Duc was an assistant to Lê Văn Kim, one of generals in the ruling junta, but was recruited into a coup plot by Generals Khánh, Trần Thiện Khiêm and Đỗ Mậu. At the time, France was advocating for South Vietnam to become neutral, and the withdrawal of the United States. Đức used his experience of France to draft fake documents purporting to show the junta of Dương Văn Minh wanting to go along with the French proposal. These were then presented to the Americans to ensure support, and Khánh toppled Minh in January 1964 without a fight.