Air-independent propulsion
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Air-independent propulsion (AIP), or air-independent power, is any
marine propulsion Marine propulsion is the mechanism or system used to generate thrust to move a watercraft through water. While paddles and sails are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting of an electr ...
technology that allows a non-nuclear
submarine A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...
to operate without access to
atmospheric An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
(by surfacing or using a snorkel). AIP can augment or replace the diesel-electric propulsion system of non-nuclear vessels. Modern non-nuclear submarines are potentially stealthier than
nuclear submarine A nuclear submarine is a submarine powered by a nuclear reactor, but not necessarily nuclear-armed. Nuclear submarines have considerable performance advantages over "conventional" (typically diesel-electric) submarines. Nuclear propulsion, ...
s; although some modern submarine reactors are designed to rely on natural circulation, most naval nuclear reactors use pumps to constantly circulate the reactor coolant, generating some amount of detectable noise. Non-nuclear submarines running on battery power or AIP, on the other hand, can be virtually silent. While nuclear-powered designs still dominate in submergence times, speed, range and deep-ocean performance; small, high-tech non-nuclear attack submarines can be highly effective in coastal operations and pose a significant threat to less-stealthy and less-maneuverable nuclear submarines. AIP is usually implemented as an auxiliary source, with the traditional
diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-call ...
handling surface propulsion. Most such systems generate electricity, which in turn drives an electric motor for propulsion or recharges the boat's batteries. The submarine's electrical system is also used for providing "hotel services"—ventilation, lighting, heating etc.—although this consumes a small amount of power compared to that required for propulsion. AIP can be retrofitted into existing submarine hulls by inserting an additional hull section. AIP does not typically provide the endurance or
power Power most often refers to: * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power * Power (social and political), the ability to influence people or events ** Abusive power Power may a ...
to replace atmospheric dependent propulsion, but allows for longer underwater endurance than a conventionally propelled submarine. A typical conventional power plant provides 3
megawatt The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units, International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), ...
s maximum, and an AIP source around 10% of that. A nuclear submarine's propulsion plant is usually much greater than 20 megawatts. The
United States Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...
uses the
hull classification symbol The United States Navy, United States Coast Guard, and United States National Oceanic and Atmospheric Administration (NOAA) use a hull classification symbol (sometimes called hull code or hull number) to identify their ships by type and by ind ...
"SSP" to designate boats powered by AIP, while retaining "SSK" for classic diesel-electric
attack submarine An attack submarine or hunter-killer submarine is a submarine specifically designed for the purpose of attacking and sinking other submarines, surface combatants and merchant vessels. In the Soviet and Russian navies they were and are called ...
s.


History

In the development of the submarine, the problem of finding satisfactory forms of propulsion underwater has been persistent. The earliest submarines were man-powered with hand-cranked propellers, which quickly used up the air inside; these vessels had to move for much of the time on the surface with hatches open, or use some form of breathing tube, both inherently dangerous and resulting in a number of early accidents. Later, mechanically driven vessels used compressed air or steam, or electricity, which had to be re-charged from shore or from an on-board aerobic engine. The earliest attempt at a fuel that would burn anaerobically was in 1867, when Spanish engineer
Narciso Monturiol Narciso may refer to: Given name * Narciso Clavería y de Palacios, Spanish architect * Narciso Clavería y Zaldúa, Governor General of the Philippines * Narciso dos Santos, Brazilian former footballer * Narciso Durán, Franciscan friar and missio ...
successfully developed a chemically 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 World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
the German firm
Walter Walter may refer to: People * Walter (name), both a surname and a given name * Little Walter, American blues harmonica player Marion Walter Jacobs (1930–1968) * Gunther (wrestler), Austrian professional wrestler and trainer Walter Hahn (born 19 ...
experimented with submarines that used high-test (concentrated) hydrogen peroxide as their source of oxygen under water. These used
steam turbine A steam turbine is a machine that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Charles Parsons in 1884. Fabrication of a modern steam turbin ...
s, employing steam heated by burning diesel fuel in the steam/oxygen atmosphere created by the decomposition of hydrogen peroxide by a
potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, that dissolves in water as K+ and , an intensely pink to purple solution. Potassium permanganate is widely used in the c ...
catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
. 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 Scuttling is the deliberate sinking of a ship. Scuttling may be performed to dispose of an abandoned, old, or captured vessel; to prevent the vessel from becoming a navigation hazard; as an act of self-destruction to prevent the ship from being ...
at the end of
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, was salvaged and recommissioned into the
Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...
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 The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...
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 A midget submarine (also called a mini submarine) is any submarine under 150 tons, typically operated by a crew of one or two but sometimes up to six or nine, with little or no on-board living accommodation. They normally work with mother ships, ...
, , 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 67A. This submarine, designated SSX, would have one of three propulsion plants under development: a Walther open cycle hydrogen peroxide plant (termed ''Alton''), a liquid oxygen steam plant (''Ellis''), and an AIP gas turbine (''Wolverine''). By late 1951 the Navy realized that while the competing nuclear designs were heavier due to shielding, they were more compact than the three AIP plants: the SSX would be longer than the SSN by nearly 40 feet. The SSN would likely be quieter and less complicated than the AIP technology of this time. By 1952 the
nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...
s were so far along in development it appeared that the SSX submarine would not be needed as a stopgap. The project was cancelled on 26 October 1953. The USSR and the UK, the only other countries known to be experimenting with the technology at that time, also abandoned it when the US developed the nuclear reactor small enough for submarine propulsion. Other nations, including Germany and Sweden, would later recommence AIP development. It was retained for propelling
torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, and with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, su ...
es by the British and the Soviet Union, although hastily abandoned by the former following the tragedy. Both this and the loss of the were due to accidents involving hydrogen peroxide propelled torpedoes.


