Larry Colburn, who became an 18-year-old American hero when he intervened with two comrades to halt the massacre of unarmed Vietnamese civilians by United States soldiers in 1968, elevating an innocuous hamlet named My Lai into a watchword for the horrors of war, died on Tuesday at his home in Canton, Ga. He was 67.

The cause was liver cancer, his wife, Lisa, said.

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.