United States Military Railroad
The U.S. Military Railroad (USMRR) was established by the United States War Department as a separate agency to operate any rail lines seized by the government during the American Civil War. An Act of Congress of 31 January 1862 authorized President Abraham Lincoln to seize control of the railroads and telegraph for military use in January 1862.
Source: Wikipedia — United States Military Railroad (CC BY-SA 4.0)