Ferdinand H. Gerdes was one of the most active members of the U.S. Coast Survey team. His most important work includes several surveys of New York Harbor as well as detailed surveys of Florida, the Gulf Coast, and up the Mississippi River. Like most of the members of the Coast Survey, Gerdes was strongly pro-Union and worked diligently during the Civil War to provide Union commanders accurate surveying and cartographic materials. Gerdes is known to have commanded the ‘Sachem' and, during the Civil War, was heavily engaged with Union efforts to map and ultimately control, the Mississippi River.