Đức joined the French-backed Vietnamese National Army which became the ARVN after the Republic of Vietnam (South Vietnam) was established. After becoming a major general in 1956 and commanding the Airborne Brigade, Đức served for a year as Ambassador to South Korea. Later, he had problems with President Ngô Đình Diệm and went into exile in France, before returning after the arrest and assassination of Diệm after a November 1963 coup.