Mr. Colburn was the last surviving member of a three-man helicopter crew that was assigned to hover over My Lai on Saturday morning, March 16, 1968, to identify enemy positions by drawing Vietcong fire.

Instead, the men encountered an eerie quiet and a macabre landscape of dead, wounded and weaponless women and children as a platoon of American soldiers, ostensibly hunting elusive Vietcong guerrillas, marauded among defenseless noncombatants.

The crew dropped smoke flares to mark the wounded, “thinking the men on the ground would come assist them,” Mr. Colburn told Vietnam Magazine in 2011.

“When we would come back to those we marked,” he said, “we’d find they were now dead.”

Audaciously and on his own initiative, the pilot, Chief Warrant Officer Hugh Thompson Jr., swooped down and landed the copter.

“Mr. Thompson was just beside himself,” Mr. Colburn recalled in an interview in 2010 for the PBS program “The American Experience.” “He got on the radio and just said, ‘This isn’t right, these are civilians, there’s people killing civilians down here.’ And that’s when he decided to intervene. He said, ‘We’ve got to do something about this, are you with me?’ And we said, ‘Yes.’”

Mr. Thompson confronted the officer in command of the rampaging platoon, Lt. William L. Calley, but was rebuffed. He then positioned the helicopter between the troops and the surviving villagers and faced off against another lieutenant. Mr. Thompson ordered Mr. Colburn to fire his M-60 machine gun at any soldiers who tried to inflict further harm.

“Y’all cover me!” Mr. Thompson was quoted as saying. “If these bastards open up on me or these people, you open up on them. Promise me!”

“You got it boss,” Mr. Colburn replied. “Consider it done.”