The National Archives at St. Louis, in Missouri stores military personnel records, including U.S. Army serial numbers, states the National Archives' National Personnel Records Center. Before July 1, 1969, the Army used service numbers as personal identifiers; after July 1, 1969, the Army began using Social Security numbers instead.
An Army identification tag, informally called a dog tag, communicates the vital statistics of the soldier wearing it, according to the U.S. Army. The information on a dog tag includes a soldier's name, Social Security number (or serial number, prior to 1969), blood type and religious preference. The Army created its first service numbers in February 1918, during World War I.