Dear Andrine Belliveau,
Thank you for contacting History Hub.
That is a great story about your grandfather being called an “idiot” by General Patton!
I would normally suggest you request a copy of his Official Military Personnel File (OMPF), however, it appears you may have done so already and were told that the OMPF was destroyed in the fire.
OMPFs and individual medical reports for enlisted men of the U.S. Army who were separated from the service after October 1912 and before 1959 are in the custody of NARA's National Personnel Records Center (NPRC) 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. For more information see Official Military Personnel Files (OMPF), Archival Records Requests.
Additionally, here is a blog post describing WWII Military Unit Records at the National Archives: https://historyhub.history.gov/community/military-records/army-and-air-force-records/blog/2017/08/25/wwii-military-unit-records-at-the-national-archives
This may be some duplication of the above links, but here is a page on Requesting Veterans’ Service Records from the National Archives:
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request. We apologize for this inconvenience and appreciate your understanding and patience.
We hope this is helpful. Best of luck in your research.