Editing Decca Navigator System (section)

== History ==
[[Image:Decca Navigator Mk 21.jpg|thumb|Decca Navigator Mk. 21, with the Decometer dials prominent.]]

=== Origins ===
In 1936 William J. O'Brien, an engineer, contracted [[tuberculosis]] that put his career on hold for a period of two years. During this period he had the idea of position fixing by means of phase comparison of continuous wave transmissions. This was not the first such system, but O'Brien apparently developed his version without knowledge of the others, and made several advancements in the art that would prove useful. He initially imagined the system being used for aircraft testing, specifically the accurate calculation of ground speed. Some experiments were carried out in California in 1938, selecting frequencies with harmonic "beats" that would allow for station identification in a network of transmitters. Both the [[U.S. Army]] and [[U.S. Navy|Navy]] considered the idea too complicated and work ended in 1939.{{sfn|Blanchard|1991|p=301}}

O’Brien's friend, Harvey F. Schwarz, was chief engineer of the [[Decca Records|Decca Record company]] in England. In 1939 O’Brien sent him details of the system so it could be put forward to the British military. Initially [[Robert Watson-Watt]] reviewed the system but he did not follow it up, deeming it too easily jammed (and likely due to the existing work on the [[Gee (navigation)|Gee]] system, being carried out by Watt's group).{{sfn|Blanchard|1991|p=302}} However, in October 1941 the British Admiralty Signal Establishment (ASE) became interested in the system, which was then classified as ''Admiralty Outfit QM''. The first marine trials were conducted between [[Anglesey]] and the [[Isle of Man]], at frequencies of 305/610&nbsp;kHz, on 16 September 1942.{{sfn|Blanchard|1991|p=301}}

Further trials were conducted in the northern [[Irish Sea]] in April 1943 at 70/130&nbsp;kHz. It was decided that the original frequencies were not ideal, and a new system using a 14&nbsp;kHz inter-signal spacing was selected. This led to the common 5, 6, 8 and 9''f'' frequencies, used throughout the life of the Decca system. 7''f'' was reserved for a [[Loran-C]]-like extension, but never developed.{{sfn|Blanchard|1991|p=302}}  A follow-up test was carried out in the [[Irish Sea]] in January 1944 to test a wide variety of upgrades and production equipment. By this time the competing Gee system was known to the Admiralty and the two systems were tested head-to-head under the code names QM and QH. QM was found to have better sea-level range and accuracy, which led to its adoption.{{sfn|Blanchard|1991|p=302}}

===D-Day landings===

A three-station trial was held in conjunction with a large-scale assault and landing exercise in the [[Moray Firth]] in February/March 1944. The success of the trials and the relative ease of use and accuracy of the system resulted in Decca receiving an order for 27 ''Admiralty Outfit QM'' receivers. The receiver consisted of an electronics unit with two dials and was known to its operators as the "Blue Gasmeter Job". A Decca chain was set up, consisting of a master station at [[Chichester]] and slaves at [[Swanage]] and [[Beachy Head]]. A fourth decoy transmitter was located in the [[Thames Estuary]] as part of the deception that the invasion would be focussed on the [[Calais]] area.
21 minesweepers and other vessels were fitted with ''Admiralty Outfit QM'' and, on 5 June 1944, 17 of these ships used it to accurately navigate across the [[English Channel]] and to sweep the minefields in the planned areas. The swept areas were marked with buoys in preparation for the [[Normandy Landings]].

After the initial ship tests, Decca conducted tests in cars, driving in the [[A3 road|Kingston By-Pass]] area to verify receiver accuracy. In the car installation, it was found possible to navigate within an individual traffic lane. The company entertained high hopes that the system could be used in aircraft, to permit much more precise navigation in the critical airspace around airports and urban centres where traffic density was highest.

=== Commercial deployment ===
[[File:DECCA unit, NMS.jpg|thumb|Decca receiver, Mk.51 seen in the [[National Museum of Scotland]]]]
After the end of [[World War II]] the Decca Navigator Co. Ltd. was formed (1945) and the system expanded rapidly, particularly in areas of [[British Empire|British influence]]; at its peak it was deployed in many of the world's major shipping areas. More than 15,000 receiving sets were in use aboard ships in 1970. There were 4 chains around England, 1 in Ireland and 2 in Scotland, 12 in Scandinavia (5 each in Norway and Sweden and 1 each in Denmark and Finland), a further 4 elsewhere in northern Europe and 2 in Spain.

Canada was another early user, with branch offices set up in [[Toronto]] in 1953.<ref>{{cite web |url=https://canada-company.com/c/402478-decca-navigator-canada-ltd |title=Corporation Information |website=Decca Navigator (Canada) Ltd. |publisher=Canada Company Directory}}</ref>{{failed verification|date=June 2022|reason=This source does not support the statement}} The first chain was installed in southwest [[Newfoundland]] in 1956 as part of a joint Canada-US Navy surveying program. This led to commercial deployments the next year in [[Nova Scotia]] and an inland system for air traffic in the busy [[Quebec City]]-[[Montreal]] area. A fourth chain covering eastern Newfoundland was added in 1958. When meetings in Montreal in 1958 led to VOR and DME being selected as the standard aviation navigation systems, the Montreal system was moved eastward to cover the [[Anticosti Island]] area of the [[Gulf of St. Lawrence]], and the western Newfoundland chain was later repositioned to better cover the [[Cabot Strait]]. A series of chains was also proposed to cover the [[Northwest Passage]] had oil tanker traffic used the area, but this never came to be. Another was briefly set up covering [[Lake Ontario]] in 1971 for the [[International Field Year for the Great Lakes]].<ref>{{cite magazine |magazine= Decca Navigator News |date=September 1976 |title= Decca Marine Canada}}</ref> The last Canadian chain shut down in 1986, after Loran-C became widespread.

