Loran-C
Loran-C was a hyperbolic radio navigation system which allowed a receiver to determine its position by listening to low frequency radio signals 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, traits that had formerly been at odds. The downside was the expense of the equipment needed to interpret the signals, which meant that Loran-C was used primarily by militaries after it was first introduced in 1957.
By the 1970s the electronics needed to implement Loran-C had been dramatically reduced due to the introduction of solid state radio electronics, and especially the use of early microcontrollers to interpret the signal. Low-cost and easy-to-use Loran-C units became common from the late 1970s, especially in the early 1980s, leading to the earlier LORAN system being turned off in favour 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 very rapid drop-off in Loran-C use. Discussions about the future of Loran-C began in the 1990s, and several turn-off dates were announced and then cancelled. In 2010 the US and Canadian systems were shut down, along with shared Loran-C/CHAYKA stations with Russia. Several other chains remained active, and some had been upgraded for continued use. At the end of 2015, navigation chains in most of Europe were turned off. In December 2015 in the US, there was also renewed discussion of funding an eLoran system and NIST was offering to fund development of a microchip sized eLoran receiver for distribution of timing signals.
The original LORAN was proposed by Alfred Lee Loomis at a meeting of the Microwave Committee. The US Army Air Corps was interested in the concept for aircraft navigation, and after some discussion they returned a requirement for a system offering accuracy of about 1 mile (1.6 km) at a range of 200 miles (320 km), and a maximum range as great as 500 miles (800 km) for high-flying aircraft. The Microwave Committee, by this time organized into what would become the Radiation Laboratory, took up development as Project 3. During the initial meetings a member of the UK liaison team, Taffy Bowen, mentioned that he was aware the British were also working on a similar concept, but had no information on its performance.
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