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Definition: Loran from Philip's Encyclopedia

(Long range navigation) Radio system of navigation for ships and aircraft. Pairs of transmitters emit signal pulses that are picked up by a receiver. By measuring the difference in time between the signals reaching the receiver, the vessel's position can be plotted.


Summary Article: Long-Range Electronic Navigation
from Encyclopedia of the Vietnam War: A Political, Social, and Military History

Navigation system that uses two or more pairs of ground-based transmitting stations to allow the crew of an aircraft (or ship) to find their position. Long-range Electronic Navigation (LORAN) was developed by the United States during World War II and was based on the British GEE Radio Navigation System. The U.S.-developed system had a range of up to three times as far as the GEE system and thus became the standard for such navigation applications.

The master unit of each pair of ground-transmitting stations transmits a series of pulses, each repeated by the slave station located several hundred miles away. Because the period between the signals of the two stations is fixed and known, the length of time between the reception of each signal can be used to determine how much closer the aircraft is to one station than to the other. This time difference is determined either by computer or by plotting the signal on an oscilloscope. A second pair of stations allows the crew to triangulate to derive its precise position. The system operates at ranges up to several thousand miles, but accuracy deteriorates at longer distances. Under ideal conditions, LORAN systems can be accurate to within 100 yards.

The Vietnam War was the first conflict in which fighter-bomber aircraft attempted to strike with precision under adverse weather conditions and at night. The advent of electronic navigation aids such as LORAN and Tactical Air Control and Navigation (TACAN) systems made these attempts possible. LORAN was the more useful system because its signals were impossible to corrupt and because, unlike TACAN, it allowed the aircraft to remain electronically “quiet.” This radio silence made the incoming aircraft more difficult to track and defend against, improving survivability.

LORAN-guided strikes were less accurate than visual navigation and bombing, however. Employed extensively during Operation LINEBACKER II (December 1972) against storage facilities and power transformers, such strikes proved only marginally effective. LORAN does have some limitations. Its signals can be affected by certain adverse weather conditions and the ionospeheric effects that occur around sunup and sundown. Magnetic storms as well as strong sunspots can also interfere with the system’s functions.

LORAN systems remain in use, but they are being quickly rendered obsolete by far more sophisticated navigational devices, especially Global Navigation Satellite Systems, which rely on the highly accurate and fast Global Positioning System (GPS). Indeed, in 2009 the U.S. Office of Management and Budget identified the current LORAN system as outdated and recommended that its support be discontinued, resulting in a savings of some $40 million per year.

See also

Airpower, Role in War; Electronic Intelligence; LINEBACKER II, Operation

References
  • Glister, Herman L. The Air War in Southeast Asia: Case Studies of Selected Campaigns. Maxwell Air Force Base, AL: Air University Press, 1993.
  • Pierce, J. A., et al., eds. LORAN: Long Range Navigation. Massachusetts Institute of Technology Radiation Laboratory Series. New York: McGraw-Hill, 1948.
  • Williams, J. E. D. From Sails to Satellites: The Origin and Development of Navigational Science. New York: Oxford University Press, 1992.
  • Crump, Matthew A.
    Pierpaoli, Paul G. Jr.
    Copyright 2011 by ABC-CLIO, LLC

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