Dear Mr. Lofft,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and 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 lists/rosters of servicemen in the 109th Sanitary Train, 34th Division (in Box 21) but were unable to locate a Leo Lofft on any of the lists. The 133rd Ambulance Company was attached to the 109th. We also searched for the records of the 309th Ambulance Company, 303rd Sanitary Train, 78th Division (in box 35) but the Division filed its medical unit records in a separate series titled Records of Medical Units and Offices of Infantry Divisions, 1917 -1919 also in Record Group 120. We searched through the files for the 309th and 303rd (in boxes 3853-3856) in this series but were unable to locate a Leo Lofft in any of the orders, returns, promotion lists, etc.
To clarify what unit he served in, we 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 prior to 1958 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.
Once you know the unit, we suggest that you request copies of the monthly rosters. Most monthly rosters from November 1912 - 1943 for U.S. Army units are in the custody of the National Archives at St. Louis, MO. For access to these records, please write to the National Archives at St. Louis, ATTN: RL-SL, P.O. Box 38757, St. Louis, MO 63138-0757 or via email at firstname.lastname@example.org.
We hope that this is helpful. Best of luck with your family research!