In the late 1950s an experimental Decca chain was set up in the United States, in the New York area, to be used for navigating the [[Boeing Vertol CH-46 Sea Knight|Vertol 107]] helicopters of [[New York Airways]]. These helicopters were operating from the principal local airports—[[John F. Kennedy International Airport|Idlewild Airport]] on Long Island, [[Newark Liberty International Airport|Newark Airport]] in New Jersey, [[LaGuardia Airport]] in the Borough of Queens, nearer to Manhattan, and a site on the top of the (then) [[MetLife Building|PanAm Building]] on Park Avenue. Use of Decca was essential because its signals could be received down to sea level, were not subject to the line-of-sight limitations of [[VHF omnidirectional range|VOR]]/[[Distance measuring equipment|DME]] and did not suffer the slant-range errors that create problems with VOR/DME close to the transmitters. The Decca installations in the New York Airways helicopters included the unique Decca 'roller map' displays that enabled the pilot to see his or her position at a glance, a concept infeasible with VOR/DME.

This chain installation was considered highly controversial at the time, for political reasons. This led to the U.S. Coast Guard, under instructions from the Treasury Department to which it reported, banning the use of Decca receivers in ships entering New York harbour for fear that the system might create a de facto standard (as it had become in other areas of the world). It also served to protect the marketing interests of the Hoffman Electronics division of ITT, a principal supplier of VOR/DME systems, that Decca might have been poised to usurp.

This situation was exacerbated by the workload problems of the Air Traffic Controllers Association (ATCA), under its executive director Francis McDermott, whose members were forced to use radar data on aircraft positions, relaying those positions by radio to the aircraft from their control locations. An example of the problem, cited by experts, was the [[1960 New York mid-air collision|collision of a Douglas DC8 and a Lockheed Constellation over Staten Island, New York]],<ref>{{Cite web |title=UNITED AIR LINES, INC, DC-8, N 8013U, AND TRANS WORLD AIRLINES, INC., CONSTELLATION 1049A, N 6907C, NEAR STATEN ISLAND, NEW YORK, DECEMBER 16, 1960 |website=Plane and Train Wrecks {{!}} Online Collections |url=https://planeandtrainwrecks.com/Document?db=DOT-AIRPLANEACCIDENTS&query=(select+0+(byhits+(eq+ACCIDENT_DATE+%601960%2F12%2F16))) |access-date=2022-06-17}}</ref> that—according to some experts—could have been avoided if the aircraft had been Decca-equipped and could not only have determined their positions more precisely but would not have suffered from the rho-theta position errors inherent in VOR/DME.

Other chains were established in Japan (6 chains); Namibia and South Africa (5 chains); India and Bangladesh (4 chains); North-West Australia (2 chains); the [[Persian Gulf]] (1 chain with stations in Qatar and the United Arab Emirates and a second chain in the north of the Gulf with stations in Iran) and the Bahamas (1 chain). Four chains were planned for Nigeria but only two were built and these did not enter into public service. Two chains in Vietnam were used during the [[Vietnam War]] for helicopter navigation, with limited success.
During the Cold War period, following WWII, the R.A.F. established a confidential chain in Germany. The Master station was in [[Bad Iburg]] near Osnabrück and there were two Slaves. The purpose of this chain was to provide accurate air navigation for the corridor between Western Germany and Berlin in the event that a mass evacuation of allied personnel may be required. In order to maintain secrecy, frequencies were changed at irregular intervals.

=== Decca, Racal, and the closedown ===
[[File:Decca Receiver Philips.jpg|thumb|An ''ap'' Decca receiver Mk II from the 1980s that could be purchased instead of leased. It could store 25 waypoints.]]

The headquarters of Decca Navigator were at New Malden, Surrey, just off the Kingston by-pass. There was a Decca School, at [[Brixham]], [[Devon]], where employees were sent on courses from time to time. [[Racal]], the UK weapons and communications company, acquired Decca in 1980. Merging Decca's radar assets with their own, Racal began selling off the other portions of the company, including avionics and Decca Navigator.

A significant amount of income from the Decca system was due to the receivers being leased to users, not sold outright. This guaranteed predictable annual income. When the patents on the original technology lapsed in the early 1980s, new receivers were quickly built by a number of companies. In particular, Aktieselskabet Dansk Philips ('Danish Philips', ''ap'') introduced receivers that could be purchased outright, and were much smaller and easier to use than the current Decca counterparts. The "ap" versions directly output the longitude and latitude to two decimals (originally in datum [[ED50]] only) instead of using the "deco meter" displays, offering accuracy better than ±9.3 m{{Citation needed|reason=Sources suggest general accuracy was nowhere near this good, more like 100 m|date=September 2023}}, much better than the Decca units. This also eliminated the need for the special charts printed with Decca lanes and zones.

Decca sued ap for infringement and, in the ensuing court battle, Decca lost the monopoly. That signalled the beginning of the end for the company. Income dwindled and eventually, the UK [[Department for Transport|Ministry of Transport]] stepped in, having the [[Trinity House|lighthouse authorities]] take responsibility for operating the system in the early 1990s.

A ruling from the European Union forced the UK government to withdraw funding. The [[general lighthouse authority]] ceased Decca transmissions at midnight on 31 March 2000. The Irish chain provided by [[Bord Iascaigh Mhara|Bórd Iascaigh Mhara]] continued transmitting until 19 May 2000. Japan continued operating their [[Hokkaido|Hokkaidō]] chain until March 2001, the last Decca chain in operation.