16. Butt of Lewis Lighthouse, Western Isles. (NB 519 661)

The lighthouse at the northern point of Lewis, operated by the Northern Lighthouse Board, is one of a number of lighthouses in the Western Isles to provide services to the military and to civilians. The lighthouse has Differential Global Positioning System equipment, which is used for satellite-based navigation. The DGPS at the Butt of Lewis monitors the integrity of the US Navstar Global Positioning Satellites, which not only benefits vessels in the area but also allows the US to ensure that their Navstar satellites are positioned and working correctly. Navstar satellites play an essential role in modern warfare as receivers for their signals have been built into planes, ships, cars and tanks to allow commanders to know where their troops are on the battlefield. Nuclear submarines also navigate using the Navstar satellites, and the system can be used for the accurate targeting of missiles and other weapons. Navstar was an important component of British and American military operations during the two Iraq wars