Submarine navigation underwater requires special skills and technologies not needed by
surface ships. The challenges of underwater
navigation have become more important as
submarines spend more time underwater, travelling greater distances and at higher speed. Military submarines travel underwater in an environment of total darkness with neither windows nor lights. Operating in stealth mode, they cannot use their
active sonar systems to
ping ahead for underwater hazards such as
undersea mountains,
drilling rigs or other submarines. Surfacing to obtain
navigational fixes is precluded by pervasive
anti-submarine warfare detection systems such as
radar and
satellite surveillance.
Antenna masts and antenna-equipped
periscopes can be raised to obtain navigational signals but in areas of heavy surveillance, only for a few seconds or minutes; current radar technology can detect even a slender periscope while submarine shadows may be plainly visible from the air. Surfaced submarines entering and leaving port navigate similarly to traditional ships but with a few extra considerations because most of the ship rides below the waterline, making them hard for other ships to see and identify.