Salvage diving presents several unique challenges. Divers salvage ships and their cargos, aircraft and other vehicles and structures that have fallen or sunk in the water. Sometimes the goal of a salvage job is to pull out tools or structures that are still valuable. Other times the goal of a salvage job is to remove objects or structures that could be environmentally intrusive. Two of the most important salvages from this century are the USS Hunley, a Civil War submarine that carried out the first successful underwater attack in Charleston, SC Harbor, and the re-floating of the Costa Concordia off the coast of Isoola del Giglio, Italy.