USS Congress—the fourth United States Navy ship to carry that name—was a sailing frigate, like her predecessor, USS Congress (1799).

CSS Virginia was the first steam-powered ironclad warship built by the Confederate States Navy during the first year of the American Civil War; she was constructed as a casemate ironclad using the razéed original lower hull and engines of the scuttled steam frigate USS Merrimack. Virginia was one of the participants in the Battle of Hampton Roads, opposing the Union's USS Monitor in March 1862. The battle is chiefly significant in naval history as the first battle between ironclads.