Osan Air Base (Osan-Ni Air Base, K-55, 오산공군기지, 烏山空軍基地)

Osan Air Base (K-55) is located in Pyeongtaek, Gyeonggi Province, South Korea, 64 km south of Seoul. Established in November 1951 during the Korean War as Osan-Ni Air Base, the site was surveyed and constructed by Aviation Engineers attached to the U.S. Air Force. The 18th Fighter-Bomber Wing began air superiority missions from the airfield in February 1953. Following the signing of the Korean Armistice Agreement, the base became a primary hub for U.S. air operations in South Korea, and was redesignated Osan Air Base in 1956. The 1968 USS Pueblo crisis led to the construction of aircraft shelters and a new control tower. Infrastructure was further updated through the "Fix Korea Initiative" starting in 1998, which replaced utility systems and industrial structures.

The installation is operated by the U.S. Air Force and the Republic of Korea Air Force (ROKAF). It serves as the headquarters for the Seventh Air Force, the 51st Fighter Wing, and the ROKAF Operations Command. The 51st Fighter Wing, the host unit, operates squadrons of A-10C Thunderbolt II and F-16C/D Fighting Falcon aircraft. Tenant units include the 5th Reconnaissance Squadron, which operates U-2S Dragon Lady aircraft, and the U.S. Army 35th Air Defense Artillery Brigade, which maintains MIM-104 Patriot missile batteries. ROKAF units stationed at the base include the Air Defense Missile Command and the Air Defense Control Command.

Infrastructure includes hardened aircraft shelters, munitions storage areas, and the ROKAF 1st Master Control and Reporting Center. The base functions as a terminal for "Patriot Express" flights connecting South Korea with Japan and the United States. Supporting facilities include the Osan American Elementary School and Osan Middle High School, operated by the Department of Defense Education Activity.

Recent developments include the reported 2010 arrival of the RQ-170 Sentinel to support reconnaissance operations. In 2012, a bronze monument was erected to commemorate U.S. airmen killed during the Korean War. During a May 2015 laboratory training exercise, 22 personnel were inadvertently exposed to anthrax. Source documentation also indicates a 2025 expression of interest by the U.S. executive in purchasing the base land.