Editing Submarine (section)

===Navigation===
{{main|Submarine navigation}}
[[File:Ocelot-Periscopes.JPG|thumb|The larger search [[periscope]], and the smaller, less detectable attack periscope on HMS ''Ocelot'']]

Early submarines had few navigation aids, but modern subs have a variety of navigation systems. Modern military submarines use an [[inertial guidance system]] for navigation while submerged, but drift error unavoidably builds over time. To counter this, the crew occasionally uses the [[Global Positioning System]] to obtain an accurate position. The [[periscope]]—a retractable tube with a [[prism (optics)|prism]] system that provides a view of the surface—is only used occasionally in modern submarines, since the visibility range is short. The {{sclass|Virginia|submarine|0}} and {{sclass|Astute|submarine|2}}s use [[photonics mast]]s rather than hull-penetrating optical periscopes. These masts must still be deployed above the surface, and use electronic sensors for visible light, infrared, laser range-finding, and electromagnetic surveillance. One benefit to hoisting the mast above the surface is that while the mast is above the water the entire sub is still below the water and is much harder to detect visually or by radar.