An aspiring pararescueman swims his final lap for his Physical Ability Stamina Test Dec., 6, 2012, at the Shellbank Fitness Center, Langley Air Force Base, Va. The PAST is used to qualify individuals for special operations career fields, and includes a swimming, running and muscular-endurance portion. (U.S. Air Force photo by Airman 1st Class R. Alex Durbin/Released)