A civilian contractor uses a concrete saw to start the construction of a B-21 Raider Environmental Protection Shelter at Ellsworth Air Force Base, S.D., Dec. 16, 2020. 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 Senior Airman Christina Bennett)