How long do you really think you can be in a submarine in the oceans depths before needing to surface ?

About 30 seconds, I'm slightly claustrophobic.




Nuclear submarines can stay submerged indefinitely, some have stayed under for many months, the actual limits are classified.




the only limit is the food. Water and air are both manufactured from sea water. The fuel rods need replacing every 3-4 years. My brother in law was down 7 months once.