Secretary of Defense Robert McNamara was beginning to have serious misgivings about the nature of the war in Vietnam by the spring of 1966. Two of his closest civilian aides (John McNaughton and Adam Yarmolinksy) began searching for alternatives to the war, and in the summer of 1966, with the assistance of the Institute of Defense Analysis, a think tank, they organized a conference of possibly fifty leading scholars at Wellesley, Massachusetts. They met there throughout the summer of 1966, and their joint report came to be known as the Jason Study. The major conclusion of the report was that American air strikes on Vietnam were having little effect and might even be counterproductive. Because much of North Vietnam was a subsistence agricultural economy, air strikes did not adequately disrupt economic affairs. The flow of supplies into South Vietnam was not materially affected by air strikes, and the People's Republic of China and the Soviet Union quickly replaced any supplies lost. Worse still, the volume of supplies making their way into the South had essentially increased since the bombing began, and the morale of the North Vietnamese had measurably strengthened. The Jason Study confirmed many of McNamara's growing suspicions about the war and converted him into a supporter of negotiation and an end to the bombing of North Vietnam.