why do we have a social security number
Social Security number The original purpose of this number was to track individuals' accounts within the Social Security program. It has since come to be used as an identifier for individuals within the United States, although rare errors occur where duplicates do exist. As numbers are now assigned by the central issuing office of the SSA, it is unlikely that duplication will ever occur again. A few duplications did occur when prenumbered cards were sent out to regional SSA offices and (originally) Post Offices.
Service number (United States Armed Forces) Service numbers were eventually phased out completely by the social security number; the Army and Air Force converted to social security numbers on 1 July 1969, the Navy and Marine Corps on 1 January 1972, and the Coast Guard on 1 October 1974.[4] Since that time, social security numbers have become the de facto military service number for United States armed forces personnel.