Loran

LORAN, which stands for LOng Range Navigation, is a hyperbolic radio navigation system that determines the position of a vessel or aircraft by measuring differences in the arrival times of low-frequency radio signals from a network of fixed transmitters. It was developed during World War II in the United States and United Kingdom and became widely used in the mid-20th century before being largely supplanted by satellite navigation systems such as GPS.

The system operates with a master station and one or more secondary stations in each chain. All transmitters are synchronized to emit pulsed signals. A LORAN receiver measures the time difference between the reception of the master signal and the secondary signals. Each time difference corresponds to a hyperbolic line of position; by obtaining two or more independent differences, the receiver determines the position at the intersection of those lines.

LORAN-C was the most common civilian variant, operating at roughly 100 kHz with long-range coverage, and chains were formed by fixed spacing between master and secondary stations. Earlier variants included LORAN-A and European LORAN-D. In later years an enhanced concept known as eLORAN or enhanced LORAN was proposed to offer improved accuracy and a GPS backup, but adoption varied by country and several networks were shut down as GPS became dominant.

Today, LORAN is largely decommissioned in many regions, though some networks persist and proposals for revival or backup use have appeared. Its historical role in maritime and aviation navigation established LORAN as a major example of hyperbolic navigation prior to the wide adoption of satellite systems.