Ground-controlled interception
Encyclopedia
Ground-controlled interception (GCI) an air defense tactic whereby one or more radar stations are linked to a command communications centre which guides interceptor aircraft
to an airborne target. This tactic was pioneered during World War II
by the Royal Air Force
with the Luftwaffe
to follow closely. Today, GCI is still important for most nations, although Airborne Early Warning and Control, with or without support from GCI, tends to be more capable and flexible.
In the original RAF system, information from the various Chain Home
coastal radar
stations was relayed by phone to a number of operators on the "ground floor" of the interception direction center. They used the information to move markers on a large operational map, representing both the enemy intruder formations and own aircraft. Radio operators were located on a balcony overlooking the map, and relayed instructions directly to a particular squadron, or more typically, a remotely located station relaying information to a group of aircraft. Above them were status boards, consisting of a series of lights showing the current status of a particular squadron, on the ground, in battle, returning, etc. Overall direction of the battle was directed by commanders who thus had "instant access" to a picture of the battle as a whole.
Because the Chain Home radar stations faced out to sea, once airborne intruders had crossed the British coast they could no longer be tracked by radar; and accordingly the interception direction centres relied on visual and aural sightings of the Royal Observer Corps
for continually updated information on the location and heading of enemy aircraft formations. While this arrangement worked acceptably during the daylight raids of the Battle of Britain
, subsequent bombing attacks of The Blitz
demonstrated that such techniques were wholly inadequate for identifying and tracking aircraft at night. Accordingly, the Royal Air Force established during 1941 a network of inland GCI radar stations, RAF Sopley
, RAF Durrington, RAF Willesborough, RAF Waldringfield, RAF Orby, and RAF Avebury, whose task was to direct searchlight
s onto intruders, and also to guide interceptor nightfighters. This network did not become fully functional till after May 1941, when the main German night-time air assault against Britain was discontinued.
During World War II, airborne radars were so primitive that the defending aircraft needed to close to within what would be easily visual distance during daytime. GCI was often used to vector the defending night fighters very close to the intruders and they then crept up on the often unsuspecting aircraft. GCI and night fighters eventually made night sorties over western Europe significantly more risky for bomber crews than they were at the beginning of the war (when they had relative impunity).
and Vietnam War
s the North Korea
ns and North Vietnam
ese had important GCI systems which helped them harass the opposing forces (although in both cases due to the superiority in the number of US planes the effect was eventually minimised ). GCI was important to the US and allied forces during these conflicts also, although not so much as for their opponents.
The most advanced GCI system deployed to date was the US's Semi Automatic Ground Environment
(SAGE) system. SAGE used massive computers to combine reports sent in via teletype from the Pinetree Line
and other radar networks to produce a picture of all of the air traffic in a particular "sector"s area. The information was then displayed on terminals in the building, allowing operators to pick defensive assets (fighters and missiles) to be directed onto the target simply by selecting them on the terminal. Messages would then automatically be routed back out via teletype with instructions on them.
The system was later upgraded to relay directional information directly to the autopilot
s of the interceptor aircraft
like the F-106 Delta Dart
. The pilot was tasked primarily with getting the aircraft into the air (and back), and then flying in a parking orbit until called for. When an interception mission started, the SAGE computers automatically flew the plane into range of the target, allowing the pilot to concentrate solely on operating the complex onboard radar.
GCI is typically augmented with the presence of extremely large early warning radar
arrays, which could alert GCI to inbound hostile aircraft hours before they arrive, giving enough time to prepare and launch aircraft and set them up for an intercept either using their own radars or with the assistance of regular radar stations once the bogeys approach their coverage. An example of this type of system is Australia
's Jindalee over-the-horizon radar. Such radars typically operate by bouncing their signal off layers in the atmosphere.
The strengths of GCI are that it can cover far more airspace than AEW&C without costing as much and areas that otherwise would be blind-spots for AEW&C can be covered by cleverly placed radar stations. AEW&C also relies on aircraft which may require defence and a few aircraft are more vulnerable than many ground-based radar stations. If a single AEW&C aircraft is shot down or otherwise taken out of the picture, there will be a serious gap in air defence until another can replace it, where in the case of GCI, many radar stations would have to be taken off the air before it became a serious problem. In both cases a strike on a command center could be very serious.
Either GCI or AEW&C can be used to give defending aircraft a major advantage during the actual interception by allowing them to sneak up on enemy aircraft without giving themselves away by using their own radar sets. Typically, to perform an interception by themselves beyond visual range, the aircraft would have to search the sky for intruders with their radars, the energy from which might be noticed by the intruder's radar warning receiver
(RWR) electronics, thus alerting the intruders that they may be coming under attack. With GCI or AEW&C, the defending aircraft can be vectored to an interception course, perhaps sliding in on the intruder's tail position without being noticed, firing passive homing missiles and then turning away. Alternatively, they could turn their radars on at the final moment, so that they can get a radar lock and guide their missiles. This greatly increases the interceptor's chance of success and survival.
