Dear Mr. Prickett,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located Records of Motor Supply Trains, 1917 - 1919 in the Records of the American Expeditionary Forces (World War I) (Record Group 120) that includes records of the 406th Motor Supply Train. For more information about these records, please contact the National Archives at College Park - Textual Reference (RDT2) via email at Archives2reference@nara.gov.
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 RDT2. We apologize for this inconvenience and appreciate your understanding and patience.
For general information about motor transportation during World War I, you may wish to contact the US Army Transportation Museum, the US Army Quartermaster Museum, and the National World War I Museum.
We hope this is helpful. Best of luck with your family research!