Editing Infrared homing (section)

==History==
===Early research===
[[File:Vampir night scope.jpg|thumb|right|The ''Vampir'' nightscope used a photomultiplier as the sighting system and provided illumination with an IR lamp mounted above the scope.]]

The ability of certain substances to give off [[electron]]s when struck by infrared light had been discovered by the famous [[Indian people|Indian]] polymath [[Jagadish Chandra Bose]] in 1901, who saw the effect in [[galena]], known today as lead sulfide, PbS. There was little application at the time, and he allowed his 1904 patent to lapse.<ref>{{cite journal |first=V |last= Mukherj |title= Some Historical Aspects of Jagadls Chandra Bose's Microwave Research During 1895—1900 |journal=Indian Journal of History of Science Calcutta |date=February 1979 |pages=87–104}}</ref> In 1917, [[Theodore Case]], as part of his work on what became the [[Movietone sound system]], discovered that a mix of thallium and sulfur was much more sensitive, but was highly unstable electrically and proved to be of little use as a practical detector.{{sfn|Rogalski|2000|p=3}} Nevertheless, it was used for some time by the [[US Navy]] as a secure communications system.<ref>{{cite book |last=Fielding |first= Raymond |date=1967 |title= A Technological History of Motion Pictures and Television: An Anthology from the Pages of "The Journal of the Society of Motion Pictures and Television" |publisher=University of California Press |page=179}}</ref>

In 1930 the introduction of the Ag–O–Cs ([[silver]]–[[oxygen]]–[[cesium]]) [[photomultiplier]] provided the first practical solution to the detection of IR, combining it with a layer of galena as the [[photocathode]]. Amplifying the signal emitted by the galena, the photomultiplier produced a useful output that could be used for detection of hot objects at long ranges.{{sfn|Rogalski|2000|p=3}} This sparked developments in a number of nations, notably the UK and Germany where it was seen as a potential solution to the problem of detecting [[night bomber]]s.

In the UK, research was plodding, with even the main research team at [[Cavendish Labs]] expressing their desire to work on other projects, especially after it became clear that [[radar]] was going to be a better solution. Nevertheless, [[Frederick Lindemann]], [[Winston Churchill]]'s favorite on the [[Tizard Committee]], remained committed to IR and became increasingly obstructionist to the work of the Committee who were otherwise pressing for radar development. Eventually they dissolved the Committee and reformed, leaving Lindemann off the roster,{{sfn|Hastings|1999|p=129}} and filling his position with well known radio expert [[Edward Victor Appleton]].<ref>{{cite book |url=https://books.google.com/books?id=TAppUf7bRLgC&pg=PA577 |title=A Scientist's War: The War Diary of Sir Clifford Paterson, 1939-45 |first1=Clifford |last1=Paterson |first2=Robert |last2=Clayton |first3=Joan |last3=Algar |page=577 |publisher= IET |date=1991|isbn=9780863412189 }}</ref>

In Germany, radar research was not given nearly the same level of support as in the UK, and competed with IR development throughout the 1930s. IR research was led primarily by [[Edgar Kutzscher]] at the [[University of Berlin]]<ref>{{cite book |first=Sean |last=Johnston |title=A History of Light and Colour Measurement: Science in the Shadows |publisher=CRC Press |date=2001 |pages=224–225 |isbn=9781420034776 |url=https://books.google.com/books?id=2wNVPfNkLpEC&pg=PA224}}</ref> working in concert with [[AEG (German company)|AEG]].{{sfn|Rogalski|2000|p=3}} By 1940 they had successfully developed one solution; the ''Spanner Anlage'' (roughly "Peeping Tom system") consisting of a detector photomultiplier placed in front of the pilot, and a large searchlight fitted with a filter to limit the output to the IR range. This provided enough light to see the target at short range, and ''Spanner Anlage'' was fitted to a small number of [[Messerschmitt Bf 110]] and [[Dornier Do 17]] [[night fighters]]. These proved largely useless in practice and the pilots complained that the target often only became visible at {{convert|200|m|feet}}, at which point they would have seen it anyway.<ref>{{cite book |first= Robert |last=Forczyk |title= Bf 110 vs Lancaster: 1942-45 |publisher= Osprey Publishing |date=2013 |page=22}}</ref> Only 15 were built and were removed as German airborne radar systems improved though 1942.<ref>{{cite book |first= Alastair |last=Goodrum |title= No Place for Chivalry |date=2005 |publisher=Grub Street |page=109}}</ref>

