how long can a submarine stay submerged
The Navy's nuclear-powered submarines can stay submerged for long periods of time. Air is isn't a problem as their make their own oxygen and keep the air clean. The limits on how long they can stay underwater are food and supplies. Submarines generally stock a 90-day supply of food, so they can spend three months underwater. The diesel-powered submarines (not now used by the Navy) had a limit of several days submerged.