The United States Department of Defense originally degraded civilian GPS accuracy relative to encrypted military signals through an intentional error mechanism termed Selective Availability

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The GPS architecture calculates distance between satellites and Earth-based receivers using the travel time of electromagnetic radio waves rather than angular triangulation

GPS satellite time and positioning calculations incorporate Albert Einstein's theories of relativity

Prior to World War II, airports in Berlin and London used radio landing systems that emitted audible tones to guide aircraft in darkness and bad weather

During World War II, British forces broadcast deceptive electromagnetic radio signals to distort German radio navigation beams

On Labor Day in 1973, the United States established the GPS office under Colonel Bradford Parkinson to merge satellite navigation concepts from the Navy and Air Force

During World War II, the German military used intersecting radio beams broadcast from towers in occupied Western Europe for blind precision bombing over Britain

Following the downing of Korean Air Lines Flight 007 in 1983, President Ronald Reagan announced that the United States Global Positioning System would be opened to civilians

A United States government database of reported GPS anomalies documented incidents of unknown interference in and around the Suez Canal

The Transit satellite navigation system was developed as a predecessor to GPS to aid submarines operating in the high Arctic

Ground-based fiber-optic cables provide an alternative to GPS for distributing resilient, high-precision timing across critical infrastructure

GPS satellite signals are faint and delicate, making them susceptible to disruption by terrestrial and airborne electromagnetic jamming and spoofing

In 2017, ships near the Russian port of Novorossiysk had their GPS navigation systems spoofed to display their location as a nearby Russian airport

Airplanes and maritime vessels encounter higher rates of GPS interference because open airspace and ocean waters lack terrain obstructions like mountains

In 2017, ships arriving at the Russian Black Sea port of Novorossiysk experienced GPS alarms indicating a loss of GPS signal

In 2000, United States President Bill Clinton ordered the removal of Selective Availability to allow civilian receivers full GPS accuracy

Following World War II, various military branches developed separate, Earth-based radio navigation systems specialized for planes, boats, and submarines

During the 1991 Gulf War, families of United States soldiers purchased civilian GPS receivers from retail stores due to a shortage of military-grade units

Katherine Dunn is the author of the book Little Blue: How GPS Shaped the Modern World

Enhanced Long-Range Navigation (eLoran) is a ground-based radio navigation system designed to provide positioning and timing as an alternative to satellite navigation

The Canadian government and the United Kingdom government have developed national positioning, navigation, and timing strategies to address infrastructure vulnerabilities