Aircrew members from the 69th Bomb Squadron perform a pre-flight check on a B-52H Stratofortress before takeoff on Minot Air Force Base, N.D., April 1, 2015. The training mission, coined “Polar Growl,” aims to support bomber training requirements, ensuring global strike capabilities are flexible, credible and responsive to various threats. (U.S. Air Force photo/Senior Airman Brittany Y. Bateman)