powered anaerobic or air independent steam engine. In 1908 the Imperial Russian Navy launched the submarine Pochtovy, which used a gasoline engine fed with compressed air and exhausted under water. These two approaches, the use of a fuel that provides energy to an open-cycle system, and the provision of oxygen to an aerobic engine in a closed cycle, characterize AIP today. Types Air independent propulsion (non-nuclear) can take various forms. All currently active AIP submarines require oxygen for AIP, which is commonly stored as a liquid (LOX). AIP submarine range is primarily limited by the amount of LOX it can carry. Open-cycle systems During World War II the German firm Walter experimented with submarines that used high-test (concentrated) hydrogen peroxide as their source of oxygen under water. These used steam turbines, employing steam heated by burning diesel fuel in the steam/oxygen atmosphere created by the decomposition of hydrogen peroxide by a potassium permanganate catalyst. Several experimental boats were produced, though the work did not mature into any viable combat vessels. One drawback was the instability and scarcity of the fuel involved. Another was that while the system produced high underwater speeds, it was extravagant with fuel; the first boat, V-80, required 28 tons of fuel to travel , and the final designs were little better. After the war one Type XVII boat, , which had been scuttled at the end of World War II, was salvaged and recommissioned into the Royal Navy as . The British built two improved models in the late 1950s, , and . Meteorite was not popular with its crews, who regarded it as dangerous and volatile; she was officially described as 75% safe. The reputations of Excalibur and Explorer were little better; the boats were nicknamed Excruciater and Exploder. The Soviet Union also experimented with the technology and one experimental boat was built which utilized hydrogen peroxide in a Walter engine. The United States also received a Type XVII boat, U-1406, and went on to begin two AIP submarine projects. Project SCB 66 developed an experimental midget submarine, , which was launched in September 1955. It was originally powered by a hydrogen peroxide/diesel engine and battery system until an explosion of her hydrogen peroxide supply on 20 May 1957. X-1 was later converted to a diesel-electric. The second U.S. Navy project was of a full sized AIP submarine under SCB 67 in 1950, later SCB