OCS Naval History Practice Test

The big jump was nuclear propulsion. A submarine powered by an onboard reactor can run its electric motors for long periods without needing to surface for air or to recharge batteries, so it can stay submerged and cover vast distances. This dramatically increases endurance, which in turn enhances stealth because the vessel can remain hidden underwater rather than popping up to refuel or recharge. The first nuclear-powered submarine, demonstrated in the 1950s, showed that submarines could operate underwater for extended durations and travel across oceans, redefining both range and stealth. Diesel-electric improvements helped before, but they still required air to run the diesels and recharge batteries, limiting submerged time. Hydrogen fuel cells offered quiet power but didn’t deliver the same long-range, sustained underwater capability, and rotary propulsion systems don’t represent the major postwar breakthrough in question.