McNamara was forced out of the position by Johnson after his secretary had provided him with responses that conflicted with the president's on the subject of the sharply divisive Vietnam War.
The former secretary in a revealing biography released in 1993, better than a generation after his Pentagon service, revealed his ultimate belief that the war could not be won.
The reason why David Halberstam and other American reporters on the Vietnam scene at the time refused to provide McNamara for candor credit after the fact were burning memories of how he questioned the patriotism of their opposition to a war he later conceded to know at that same time to be a lost cause.
McNamara urged that a quarantine be employed against Russian incoming ships while aggressively pursuing diplomacy to end the superpower conflict between the U.S. and the Soviet Union, which could have resulted in a nuclear holocaust.
Attorney General Robert Kennedy in his book "Thirteen Days" that provided his insight and analysis during that crucial period when the leaders of the two nuclear superpowers, JFK and Soviet boss Nikita Khrushchev, stood "eyeball to eyeball" with the nuclear precipice looming on the imminent horizon, made his most critical disclosure about a clash he had with former Secretary of State Dean Acheson.
Kennedy countered that such a response would cause the world community to compare such an action to Pearl Harbor. McNamara concurred with Robert Kennedy's position, one that ultimately prevailed.
McNamara's success in gaining JFK's support is now perceived by many international affairs experts as having prevented a nuclear confrontation between the United States and the Soviet Union.
This conclusion has been supported by the release of Soviet Union documents of that critical period, which revealed that, had the U.S. delivered such a military response, the USSR would have responded with a nuclear attack on the United States.
The hawkish posture of Acheson was later explained by John Kenneth Galbraith in a favorable review of the former secretary of state's 1970 memoir, "Present at the Creation."
Galbraith explained a view that was shared by many in the Washington community in the late sixties that Acheson, the critical player who sold the Marshall Plan and the Truman Doctrine to America's allies, assumed a later hawkish position in international affairs due to his response to an ideological cancer that plagued America in the fifties.
Acheson had served during the overthrow of the Chinese Nationalist regime of Chiang Kai-shek and assumption of power by Mao Zedong's Communist forces.
Though independent study reveals that the Chinese people felt great dissatisfaction toward the Nationalist regime, from which Mao's guerrilla forces capitalized through eventual overthrow, the forces of Joseph McCarthy and Richard Nixon sought to make political capital.
Acheson was also pilloried, as was Truman, for not allowing General Douglas MacArthur to cross the Yalu River and carry the Korean War into Communist China.