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From Wikipedia: Today, six countries deploy some form of nuclear-powered strategic submarines: the United States, Russia, France, the United Kingdom, People's Republic of China, and India Several other countries, including Argentina and Brazil, have ongoing projects in different phases to build nuclear-powered submarines.
The PLA navy has more than 225,000 personnel and is thought to have as many as 70 submarines, 10 of them nuclear-powered
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Reactors power submarines and many surface ships. Nuclear weapons.
Most submarines now have a single nuclear reactor. Some smaller, coastal submarines have a single diesel.
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In the US Navy alone, there have been 25 classes of nuclear submarines, resulting in some 211 hulls. Each class of submarine has different specifications, and different ranges of speeds, each being used for different missions. Submarines within each class can differ in specifications that can affect their top speeds. By and large, the actual specifications such as speed for any nuclear equipment is classified, but the unclassified top speed ranges vary surface and submerged from around 15 knots of the Skipjack class (surfaced) to 35 knots of the Seawolf class (submerged). It is just not possible to give a more specific answer as there are literally so many different nuclear submarines in the world with so many different capabilities. Generally, the US has stood at the forefront of submersible technology, and while the nuclear boats of other nations may for a time exceed the capabilities of current US vessels, it is typically a short lived place for them.
About 2,100 by many different countries.
Nuclear power plants are very large fixed installations on land. There are many reactors however in the US navy ships and submarines