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Diesel-electric transmission, or diesel-electric powertrain is used by a number of vehicle and ship types for providing locomotion.
Before diesel engines came into widespread use, a similar system, using a petrol (gasoline) engine and called petrol-electric or gas-electric, was sometimes used.
This kind of power transmission is used on railways by diesel electric locomotives and diesel electric multiple units, as only electric motors are able to supply full torque at 0 RPM. Diesel-electric systems are also used in submarines and surface ships and some land vehicles.
The first diesel motorship was also the first diesel-electric ship, the Russian tanker Vandal from Branobel, which was launched in 1903. Steam turbine-electric propulsion has been in use since the 1920s (Tennessee-class battleships), using diesel-electric powerplants in surface ships has increased lately. The Finnish coastal defence ships Ilmarinen and Väinämöinen laid down in 1928–1929, were among the first surface ships to use diesel-electric transmission. Later, the technology was used in diesel powered icebreakers.
During World War II the United States built diesel-electric surface warships. Due to machinery shortages destroyer escorts of the Evarts and Cannon classes were diesel-electric, with half their designed horsepower (The Buckley and Rudderow classes were full-power steam turbine-electric). The Wind-class icebreakers, on the other hand, were designed for diesel-electric propulsion because of its flexibility and resistance to damage.
Gas turbines are also used for electrical power generation and some ships use a combination: the Queen Mary 2 has a set of diesel engines in the bottom of the ship plus two gas turbines mounted near the main funnel; all are used for generating electrical power, including those used to drive the propellers. This provides a relatively simple way to use the high-speed, low-torque output of a turbine to drive a low-speed propeller, without the need for excessive reduction gearing.
Early submarines used a direct mechanical connection between the engine and propeller, switching between diesel engines for surface running, and electric motors for submerged propulsion. This was effectively a "parallel" type of hybrid, since the motor and engine were coupled to the same shaft, with the option to disconnect the engine for submerged operation, and using the motor as a generator to recharge the batteries while on the surface.
True diesel-electric transmissions for submarines were first proposed by the United States Navy's Bureau of Engineering in 1928; instead of driving the propeller directly while running on the surface, the submarine's diesel would instead drive a generator that could either charge the submarine's batteries or drive the electric motor. This meant that motor speed was independent of the diesel engine's speed, and the diesel could run at an optimum and non-critical speed, while one or more of the diesel engines could be shut down for maintenance while the submarine continued to run using battery power. The concept was pioneered in 1929 in the S-class submarines S-3, S-6, and S-7 to test the concept. No other navy adopted the system before 1945 except for the British Royal Navy's U-class submarines, although some submarines of the Imperial Japanese Navy used separate diesel generators for low-speed running.
In a diesel-electric direct drive arrangement, the propellers are driven directly by an electric motor, while two or more diesel-generators provide electric energy for charging the batteries and/or driving the electric motors. This mechanically isolates the noisy engine compartment from the outer pressure hull and reduces the acoustic signature of the submarine. Some nuclear submarines also decouple their reactor room this way, having turbo-electric propulsion driven by reactor steam. Many submarines with diesel and electrical propulsion are mistakenly referred to as "diesel-electric" when they in fact have separately coupled diesel and electric engines.
In the 1920s, diesel-electric technology first saw limited use in switchers (or shunters), locomotives used for moving trains around in railroad yards and assembling and disassembling them. One of the first companies to offer "Oil-Electric" locomotives was the American Locomotive Company (ALCO). The ALCO HH series of diesel-electric switcher entered series production in 1931. In the 1930s, the system was adapted for streamliners, the fastest trains of their day. Diesel-electric powerplants became popular because they greatly simplified the way motive power was transmitted to the wheels and because they were both more efficient and had greatly reduced maintenance requirements. Direct-drive transmissions can become very complex, considering that a typical locomotive has four or more axles. Additionally, a direct-drive diesel locomotive would require an impractical number of gears to keep the engine within its powerband; coupling the diesel to a generator eliminates this problem. An alternative is to use a torque converter or fluid coupling in a direct drive system to replace the gearbox. Hydraulic transmissions are claimed to be somewhat more efficient than diesel-electric technology.
