What was a Confederate warship used to halt the Union blockade?

Answer 1

In an early effort to break the Union blockade, the Confederate Ironclad Merrimack [renamed CSS Virginia] sank the wooden Union warships Cumberland and Congress at the battle of Hampton Roads, Va. on March 8th, 1862. The next day, the CSS Virginia was met by the Union Ironclad USS Monitor in the more famous "battle between the Ironclads" at Hampton Roads. This fight was a draw with neither Ironclad inflicting major damage to the other. The Virginia never had another chance to destroy more of the Union blockaders, so the blockade here was never truly broken.

Other Ironclad warships were built by the Confederacy during the war with the intent of breaking the blockades of other southern ports, but the South lacked the industrial power to match the Union in production of Ironclads, so the few others that were built by the South were all either sunk in battle or captured, or never completed due to a lack of armor or engines.

A different kind of attempt was made to break the blockade of Charleston, SC by using a submersible boat, called the "H.L. Hunley", named for her inventor. On the night of February 17th, 1864, the Hunley attacked and sank the blockading Union warship USS Housatonic in the world's first successful attack by a submarine. However, the Hunley also sank for unknown reasons soon after the attack and no further attempts were made by the Confederates to duplicate the success of the Hunley.