premise: Fort Davis National Historic Site is a United States National Historic Site located in the unincorporated community of Fort Davis, Jeff Davis County, Texas. Located within the Davis Mountains of West Texas, the historic site was established in 1961 to protect one of the best remaining examples of a United States Army fort in the southwestern United States.
hypothesis: Fort Davis was once a United States Air Force Base situated in Texas.
reason: The statement clearly identifies it as an example of an "Army"