The mission of the Navy is to maintain, train and equip combat-ready Naval forces capable of winning wars, deterring aggression and maintaining freedom of the seas. The U.S. Navy was founded on 13 October 1775, and the Department of the Navy was established on 30 April 1798. The Department of the Navy has three principal components: The Navy Department, consisting of executive offices mostly in Washington, D.C.; the operating forces, including the Marine Corps, the reserve components, and, in time of war, the U.S. Coast Guard (in peace, a component of the Department of Homeland Security); and the shore establishment.

Excerpted from the Navy’s official web site.