Interceptor aircraft
An interceptor aircraft is a type of fighter aircraft designed specifically to prevent missions of enemy aircraft, particularly bombers and reconnaissance aircraft. Interceptors generally rely on high speed and powerful armament in order to complete their mission as quickly as possible and set up...
to an airborne target. This tactic was pioneered during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
by the Royal Air Force
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...
with the Luftwaffe
Luftwaffe
Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....
to follow closely. Today, GCI is still important for most nations, although Airborne Early Warning and Control, with or without support from GCI, tends to be more capable and flexible.
World War II
Chain Home
Chain Home was the codename for the ring of coastal Early Warning radar stations built by the British before and during the Second World War. The system otherwise known as AMES Type 1 consisted of radar fixed on top of a radio tower mast, called a 'station' to provide long-range detection of...
coastal radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
stations was relayed by phone to a number of operators on the "ground floor" of the interception direction center. They used the information to move markers on a large operational map, representing both the enemy intruder formations and own aircraft. Radio operators were located on a balcony overlooking the map, and relayed instructions directly to a particular squadron, or more typically, a remotely located station relaying information to a group of aircraft. Above them were status boards, consisting of a series of lights showing the current status of a particular squadron, on the ground, in battle, returning, etc. Overall direction of the battle was directed by commanders who thus had "instant access" to a picture of the battle as a whole.
Because the Chain Home radar stations faced out to sea, once airborne intruders had crossed the British coast they could no longer be tracked by radar; and accordingly the interception direction centres relied on visual and aural sightings of the Royal Observer Corps
Royal Observer Corps
The Royal Observer Corps was a civil defence organisation operating in the United Kingdom between 29 October 1925 and 31 December 1995, when the Corps' civilian volunteers were stood down....
for continually updated information on the location and heading of enemy aircraft formations. While this arrangement worked acceptably during the daylight raids of the Battle of Britain
Battle of Britain
The Battle of Britain is the name given to the World War II air campaign waged by the German Air Force against the United Kingdom during the summer and autumn of 1940...
, subsequent bombing attacks of The Blitz
The Blitz
The Blitz was the sustained strategic bombing of Britain by Nazi Germany between 7 September 1940 and 10 May 1941, during the Second World War. The city of London was bombed by the Luftwaffe for 76 consecutive nights and many towns and cities across the country followed...
demonstrated that such techniques were wholly inadequate for identifying and tracking aircraft at night. Accordingly, the Royal Air Force established during 1941 a network of inland GCI radar stations, RAF Sopley
RAF Sopley
RAF Sopley was a WWII airbase, codenamed Starlight, near the village of Sopley in Hampshire. It was opened in December 1940. In 1959 it became an air traffic control radar station, and finally closed on 27 September 1974...
, RAF Durrington, RAF Willesborough, RAF Waldringfield, RAF Orby, and RAF Avebury, whose task was to direct searchlight
Searchlight
A searchlight is an apparatus that combines a bright light source with some form of curved reflector or other optics to project a powerful beam of light of approximately parallel rays in a particular direction, usually constructed so that it can be swiveled about.-Military use:The Royal Navy used...
s onto intruders, and also to guide interceptor nightfighters. This network did not become fully functional till after May 1941, when the main German night-time air assault against Britain was discontinued.
During World War II, airborne radars were so primitive that the defending aircraft needed to close to within what would be easily visual distance during daytime. GCI was often used to vector the defending night fighters very close to the intruders and they then crept up on the often unsuspecting aircraft. GCI and night fighters eventually made night sorties over western Europe significantly more risky for bomber crews than they were at the beginning of the war (when they had relative impunity).
Post WWII
More recently, in both the KoreanKorean War
The Korean War was a conventional war between South Korea, supported by the United Nations, and North Korea, supported by the People's Republic of China , with military material aid from the Soviet Union...
and Vietnam War
Vietnam War
The Vietnam War was a Cold War-era military conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. This war followed the First Indochina War and was fought between North Vietnam, supported by its communist allies, and the government of...
s the North Korea
North Korea
The Democratic People’s Republic of Korea , , is a country in East Asia, occupying the northern half of the Korean Peninsula. Its capital and largest city is Pyongyang. The Korean Demilitarized Zone serves as the buffer zone between North Korea and South Korea...
ns and North Vietnam
North Vietnam
The Democratic Republic of Vietnam , was a communist state that ruled the northern half of Vietnam from 1954 until 1976 following the Geneva Conference and laid claim to all of Vietnam from 1945 to 1954 during the First Indochina War, during which they controlled pockets of territory throughout...
ese had important GCI systems which helped them harass the opposing forces (although in both cases due to the superiority in the number of US planes the effect was eventually minimised ). GCI was important to the US and allied forces during these conflicts also, although not so much as for their opponents.
