While at Hong Kong, the weary destroyer's rest was abruptly cut short. On 1 November, 1963, members of the Republic of Vietnam military staged a coup against the regime of President Ngo Dinh Diem. In response, the U.S. Navy deployed a flotilla off the mouth of the Mekong River for the potential evacuation of American citizens and service members. As part of this operation, "Buchanan" departed Hong Kong escorting the aircraft carrier with "Southerland" and on 2 November. The coup had ended with assassination of Diệm, his brother Ngȏ Ðình Nhu, and Col. Hồ Tần Quyền, the commander of the Vietnamese navy. With reassurance from the new leadership under General Dương Văn Minh that order had been restored and alliances unchanged, the Navy reduced its presence off of South Vietnam. "Buchanan" departed the area on 5 November for Subic Bay. On 15 November, 1963 she left Subic Bay for San Diego arriving on 27 November. After the holidays, "Buchanan" operated out of San Diego before moving to the San Francisco Naval Shipyard at Hunters Point, California (USA), for overhaul (7 May–22 September). Several days after emerging from overhaul, she rejoined Destroyer Squadron 15 to participate in fleet exercise "Union Square" (28 September – 1 October, 1964).