The jack of the United States of America is a maritime flag representing United States nationality flown on the jackstaff in the bow of American vessels. The U.S. Navy is a prime user of jacks, but they are also used by ships of the U.S. Coast Guard, Military Sealift Command, National Oceanic and Atmospheric Administration, and other governmental entities. "The jack is flown on the bow (front) of a ship and the ensign is flown on the stern (rear) of a ship when anchored or moored. Once under way, the ensign is flown from the main mast."