Editing Submarine (section)

====Diesel–electric transmission<span class="anchor" id="Diesel-electric transmission"></span>====
[[File:Submarine recharging (JMSDF).jpg|thumb|Recharging battery ([[Japan Maritime Self-Defense Force|JMSDF]])]]
{{Further|Diesel–electric powertrain}}

While most early submarines used a direct mechanical connection between the combustion engine and the propeller, an alternative solution was considered as well as implemented at a very early stage.<ref>{{cite book|last=Granholm|first=Fredrik|title=Från Hajen till Södermanland: Svenska ubåtar under 100 år|publisher=Marinlitteraturföreningen|year=2003|pages=12–13|isbn=9185944-40-8}}</ref> That solution consists in first converting the work of the combustion engine into electric energy via a dedicated generator. This energy is then used to drive the propeller via the electric motor and, to the extent required, for charging the batteries. In this configuration, the electric motor is thus responsible for driving the propeller at all times, regardless of whether air is available so that the combustion engine can also be used or not.

Among the pioneers of this alternative solution was the very first submarine of the [[Swedish Navy]], {{ill|HSwMS Hajen (1904)|sv|HMS Hajen (1904)|lt=HSwMS ''Hajen''}} (later renamed ''Ub no 1''), launched in 1904. While its design was generally inspired by the first submarine commissioned by the US Navy, [[USS Holland (SS-1)|USS ''Holland'']], it deviated from the latter in at least three significant ways: by adding a periscope, by replacing the gasoline engine by a semidiesel engine (a [[hot-bulb engine]] primarily meant to be fueled by kerosene, later replaced by a true diesel engine) and by severing the mechanical link between the combustion engine and the propeller by instead letting the former drive a dedicated generator.<ref>{{cite book|last=Granholm|first=Fredrik|title=Från Hajen till Södermanland: Svenska ubåtar under 100 år|publisher=Marinlitteraturföreningen|year=2003|pages=12–15|isbn=9185944-40-8}}</ref> By so doing, it took three significant steps toward what was eventually to become the dominant technology for conventional (i.e., non-nuclear) submarines.

[[File:Submarine Hajen 1.jpg|thumb|One of the first submarines with diesel–electric transmission, HMS ''Hajen'', on display outside [[Marinmuseum]] in [[Karlskrona]]]]
In the following years, the Swedish Navy added another seven submarines in three different classes ({{ill|2nd-class submarine|sv|2:a klass ubåt|lt=''2nd'' class}}, {{ill|Laxen-class submarine|sv|Laxen-klass|lt=''Laxen'' class}}, and {{ill|Braxen-class submarine|sv|Braxen-klass|lt=''Braxen'' class}}) using the same propulsion technology but fitted with true diesel engines rather than semidiesels from the outset.<ref>{{cite book|last=Granholm|first=Fredrik|title=Från Hajen till Södermanland: Svenska ubåtar under 100 år|publisher=Marinlitteraturföreningen|year=2003|pages=18–19, 24–25|isbn=9185944-40-8}}</ref> Since by that time, the technology was usually based on the diesel engine rather than some other type of combustion engine, it eventually came to be known as [[diesel–electric transmission]].

Like many other early submarines, those initially designed in Sweden were quite small (less than 200 tonnes) and thus confined to littoral operation. When the Swedish Navy wanted to add larger vessels, capable of operating further from the shore, their designs were purchased from companies abroad that already had the required experience: first Italian ([[Fiat S.p.A.|Fiat]]-[[Cesare Laurenti (engineer)|Laurenti]]) and later German ([[AG Weser|A.G. Weser]] and [[NV Ingenieurskantoor voor Scheepsbouw|IvS]]).<ref>{{cite book|last=Granholm|first=Fredrik|title=Från Hajen till Södermanland: Svenska ubåtar under 100 år|publisher=Marinlitteraturföreningen|year=2003|pages=16–17, 20–21, 26–29, 34–35, 82|isbn=9185944-40-8}}</ref> As a side-effect, the diesel–electric transmission was temporarily abandoned.

However, diesel–electric transmission was immediately reintroduced when Sweden began designing its own submarines again in the mid-1930s. From that point onwards, it has been consistently used for all new classes of Swedish submarines, albeit supplemented by [[Air-independent propulsion|air-independent propulsion (AIP)]] as provided by [[Stirling engine]]s beginning with [[HSwMS Näcken (Näk)|HMS ''Näcken'']] in 1988.<ref>{{cite book|last=Granholm|first=Fredrik|title=Från Hajen till Södermanland: Svenska ubåtar under 100 år|publisher=Marinlitteraturföreningen|year=2003|pages=40–43, 48–49, 52–61, 64–67, 70–71|isbn=9185944-40-8}}</ref>

