Airmen of the 191st Aircraft Maintenance Squadron begin their day by towing a KC-135 Stratotanker out of a hangar at Selfridge Air National Guard Base, Mich., in the pre-dawn hours of Dec. 19, 2014. Each aircraft undergoes a complete inspection, known as an ISO or isochronical inspection, at various points in the aircraft’s operational cycle. (U.S. Air National Guard photo by Terry Atwell)