Robert McNamara, the American Defence Secretary who achieved notoriety as the architect of the Vietnam War, only to denounce it years later as futile and immoral, has died at the age of 93.

McNamara, who succumbed after a long illness at his home in Washington yesterday, spent much of the second half of his life haunted by the moral consequences of the conflict that became known as “McNamara’s War”.

McNamara, who served under the presidents John F. Kennedy and Lyndon Johnson, left the Pentagon in 1968 after a run-in with the White House over a paper he wrote urging the president to negotiate peace rather than escalate the war.

He left to run the World Bank, remaining deeply but privately disturbed by his role in a war that was to kill more than 58,000 Americans and hundreds of thousands of Vietnamese soldiers and civilians.

In 1972 an unnamed Vietnam veteran attacked McNamara on board a ferry off Cape Cod, and attempted to throw him into the ocean. McNamara declined to press charges. It took until 1995 for him to take a public stand on the war, confessing in his memoir that its conduct had been “wrong, terribly wrong”.

A firestorm of criticism descended, with a New York Times editorial declaring that he “must not escape the lasting moral condemnation of his countrymen”. It added: “What he took from those poor boys cannot be repaid by prime-time apology and stale tears, three decades later.” In 2003, McNamara joined forces with the director Errol Morris to make the Oscar-winning documentary The Fog of War. The film was subtitled Eleven Lessons from the Life of Robert S. McNamara.

In it, he condemned not only the conflict in Vietnam, but also the American firebombing of Japanese cities in the Second World War, in which he played a supporting role. “If we’d lost the war we would have been prosecuted as war criminals,” he said. “What makes it immoral if you lose and not immoral if you win?” Perhaps his most enduring lesson was his first. “We didn’t know our opposition,” he said in 2003. “We didn’t understand the Chinese, we didn’t understand the Vietnamese. So the first lesson is know your opponents. I want to suggest to you that we don’t know our potential opponents today.”

McNamara died in his sleep. He is survived by a son and daughter and his second wife, Diana.

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