AEG had been working with the same systems for use on [[tank]]s, and deployed a number of models through the war, with limited production of the [[FG 1250]] beginning in 1943.{{sfn|Rogalski|2000|p=3}} This work culminated in the [[Zielgerät 1229]] ''Vampir'' riflescope which was used with the [[StG 44]] [[assault rifle]] for night use.<ref>{{cite book |first=Chris |last=McNab |title=German Automatic Rifles 1941-45 |publisher=Osprey |date=2013 |pages=63–64 |isbn=9781780963853 |url=https://books.google.com/books?id=qU2kAwAAQBAJ&pg=PA63 }}{{Dead link|date=September 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

===German seekers===
<!-- [[WP:NFCC]] violation: [[File:He 111 - BV 143a Test (1941).jpg|thumb|right|An IR seeker known as ''Hamburg'' would have equipped the BV 143 in the anti-shipping role.]] -->
[[File:Enzian anti-aircraft missile at the Treloar Technology Centre in September 2012.JPG|thumb|right|The ''Madrid'' seeker was being developed for the [[Enzian]] surface-to-air missile.]]

The devices mentioned previously were all ''detectors'', not ''seekers''. They either produce a signal indicating the general direction of the target, or in the case of later devices, an image similar to a television image. Guidance was entirely manual by an operator looking at the image. There were a number of efforts in Germany during the war to produce a true automatic seeker system, both for anti-aircraft use as well as against ships. These devices were still in development when the war ended; although some were ready for use, there had been no work on integrating them with a missile airframe and considerable effort remained before an actual weapon would be ready for use. Nevertheless, a summer 1944 report to the [[German Air Ministry]] stated that these devices were far better developed than competing systems based on radar or acoustic methods.{{sfn|Kutzscher|1957|p=201}}

Aware of the advantages of passive IR homing, the research program started with a number of theoretical studies considering the emissions from the targets. This led to the practical discovery that the vast majority of the IR output from a piston-engine aircraft was between 3 and 4.5 micrometers. The exhaust was also a strong emitter, but cooled rapidly in the air so that it did not present a false tracking target.{{sfn|Kutzscher|1957|p=204}} Studies were also made on atmospheric attenuation, which demonstrated that air is generally more transparent to IR than visible light, although the presence of [[water vapour]] and [[carbon dioxide]] produced several sharp drops in transitivity.{{sfn|Kutzscher|1957|p=206}} Finally, they also considered the issue of background sources of IR, including reflections off clouds and similar effects, concluding this was an issue due to the way it changed very strongly across the sky.{{sfn|Kutzscher|1957|p=207}} This research suggested that an IR seeker could home on a three-engine bomber at {{convert|5|km}} with an accuracy of about {{frac|10}} degree,{{sfn|Kutzscher|1957|p=210}} making an IR seeker a very desirable device.

Kutzscher's team developed a system with the Eletroacustic Company of Kiel known as ''Hamburg'', which was being readied for installation in the [[Blohm & Voss BV 143]] [[glide bomb]] to produce an automated fire-and-forget anti-shipping missile. A more advanced version allowed the seeker to be directed off-axis by the bombardier in order to lock on to a target to the sides, without flying directly at it. However, this presented the problem that when the bomb was first released it was traveling too slowly for the aerodynamic surfaces to easily control it, and the target sometimes slipped out from the view of the seeker. A [[stabilized platform]] was being developed to address this problem. The company also developed a working IR [[proximity fuse]] by placing additional detectors pointing radially outward from the missile centerline, which triggered when the signal strength began to decrease, which it did when the missile passed the target. There was work on using a single sensor for both tasks instead of two separate ones.{{sfn|Kutzscher|1957|p=215}}

Other companies also picked up on the work by Eletroacustic and designed their own scanning methods. AEG and Kepka of Vienna used systems with two movable plates that continually scanned horizontally or vertically, and determined the location of the target by timing when the image disappeared (AEG) or reappeared (Kepka). The Kepka ''Madrid'' system had an instantaneous field of view (IFOV) of about 1.8 degrees and scanned a full 20 degree pattern. Combined with the movement of the entire seeker within the missile, it could track at angles as great as 100 degrees. Rheinmetall-Borsig and another team at AEG produced different variations on the spinning-disk system.{{sfn|Kutzscher|1957|p=216}}

===Post-war designs===
[[File:Hughes MX904 Falcon missile.jpg|thumb|right|The [[AIM-4 Falcon]] was the first IR guided missile to enter service. The translucent dome allows the IR radiation to reach the sensor.]]
[[File:Sidewider missile 20040710 145400 1.4.jpg|thumb|right|The [[AIM-9]] Sidewinder closely followed Falcon into service. It was much simpler than the Falcon and proved far more effective in combat.]]
[[File:Firestreak AAM - Elvington - BB.jpg|thumb|right|[[Firestreak]] was the third IR missile to enter service. It was larger and almost twice as heavy as its US counterparts, much of this due to a larger warhead.]]

