Book excerpt: This regulation, Army Regulation AR 40-501 Medical Services: Standards of Medical Fitness June 2019, governs medical fitness standards for enlistment, induction, and appointment, including officer procurement programs; medical fitness standards for retention and separation, including retirement; medical standards and policies for aviation; and medical fitness standards for diving, Special Forces, airborne, Ranger, free fall parachute training and duty, small unmanned aircraft system (SUAS) operators, and certain enlisted military occupational specialties (MOSs) and officer assignments such as civil affairs, psychological operations, and Army maritime sea duty. This regulation applies to the Regular Army, the Army National Guard/Army National Guard of the United States, and the U.S. Army Reserve, unless otherwise stated. It also applies to candidates for military service. During mobilization, the proponent may modify chapters and policies contained in this regulation.