Drydock Number One, Norfolk Naval Shipyard, also known as Drydock No. 1, is the site where the USS Merrimack was modified to be the Confederate Navy ironclad CSS Virginia. It is now included within the Norfolk Naval Shipyard. It remains in use. The drydock can accommodate a maximum vessel length of with a beam. Depth is . Primarily used for service craft, the dock can be dewatered in 40 minutes and flooded in 90 minutes It was declared a National Historic Landmark in 1971.