H. L. Hunley, also known as the Hunley, CSS H. L. Hunley, or CSS Hunley, was a submarine of the Confederate States of America that played a small part in the American Civil War. Hunley demonstrated the advantages and dangers of undersea warfare. She was the first combat submarine to sink a warship, although Hunley was not completely submerged and, following her attack, was lost along with her crew before she could return to base.