OSAN AIR BASE, Republic of Korea -- U.S. Air Force Airmen with the 51st Civil Engineer Squadron prepare for a F-16 Fighting Falcon to utilize an alternate landing strip during Vigilant Defense 24 at Osan Air Base, Republic of Korea, Oct. 29, 2023. In contingency environments, the ALS is activated when the main runway sustains heavy damage, which allows pilots to maintain readiness and continue flying operations. VD24 is a routine training event that tests the military capabilities across the peninsula, allowing combined and joint training at both the operational and tactical levels.