Dear Ms. Church,
Thank you for posting your request on History Hub!
To determine if your son-in-law was in the military, we suggest that you begin by requesting a copy of his Official Military Personnel File (OMPF). OMPFs for those who served in the U.S. Armed Forces after 1957 and prior to 1999 are in the custody of NARA's National Personnel Records Center in St. Louis. In many cases where Army and Air Force personnel records were destroyed in the 1973 fire, proof of service can be provided from other records such as morning reports, payrolls, and military orders, and a certificate of military service will be issued. Navy and Marine Corps OMPFs were not affected by the fire. Please complete a GSA Standard Form 180 and mail it to NARA's National Personnel Records Center, (Military Personnel Records), 1 Archives Drive, St. Louis, MO 63138-1002.
We hope this information is helpful.