Airmen of the Royal Australian Air Force, Republic of Korea Air Force, Republic of Singapore Air Force and U.S. Air Force fill concrete mix into a hole during exercise Silver Flag, at Northwest Field, Guam, April 24, 2018. Teams faced a simulated aftermath of a base attack and having to repair facilities and the airfield to ensure that they can repair the airfield and return it to safe use for aviators. (U.S. Air Force by Airman 1st Class Christopher Quail)