when did it become mandatory to have a social security number
Social Security number Social Security numbers were first issued by the Social Security Administration in November 1935 as part of the New Deal Social Security program. Within three months, 25 million numbers were issued.[4]
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.