In the post-war era, as the German developments became better known, a variety of research projects began to develop seekers based on the PbS sensor. These were combined with techniques developed during the war to improve accuracy of otherwise inherently inaccurate radar systems, especially the [[conical scanning]] system. One such system developed by the [[US Army Air Force]] (USAAF), known as the "Sun Tracker", was being developed as a possible guidance system for an [[intercontinental ballistic missile]]. Testing this system led to the [[1948 Lake Mead Boeing B-29 crash]].<ref name=smithsonianmag70888901>{{cite journal |first=Julian |last=Smith |title=Dive Bomber |journal= Smithsonian Magazine |date=October 2005 |url=http://www.smithsonianmag.com/history/dive-bomber-70888901}}</ref>

USAAF project MX-798 was awarded to [[Hughes Aircraft]] in 1946 for an infrared tracking missile. The design used a simple reticle seeker and an active system to control roll during flight. This was replaced the next year by MX-904, calling for a supersonic version. At this stage the concept was for a defensive weapon fired rearward out of a long tube at the back end of [[bomber aircraft]]. In April 1949 the [[AAM-A-1 Firebird|Firebird]] missile project was cancelled and MX-904 was redirected to be a forward-firing fighter weapon.<ref>{{cite journal |first= Sean |last= O'Connor |title= Arming America's Interceptors: The Hughes Falcon Missile Family |date= June 2011 |website= Airpower Australia |pages= 1 |url= http://www.ausairpower.net/Falcon-Evolution.html |access-date= 2015-09-14 |archive-date= 2015-09-08 |archive-url= https://web.archive.org/web/20150908124557/http://www.ausairpower.net/Falcon-Evolution.html |url-status= live }}</ref> The first test firings began in 1949, when it was given the designation AAM-A-2 (Air-to-air Missile, Air force, model 2) and the name Falcon. IR and [[semi-active radar homing]] (SARH) versions both entered service in 1956, and became known as the [[AIM-4 Falcon]] after 1962. The Falcon was a complex system offering limited performance, especially due to its lack of a proximity fuse, and managed only a 9% kill ratio in 54 firings during [[Operation Rolling Thunder]] in the [[Vietnam War]].<ref name="Dunnigan-2014">{{cite book |first1=James |last1=Dunnigan |first2=Albert |last2=Nofi |title= Dirty Little Secrets of the Vietnam War |publisher= Macmillan |date= 2014 |pages=118–120}}</ref> However, this relatively low success rate must be appreciated in the context of all these kills representing direct hits, something that was not true of every kill by other American AAMs.

In the same year as MX-798, 1946, [[William B. McLean]] began studies of a similar concept at the Naval Ordnance Test Station, today known as [[Naval Air Weapons Station China Lake]]. He spent three years simply considering various designs, which led to a considerably less complicated design than the Falcon. When his team had a design they believed would be workable, they began trying to fit it to the newly introduced [[Zuni (rocket)|Zuni 5-inch rocket]]. They presented it in 1951 and it became an official project the next year. [[Wally Schirra]] recalls visiting the lab and watching the seeker follow his cigarette.{{sfn|Hollway|2013}}  The missile was given the name [[AIM-9 Sidewinder|Sidewinder]] after a local snake; the name had a second significance as the [[Crotalus cerastes|sidewinder]] is a [[pit viper]] and hunts by heat, and moves in an undulating pattern not unlike the missile.<ref name=airspacemag57687913>{{cite journal |first=Preston |last=Lerner |title=Sidewinder |journal=Air and Space Magazine |date=November 2010 |url=http://www.airspacemag.com/military-aviation/sidewinder-57687913/?no-ist |access-date=2015-09-11 |archive-date=2015-10-02 |archive-url=https://web.archive.org/web/20151002230107/http://www.airspacemag.com/military-aviation/sidewinder-57687913/?no-ist |url-status=live }}</ref> The Sidewinder entered service in 1957, and was widely used during the Vietnam war. It proved to be a better weapon than the Falcon: B models managed a 14% kill ratio, while the much longer-ranged D models managed 19%. Its performance and lower cost led the Air Force to adopt it as well.<ref name="Dunnigan-2014"/><ref>{{cite encyclopedia |first=Marcelle |last=Size Knaak |title=F-4E |encyclopedia= Encyclopedia of US Air Force aircraft and missile systems  |publisher= US Air Force History Office, DIANE Publishing |year=1978 |page=278 }}</ref>

