How a Nuclear Submarine Works

Nuclear reactors are basically heat engines. As uranium fissions, the decay of atoms releases energy, much of it in the form of heat, which can then be used to do the job. In the nuclear submarine, reactor heat produces steam to drive the turbines that provide the real power of the boat. The development of compact, safe and reliable pressurized water reactors for naval use in the early 1950-ies was a major technological achievement that made nuclear-powered submarines possible.

Source: http://americanhistory.si.edu