Arguably the main distinction between USS X-1 and its Royal Navy counterparts relates to its engine. Unlike the standard diesel engines of the X class and XE class, USS X-1 featured a more advanced, closed-cycle hydrogen peroxide diesel engine, similar in principle to the engine on the German Type-XVII coastal submarine. When submerged, USS X-1’s engine relied on the catalytic decomposition of the hydrogen peroxide to generate oxygen (on the surface, a small air inlet was used to operate the engine).
The hydrogen peroxide – a colorless liquid that is often used as a bleaching agent in high quantities and can cause irritation to the eyes, nose, skin, and throat if ingested – was transported onto the vessel in rubber bags, surrounded by seawater. In using hydrogen peroxide, it was envisaged that USS X-1 would be able to travel at faster speeds without the need to resurface.
When the vessel was placed into service in October 1955, it began work in a research capacity in order to test the Navy’s ability to defend harbors against small, adversary submarines. The vessel was also designed for more offensive purposes – principally, as a means of attacking enemy ships using its side-mounted charges which, according to Sutton, would be dropped below the target vessel.
USS X-1 in Long Island Sound, 1955. U.S. Naval Institute via Naval History and Heritage Command
While the Navy Underwater Demolition Teams were interested in utilizing midget submarines for beach reconnaissance, with hopes for four X-1 submarines in support of UDT-2 (which, along with UDT-1, was one of the original UDT groups formed during World War II), hopes for multiple midget submarines were dashed by procurement politics. U.S. Submarine Force, unhappy with the decision of providing UDT groups with their own dedicated submarines, only agreed to one midget submarine being built under the condition that USS X-1 would also be a Submarine Force vessel.
Ultimately, USS X-1’s use of hydrogen peroxide proved to be near fatal. On May 20, 1957, its hydrogen peroxide bags blew up. No personnel were injured in the explosion, thankfully, but the blast was significant enough that the vessel’s entire bow section was blown off entirely. As a result, it was refitted with a regular diesel-electric drive engine.
By this stage, however, with focus having swiftly moved towards nuclear-powered submarine technology, the desire to keep USS X-1 as an active service vessel waned. On December 2, 1957, X-1 was taken out of service and inactivated in Philadelphia, Pennsylvania. After being towed to Annapolis, Maryland, in December 1960, it was reactivated (and painted in vivid colors) in order to perform experimental duties for Submarine Squadron 6 at the Small Craft Facility of the Severn River Command in Chesapeake Bay. USS X-1 was taken out of service for good on February 16, 1973. In April of that year, the vessel was transferred to the Naval Ship Research and Development Center, Annapolis, and by July it was slated for use as a historical exhibit. USS X-1 is now preserved at the Submarine Force Museum at Groton, Connecticut.
Although USS X-1 was something of a novelty for the U.S. Navy in the immediate postwar period, the legacy of its midget submarine efforts can be seen into the latter twentieth century and even the twenty-first century.
For decades, U.S. Navy SEALS have used self-propelled 'wet' SEAL Delivery Vehicles (SDV), meaning that passengers must wear wetsuits and breathing apparatus due to the lack of a pressurized hull. Other small self-propelled underwater vehicles used by the Navy in the latter twentieth and early twenty-first centuries include, for example, the deep-submergence rescue vehicles DSRV-1 Mystic and DSRV-2 Avalon. Both were launched in the 1970s but were retired from service in 2008 and 2000, respectively.