The first heat-seeker built outside the US was the UK's [[de Havilland Firestreak]]. Development began as OR.1056 [[Red Hawk missile|Red Hawk]], but this was considered too advanced, and in 1951 an amended concept was released as OR.1117 and given the code name [[Blue Jay (missile)|Blue Jay]]. Designed as an anti-bomber weapon, the Blue Jay was larger, much heavier and flew faster than its US counterparts, but had about the same range. It had a more advanced seeker, using PbTe and cooled to −180&nbsp;°C (−292.0&nbsp;°F) by [[anhydrous ammonia]] to improve its performance. One distinguishing feature was its faceted nose cone, which was selected after it was found ice would build up on a more conventional hemispherical dome. The first test firing took place in 1955 and it entered service with the [[Royal Air Force]] in August 1958.<ref>{{Cite book  | last1 = Gibson| first1 = Chris  | first2 = Tony| last2 = Buttler  | title = British Secret Projects: Hypersonics, Ramjets and Missiles  | publisher = Midland  | date= 2007  | pages = 33–35 }}</ref>

The French [[R.511|R.510]] project began later than Firestreak and entered experimental service in 1957, but was quickly replaced by a radar-homing version, the R.511. Neither was very effective and had short range on the order of 3&nbsp;km. Both were replaced by the first effective French design, the [[R.530]], in 1962.<ref>{{cite journal |title=Matra R.511 |journal=Flight International |page=714 |date=2 November 1961}}</ref>

The Soviets introduced their first infrared homing missile, the [[Vympel K-13]] in 1961, after reverse engineering a Sidewinder that stuck in the wing of a Chinese [[MiG-17]] in 1958 during the [[Second Taiwan Strait Crisis]]. The K-13 was widely exported, and faced its cousin over Vietnam throughout the war. It proved even less reliable than the AIM-9B it was based on, with the guidance system and fuse suffering continual failure.<ref name="Dunnigan-2014"/>

===Later designs===
[[File:SRAAM missile.jpg|thumb|right|SRAAM was designed to address most of the problems found with earlier IR missiles in a very short-range weapon.]]
[[File:AIM-9L DF-ST-82-10199.jpg|thumb|right|More than half a century after its introduction, upgraded versions of the Sidewinder remain the primary IR missile in most western air forces.]]
[[File:R-73.jpg|thumb|right|The R-73 was a leap forward for Soviet designs, and cause for considerable worry among western air forces.]]

As Vietnam revealed the terrible performance of existing missile designs, a number of efforts began to address them. In the US, minor upgrades to the Sidewinder were carried out as soon as possible, but more broadly pilots were taught proper engagement techniques so they would not fire as soon as they heard the missile tone, and would instead move to a position where the missile would be able to continue tracking even after launch. This problem also led to efforts to make new missiles that would hit their targets even if launched under these less-than-ideal positions. In the UK this led to the [[SRAAM]] project, which was ultimately the victim of continually changing requirements.<ref name=19810606flightglobal>{{cite journal |url=http://www.flightglobal.com/pdfarchive/view/1981/1981%20-%201812.html |title=ASRAAM - Europe's new dogfight missile |journal=Flight International |date=6 June 1981 |page=1742 |access-date=9 October 2015 |archive-date=7 January 2018 |archive-url=https://web.archive.org/web/20180107232853/https://www.flightglobal.com/pdfarchive/view/1981/1981%20-%201812.html |url-status=live }}</ref> Two US programmes, [[AIM-82]] and [[AIM-95 Agile]], met similar fates.<ref>{{cite journal |title=Naval Weapons Center AIM-95 Agile |journal=Flight International |date=8 May 1975 |page=765}}</ref>

New seeker designs began to appear during the 1970s and led to a series of more advanced missiles. A major upgrade to the Sidewinder began, providing it with a seeker that was sensitive enough to track from any angle, giving the missile ''all aspect'' capability for the first time. This was combined with a new scanning pattern that helped reject confusing sources (like the sun reflecting off clouds) and improve the guidance towards the target. A small number of the resulting L models were rushed to the UK just prior to their engagement in the [[Falklands War]], where they achieved an 82% kill ratio, and the misses were generally due to the target aircraft flying out of range.{{sfn|Hollway|2013}} The Argentine aircraft, equipped with Sidewinder B and [[R.550 Magic]], could only fire from the rear aspect, which the British pilots simply avoided by always flying directly at them. The L was so effective that aircraft hurried to add flare countermeasures, which led to another minor upgrade to the M model to better reject flares.{{Citation needed|date=November 2024}} The L and M models would go on to be the backbone of Western air forces through the end of the [[Cold War]] era.

