Nuclear submarines can stay underwater for an unlimited amount of time, or at least until the food runs out. Prior to nuclear subs, there were diesel-electric subs, that still exist today. However, these subs use diesel engines to recharge batteries. Therefore, diesel subs must surface to turn on the diesel engines and recharge their batteries, limiting their range.
Nuclear submarines, including the first one, were designed to remain underwater indefinitely. Rather than remaining close to coastal waters, nuclear submarines are able to travel the globe. In particular, nuclear sub routinely sail under the polar ice caps and are capable of breaking through the ice to surface.
Background
The first nuclear submarine is the Nautilus, launched Jan. 21, 1954. It was tested for years, becoming the first ship to reach the North Pole on Aug. 3, 1958. Eventually, in 1960, it was assigned to the Sixth Fleet as an active-duty submarine. However, by 1966 new technologies rendered Nautilus obsolete and it was retired as a training submarine.
Nuclear submarine technology evolved and, eventually, the ships were equipped with all manner of weapons besides ordinary torpedoes. Nuclear submarines can launch cruise missiles and even full-blown nuclear ballistic missiles. Since they’re quiet and travel under the polar ice caps it is virtually impossible to destroy a nuclear submarine before it launches missiles unless an enemy submarine is nearby.
The USSR eventually developed their own nuclear sub but the early versions, and even some more recent models, lack reliability. The first Soviet nuclear submarine, the K-19, launched in 1958 and earned the nickname “the widowmaker.”
Both the US and USSR/Russia developed two basic types of nuclear submarines, bombers that launched ballistic missiles and hunters that destroyed other submarines and supported special operation missions. There is a broad consensus that the combination of a nuclear submarine armed with nuclear ballistic missiles is the most powerful weapon developed in history.