formidable force by the late 1990s, political and military leaders from both countries reexamined the role of U.S. forces based on the peninsula. A major change in U.S. strategic policy coinciding with the 9/11 terrorist attacks required a "transformation" of global U.S. military commitments and basing. The military had to adapt from a fixed, in-garrison-type force to a mobile, responsive force. For its part, U.S. Forces in Korea studied how technological advances in weaponry could mitigate a reduction in personnel while the ROK military forces carried out an increasing role to protect its sovereignty. The result of this effort led to the landmark agreement known as the Land Partnership Plan in 2002 and the Security Policy Initiative in 2003 between the U.S. and the South Korean governments. These decisions reflected a realignment in the roles and missions of USFK that forecast a significant reshaping and growth at Osan AB through 2011. The 607th Combat Operations Squadron was dissolved. In December 2009, South Korea's JoongAng Daily newspaper reported that the RQ-170 Sentinel was to replace U-2s operating from Osan Air Base in 2010. On December 1, 2014, a lockdown in the high school and middle school occurred as an active shooter drill went off. On May 28, 2015, the USAF said that as many as 22 people were inadvertently exposed to anthrax during a laboratory training exercise. Major USAF units assigned 18th Fighter-Bomber Wing (December 1952 – November 1954) 30th Weather Squadron (January 1954 – May 1957)* Fifth Air Force (January – September 1954) 314th Air Division (March 1955 – November 1978, April 1979 – September 1986) 335th Fighter-Bomber Squadron (February 1955)** 334th Fighter-Bomber Squadron (March 1955)** 58th Fighter-Bomber Wing (March 1955 – July 1958) 58th Tactical Missile Group (July 1958 – March 1962) 51st Fighter Wing (November 1971–present) Seventh Air Force (September 1986–present) Defense Media Agency-American Force Network Osan (September 1957–present) * Detached from the 2143rd Air Weather Wing based at Tageu AB (K-2), South Korea ** Detached from the 4th Fighter-Bomber Wing based at Chitose AB, Japan Kunsan has provided support for F-51D Mustang, F-86 Sabre, F-84 Thunderjet, F-4 Phantom II, F-106 Delta Dart, OV-10 Bronco, A-10 Thunderbolt II, and F-16 Fighting Falcon operations. Based units Flying and notable non-flying units based at Osan Air Base. Units marked GSU are Geographically Separate Units, which although based at Osan, are subordinate to a parent unit based at another location. United