The United States Navy

The United States Navy (USN) is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S. Navy also has the world's largest carrier fleet, with 11 in service, one under construction (two planned), and one in reserve. The service had 328,516 personnel on active duty and 101,689 in the Navy Reserve in January 2011. It operates 286 ships in active service and more than 3,700 aircraft.
The Navy traces its origins to the Continental Navy, which was established during the American Revolutionary War and was essentially disbanded as a separate entity shortly thereafter. The United States Constitution provided the legal basis for a military force by giving Congress the power "to provide and maintain a navy".
Depredations against U.S. shipping by Barbary Coast pirates in the Mediterranean Sea spurred Congress to employ this power by passing the Naval Act of 1794 ordering the construction and manning of six frigates. These ships were used to end most pirate activity off the Barbary Coast. In the 20th century American blue-water navy capability was demonstrated by the 1907–1909 world tour of the Great White Fleet.