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.”