General Electric, with one reactor powering each vessel. Rolls-Royce built similar units as the PWR1 for Royal Navy submarines and then developed the design further to the PWR2. Numerous submarines with an S5W reactor plant were built. At the end of the Cold War in 1989, there were over 400 nuclear-powered submarines operational or being built. Some 250 of these submarines have now been scrapped and some on order canceled, due to weapons reduction programs. The Russian Navy and United States Navy had over one hundred each, with the United Kingdom and France less than twenty each and China six. The total today is about 160. The United States is the main navy with nuclear-powered aircraft carriers (10), while Russia has nuclear-powered cruisers. Russia has eight nuclear icebreakers in service or building. Since its inception in 1948, the U.S. Navy nuclear program has developed 27 different plant designs, installed them in 210 nuclear-powered ships, taken 500 reactor cores into operation, and accumulated over 5,400 reactor years of operation and 128,000,000 miles safely steamed. Additionally, 98 nuclear submarines and six nuclear cruisers have been recycled. The U.S. Navy has never disclosed a reactor accident, but has suffered at least one coolant loss accident, on the USS Guardfish. All nine of the U.S. Navy nuclear-powered cruisers (CGN) have now been stricken from the Naval Vessel Register, and those not already scrapped by recycling are scheduled to be recycled. While reactor accidents have not sunk any U.S. Navy ships or submarines, two nuclear-powered submarines, and were lost at sea. The condition of these reactors has not been publicly released, although both wrecks have been investigated by Robert Ballard on behalf of the Navy using remotely operated vehicles (ROVs). Congress has mandated that the U.S. Navy consider nuclear power as an option on all large surface combatants (cruisers, destroyers) and amphibious assault ships. If proven cost-effective in a life cycle cost analysis during the Analysis of Alternatives (AoA) phase of preliminary ship design, new ship classes (e.g. CG(X)) could proceed with nuclear propulsion. Power plants Current U.S. naval reactors are all pressurized water reactors, which are identical to PWR commercial reactors producing electricity, except that: They have a high power density in a small volume and run either on low-enriched uranium (as do some French and Chinese submarines) or on highly enriched uranium (>20% U-235, current U.S. submarines use fuel enriched to at least