Dear Mr. Contreras,
Thank you for posting your request on History Hub!
We suggest that you begin your research by requesting a copy of your father’s Official Military Personnel File (OMPF). OMPFs and individual medical reports for those who served in the U.S. Air Force after 1958 and prior to May 1, 1994 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. For more information see Request Military Service Records.
Due to the COVID-19 pandemic, the NPRC is closed except for emergencies. Currently, NPRC will continue servicing requests ONLY associated with medical treatments, burials, and homeless veterans seeking admittance to a homeless shelter. If your request is urgent, please see Emergency Requests and Deadlines. Please refrain from submitting non-emergency requests such as replacement medals, administrative corrections, or records research until NPRC returns to pre-COVID staffing levels. Please check archives.gov/veterans for updates to the NPRC operating hours and status. We apologize for any inconvenience.
Also, it is possible that the birth of your half-brother was registered at the American Embassy or Consulate in France. Records of overseas births are kept by the Department of State (IF they were reported to the consulate - for both civilian and military-base births). Please use the following link to the Department of State's website regarding How to Apply for a Certified Copy of a Consular Report of Birth Abroad.
Further, we suggest contacting the local town hall or local magistrate’s court in the Evreux region in France as they hold vital records including birth certificates.
We hope this is helpful. Best of luck with your family research!