Dear Mr. Kirby,
Thank you for posting your request on History Hub!
If you served in the military after 1970, your Social Security Number would be your Service Number.
If your service took place prior to 1971, we suggest submitting a GSA Standard Form 180 to NARA's National Personnel Records Center (NPRC), (Military Personnel Records), 1 Archives Drive, St. Louis, MO 63138-1002. Please provide as much information as you can.
We hope this is helpful!