[[File:Hajen & Neptun Marinmuseum Karlskrona 002.jpg|thumb|Two widely different generations of Swedish submarines but both with diesel–electric transmission: {{ill|HSwMS Hajen (1904)|sv|HMS Hajen (1904)|lt=HSwMS ''Hajen''}}, in service 1905–1922, and [[HSwMS Neptun (Nep)|HMS ''Neptun'']], in service 1980–1998]]
Another early adopter of diesel–electric transmission was the [[United States Navy|US Navy]], whose Bureau of Engineering proposed its use in 1928. It was subsequently tried in the [[United States S-class submarine|S-class submarines]] {{USS|S-3|SS-107|2}}, {{USS|S-6|SS-111|2}}, and {{USS|S-7|SS-112|2}} before being put into production with the [[United States Porpoise-class submarine|''Porpoise'' class]] of the 1930s. From that point onwards, it continued to be used on most US conventional submarines.<ref name="Book1">{{cite book|last=Friedman|first=Norman|title=U.S. submarines through 1945: an illustrated design history|publisher=Naval Institute Press|year=1995|pages=259–260|isbn=978-1-55750-263-6}}</ref>

Apart from the British [[British U-class submarine|U-class]] and some submarines of the Imperial Japanese Navy that used separate diesel generators for low speed running, few navies other than those of Sweden and the US made much use of diesel–electric transmission before 1945.<ref name="Book1" /> After World War II, by contrast, it gradually became the dominant mode of propulsion for conventional submarines. However, its adoption was not always swift. Notably, the Soviet Navy did not introduce diesel–electric transmission on its conventional submarines until 1980 with its [[Kilo-class submarine|''Paltus'' class]].<ref>{{cite web|url=http://www.deepstorm.ru/DeepStorm.files/45-92/dts/877/list.htm|title=Проект "Пaлтyc" (NATO-"Kilo")|last=Никoлaeв|first=A.C.|website=Энциклопедия отeчествeннoгo подводнoгo флотa|access-date=2 June 2020}}</ref>

If diesel–electric transmission had only brought advantages and no disadvantages in comparison with a system that mechanically connects the diesel engine to the propeller, it would undoubtedly have become dominant much earlier. The disadvantages include the following:<ref name="electrotechnical-officer.com">{{cite web|url=http://electrotechnical-officer.com/what-is-motivations-for-ship-electric-propulsion/|archive-url=https://web.archive.org/web/20190305075645/http://electrotechnical-officer.com/what-is-motivations-for-ship-electric-propulsion/|url-status=live|archive-date=March 5, 2019|title=What is motivations for ship electric propulsion|website=Electro-technical officer|access-date=2 June 2020}}</ref><ref name="diesel eletric drives guideline">{{cite web|url=https://marine.mandieselturbo.com/docs/librariesprovider6/marine-broschures/diesel-electric-drives-guideline.pdf|archive-url=https://web.archive.org/web/20190809071316/https://marine.mandieselturbo.com/docs/librariesprovider6/marine-broschures/diesel-electric-drives-guideline.pdf|url-status=dead|archive-date=August 9, 2019|title=Diesel–electric Propulsion Plants: A brief guideline how to engineer a diesel–electric propulsion system|website=MAN Energy Solutions|pages=3–4|access-date=2 June 2020}}</ref>
* It entails a loss of fuel-efficiency as well as power by converting the output of the diesel engine into electricity. While both generators and electric motors are known to be very efficient, their efficiency nevertheless falls short of 100 percent.
* It requires an additional component in the form of a dedicated generator. Since the electric motor is always used to drive the propeller it can no longer step in to take on generator service as well.
* It does not allow the diesel engine and the electrical motor to join forces by simultaneously driving the propeller mechanically for maximum speed when the submarine is surfaced or snorkeling. This may, however, be of little practical importance inasmuch as the option it prevents is one that would leave the submarine at a risk of having to dive with its batteries at least partly depleted.

The reason why diesel–electric transmission has become the dominant alternative in spite of these disadvantages is of course that it also comes with many advantages and that, on balance, these have eventually been found to be more important. The advantages include the following:<ref name="electrotechnical-officer.com"/><ref name="diesel eletric drives guideline" />
* It reduces external noise by severing the direct and rigid mechanical link between the relatively noisy diesel engine(s) on the one hand and the propeller shaft(s) and hull on the other. With [[Stealth ship|stealth]] being of paramount importance to submarines, this is a very significant advantage.
* It increases the [[Crash dive|readiness to dive]], which is of course of vital importance for a submarine. The only thing required from a propulsion point of view is to shut down the diesel(s).
* It makes the speed of the diesel engine(s) temporarily independent of the speed of the submarine. This in turn often makes it possible to run the diesel(s) at close to optimal speed from a fuel-efficiency as well as durability point of view. It also makes it possible to reduce the time spent surfaced or snorkeling by running the diesel(s) at maximum speed without affecting the speed of the submarine itself.
* It eliminates the clutches otherwise required to connect the diesel engine, the electric motor, and the propeller shaft. This in turn saves space, increases reliability and reduces maintenance costs.
* It increases flexibility with regard to how the driveline components are configured, positioned, and maintained. For example, the diesel no longer has to be aligned with the electric motor and propeller shaft, two diesels can be used to power a single propeller (or vice versa), and one diesel can be turned off for maintenance as long as a second is available to provide the required amount of electricity.
* It facilitates the integration of additional primary sources of energy, beside the diesel engine(s), such as various kinds of [[Air-independent propulsion|air-independent power (AIP)]] systems. With one or more electric motors always driving the propeller(s), such systems can easily be introduced as yet another source of electric energy in addition to the diesel engine(s) and the batteries.