Common features found inside a submarine include navigational equipment, a GPS station and a periscope. The interiors of submarines can vary greatly, depending in part on the type of submarine under discussion.
Most submarines have a control station that somewhat resembles those used in an aircraft. Submarines generally have a sonar station for detecting other vessels, since visibility underwater is very limited, as well as a radar station for detecting objects and vessels at and above the surface of the water.
Modern submarines also use GPS for navigation. Submarines have traditionally also used periscopes to see above the water, but these are becoming less common in modern military submarines due to their short visibility range. Some military subs instead have photonics masts that deploy above the surface of the water.
Submarines also have a communications station. These often use low-frequency radio waves to communicate with land and other ships. Submarines also often use a form of sonar telephone to communicate with other submerged submarines.
Submarines also require sleeping and eating quarters for their crew. Modern military subs often have crews of over 80, so bunk beds are used to conserve space. In addition, submarines need machinery to convert carbon monoxide to carbon dioxide and to generate breathable air through the electrolysis of water.