On 7 December, the uncommissioned submarine conducted a dive off Penfield Reef in Long Island Sound as part of builder's trials. A manhole plate in one of the aft ballast tanks was left unsecured, several aft compartments flooded, and S-48 sank in 80 feet of water. The crew, contractor's personnel, and naval observers brought the bow to the surface and escaped through a torpedo tube to a tug which took them to New York City.