Physics reportedly developed 100-kW and 1000-kW fuel cell engines. The Naval Materials Research Laboratory of Indian Defence Research and Development Organisation in collaboration with Larsen & Toubro and Thermax has developed a 270 kilowatt phosphoric acid fuel cell (PAFC) to power the s, which are based on the design. All six Kalvari-class submarines will be retrofitted with AIP during their first upgrade. It produces electricity by reacting with hydrogen generated from sodium borohydride and stored oxygen with phosphoric acid acting as an electrolyte. The Portuguese Navy s are also equipped with fuel cells. Nuclear power Air-independent propulsion is a term normally used in the context of improving the performance of conventionally propelled submarines. However, as an auxiliary power supply, nuclear power falls into the technical definition of AIP. For example, a proposal to use a small 200-kilowatt reactor for auxiliary power—styled by AECL as a "nuclear battery"—could improve the under-ice capability of Canadian submarines. Nuclear reactors have been used since the 1950s to power submarines. The first such submarine was USS Nautilus commissioned in 1954. Today, China, France, India, Russia, the United Kingdom and the United States are the only countries to have built and operated nuclear-powered submarines successfully. Non-nuclear AIP submarines As of 2017, some 10 nations are building AIP submarines with almost 20 nations operating AIP based submarines: References Notes Sources Further reading Submarine design Marine propulsion Spanish inventions