But the worst numbers appeared from the mid-1960s, in a series of ever-increasing demands from General William Westmoreland in Vietnam: a force of 210,000 by the end of 1965, 325,000 by July 1966, 410,000 by that December. Vietcong numbers smoothly kept pace, despite losses estimated at 60,000 a year. Figures for Americans killed in action ran at 400-500 a month, ever upwards. Mr McNamara, ordered to win the war and clinging to his statistical strategy of attrition, approved the troop increases. But his company-man efficiency was often rattled. At cabinet meetings, especially with the "rough", Lyndon Johnson, he would nervously hitch up his trousers, sigh, bury his head in his hands. It was all unravelling. When in 1968 "Westy" asked for 200,000 more men, he left. He had once been happy to take responsibility for "McNamara's war". But as he admitted later, in penitent memoirs and interviews, he had not understood the variables of war itself.

The limits of reason

At the height of the conflict, he was called a baby-burner. His son marched against him. Jackie Kennedy once pummelled his chest with her fists, crying at him to "stop the slaughter". All this was difficult. He was an instinctive liberal, driving a battered Ford, living in university suburbs, where his recommended book for the reading group was Camus's "L'Etranger". Warmongering was not in his nature.

He was haunted by the thought that amid all the objective-setting and evaluating, the careful counting and the cost-benefit analysis, stood ordinary human beings. They behaved unpredictably. During the Cuban missile crisis of 1962, which he had lived through at cabinet level, "Kennedy was rational. Khrushchev was rational. Castro was rational." Yet between them they had pushed the world to the brink. Rationality, he concluded, "will not save us." Perhaps what would were the little quirks that had made him love John Kennedy: the president's sudden capacity to be empathetic, surprised, intuitive, and ready to jettison his most confident calculations.

... contd.