Answer:
The Confederate submarine H.L. Hunley (now being restored in Charleston, S.C., after being found and recovered several years ago) is the only submarine ever used by the CSA. Though she was successful in sinking the USS Housatonic in Charleston Harbor during the Civil War, she sank shortly afterward on her return to base, killing all hands.
Her feat is considered to be the first combat sinking of a ship by a submarine in war.