I interviewed McNamara on July 24, 1981, and January 18, 1982, for a book I was writing on the history of U.S. nuclear strategy (The Wizards of Armageddon, 1983). During one of those interviews, McNamara said, as an example of ideas he unalterably opposed, "I would never have approved something like the MIRV" (meaning intercontinental ballistic missiles fitted with multiple warheads). By coincidence, I had with me a document (which I'd had declassified), dated Dec. 3, 1964, signed by McNamara, approving research and development for the MIRV. I showed it to him. He said, dismissively, "Well, I didn't understand its implications at the time." It is doubtful that the implications of any major weapon system eluded McNamara at the time.