Road and other land vehicles 
- Large mining machines, such as the Liebherr T 282B dump truck or LeTourneau L-2350 wheel loader.
- NASA's huge Crawler-Transporters.
- Mitsubishi Fuso Canter Eco Hybrid commercial truck.
- International DuraStar Hybrid diesel-electric truck.
- Dodge is conducting fleet tests of a diesel-electric version of the Dodge Sprinter.
In the automobile industry, diesel engines in combination with electric transmissions and battery power are being developed for future vehicle drive systems. Partnership for a New Generation of Vehicles was a cooperative research program between the U.S. government and "The Big Three" automobile manufacturers (DaimlerChrysler, Ford Motor Company, and General Motors Corporation) that developed diesel hybrid cars.
- "Third-Millennium Cruiser", an attempt to commercialize a diesel-electric automobile in the very early 1980s.
- General Motors Precept
- Ford Prodigy
- Dodge Intrepid ESX
- Ford Reflex is a diesel hybrid concept car.
- Zytek develops a diesel hybrid powertrain
- Citroën C-Cactus
- Chevrolet Volt/Opel Flextreme
- Top Gear Hammerhead Eagle i-Thrust
- Rivian Automotive is developing a diesel-electric engine that should achieve an estimated 90 miles per gallon in the city and over 100 miles per gallon on the highway
Production-ready cars 
- Volkswagen Golf TDI Hybrid
- Mercedes-Benz E-Class E300 BlueTEC hybrid
- Peugeot 3008 Crossover with HYbrid4 technology
- Volvo V60 plug-in diesel hybrid
- Citroën DS5 with Hybrid4 drive
Other land vehicles 
Diesel-electric propulsion was tried on some military vehicles, such as tanks. Petrol-electric systems were tested on the British Mark II tank in 1917. Ferdinand Porsche was the main developer of such drive-trains for military vehicles in World War II Nazi Germany, and created the Elefant tank destroyer and the prototypes of the never-produced, 200-ton class Maus super-heavy tank.
Diesel electric based buses have also been produced, including hybrid systems able to run on and store electrical power in batteries. The two main providers of hybrid systems for diesel-electric transit buses include Allison Transmission and BAE Systems. New Flyer Industries, Gillig Corporation, and North American Bus Industries are major customers for the Allison EP hybrid systems, while Orion Bus Industries is a major customer for the BAE HybriDrive system. Mercedes-Benz makes their own diesel-electric drive system, which is used in their Citaro.
- Silverstone, Paul H (1966). U.S. Warships of World War II. Doubleday and Company. pp. 153–167.
- Silverstone(66), page378
- "USCG Icebreakers". U.S. Coast Guard Cutter History. United States Coast Guard. Retrieved 2012-12-12.
- Friedman, Norman (1995). U.S. submarines through 1945: an illustrated design history. Naval Institute Press. pp. 259–260. ISBN 1557502633.
- International starts hybrid production - eTrucker
- Dodge Sprinter Plug-in Hybrid Electric Vehicle (PHEV)
- Dodge - 2007 Sprinter - Passenger Vans, Cargo Vans
- Diesel hybrid car also taps the sun - Green Machines - MSNBC.com
- World’s first affordable diesel hybrid powertrain
- UK Company Zytek develops Affordable Ultra Efficient Diesel Hybrid System
- Frankfurt Green: Citroen C-Cactus - The Car Connection
- "Rivian Automotive - Waves of Change". Automoblog. 11 August 2011. Retrieved 11 August 2011.
- Geneva 2008: Volkswagen Golf TDI Hybrid
- Volvo's production-ready V60 Plug-in Diesel Hybrid