There are many ships and submarines using nuclear propulsion. However, most of them are military.
A nuclear reactor can produce a lot of energy from a very small amount of fuel and at the same time does not need air for combustion. This is particulary useful for submarines, which can stay under water for many months without needing extra fuel or air.
The Norwegian non-governmental organization Bellona estimated that the following number of nuclear vessels existed in the world in 1996:
Number of nuclear vessels