 Known as Double Seven Day , July 7 was the ninth anniversary of Diệm 's 1954 ascension to Prime Minister of the State of Vietnam . In October 1955 , following a fraudulent referendum , Diệm established the Republic of Vietnam , generally known as South Vietnam , and declared himself President . The night of July 6 , 1963 , had started in a festive mood as Diệm awarded decorations to military officers at a ceremony . Among those in the audience were Generals Trần Văn Đôn and Dương Văn Minh , the Chief of Staff of the Army of the Republic of Vietnam and the Presidential Military Advisor , respectively . They had returned from observing SEATO military exercises in Thailand , where they had been informed about the regional disquiet over Diem 's policies towards the Buddhists . 
