Libraries and game rooms help ease the monotony of life beneath the sea. On most submarines, ever member of the crew works a daily four-hour shift called a watch . At the end of his watch, a crewman is relieved and goes off duty for eight hours. He may have to do some maintenance work on the ship but is mostly free to relax or study until he returns to his station. The work assignments vary so that all the crewmen have days off.
Nuclear submarines produce their own air and drinking water.
A process called electrolysis extracts oxygen from seawater and provides all the air needed for the crew. Chemical filters remove any harmful elements from the air in a submarine. Thick lead plates around the nuclear reactor shield the crew from any dangerous radiation. Machines distill ocean water into pure drinking water. A submarine returns to port at the end of its cruise.