Dear Mr. Hoggatt,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and locate the series Enlistment Papers, 1798 - October 31, 1912 in the Records of the Adjutant General's Office, 1762 - 1917 (Record Group 94) that include military service files of the Regular Army. We also located 3 series pertaining to Fort Assinniboine in the Records of U.S. Army Continental Commands (Record Group 393). To request a search of this series, please contact the National Archives at Washington, DC - Textual Reference (RDT1) via email at firstname.lastname@example.org.
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 acknowledgment as well as a substantive response to your reference request by RDT1. We apologize for this inconvenience and appreciate your understanding and patience.
For a history and photographs, please see Fort Assinnibone in Havre, Montana website.
We hope this is helpful. Best of luck with your family research!