Editing Submarine (section)

====Air-independent propulsion====
{{main|Air-independent propulsion}}
[[File:2004-Bremerhaven U-Boot-Museum-Sicherlich retouched.jpg|thumb|[[German Type XXI submarine]]]]
[[File:SS X-1 Midget Submarine.jpg|thumb|American X-1 Midget Submarine]]

During World War II, [[German Type XXI submarine]]s (also known as "''Elektroboote''") were the first submarines designed to operate submerged for extended periods. Initially they were to carry hydrogen peroxide for long-term, fast air-independent propulsion, but were ultimately built with very large batteries instead. At the end of the War, the [[United Kingdom|British]] and Soviets experimented with hydrogen peroxide/kerosene (paraffin) engines that could run surfaced and submerged. The results were not encouraging. Though the Soviet Union deployed a class of submarines with this engine type (codenamed {{sclass2|Quebec|submarine|5}} by NATO), they were considered unsuccessful.

The United States also used hydrogen peroxide in an experimental [[midget submarine]], [[USS X-1|X-1]]. 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 use diesel–electric drive.<ref>{{cite web|title=SS X-1 |url=http://www.hnsa.org/ships/x1.htm |publisher=Historic Naval Ships Association |access-date=24 February 2014 |url-status=dead |archive-url=https://web.archive.org/web/20130818031654/http://www.hnsa.org/ships/x1.htm |archive-date=18 August 2013 }}</ref>

Today several navies use air-independent propulsion. Notably [[Sweden]] uses [[Stirling engine|Stirling technology]] on the {{sclass|Gotland|submarine|0}} and {{sclass|Södermanland|submarine|2}}s. The Stirling engine is heated by burning diesel fuel with [[liquid oxygen]] from [[cryogenic]] tanks. A newer development in air-independent propulsion is [[hydrogen]] [[fuel cell]]s, first used on the [[Germany|German]] [[Type 212 submarine]], with nine 34&nbsp;kW or two 120&nbsp;kW cells. Fuel cells are also used in the new [[Spanish Navy|Spanish]] {{sclass2|S-80|submarine|2}}s although with the fuel stored as ethanol and then converted into hydrogen before use.<ref>{{cite news|publisher=Defense Industry Daily|title=S-80: A Sub, for Spain, to Sail Out on the Main|date=15 December 2008|url=http://www.defenseindustrydaily.com/s80-a-sub-for-spain-to-sail-out-on-the-main-02517/|url-access=registration}}</ref>

One new technology that is being introduced starting with the Japanese Navy's eleventh [[Sōryū-class submarine|''Sōryū''-class submarine]] (JS ''Ōryū'') is a more modern battery, the [[lithium-ion battery]]. These batteries have about double the electric storage of traditional batteries, and by changing out the lead-acid batteries in their normal storage areas plus filling up the large hull space normally devoted to [[Air-independent propulsion|AIP]] engine and fuel tanks with many tons of lithium-ion batteries, modern submarines can actually return to a "pure" diesel–electric configuration yet have the added underwater range and power normally associated with AIP equipped submarines.{{citation needed|date=October 2018}}