Loran-C

Loran-C is a hyperbolic radio navigation system that allows a receiver to determine its position by listening to low frequency radio signals that are transmitted by fixed land-based radio beacons. Loran-C combined two different techniques to provide a signal that was both long-range and highly accurate, features that had been incompatible. Its disadvantage was the expense of the equipment needed to interpret the signals, which meant that Loran-C was used primarily by militaries after it was introduced in 1957.

By the 1970s, the cost, weight and size of electronics needed to implement Loran-C had been dramatically reduced because of the introduction of solid-state electronics and, from the mid-1970s, early microcontrollers to process the signal. Low-cost and easy-to-use Loran-C units became common from the late 1970s, especially in the early 1980s, and the earlier LORAN system was discontinued in favor of installing more Loran-C stations around the world. Loran-C became one of the most common and widely-used navigation systems for large areas of North America, Europe, Japan and the entire Atlantic and Pacific areas. The Soviet Union operated a nearly identical system, CHAYKA.

The introduction of civilian satellite navigation in the 1990s led to a rapid drop-off in Loran-C use. Discussions about the future of Loran-C began in the 1990s; several turn-off dates were announced and then cancelled. In 2010, the US and Canadian systems were shut down, along with Loran-C/CHAYKA stations that were shared with Russia. Several other chains remained active; some were upgraded for continued use. At the end of 2015, navigation chains in most of Europe were turned off.

In December 2015 there was also renewed discussion of funding an eLoran system, and NIST offered to fund development of a microchip-sized eLoran receiver for distribution of timing signals. The National Timing Resilience and Security Act of 2017, proposed resurrecting Loran as a backup for the United States in case of a GPS outage caused by space weather or attack.