A B-1 bomber takes off as part of exercise Combat Raider at Ellsworth Air Force Base, S.D., March 15, 2017. The B-1 bomber is a four-engine supersonic heavy strategic bomber first envisioned in the 1960s as a replacement for the Boeing B-52 Stratofortress. (U.S. Air Force photo by Airman 1st Class Donald C. Knechtel)