U.S. Air Force Master Sgt. Ronnie Martin, with 134th Air Refueling Wing quality assurance, observes maintenance being conducted outside a KC-135 Stratotanker window during Exercise Trident Juncture 18 at Kallax Air Base, Sweden, Oct. 29, 2018. The KC-135 entered service with the Air Force in 1957, it is one of six military fixed-wing aircraft with more than 50 years of continuous service. (U.S. Air Force photo by Staff Sgt. Jonathan Snyder)