A term referring to a method of propulsion for submarines. Boats of this type typically have two motor sets onboard, one set of Diesels and one of electric motors. The Diesels are used on the surface (or when schnorkeling) for propulsion and to charge large banks of batteries aboard. When submerged, the Diesels are shut down (as they would suffocate the crew and run out of air in perhaps twenty seconds) and the electric motors are engaged to propel the boat using the batteries.

Diesel-electric submarines are not nearly as 'old-fashioned' as their name suggests. Modern diesel-electrics are typically quieter than nuclear submarines when on electric power, and noise-deadening technologies (such as isolation rafts and anechoic coatings) invented for use on the larger nuclear submarines work on their smaller cousins as well. The prime disadvantage to these submarines is that the amount of charge that can be contained in their batteries is quite limited; a diesel-electric boat must break off a sustained engagement to surface and recharge batteries as well as refresh its air supply. A nuclear submarine makes its own air, and can remain underwater and at full speed practically indefinitely.

On the other hand, diesel-electrics are much, much cheaper than nuclear submarines, and the technology is quite easily obtained. They are ideal defensive assets, and are still better than anything else save a nuclear attack sub for sinking shipping, especially in chokepoints where the shipping lanes are restricted (such as the Straits of Malacca or the Persian Gulf). Russia makes the Kilo-class (Project 636) diesel-electric for sale abroad. There are quite capable German and Dutch makes (Kockums Type-209, etc.) as well as British, Scandinavian, Spanish, French, Chinese, Japanese etc. available for sale around the world, if you have a plutonium American Express card and, in some cases, an end-user certificate.

The Diesel-Electric (or D-E) boats do have one very big advangage over a nuclear submarine such as the Akula, 688 class, or the Ohio class. Stealth is the main advantage of any submarine and the D-E boats are inherently quieter when submerged (with the possible exception of the new Seawolf class SSN). SSN (Submersable Ship, Nuclear) boats are powered by nuclear reactors. The problem is that the reactor must be constantly cooled to prevent an overload and thus a reactor scram. This means that the coolant pumps must be running all the time, even if nothing else on the boat is turned on (such as ventilation).

The SS (Submersable Ship) boats run on electic motors when submereged. When they don't want to be heard they simply stop and "make like a hole in the water." Since the SS boats don't have coolant pumps to run they can go completely silent.

In short engagements the SS boat has an advantage over the SSN boats, however all the SSN has to do is stand off an wait until the bad guy's batteries run low or the crew starts to run out of air. When the SS comes up to snorkel her diesel engines will be heard for miles, making her an easy target.

Despite their advantages (listed in the other writeups), diesel-electric submarines suffer from two major disadvantages;

  • Extremely limited endurance - when the submarines battery runs out, it must surface and recharge. if a hunter is waiting for it, the boat is dead.
  • Very limited range -because it requires fuel tankage, there is a hard limit on how far it can roam from it's home base before it must return to refuel. Fuel limits also shorten the amount of time the boat can spend at full speed
Because of these limitations diesel-electric submarines have been referred to 'intelligent mobile minefields', deadly in their sphere, but limited in their application. All this will change if a practical air independent propulsion system is ever developed.

I should mention that Diesel-Electric locomotion isn't unique to watergoing vessels. Most diesel locomotives that you see pulling freight trains are diesel-electric. Also, the giant dump trucks you see at mine sites are usually D-E.

DE is ideal for these types of applications. It brings the long distance and long run-time capabilities of a gasoline-fueled internal combustion engine, with the simplicity of an all-electric car.

A diesel engine is much simpler than a gasoline/petrol engine, and provides more torque, while burning a fluid that is less explosive. The diesel engine spins an electric generator. The engine can be brought up to its most efficient RPM range, and left there. The engine is never expected to perform outside of its powerband.

The electricity is then sent to individual wheel motors. There is no need for any gearing or transmission parts.

As an interesting aside, the electric motors are run backwards to provide braking for these behemoths. In the case of the giant dump trucks, the resulting energy is just fed through an enormous rack of heater-wire, that glows like a toaster while it expends the excess speed as heat. The trucks actually do have standard brake pads, but they are usually only good for an emergency, and if you use them while moving any faster than about 15mph, then you instantly burn them up and they must be replaced.

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