U.S. Air Force F-15 Eagles from 104th Fighter Wing, Barnes Air National Guard Base, Mass., form up next to Swedish Air Force F-16 Falcons behind a KC-135 Stratotanker, McGuire Air Force Base N.J., after receiving fuel over Sweden, May 24, 2019. The aircraft are supporting Arctic Challenge Exercise 19, a Nordic aviation exercise intended to provide scenario-based training to prepare partner forces for enemy defensive systems. (U.S. Air Force photo by Staff Sgt. Kenneth Shaner Brown)

U.S. Air Force F-15 Eagles fly in formation with Swedish air force F-16 Falcons after receiving fuel from a KC-135 Stratotanker over Sweden, May 24, 2019.