Editing Decca Navigator System (section)

{{Short description|Radio navigation system for ships and aircraft}}
{{more citations needed|date=November 2011}}
{{Use dmy dates|date=July 2020}}

[[Image:Accuracy of Navigation Systems.svg|300px|thumb]]
[[Image:Decca Navigator Mk 12.jpg|thumb|300px|The display panel of a Decca Navigator Mk 12 (ca. 1962). Decca position coordinates were directly displayed by four decometers and these were plotted on a conventional chart that had been over-printed with Decca lattices.]]

The '''Decca Navigator System''' was a [[hyperbolic navigation|hyperbolic]] [[radio navigation]] system that allowed ships and aircraft to determine their position by using radio signals from a dedicated system of static radio transmitters. The system used phase comparison between pairs of [[low frequency]] signals between 70 and 129&nbsp;[[kilohertz|kHz]], as opposed to pulse timing systems like [[Gee (navigation)|Gee]] and [[LORAN]]. This made it much easier to design receivers using 1940s electronics, and operation was simplified by giving a direct readout of Decca coordinates without the complexity of a [[cathode-ray tube]] and highly skilled operator.

The system was developed by [[Decca Radar|Decca]] in the UK. It was first deployed by the [[Royal Navy]] during [[World War II]] for the vital task of clearing the minefields to enable the [[D-Day]] landings. The Allied forces needed an accurate system not known to the Germans and thus free of jamming. After the war, it came off the secret list and was commercially developed by the Decca Company and deployed around UK and later used in many areas around the world. At its peak there were about 180 transmitting stations using "chains" of three or four transmitters each to allow position fixing by plotting intersecting electronic lines. Decca's primary use was for ship navigation in coastal waters, offering much better accuracy than the competing LORAN system. Fishing vessels were major post-war users, but it was also used on some aircraft, including a very early (1949) application of [[moving map display]]s. The system was deployed extensively in the [[North Sea]] and was used by helicopters operating to [[oil platform]]s.

The opening of the more accurate [[Loran-C]] system to civilian use in 1974 offered stiff competition, but Decca was well established by this time and continued operations to 2000. Decca Navigator, along with Loran and similar systems, was eventually replaced by the [[Global Positioning System|GPS]] in 2000, when that became available for public use.