U.S. Air Force Staff Sgt. Nathan Davis, an aircrew flight equipment technician with the 18th Operations Support Squadron, cleans the face mask of an HGU-55/P helmet while conducting a periodic inspection during the Northern Edge 2011 premier joint training exercise at Eielson Air Force Base, Alaska, June 21, 2011. Northern Edge is an annual joint training exercise designed to test military and civilian response and coordination capabilities while enhancing the command, control and communications relationships associated with joint operations.