Gosport Navy Yard, also known as Norfolk Naval Shipyard, is the oldest Navy shipyard in the nation. It was established in 1767 by British naval agent Andrew Sprowle, occupied by patriot forces in 1775, and operated as a shipyard by the Virginia State Navy before being burned by the British in 1779 during their occupation of Portsmouth. In 1794 the yard was loaned to the U.S. government and in 1801 purchased by the U.S. Navy Department. The USS Chesapeake, one of six frigates authorized by Congress to provide a naval armament, was the first ship built there in 1798–1799. On June 17, 1833, the 74-gun USS Delaware entered newly completed Dry Dock No. 1 as the first ship to enter a dry dock in America. When Virginia left the Union, the U.S. Navy evacuated and burned the yard, which local Confederates immediately occupied. Salvaged stores and equipment, including 1,085 cannons, were used to equip and fortify land batteries in the Tidewater region and elsewhere in the South. The steam frigate Merrimack, under repair there and burned and sunk during the Federal evacuation, was raised by the Confederates, placed in Dry Dock No. 1, and converted from designs by Portsmouth native Naval Constructor John L. Porter into the ironclad CSS Virginia. In Hampton Roads on March 8, 1862, Virginia sank the USS Cumberland and USS Congress, and the next day fought the ironclad USS Monitor, proving wooden warships obsolete. Gosport also produced several other gunboats and part of the ironclad CSS Richmond. On May 10, 1862, the yard was burned again by evacuating Confederates, immediately reoccupied by the U.S. Navy, and then controlled by the Union for the rest of the war.