The Crater-class cargo ship were converted EC2-S-C1 type, Liberty cargo ships, constructed by the United States Maritime Commission (USMC) for use by the US Navy during World War II. The designation 'EC2-S-C1': 'EC' for Emergency Cargo, '2' for a ship between 400 and 450 ft long, 'S' for steam engines, and 'C1' for design C1.