They Can Stay Submerged for a Very Long Time

Traditional diesel-powered submarines can only stay submerged for a short period of time. At most, they can submerge themselves for a few days. Nuclear submarines, however, have a substantial advantage in this area. A submarine can only remain submerged for as long as its supplies will allow. In light of this, the majority of nuclear submarines can survive underwater for 90 days without ever coming to the surface. As long as the crew has access to food and water, which is typically just for three months, everything will be fine because they create their own air. But what if there were no shortage of supplies?

A nuclear submarine may potentially spend years underwater instead of merely months. In reality, if necessary, the UK's Astute nuclear submarine can remain submerged for up to 25 years. It has a 10-year increase over earlier models in the amount of time it can travel before needing to worry about fuelling. The crew might theoretically live decades under the water if resources were limited and a sizable garden was growing there. Is it plausible? In no way. But it's still conceivable.