Daily AncestorArmy serial number
An Army serial number was the personal identification number the U.S. Army gave each soldier from 1918, used until Social Security numbers replaced it in 1969.
The Army began service numbers in 1918, and John J. Pershing held officer number O-1. Army numbers ran into the tens of millions, and the National Guard had its own block, 20 to 29 million, so a number in that range points to Guard service. The Army switched to Social Security numbers on July 1, 1969.
The number appears on World War I service cards and burial case files, and the National Archives asks for it when searching for a burial file. Do not confuse it with the serial or order number printed on a draft card.
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Daily Ancestor. "Army serial number." Dictionary of Old Record Words. https://dailyancestor.com/dictionary/military/army-serial-number. Last checked 2026-10-12.