Closed-cycle diesel engines

This technology uses a submarine
diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-call ...
which can be operated conventionally on the surface, but which can also be provided with
oxidant An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxi ...
, usually stored as
liquid oxygen Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries—is the liquid form of molecular oxygen. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an applica ...
, when submerged. Since the metal of an engine would burn in pure oxygen, the oxygen is usually diluted with recycled
exhaust gas Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline (petrol), diesel fuel, fuel oil, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through an ...
.
Argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
replaces exhaust gas when the engine is started. In the late 1930s the Soviet Union experimented with closed-cycle engines, and a number of small M-class vessels were built using the
REDO Undo is an interaction technique which is implemented in many computer programs. It erases the last change done to the document, reverting it to an older state. In some more advanced programs, such as graphic processing, undo will negate the las ...
system, but none were completed before the German invasion in 1941. During World War II the German ''
Kriegsmarine The (, ) was the navy of Germany from 1935 to 1945. It superseded the Imperial German Navy of the German Empire (1871–1918) and the inter-war (1919–1935) of the Weimar Republic. The was one of three official branches, along with the a ...
'' experimented with such a system as an alternative to the Walter peroxide system, designing variants of their
Type XVII U-boat The Type XVII U-boats were small coastal submarines that used a high-test peroxide propulsion system, which offered a combination of air-independent propulsion and high submerged speeds. Background In the early 1930s Hellmuth Walter had design ...
and their Type XXVIIB ''Seehund'' midget submarine, the Type XVIIK and Type XXVIIK respectively, though neither was completed before the war's end. After the war the USSR developed the small 650-ton submarine, of which thirty were built between 1953 and 1956. These had three diesel engines—two were conventional and one was closed cycle using liquid oxygen. In the Soviet system, called a "single propulsion system", oxygen was added after the exhaust gases had been filtered through a lime-based chemical absorbent. The submarine could also run its diesel using a snorkel. The Quebec had three
drive shaft A drive shaft, driveshaft, driving shaft, tailshaft (Australian English), propeller shaft (prop shaft), or Cardan shaft (after Girolamo Cardano) is a component for transmitting mechanical power (physics), power and torque and rotation, usually ...
s: a 32D diesel on the centre shaft and two M-50P diesels on the outer shafts. In addition a "creep" motor was coupled to the centre shaft. The boat could be run at slow speed using the centreline diesel only. Because liquid oxygen cannot be stored indefinitely, these boats could not operate far from a base. It was dangerous; at least seven submarines suffered explosions, and one of these, , sank following an explosion and fire. They were sometimes nicknamed cigarette lighters. The last submarine using this technology was scrapped in the early 1970s. The
German Navy The German Navy (, ) is the navy of Germany and part of the unified ''Bundeswehr'' (Federal Defense), the German Armed Forces. The German Navy was originally known as the ''Bundesmarine'' (Federal Navy) from 1956 to 1995, when ''Deutsche Mari ...
's former
Type 205 submarine The Type 205 was a class of German diesel-electric submarines. They were single- hull vessels optimized for the use in the shallow Baltic Sea. The Type 205 is a direct evolution of the Type 201 class with lengthened hull, new machinery and senso ...
(launched 1967) was fitted with an experimental unit.


