The first satellite navigation system to use Doppler-shift measurements from satellites was Transit.
Developed by the Johns Hopkins University Applied Physics Laboratory for the U.S. Navy, Transit grew from an insight after Sputnik 1: a satellite’s changing radio frequency could reveal its motion and help determine a receiver’s position. The system began development in 1958, successfully tested its early satellites in 1960, and entered naval service in 1964.
Transit satellites traveled in low polar orbits and broadcast highly stable signals. As a satellite approached a receiver, its frequency shifted upward; as it receded, the frequency shifted downward. By analysing the complete frequency curve, a receiver could calculate its location. This was the Doppler effect applied to navigation, not merely a communication signal.
Transit initially served Polaris missile submarines and later ships, surveyors, and civilian users. It usually provided an intermittent fix rather than continuous navigation. GPS eventually replaced it, offering more frequent positioning and broader capability; Transit navigation service ended in 1996.