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." 
What was Richard's nickname?
Dick and his crew