here today, the love that inspired him to serve...the love for his country and love for his family."
The president noted that the same love motivates troops serving today, "And as Americans, we remain worthy of their example...by remaining true to the values and freedoms for which they fight."
CNN's Jim Spellman, Sara Weisfeldt and Floyd Yarmuth contributed to this report.