BANGKOK — Don Luce, a persistent opponent of the Vietnam War whose activism led the last American ambassador to South Vietnam to call him one of the principal reasons the United States lost the war, died on Nov. 17 in Niagara Falls, N.Y. He was 88.
His death, at Niagara Falls Memorial Hospital after suffering a sudden cardiac ischemia, was confirmed by his husband and sole survivor, Mark Bonacci.
Mr. Luce, a civilian aid worker, was best known for exposing the existence of “tiger cages,” where the South Vietnamese government imprisoned and tortured its opponents and critics in cramped cells.
In response, both the Vietnamese and American governments turned against him and he was expelled by South Vietnam in 1971.
In reporting his expulsion, Time magazine said: “Don Luce is to the South Vietnamese government what Ralph Nader is to General Motors.”
Back in the United States, Mr. Luce, together with other former members of his aid mission, created the Indochina Mobile Education Project, affiliated with the Indochina Resource Center, and toured the United States to spread an antiwar message.
The project was part of a broader antiwar movement that Ambassador Graham Martin blamed for America’s defeat in Vietnam in April 1975, turning the public against the war and leading to a reduction in Congressional funding.
“The main organization, I think, is the Indochina Resource Center,” he told a Congressional hearing in 1976, “and I really think that another principal element would be the multifaceted activities of Mr. Don Luce.”
Calling the antiwar movement “one of the best propaganda and pressure campaigns the world has ever seen,” he added: “These individuals deserve enormous credit for a very effective performance.”
Mr. Luce had lived and worked in Vietnam since 1958, first as an agricultural specialist and then as the country director for International Voluntary Services, a church-supported forerunner of the Peace Corps. He was fluent in Vietnamese and sensitive to the country’s culture.
People who knew him then described him as consistently calm and understated.
“His manner was always quiet, his humor sharp,” Thomas Fox, a colleague at I.V.S., said in an email. “He was a shy person, in that sense ill-equipped to play the prophet role he came to endure.
“Don had no rough edges. His strength — and it was enormous — came from his ability to fasten onto a truth and speak it plainly. He was always most passionate when he spoke on behalf of those who were never allowed that opportunity.”
His experiences among Vietnamese suffering from the devastation and dislocations of warfare turned him from being a supporter to a critic to an increasingly vocal opponent of the war.
In 1967, Mr. Luce and three other senior staff members of I.V.S. resigned in protest and composed a widely published five-page open letter to President Lyndon Johnson, signed by 49 members of the agency, setting forth in detail their criticisms and recommendations.
“We are finding it increasingly difficult to quietly pursue our main objective: helping the people of Vietnam,” the letter stated. “The war as it is presently being waged is self-defeating in approach.”
After his resignation, Mr. Luce returned to the United States, where he spent a year as a research associate at the Center for International Studies at Cornell University.
In 1969, together with an I.V.S. colleague, John Sommer, he published “Vietnam: The Unheard Voices,” in which they told of their disillusionment with the American conduct of the war which, they said, was perversely aiding the Viet Cong, the North Vietnamese-backed guerrillas in South Vietnam.
“Because American understanding of the people has been so limited, the tactics devised to assist them have been either ineffective or counterproductive,” the authors wrote. “They have served to create more Viet Cong than they have destroyed.”
Mr. Luce then returned to Vietnam, accredited as a journalist for the World Council of Churches, and with his fluency in the language and local contacts served as a source for American reporters.
One of his concerns in Vietnam was the treatment of political prisoners, and in 1970 he guided members of a congressional delegation to uncover the brutality of a prison on Con Son Island that housed thousands.
Some 500 were political prisoners — government opponents, underground Communists, student protesters and activist Buddhist monks — held in tiny cells known as “tiger cages” in a hidden, walled-off section.
Tom Harkin, a staff assistant to the delegation who later became a member of Congress, arranged to have two of the 12 members break away to travel with Mr. Luce to the prison.
Mr. Luce had a hand-drawn map that led to a secret door behind which the visitors found hundreds of starving and brutalized men and women crammed together in cages under grates in a walkway.
“I remember clearly the terrible stench from diarrhea and the open sores where shackles cut into the prisoners’ ankles,” Mr. Luce wrote in an account of the visit. “‘Donnez-moi de l’eau’ (Give me water), they begged. They sent us scurrying between cells to check on other prisoners’ health and continued to ask for water.”
Mr. Harkins’s clandestine photographs were published in a photo essay in the July 17, 1970, issue of Life magazine that drew international condemnation and led to the transfer of the prisoners.
Donald Sanders Luce was born on Sept. 20, 1934, in East Calais, Vt., to Collins and Margaret (Sanders) Luce. His father ran a dairy farm and his mother was a teacher.
He earned a bachelor’s degree from the University of Vermont and a master’s in agricultural development from Cornell before heading to Vietnam with I.V.S.
After the war, he relocated to Washington, D.C., where he rejoined I.V.S. and served as its director until 1997.
He then embarked on a quiet life in upstate New York with his husband, Dr. Bonacci, a professor at Niagara County Community College in Sanborn, N.Y.
For two years he taught sociology at the same school, then became the public relations director for Community Missions of Niagara Frontier, which offers a range of social services including a homeless shelter and soup kitchen. He also led study groups to Vietnam and accompanied journalists on reporting trips to Vietnam and Cambodia.
The Community Missions job was a step down in scale if not in idealistic ambition, Mr. Luce told Ted Lieverman, a freelance documentary photographer and writer, for an article published online in 2017.
In his 30s and 40s, Mr. Luce said, he had tried to change national policies. “Now I try to concentrate on helping a few people have an easier life,” he said, and look out at the world “from a Niagara Falls soup kitchen perspective.”