Many people may think that before GPS, military or civilian travelers had to rely on a compass, map, or sextant, but this is far from being the case.
The first radio direction-finding systems were patented at the turn of the century, and by the 1930s it was already a great way for planes or ships to navigate by the signals of broadcasting radio transmitters – more or less.
The real breakthrough came in the Second World War when the Germans developed a precise radio navigation system that could find the center of a small British town at night, while the British tried to use jamming devices to ensure that when a German bomber officer thought his plane was over the target, he was actually dropping his bombs in the ocean.
During the Cold War, both sides developed a number of military navigation systems, and increasingly accurate radio direction finding techniques were introduced in civil aviation. But what they all had in common was the need to deploy radio stations with many large antennas, preferably all over the planet. Something more universal was needed.
In 1958, the US started developing a satellite system called Transit, and soon afterward there were five Transit satellites orbiting the planet. Only one satellite was visible at any one time from any one geographical location, but the signals from that satellite were enough to determine the location in a few minutes.
From 1967 onwards, civilian users could buy Transit receivers, and the maximum accuracy available was on the order of one meter. The system was decommissioned in 1996, by which time the GPS system was fully operational.