Four U.S. Air Force F-16 Fighting Falcons assigned to the 555th Fighter Squadron prepare to land at Graf Ignatievo Air Base, Bulgaria, for exercise Thracian Star 21, July 9, 2021. Exercise objectives include maximizing interoperability, combat effectiveness and survival awareness while operating in a dynamic high-threat environment. (U.S. Air Force photo by Airman 1st Class Brooke Moeder)