GEE (navigation)

GEE or AMES Type 7000 was a British radio navigation system used by the Royal Air Force during World War II. GEE was designed to improve aircraft navigation accuracy, thereby increasing the destructiveness of raids by Avro Lancasters and various other bombers.

The technology of GEE was developed by the Americans into the LORAN system. LORAN was used by the US Navy and Royal Navy during World War II, and after the war came into common civilian use world-wide for coastal navigation, until GPS made it obsolete.

Technical details

Gee was a hyperbolic navigation system, similar to the OMEGA Navigation System and the current-day LORAN-C.

GEE transmitters sent out precisely timed pulses. There were three Gee stations, one master and two slaves. The master sent a pulse followed two milliseconds later by a double pulse. The first slave station sent a single pulse one millisecond after the master's single pulse, and the second slave sent a single pulse one millisecond after the master's double pulse. The whole cycle repeated on a four millisecond cycle. On board the aircraft, the signals from the three stations were received. The on board equipment would display the two slaves' signals as blips on an oscilloscope type display. Since the display timing was controlled by the pulses from the master station, the display equipment gave the difference in reception time of the pulses and hence the relative distance from the master and each slave. The aircraft carried a navigation chart with several hyperbolae plotted on it. Each hyperbolic line represented a line of constant time difference for the master and one slave station. All the navigator had to do was find the intersection of the two hyperbolae representing the two slave stations.

ystem almost compromised

Eager to utilize the system, the prototype Gee sets were used on marker raids well before the production sets were available in numbers for large raids. This risked detection of the system before it could be fully utilized. Indeed, one of the prototypes was lost on the 13 August 1941 raid over Hanover. Although equipped with demolition charges, the British couldn't be sure the set wouldn't be studied by the Germans. [Jones. p.218]

R. V. Jones was tasked with trying to hide the existence of the system. First, the use of the codename 'Gee' in communications traffic was dropped, and false communications were sent referring to a non-existent system called 'Jay'; it was hoped the similarity would cause confusion. Extra antennae were added to the Gee transmitters to radiate false, unsynchronized signals. A couple of RAF personnel were sent to talk 'carelessly' in a restaurant about how Jay was in fact a copy of the German Knickebein system, and it was also arranged for this story to be reported via the Double Cross system. Finally, false Knickebein signals were transmitted over Germany. [Jones. pp.219-221. Jones noted all this appealed to his penchant for practical joking.]

The ruses seemed to delay the introduction of jammers, for they were not encountered until nearly 5 months after Gee entered serice. [Jones. p.221] Gee was highly susceptible to jamming since all the Germans had to do was radiate surplus pulses, but such jamming was effective only over their territory; Gee remained usable over Britain. [Fake pulses over Germany would have to be similar in strength to those sent from Britain, and so over Britain, the fake pulses would be easily recognized as weak as well as improperly synchronized.]

ervice history

GEE entered service in March 1942 and was accurate to about convert|165|yd at short ranges, and up to a mile at longer ranges over Germany. At its extreme range, which was about convert|400|mi|km, it had an accuracy of convert|2|mi|km. Unlike the German beam systems where the bombers flew to their targets along the beam, the GEE pulses were radiated in all directions, so even if detected, they would not reveal the bombers' likely destinations. As the system was passive, unlike H2S, there were no return signals which could give away the bombers' positions to night fighters. The aircraft receivers themselves were designated "ARI 5033" in GEE Mk.I and "ARI 5083" in GEE Mk.II.

German bombers also used the GEE system for attacks on the U.K.; captured GEE receivers provided the electronics. [Jones. p.397]

tations

Eastern chain

The Eastern chain operated from 22 June 1942. The master station was at Daventry, Northamptonshire. (gbmappingsmall|SP5766081)

The monitor station was RAF Barkway [ [http://viewfinder.english-heritage.org.uk/search/reference.asp?index=26917&main_query=&theme=&period=&county=&district=&place_name=&imageUID=113888 English Heritage] ] [ [http://viewfinder.english-heritage.org.uk/search/reference.asp?index=26905&imageUID=113884&main_query=&theme=&period=&county=&district=&place_name= English Heritage] ] [ [http://www.geograph.org.uk/photo/48974 Geograph] ] , near Royston, Hertfordshire. (gbmappingsmall|TL380364)

Other stations included

* Clee Hill, Shropshire (gbmappingsmall|SO598779)
* Stenigot (gbmappingsmall|TF257825)
* Gibbet Hill, Hindhead, Surrey (gbmappingsmall|SU899359)

Northern chain

The Northern GEE chain operated from late 1942 until March 1946 [http://www.radarpages.co.uk/mob/navaids/gee/gee1.htm] . The master and monitor stations were on Burifa Hill on Dunnet Head, in Caithness, Scotland. (gbmappingsmall|ND201755)

Slave stations included:
* Scousburgh, Shetland Islands (gbmappingsmall|HU387187)
* Windyhead Hill, Pennan, Aberdeenshire (gbmappingsmall|NJ854619)
* Sango, Durness, Sutherland (gbmappingsmall|NC414677)

South Western Chain

* Master Sharpitor (gbmappingsmall|SX73)
* Slave B Worth Matravers (gbmappingsmall|SY964778)
* Slave C Sennen (gbmappingsmall|SW3625)
* Slave D Folly (gbmappingsmall|SM858195)
* Chain Monitor Trerew (gbmappingsmall|SW812585) [http://www.subbrit.org.uk/rsg/sites/t/trerew_rotor/index.html]

A chain of Gee stations was opened after the war in North Germany. Stations were at Winterberg, Ibug, Nordhorn and Uchte.

There were several stations during the 1955-1959 period that appeared to be more of a deception than really operational. They were 550 SU at Fort Spijkerboor outside of Pumerand, Holland; 889 SU at Eckendforde in North Germany; and 330 SU outside of Ingolstadt in Bavaria, Germany. These stations were rarely if ever operation in the late 1950's.

Worth Matravers was used after the war as a training base for Gee operators.

References

* Johnson, Brian. "The Secret War" (BBC, London, Methuen, New York, 1978) pp. 84–89
* Jones, R. V. (1978) "Most Secret War" Hamish Hamilton Ltd, London. ISBN 0 241 89746 7. Also published as "The Wizard War: British Scientific Intelligence 1939–1945" (Coward, McCann and Geoghegan, New York)
* Price, Alfred. "Instruments of Darkness: The History of Electronic Warfare" (Peninsula, Los Altos, 1977) pp. 98–104

Notes

Further reading

* Colin Latham and Anne Stobbs. "Radar, A Wartime Miracle" (Sutton Publishing Ltd, Stroud, Gloucestershire 1996) ISBN 0750916431

External links

* [http://www.vectorsite.net/ttwiz.html Radio Navigation Systems in Greg Goebel's THE WIZARD WAR]
* [http://www.duxfordradiosociety.org/restoration/restoredequip/r1355/r1355.html Imperial War Museum page] ; information about restored GEE receivers.
* [http://www.radarpages.co.uk/mob/navaids/gee/gee1.htm Radarpages.co.uk page] ; information about the mechanics of the system.
* [http://www.rafwinterberg.co.uk. History of RAF Wintenberg and North German Gee chain]
* [http://www.jproc.ca/hyperbolic/gee.html THE GEE SYSTEM by W. F. BLANCHARD including 1948 map]

ee also