The 37th and 38th Congresses (1861–1865) played an active role during the Civil War through legislation, appropriations, and oversight. In 1861, Congress encouraged development of the ironclad warship. The U.S.S. Monitor, designed by Swedish-American engineer John Ericsson, was tested in an encounter with the Merrimac, a Union ship the Confederates had captured, fitted with iron armor, and renamed the C.S.S. Virginia. Their March 9, 1862 battle at Hampton Roads, Virginia—the world’s first between steam-powered ironclads—revolutionized naval warfare.