A radionavigation tool used to determine geographic position, commonly used in the nautical world. It's more modern and effective than dead reckoning, but older and less precise than GPS.

Loran is an acronym for LOng RAnge Navigation. It's a system which uses several radio transmitters to determine your exact location. Basically your boat/plane/vehicle has a 4 inch diameter circular antenna. It broadcasts a signal which gets picked up by the nearby Loran stations, usually in a radio tower. The antennas are based on the ground, and mantained and funded by the US Coast Guard.

Here's how it works: The antennas triangulate your location working together. The Loran stations can determine how close your signal is to them, but they cannot determine bearing. Each station narrows your location down to a circle around the tower, which can be miles in diameter. The further away, the larger the circle. Working with other stations, the towers try to figure where the circles overlap. That overlap point is your location. A loran device provides its user with fairly accurate latitude and longitude.

Basically, Loran is a highly accurate (to within 0.25 nautical miles), ubiquitous (99.7% coverage of the US including Alaska) 24-hour-a-day, all-weather radionavigation system. Most people refer to Loran in its latest version; Loran-C.

Loran is also used extensively to establish a precise time reference. Power companies, telephone companies, and many others use Loran-C as a source of timing information for such purposes as controlling and monitoring cesium clocks. The radio clocks that get their exact time from the US Atomic Clock receive the time from this radio network.

While very common for boating, aviation, and ground-based transport, and mostly in North America, which has 30-35 Loran stations throughout the continent, it's been losing popularity ever since the 1990's, when the US's Global Positioning System (GPS) became availible to civillians. Loran had the advantage of being more accurate, since the US government added a margin of error to the satellites (so the enemies could not use it for precision missile attacks), but GPS was easier to use, and gained a foothold in portability. Some people used both together, the Loran could calibrate the GPS, and take away the GPS's several hundred feet of error. In 2000, Clinton relaxed restrictions, allowing complete GPS accuracy. Since then, GPS has overtaken Loran in terms of accuracy and availibility. Most marine stores sell GPS, Loran looks as it it's on its way out.

It's difficult to find numbers for this system, since it's by and large diminishing in users. According to estimates given in the 1990 Federal Radionavigation Plan (FRP), in 1991 there were expected to be more than 572,000 users of the Loran-C system, as opposed to GPS' then paltry figure of 15,000. In the last decade, GPS has grown worldwide, while Loran seems to be getting less popular.

The first loran-like hyperbolic radionavigation system was proposed by R. J. Dippy in 1937, and later implemented as the British Gee system in early 1942. Using a master and slave antenna system, it was limited to only line-of-sight use. Gee was intended as a system to assist bomber navigation in World War II.

The Loran we know and love today came from research at the MIT Radiation Laboratory. John Alvin Pierce is generally credited as being the father of Loran, as well as the marine navigation system, Omega. LCDR L. M. Harding, USCG gave it the name Loran because of security reasons, it sounded less obvious than "Long Range Navigation research". Due to World War II, the system was rapidly developed and rolled out into use throughout the US by 1943.

First came Loran-A, and offered coverage about 400-800 miles from the transmitting station during the daytime. It could triangulate your position to about one square nautical mile. By the close of the war, at least 75,000 receivers had been distributed, as well as 2.5 million Loran charts. Some 70 transmitters were in operation offering nighttime coverage over 30% of the earth's surface.

Loran-A continued to operate after the war, serving both military and civilian users, as researchers sought to develop more reliable and accurate systems. Indeed, Loran-A continued to be operated in the United States until 1980, when this system was finally phased out in favor of Loran-C. (Some stations in a Canadian Loran-A chain continued operation until 1983 and the system was still in operation in Japan as of 1991)

Postwar research sponsored by the US Department Of Defense and other agencies was directed at developing a more accurate and longer range version of Loran. Various improvements, with names such as Loran-B, Cyclan, Cytac, ultimately culminated in the creation of the Loran-C system, which was made operational in 1957 and placed under USCG control in 1958. Loran-C offered greater accuracy and longer range than Loran-A. Loran-A and Loran-C systems were operated in parallel for many years to ease the transition between A and C, as well as let the Loran-A receivers still function. By 1974, however, the decision was made to phase out the Loran-A system, and to designate Loran-C the primary navigation system for Alaska and the Coastal Confluence Zone of the United States.

Obviously this navigation system brought new standards of accuracy to marine navigation. As of 1991, the USCG operates 49 Loran-C stations worldwide (including those in Italy, Japan, Spain, and Turkey). Other Loran chains are operated by several other countries of the world, including China (Guoqiang, 1991), the Soviet Union (Funtikov, 1991), South Korea, Germany, Egypt, France, Denmark, Norway, Iceland, Canada, and Saudi Arabia. Additional Loran chains were being considered as of 1991 to extend coverage to other areas in Europe, India, South Africa, and off the northern coast of South America.

The USCG Loran center is at http://www.navcen.uscg.gov/loran/default.htm
There is a map of the Loran coverage in the US at http://www.loran.org/NewsAndLiterature/TheCaseForLoran/NorthAmericaIntegrityCoverage.jpg

The Loran-C Users Handbook (courtesy of USCG) http://www.navcen.uscg.gov/ftp/loran/lgeninfo/h-book/book-1.txt