active duty
(6)The term “active duty” does not include any period during which an individual (A) was assigned full time by the Armed Forces to a civilian institution for a course of education which was substantially the same as established courses offered to civilians, (B) served as a cadet or midshipman at one of the service academies, or (C) served under the provisions ofsection 12103(d) of title 10pursuant to an enlistment in the Army National Guard or the Air National Guard, or as a Reserve for service in the Army Reserve, Navy Reserve, Air Force Reserve, Marine Corps Reserve, or Coast Guard Reserve.