In mid-1964 Ellsberg joined the Defense Department as Special Assistant to Assistant Secretary of Defense for International Security Affairs John T. McNaughton. This was Ellsberg’s chance, McNaughton said, to study high-level decision-making from the inside as a participant, rather than as a researcher after the facts: “You want to study crises; Vietnam is a continuous crisis.”
Ellsberg was hired to work principally on Vietnam, which at that time was a low-level American engagement. In 1964-65, by direction of Secretary of Defense Robert McNamara, Ellsberg assisted McNaughton’s work on secret plans to escalate the war in Vietnam, although both of them personally regarded these as wrongheaded and dangerous. Regrettably, by decisions of President Johnson and McNamara, these plans were carried out in the spring of 1965.
With his country at war, Ellsberg volunteered to go to Vietnam, transferring to the State Department in mid-1965. Based at the Embassy in Saigon, he evaluated pacification on the front lines throughout South Vietnam.
On return to the RAND Corporation in 1967, Ellsberg worked on the Top Secret McNamara study of U.S. Decision-making in Vietnam, 1945-68, which later came to be known as the Pentagon Papers. He was the first person other than the two project directors to read the entire study—a continuous record of governmental deception and fatally unwise decision-making, cloaked by secrecy, that unfolded under four presidents.