Promoted to acting air commodore on 12 April 1971, McNamara became the last Commander RAAF Forces Vietnam and Deputy Commander Australian Force Vietnam (AFV) that month. Believing that the Air Force paid "lip service" to its army co-operation responsibilities in the 1950s and 1960s, he familiarised himself with the finer points of air/ground operations by accompanying No. 9 Squadron helicopters on missions supporting 1st Australian Task Force in Phuoc Tuy Province. Given the responsibility of overseeing the withdrawal of the RAAF from Vietnam in 1972, McNamara was praised for his "wise and patient counsel, devotion to duty and firm control", leading to his appointment as a Commander of the Order of the British Empire in September that year. He had been promoted to substantive air commodore on 1 January. In 1973, he was posted to the United States as the Australian Air Attache to Washington, D.C. Promoted to air vice marshal on 20 March 1975, he returned to Australia that year and took up duties as the Deputy Chief of Air Staff, which he later described as "an invaluable learning experience for the top job". He was appointed an Officer of the Order of Australia (AO) on 7 June 1976 for "distinguished service in responsible positions".