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Although the Coast Guard played a vital combat role during WWII, one of the most lasting legacies of the war was LORAN.

LORAN used radio signals to help ships and aircraft obtain an accurate position. Clearly, any devise that could help navigation in the vast expanse of the Pacific would be beneficial to the war effort. LORAN was an American development of the British GEE radio navugation system. While GEE had a range of about 400 miles), early LORAN systems had a range of 1,200 miles.

The navigational method provided by LORAN was based on the principle of the time difference between the receipt of signals from a pair of radio transmitters. A given constant time difference between the signals from the two stations could be represented by a hyperbolic line of position (LOP). If the position of the two synchronized stations were known, then the position of the receiver could be determined as being somewhere on a particular hyperbolic curve where the time difference between the received signals was constant. In ideal conditions, this was proportionally equivalent to the difference of the distances from the receiver to each of the two stations. By itself, with only two stations, the two-dimensional position of the receiver could not be fixed. A second application of the same principle had to be used, based on the time difference of a different pair of stations. By determining the intersection of the two hyperbolic curves identified by the application of this method, a geographic fix could be determined. In the case of LORAN, one station remained constant in each application of the principle, the master. The master was paired separately with at least two slave, or secondary, stations. Given two secondary stations, the time difference (TD) between the master and first secondary identified one curve, and the time difference between the master and second secondary identified another curve, the intersections of which would determine a geographic point in relation to the position of the three stations. These curves were often referred to as “TD lines.”

In practice, LORAN was implemented in integrated regional arrays, or chains, consisting of one master station and at least two (but often more) secondary stations, with a uniform “group repetition interval” (GRI) defined in microseconds. The master station transmitted a series of pulses, then paused for that amount of time before transmitting the next set of pulses. The secondary stations received this pulse signal from the master, then waited a preset amount of milliseconds, known as the secondary coding delay, to transmit a response signal. In a given chain, each secondary’s coding delay was different, allowing for separate identification of each secondary’s signal.

On 1 March 1944, LT Alvin Loose and a small work party built the first LORAN A station on Baker Island n the Pacific. From 8 November 1944 to 22 June 1945, 19 stations were built throughout the Pacific. The stations were classified as SECRET. The typical tour lasted 18 months. It was dull, monotonous duty. Logistics were a serious problem. The distance from Hawaii to the Marianas stations was 4,600 miles. Sometimes months would pass before a supply ship showed up.

After the war, the Coast Guard continued to expand and modernize the LORAN system.. Stations were set up in Europe to serve the Atlantic. LORAN A gave way to LORAN C. LORAN A was a less accurate system operating in the 1,750-1,950 KHz frequency band. It continued in operation partly due to the economy of the receivers and widespread use in civilian recreational and commercial navigation LORAN C transmitters transmit with power between 100 kilowatts and 4,000 kilowatts, comparable to the transmission power of longwave broadcasting stations. As aerials for stations below a transmission power of 500 kilowatts, guyed masts insulated against ground with a height of approximately 200 yards were used.

Typically, LORSTAs had a LTJG as the commanding officer and a bo’s’n chief (BMC) as the executive officer. Large stations, or those in politically hot locations may have had a LT and a Warrant Electronics Officer. War zone stations had two officers. The crew consisted mostly of electronic technicians (ETs) to care for the sensitive transmitters and receivers, a machinist mate (MK) to keep generators and engines running, and a couple of seamen to do building and grounds maintenance. Truly isolated stations had cooks. Stations that were tenants to other commands generally shared the mess with the host command. The tour of duty was 12 months.
Immediately after the war, the stations were supplied by ship. USCGC Kukui was a 399-foot freighter that was instrumental in building and supplying the stations. Later, the stations were supplied by C-130s flying out of CG AIRSTA Barber’s Point. Stations that were tenants were generally supplied by the host command, generally by Air Force C-141s.

One of the most isolated of all stations became the post-war symbol of Coast Guard LORAN stations. US Coast Guard LORAN A Station French Frigate Shoals was 500 miles west-northwest of Honolulu. The station was built on Tern Island, which had been bulldozed into the shape of an aircraft carrier during the war to provide a landing strip for the invasion of Midway. The runway was 3,100 feet long, 410 feet wide, and had a mean elevation of nine feet. Two officers and 18 enlisted men called this speck home. The station was supplied by C-130. Once, in 1969, the crew had to be evacuated by the helicopter of a New Zealand frigate when heavy seas washed over the island. The station was disestablished on 30 June 1979.

LORAN suffered from electronic effects of weather and in particular atmospheric effects related to sunrise and sunset. The most accurate signal was the groundwave, that following the Earth’s surface, preferably along a sea water path. At night the indirect skywave, taking paths bent back to the surface by the ionosphere, was a particular problem as multiple signals arrived via different paths. The ionosphere’s reaction to sunrise and sunset accounts for the particular disturbance during those periods. Magnetic storms had serious effects on LORAN as with any radio based system.

As other, more reliable, navigation systems began to come on line, there was no need to build more LORAN stations. In 1972, when it became apparent that no more stations would be built and resupply was done totally by air, Kukui was decommissioned. Most LORAN A stations were decommissioned by 1979. LORAN C has been modernized and served well into the 21st century. The last LORAN C station was disestablished in 2010.