Contractors use cranes to place a pair of beams as part of the B-21 Raider Environmental Protection Shelter prototype construction project at Ellsworth Air Force Base, S.D., Jan. 28, 2021. Ellsworth AFB was selected as the test location for the B-21 EPS as it provides the most extreme and diverse weather conditions to test the temporary structures. The testing of the EPS prototypes at Ellsworth AFB does not interfere with Air Force compliance to the National Environmental Protection Act/Environmental Impact Statement preparation for the first B-21 Main Operating Base. (U.S. Air Force photo by 2nd Lt. Calvin Ross)