How Long Can a Submarine Stay Underwater?

A submarine needs to come to the surface once every few days (or even more frequently than that), not only to obtain a fresh supply of atmospheric oxygen from above the waters surface but also to dispose of the waste gases it produces onboard. Furthermore, radio signals dont travel well deep underwater, particularly at the depths at which submarines usually operate during a mission. Therefore, both nuclear and diesel submarines must resurface to communicate with their home base, receive orders, and convey vital information.