CHARLESTON, SOUTH CAROLINA—Two hundred years ago this week, the U.S. Revenue Cutter Gallatin exploded due to an accident and sank in Charleston Harbor. Three crew members were killed and five were severely injured. The Gallatin had been charged with enforcing maritime regulations and conducting incoming cargo inspections for the Treasury Department, and during the War of 1812, performing combat patrols and seizing enemy ships. Archaeologists will use side-scan sonar to look for the wreckage and the ship’s eight cannons. “The odds are long. If we don’t look, we’ll never know,” said Jim Spirek of the South Carolina Institute of Archaeology and Anthropology.