Closed-cycle steam turbines

The French MESMA (Module d'Energie Sous-Marin Autonome) system is offered by French shipyard DCNS. MESMA is available for the ''Agosta'' 90B and s. It is essentially a modified version of their nuclear propulsion system with heat generated by
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
and oxygen. Specifically, a conventional steam turbine power plant is powered by steam generated from the combustion of ethanol and stored oxygen at a pressure of 60 atmospheres. This pressure-firing allows exhaust
carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
to be expelled overboard at any depth without an exhaust compressor. Each MESMA system costs around $50–60 million. As installed on the Scorpènes, it requires adding an , 305-tonne hull section to the submarine, and results in a submarine able to operate for greater than 21 days underwater, depending on variables such as speed. On the Agosta 90B, the AIP system allows the submarine to operate 16 days under water and gives it a range of . An article in ''Undersea Warfare Magazine'' notes that: "although MESMA can provide higher output power than the other alternatives, its inherent efficiency is the lowest of the four AIP candidates, and its rate of oxygen consumption is correspondingly higher."


Stirling cycle engines

The Swedish shipbuilder
Kockums Saab Kockums AB is a shipyard headquartered in Malmö, Sweden, owned by the Swedish defence company Saab Group. Saab Kockums AB is further operational in Muskö, Docksta, and Karlskrona. While having a history of civil vessel construction, Koc ...
constructed three s for the
Swedish Navy The Swedish Navy ( sv, Svenska marinen) is the naval branch of the Swedish Armed Forces. It is composed of surface and submarine naval units – the Fleet () – as well as marine units, the Amphibious Corps (). In Swedish, vessels o ...
that are fitted with an auxiliary
Stirling engine A Stirling engine is a heat engine that is operated by the cyclic compression and expansion of air or other gas (the ''working fluid'') between different temperatures, resulting in a net conversion of heat energy to mechanical work. More specif ...
that burns diesel fuel with
liquid oxygen Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries—is the liquid form of molecular oxygen. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an applica ...
to drive 75 kW electrical generators for either propulsion or charging batteries. The underwater endurance of the 1,500-tonne boats is around 14 days at , with an approximate range of 1700 nautical miles. Kockums refurbished and upgraded the Swedish submarines with a Stirling AIP plugin section. Two (''Södermanland'' and ''Östergötland'') are in service in Sweden as the , and two others are in service in Singapore as the (''Archer'' and ''Swordsman''). Kockums also delivered Stirling engines to Japan. Ten Japanese submarines were equipped with Stirling engines. The first submarine in the class, , was launched on 5 December 2007 and delivered to the navy in March 2009. The eleventh of the class is the first one that is equipped with lithium-ion batteries without a Stirling engine. This submarine may have a range from AIP of 6500 nautical miles and can remain submerged for 40 days. The new Swedish has the Stirling AIP system as its main energy source. The submerged endurance will be more than 18 days at 5 knots using AIP.


