The great advantage of nuclear propulsion is that the submarine seldom has to refuel and can stay submerged for weeks or months at a time.
Also, it can maintain high speed almost indefinitely.
A modern attack submarine like the Virigina class can cruise at more than 45 kilometers per hour on the surface or 60 submerged, for months on end until the food runs out.
It carries 27 torpedoes and missiles and is rumored to be able to dive to depths of almost 500 meters.
All this ideally suited another development made possible by nuclear fission,
namely the use of nuclear warheads on cruise missiles.
With the introduction of nuclear power, some submarines became strategic ballistic missile submarines, stealthy launching platforms for these missiles.
Nuclear propulsion is also used for attack submarines without ballistic missiles, though many countries stick with traditional diesel-electric power because it is cheaper.
The nuclear reactors used on submarines are relatively small and use highly enriched uranium to achieve good efficiency.
They transfer power to the engines either by electricity or by steam turbines.
The noise and heat generated by nuclear propulsion is a disadvantage compared to diesel-electric engines, which are much harder to detect when running on batteries.
The first cruise missile launch from a submarine was in 1953 CE.
The first nuclear submarine, launched a year later, was the American vessel USS Nautilus, named after the 18th century CE invention by Robert Fulton.
The Soviet Union soon followed suit and later a handful other countries too.
War Matrix - Nuclear submarine
Cold War 1945 CE - 1991 CE, Weapons and technology