USS X-1 (SSX-1) was the first midget submarine built for the U.S. Navy. It was designed to penetrate enemy harbors and conduct offensive operations against moored ships and support facilities, with principal armament consisting of swimmer delivered limpet mines. It had a lock-out capability for submerged launch and recovery of underwater demolition teams, and it could also be configured to deliver a single large XT-20A mine. X-1 was initially designed by Portsmouth Naval Shipyard as a Diesel-battery craft, but the design was later turned over to Fairchild Engine and Aircraft Corporation, where the boat was constructed and placed in service with a partial closed cycle Diesel propulsion system using Hydrogen Peroxide for submerged operations. Technical problems with that propulsion system culminated in an explosion in the Hydrogen Peroxide storage cell in May 1957, leading to removal of the Peroxide systems. The boat then returned to service and completed her useful life as a Diesel-electric submarine conducting oceanographic research for the Naval Research Laboratory. X-1 was 50 feet long, or 54 feet with the XT-20A mine, had a 7-foot beam, a submerged displacement of 36 tons, a design test depth of 200 feet, a speed of 5 knots surfaced and 6 knots submerged, and a maximum submerged range of 185 nautical miles at 6 knots. It was in service from October 1955 to December 1957 and from November 1960 to February 1973.