Sonne (German for "sun") was a radio navigation system developed in Germany during World War II. It was developed from an earlier experimental system known as Elektra, and therefore the system is also known as Elektra-sonnen. When the British learned of the system they started using it as well, under the name Consol, meaning "by the sun".
Elektra was an updated version of the beam-based low-frequency radio range (LFR) used in the United States during the 1930s. This was further modified to create Sonne by electronically rotating the signal to create a series of beams sweeping across the sky. Using simple timing of the signal, the navigator could determine the angle to the station. Two such measurements then provided a radio fix. Accuracy and range were excellent, with fixes around ¼ of a degree being possible at 1,000 miles (1,600 km) range.
Sonne was so useful that it found widespread use by UK forces as well, and they took over operation after the war. The system was used for long-range navigation under the Consol name, and supported by ICAO as one of the suggested long-range air navigation systems. New stations were constructed around the world over the next twenty years. The system remained in partial use into the 1990s, with the last transmitter in Norway turned off in 1991.