 Serong left the Australian Army in August 1968, at which time he was granted the honorary rank of brigadier.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."