A much better version of its predecessor, the Nuclear Submarine is truly the most terrifying naval unit if the player has access to Uranium. Although it fixes none of the problems the Submarine has (detailed here), it compensates for these shortcomings with the capability to deploy nukes across the sea. With their ability to deal vast damage to targets 12 or 15 tiles away (depending on whether they're launching Nuclear Devices or Thermonuclear Devices), Nuclear Submarines are not susceptible to Destroyers like other naval raider units. Moreover, this can catch enemies by surprise because nukes do not need vision to detonate, so there is no need for "spotting units" close to enemy borders like when you attack with regular ranged units. Since the Nuclear Submarine is essentially a mobile Missile Silo with invisibility, it is incredibly hard for Destroyers to pinpoint its location and reveal it.
In Gathering Storm, the Nuclear Submarine does not require Uranium to build, but since almost 100% of its strength lies in its nuclear armaments, having Uranium is necessary to realize its potential. Without it, there's less of a need to bother with this unit, as a fleet of Destroyers and Battleships or Missile Cruisers will serve you better in large-scale naval warfare.
Civilopedia entry Edit
The conceptual design of a nuclear-powered submarine was first proposed by the American Naval Research Laboratory in 1939 AD; it was finally realized with the launch of the U.S.S. Nautilus in 1954, which could stay underwater without surfacing for four months … although why one would wish to do so was never explained. Since underwater craft were ideal for launching nuclear-tipped ballistic missiles without warning, it was the perfect Cold War weapon, there not being much other use for such craft. Thus the Soviet Union soon followed the United States in filling the seas with nuclear submarines, beginning with the ill-fated K-19 in 1959. Despite reactor accidents, breakdowns and sinkings, both sides rushed to build ever larger SSBNs. At the height of the Cold War, some five to ten new nuclear submarines were being commissioned each month. Although the pace has slowed somewhat, today six countries deploy nuclear-powered “strategic” submarines (i.e., those meant to kill cities, not other ships): United States, Russia, China, France, United Kingdom and India.