The 21st Tactical Air Support Squadron (21st TASS) was a United States Air Force unit activated in 1965, primarily tasked with forward air control and reconnaissance missions during the Vietnam War. Stationed at various locations in Southeast Asia, including Nha Trang and Cam Ranh Bay, the squadron operated aircraft such as the O-1 Bird Dog and the O-2 Skymaster to coordinate close air support and direct air strikes in support of ground forces. The 21st TASS played a crucial role in enhancing the effectiveness of air-ground operations by providing real-time intelligence and target marking. The unit was inactivated in 1971 as U.S. involvement in Vietnam was reduced.