Blair later wrote that Serong had accepted the defence of South Vietnam from communism as his "personal mission", and his decision to take an early retirement had been due to his increasing involvement with US organisations, the value they placed on his work and his profile as an international figure, as well as a growing "emotional distance" from the Australian Army and its senior leadership. He later wrote that he "... found a way of being of more service to the country outside it than in it." Serong stayed in South Vietnam as a security and intelligence adviser to the Vietnamese government. He also instructed at the National Defense College of South Vietnam and worked for the Rand organisation, Hudson Institute and other corporations, preparing strategic analyses. He was also a consultant to the Pentagon and the policy planning teams of several US presidents, including the Nixon administration. In 1971, Serong declared that South Vietnam had essentially won the war. Remaining long after the withdrawal of Australian forces, he continued to serve in South Vietnam until the Fall of Saigon. Serong departed Saigon the day prior to its capture, leaving by helicopter in the final airlift from the US embassy on 29 April 1975. He received several US and South Vietnamese awards, including the United States Legion of Merit, the (Vietnam) Medal of Honour, Cross of Gallantry (with palm), and Knight of the National Order of Vietnam.