Fuel cells

Siemens Siemens AG ( ) is a German multinational conglomerate corporation and the largest industrial manufacturing company in Europe headquartered in Munich with branch offices abroad. The principal divisions of the corporation are ''Industry'', '' ...
has developed a 30–50 kilowatt
fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requ ...
unit, a device that converts the
chemical energy Chemical energy is the energy of chemical substances that is released when they undergo a chemical reaction and transform into other substances. Some examples of storage media of chemical energy include batteries, Schmidt-Rohr, K. (2018). "How ...
from a fuel and oxidiser into electricity. Fuel cells differ from batteries in that they require a continuous source of fuel (such as hydrogen) and oxygen, which are carried in the vessel in pressurized tanks, to sustain the chemical reaction. Nine of these units are incorporated into Howaldtswerke Deutsche Werft AG's 1,830 t submarine , lead ship for the Type 212A of the
German Navy The German Navy (, ) is the navy of Germany and part of the unified ''Bundeswehr'' (Federal Defense), the German Armed Forces. The German Navy was originally known as the ''Bundesmarine'' (Federal Navy) from 1956 to 1995, when ''Deutsche Mari ...
. The other boats of this class and HDW's AIP equipped export submarines, , Type 209 mod and
Type 214 The Type 214 is a diesel-electric submarine developed by Howaldtswerke-Deutsche Werft GmbH (HDW). It features diesel propulsion with an air-independent propulsion (AIP) system using Siemens polymer electrolyte membrane (PEM) hydrogen fuel ...
, use two modules, also from Siemens. The Type 212 can remain submerged for 21 days; one such submarine conducted a 1600 nautical mile journey solely on AIP in 2016. After the success of Howaldtswerke Deutsche Werft AG in its export activities, several builders developed fuel-cell auxiliary units for submarines, but as of 2008 no other shipyard has a contract for a submarine so equipped. The AIP implemented on the of the
Spanish Navy The Spanish Navy or officially, the Armada, is the maritime branch of the Spanish Armed Forces and one of the oldest active naval forces in the world. The Spanish Navy was responsible for a number of major historic achievements in navigation, ...
is based on a bioethanol-processor (provided by Hynergreen from
Abengoa Abengoa, S.A. was a Spanish multinational company in the green infrastructure, energy and water sectors. The company was founded in 1941 by Javier Benjumea Puigcerver and José Manuel Abaurre Fernández-Pasalagua, and was based in Seville, Sp ...
, SA) consisting of a reaction chamber and several intermediate Coprox reactors, that transform the BioEtOH into high purity hydrogen. The output feeds a series of
fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requ ...
s from Collins Aerospace (which also supplied fuel cells for the
Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...
). The reformer is fed with
bioethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a hyd ...
as fuel, and oxygen (stored as a liquid in a high pressure cryogenic tank), generating hydrogen as a sub-product. The produced hydrogen and more oxygen is fed to the
fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requ ...
s. China has been researching fuel cell engines for AIP submarines. The Dalian Institute of Chemical Physics reportedly developed 100-kW and 1000-kW fuel cell engines. The Naval Materials Research Laboratory of Indian
Defence Research and Development Organisation The Defence Research and Development Organisation (DRDO) (IAST: ''Raksā Anūsandhān Evam Vikās Sangaṭhan'') is the premier agency under the Department of Defence Research and Development in Ministry of Defence of the Government of India ...
in collaboration with
Larsen & Toubro Larsen & Toubro Ltd, commonly known as L&T, is an Indian multinational conglomerate company, with business interests in engineering, construction, manufacturing, technology, information technology and financial services, headquartered in Mumba ...
and
Thermax Thermax Ltd is an Indian multinational engineering conglomerate, involved in clean air, clean energy and clean water, headquartered in Pune. History Thermax manufactures boilers to harness the power of steam. The company started with produc ...
has developed a 270 kilowatt
phosphoric acid fuel cell Phosphoric acid fuel cells (PAFC) are a type of fuel cell that uses liquid phosphoric acid as an electrolyte. They were the first fuel cells to be commercialized. Developed in the mid-1960s and field-tested since the 1970s, they have improved sig ...
(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 Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula Na BH4. This white solid, usually encountered as an aqueous basic solution, is a reducing agent that finds applica ...
and stored oxygen with
phosphoric acid Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, w ...
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 Atomic Energy of Canada Limited (AECL) is a Canadian federal Crown corporation and Canada's largest nuclear science and technology laboratory. AECL developed the CANDU reactor technology starting in the 1950s, and in October 2011 licensed this ...
as a "
nuclear battery An atomic battery, nuclear battery, radioisotope battery or radioisotope generator is a device which uses energy from the decay of a radioactive isotope to generate electricity. Like nuclear reactors, they generate electricity from nuclear en ...
"—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 China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
,
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
,
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
,
Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
, the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
and the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
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

* * * {{DEFAULTSORT:Air-Independent Propulsion Submarine design Marine propulsion Spanish inventions