X-1 was the United States Navy's only midget submarine (but see the NR-1 Deep Submergence Craft), laid down on June 8, 1954, at Deer Park, Long Island, New York, by the Engine Division of Fairchild Engine and Airplane Corporation, launched on September 7, 1955, at Oyster Bay, Long Island, by Jakobson's Shipyard ; delivered to the Navy on October 6 at New London, Connecticut, and placed in service on October 7, 1955, with Lieutenant. K. Hanlon in command.

X-1 served in a research capacity in rigorous and extensive tests to assist the Navy to evaluate its ability to defend harbors against very small submarines. Further tests conducted with the X-1 helped to determine the offensive capabilities and limitations of this type of submersible.

Originally powered by a hydrogen peroxide/diesel engine and battery system, an explosion of her hydrogen peroxide supply on May 20, 1957, resulted in the craft's modification to diesel-electric drive. On December 2, 1957, X-1 was taken out of service and inactivated at Philadelphia, Pennsylvania.

Towed to Annapolis, Maryland, in December 1960, X-1 was reactivated and attached to Submarine Squadron 6 and based at the Small Craft Facility of the Severn River Command for experimental duties in Chesapeake Bay. In tests conducted under the auspices of the Naval Research Laboratory, X-1 performed for scientists who observed her operations from a platform suspended beneath the Bay Bridge, to learn more about the properties and actions of sea water.

Remaining in an active, in-service, status through January 1973, X-1 was again taken out of service on February 16, 1973, and, on April 26, was transferred to the Naval Ship Research and Development Center, Annapolis. On July 9, 1974, the submersible was slated for use as a historical exhibit; and she was subsequently placed on display on the grounds of the Naval Station complex, North Severn, near Annapolis.

General characteristics

• Displacement: 36.3 tons submerged, 31.5 tons surfaced
• Length: 49.5 feet
• Beam: 7 feet
• Draft: 6.2 feet
• Complement: 10