A line of flags at a training area in Koren, Bulgaria, on July 19 during exercise Peace Sentinel, a combined arms live fire exercise between Bulgarian Land Forces, 4th Infantry Division, and 10th Combat Aviation Brigade, as part of a larger exercise. Exercise Saber Guardian 17 is a U.S. European Command, U.S. Army Europe-led exercise in the Black Sea Region that builds readiness and improves interoperability among the 20 Allies who participate. (U.S. Army photo by Spc. Thomas Scaggs) 170717-A-TZ475-123