The United States Navy (USN) is the sea branch of the U.S. Armed Forces. It is one of the seven uniformed services of the United States. As of 31 December 2008, the U.S. Navy had about 331,682 personnel on active duty and 124,000 in the Navy Reserve. It operates 283 ships in active service and more than 3,700 aircraft. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest combined. The U.S. Navy also has the world's largest carrier fleet, with 11 in service and one under construction.