LORAN (LOng RAnge Navigation) is a terrestrial navigation system using ground-based transmitters. Hyperbolic LORAN lines of position (LOP) are formed by measuring the difference in reception times of synchronized signals. Groups of LORAN stations are used to form intersecting LOP to provide cross fixing. A LORAN net, or chain, requires a master station, initiating the pulse, and a series of slave stations. In very simplified terms, the master transmits and the slave responds.
It is the calculated difference in arrival times of master-slave pairs that form charted rates and the observed arrivals that form the navigational information. If the observation is exactly that of the charted value one is somewhere along the hyperbola of that value. That information is of little value without a second pair’s hyperbola intersecting to provide a definitive fix along the first hyperbola. The station configurations thus must provide a geometry that allows such intersection. Where LORAN chains overlap one may obtain cross fixes from two different master/slave pairs.
The initial LORAN system, known as LORAN A, operated in the 1850khz-1950khz radio band, was developed during World War II in response to the need for precise navigation for military ships and aircraft. Scientists at the Massachusetts Institute of Technology and the Bell Laboratories, with the support of the War and Navy Departments made theory a reliable reality. The Coast Guards involvement began in 1942 when Admiral Waesche, Commandant of the Coast Guard, was asked to recommend an officer to direct the program. Lieutenant Commander Lawrence M. Harding was given the task and brought rapid progress to the project. By mid 1943 the system was operational in the North Atlantic. The success in the North Atlantic led to rapid expansion elsewhere. The Coast Guard had been involved with the development from the start so when the time came to provide trained personnel the Coast Guard found itself in the Loran business. This would continue to be a Coast Guard responsibility after the war.
The Pacific war showed the need for a Loran-like system that could be operated over much greater distances than Loran A could provide. (600-700 nm daylight operation). The potential solution was to use lower frequencies so an experimental set of stations were set up. The main result of these tests was to show that pulse envelope matching, as used in Loran A, was too inaccurate with the long pulses at the low frequencies required and that a phase comparison system would be required. With the end of the war these experiments were not followed up on.
By the early 1950s, the Department of Defense required a highly accurate long range radionavigation capability. The Sperry Company had proposed a navigation system which would use phase comparison and operated on two frequencies. This was later reduced to one frequency and the Air Force tried to adapt it for tactical needs but had given up on it. The system was known as Cytac. Capt Peter V. Colmar USCG saw the value in the system as a long range precision navigation system. He convinced the Navy to fund a test using the CG Cutter Androscoggin which showed it would work. A test chain was set up on the East Coast and the Navy Survey Ships USNS Bowditch and USNS Dutton conducted a controlled survey test out as far as Bermuda. This convinced Admiral Hyman G. Rickover, father of the nuclear submarine, to go operational with it. He fought for money, got it, and Capt Loren “Zeke” Brunner USCG drove the effort and the system would become known as Loran C. The Coast Guard was up and operational in a year and a half during which time Sperry designed and built the equipment. CDR Al Manning, who had been assigned to oversee equipment design, inspection and delivery, flew out with the final pieces of equipment on December 28, 1958. The Mediterranean Loran C Chain was up and operational nine months later. The Norwegian Sea Chain was commenced in late March of 1960. Loran C operates in the 90khz – 110khz band. Under Coast Guard operation it provided a repeatable accuracy of 18 – 90 meters with a 99.7% availability factor.
The LORAN C chains continued to be built to provide navigational coverage in those parts of the world where a third world war was likely to occur. Coast Guard Aviation was providing logistic support to the LORAN A Stations. This was continued and expanded to also provide air logistics to LORAN C stations. Eight C-123 cargo aircraft were obtained from the Department of Defense by the Coast Guard to provide for the increase in operations.
LORAN came into widespread civilian use as the initially expensive receivers came into commercial production and the cost went down. LORAN C offered much greater accuracy than LORAN A and the A system would come to be phased out. Due in large part to the continued widespread civilian use, LORAN C survived the initial Doppler navigation satellites and on into the current era of the Global Positioning System usually called GPS.
What is the status of LORAN C today? — The main concern today is that it has become known that GPS signals are not difficult to jam. LORAN C signals on the other hand goes through everything. Therefore LORAN C will not be phased out for the foreseeable future. Interest is now being shown in an integrated GPS + LORAN C receiver thus providing back up and additional navigation capabilities.
Cost is another concern as navigation capabilities and facilities continue to be increasingly provided by the civilian world. For the cost of one launch of a satellite you can build a couple of LORAN C stations and run them for as long as a satellite would last. You would need 20-30 satellites to establish a complete navigation system.
The closure of the Loran- C system in the United States occurred on February 8, 2010. This is the official statement issued by the United States Coast Guard. The termination did not affect U.S. participation in the Russian American or Canadian LORAN-C chains. U.S. participation in these chains will continue in accordance with international agreements. The Canadian Coast Guard has also issued a statement, which is shown on their website.
