Dear Ms. McManus,
Thank you for posting your question on History Hub!
The information you seek may be in the World War I selective service (draft) records or/and in his Official Military Personnel File (OMPF).
The First World War selective service (draft) records (including the 4th registration) are in the custody of the National Archives at Atlanta (RE-AT). You can contact them via email at firstname.lastname@example.org.
Official Military Personnel Files (OMPFs) and individual medical reports for enlisted men of the U.S. Army who were separated from the service after October 1912 and prior to 1955 are in the custody of NARA's National Personnel Records Center in St. Louis. In many cases where 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. 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. Or you may apply online at https://www.archives.gov/veterans/military-service-records/.
We hope this information is helpful. Best of luck with your family research!