Dear Mr. Sullivan,
Thank you for posting your request on History Hub!
As you suggested, the information you seek may be contained in Pvt. Fitzgerald’s Army burial case file. Burial case files for 1915 to 1939 are in the custody of the National Archives at St. Louis (RL-SL). For more information about these non-digitized records, please contact RL-SL via email at email@example.com.
If you have not done so already, we also suggest that you request a copy of his Official Military Personnel File (OMPF). 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.
Next, we searched the National Archives Catalog and located the series Records of the 1st Through 338th and the 559th Infantry Regiment, 1916-1921 in the Records of U.S. Regular Army Mobile Units (Record Group 391) that include the records of the 39th Infantry Regiment during WWI that may contain some relevant information. In addition, we located a series titled Records of Divisions, 1917 - 1920 in the Records of the American Expeditionary Forces (World War I) (Record Group 120) that includes the 4th Division and files of the 39th Infantry Regiment in Boxes 29-32. For more information about these non-digitized records, please contact the National Archives at College Park - Textual Reference (RDT2) via email at firstname.lastname@example.org. We were unable to locate specific records of Company B or the 1st Battalion. Records of lower echelon units sometimes were incorporated into the files of the regiment.
Plus, we located the series American Unofficial Collection of World War I Photographs in the Records of the War Department General and Special Staffs (Record Group 165) that includes 1 photograph of the 39th Regiment that may be of interest to you. This image has been digitized and may be viewed online using the Catalog.
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 from RL-SL and RDT2. Also, NPRC will continue servicing requests ONLY associated with medical treatments, burials, homeless veterans seeking admittance to a homeless shelter, and those involving the VA Home Loan program. 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 this inconvenience and appreciate your understanding and patience.
Finally, the US Army Center of Military History provides some information online about the 39th Infantry Regiment | Lineage and Honors and about Aisne-Marne that may be useful. We suggest that you contact them directly for further assistance.
We hope this information is helpful. Best of luck with your family research!