U.S. War Department

The U.S. War Department had it many purposes for supplying the army with it's payment and supply, consisting of,

Organizing and supplying the Army.
Managing forts, arsenals, and military logistics.
Overseeing military operations.
Administering Indian affairs for part of its early history.
Defending the United States when Congress declared war.

When the War of 1812 began in June 1812, the War Department became the department responsible for directing the Army's role in that conflict, but it had existed for more than two decades before the war and continued afterward.