The most advanced GCI system deployed to date was the US's Semi Automatic Ground Environment
Semi Automatic Ground Environment
The Semi-Automatic Ground Environment was an automated control system for tracking and intercepting enemy bomber aircraft used by NORAD from the late 1950s into the 1980s...
(SAGE) system. SAGE used massive computers to combine reports sent in via teletype from the Pinetree Line
Pinetree Line
The Pinetree Line was a series of radar stations located across the northern United States and southern Canada at about the 50th parallel north, along with a number of other stations located on the Atlantic and Pacific coasts. Run by NORAD , over half were manned by United States Air Force...
and other radar networks to produce a picture of all of the air traffic in a particular "sector"s area. The information was then displayed on terminals in the building, allowing operators to pick defensive assets (fighters and missiles) to be directed onto the target simply by selecting them on the terminal. Messages would then automatically be routed back out via teletype with instructions on them.
The system was later upgraded to relay directional information directly to the autopilot
Autopilot
An autopilot is a mechanical, electrical, or hydraulic system used to guide a vehicle without assistance from a human being. An autopilot can refer specifically to aircraft, self-steering gear for boats, or auto guidance of space craft and missiles...
s of the interceptor aircraft
Interceptor aircraft
An interceptor aircraft is a type of fighter aircraft designed specifically to prevent missions of enemy aircraft, particularly bombers and reconnaissance aircraft. Interceptors generally rely on high speed and powerful armament in order to complete their mission as quickly as possible and set up...
like the F-106 Delta Dart
F-106 Delta Dart
The Convair F-106 Delta Dart was the primary all-weather interceptor aircraft for the United States Air Force from the 1960s through the 1980s. Designed as the so-called "Ultimate Interceptor", it has proven to be the last dedicated interceptor in USAF service to date...
. The pilot was tasked primarily with getting the aircraft into the air (and back), and then flying in a parking orbit until called for. When an interception mission started, the SAGE computers automatically flew the plane into range of the target, allowing the pilot to concentrate solely on operating the complex onboard radar.
GCI is typically augmented with the presence of extremely large early warning radar
Early warning radar
An early warning radar is any radar system used primarily for the long-range detection of its targets, i.e., allowing defences to be alerted as early as possible before the intruder reaches its target, giving the defences the maximum time in which to operate...
arrays, which could alert GCI to inbound hostile aircraft hours before they arrive, giving enough time to prepare and launch aircraft and set them up for an intercept either using their own radars or with the assistance of regular radar stations once the bogeys approach their coverage. An example of this type of system is Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
's Jindalee over-the-horizon radar. Such radars typically operate by bouncing their signal off layers in the atmosphere.
Airborne Early Warning and Control
In more recent years, GCI has been supplanted, or replaced outright, with the introduction of Airborne Early Warning and Control (AEW&C, often called AWACS) aircraft. AEW&C tends to be superior in that, being airborne and being able to look down, it can see targets fairly far away at low level, as long as it can pick them out from the ground clutter. AEW&C aircraft are extremely expensive, however, and generally require aircraft to be dedicated to protecting them. A combination of both techniques is really ideal, but GCI is typically only available in the defence of one's homeland, rather than in expeditionary types of battles.The strengths of GCI are that it can cover far more airspace than AEW&C without costing as much and areas that otherwise would be blind-spots for AEW&C can be covered by cleverly placed radar stations. AEW&C also relies on aircraft which may require defence and a few aircraft are more vulnerable than many ground-based radar stations. If a single AEW&C aircraft is shot down or otherwise taken out of the picture, there will be a serious gap in air defence until another can replace it, where in the case of GCI, many radar stations would have to be taken off the air before it became a serious problem. In both cases a strike on a command center could be very serious.
Either GCI or AEW&C can be used to give defending aircraft a major advantage during the actual interception by allowing them to sneak up on enemy aircraft without giving themselves away by using their own radar sets. Typically, to perform an interception by themselves beyond visual range, the aircraft would have to search the sky for intruders with their radars, the energy from which might be noticed by the intruder's radar warning receiver
Radar warning receiver
Radar warning receiver systems detect the radio emissions of radar systems. Their primary purpose is to issue a warning when a radar signal that might be a threat is detected. The warning can then be used, manually or automatically, to evade the detected threat...
(RWR) electronics, thus alerting the intruders that they may be coming under attack. With GCI or AEW&C, the defending aircraft can be vectored to an interception course, perhaps sliding in on the intruder's tail position without being noticed, firing passive homing missiles and then turning away. Alternatively, they could turn their radars on at the final moment, so that they can get a radar lock and guide their missiles. This greatly increases the interceptor's chance of success and survival.
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