An even larger step was taken by the Soviets with their [[R-73 (missile)|R-73]], which replaced the K-13 and others with a dramatically improved design. This missile introduced the ability to be fired at targets completely out of view of the seeker; after firing the missile would orient itself in the direction indicated by the launcher and then attempt to lock on. When combined with a [[helmet mounted sight]], the missile could be cued and targeted without the launch aircraft first having to point itself at the target. This proved to offer significant advantages in combat, and caused great concern for Western forces.<ref name=":0">{{cite web |publisher=Federation of American Scientists |title=AA-11 ARCHER R-73 |url=http://fas.org/man/dod-101/sys/missile/row/aa-11.htm |date=3 September 2000 |access-date=9 October 2015 |archive-date=2 September 2016 |archive-url=https://web.archive.org/web/20160902160451/http://fas.org/man/dod-101/sys/missile/row/aa-11.htm |url-status=dead }}</ref>

The solution to the R-73 problem was initially going to be the [[ASRAAM]], a pan-European design that combined the performance of the R-73 with an imaging seeker. In a wide-ranging agreement, the US agreed to adopt ASRAAM for their new short-range missile, while the Europeans would adopt [[AMRAAM]] as their medium-range weapon. However, ASRAAM soon ran into intractable delays as each of the member countries decided a different performance metric was more important. The US eventually bowed out of the program, and instead adapted the new seekers developed for ASRAAM on yet another version of the Sidewinder, the AIM-9X.{{Citation needed|reason=Some sort of citation is required for the trajectory and eventual outcome of these negotations|date=November 2024}} This so extends its lifetime that it will have been in service for almost a century when the current aircraft leave service. ASRAAM did, eventually, deliver a missile that has been adopted by a number of European forces and many of the same technologies have appeared in the Chinese PL-10 and Israeli [[Python (missile)|Python-5]].{{Citation needed|date=November 2024}}

===MANPADs===
[[File:Launched FIM-92A Stinger missile.jpg|thumb|The Stinger has been used in Afghanistan since 1986. It was provided to the anti-Soviet forces by the US]]
Based on the same general principles as the original Sidewinder, in 1955 [[Convair]] began studies on a small man-portable missile ([[MANPADS]]) that would emerge as the [[FIM-43 Redeye]]. Entering testing in 1961, the preliminary design proved to have poor performance, and a number of major upgrades followed. It was not until 1968 that the Block III version was put into production.<ref name="Cagle-1974">{{cite tech report |first=Mary |last=Cagle |title=History of the Redeye Weapon System |publisher=Historical Division, Army Missile Command |date=23 May 1974 |url=https://fas.org/asmp/campaigns/MANPADS/2005/redeye.pdf |access-date=11 September 2015 |archive-date=29 March 2016 |archive-url=https://web.archive.org/web/20160329151913/https://fas.org/asmp/campaigns/MANPADS/2005/redeye.pdf |url-status=dead }}</ref>

The Soviets started development of two almost identical weapons in 1964, Strela-1 and Strela-2. Development of these proceeded much more smoothly, as the [[9K32 Strela-2]] entered service in 1968 after fewer years of development than the Redeye.<ref>Jane's Land Based Air Defence 2005–2006.</ref> Originally a competing design, the [[9K31 Strela-1]] was instead greatly increased in size for vehicle applications and entered service at around the same time. The UK began development of its [[Blowpipe (missile)|Blowpipe]] in 1975, but placed the seeker on the launcher instead of the missile itself. The seeker sensed both the target and the missile and sent corrections to the missile via a radio link. These early weapons proved ineffective, with the Blowpipe failing in almost every combat use,<ref>{{cite journal |first1= Lester |last1= Grau |first2= Ali |last2= Ahmad Jalali |title= The Campaign For The Caves: The Battles for Zhawar in the Soviet-Afghan War |journal= The Journal of Slavic Military Studies |date= September 2001 |url= http://fmso.leavenworth.army.mil/documents/zhawar/zhawar.htm |quote= 13 Blowpipe missiles fired for no hits |doi= 10.1080/13518040108430488 |volume= 14 |issue= 3 |pages= 69–92 |s2cid= 144936749 |url-status= dead |archive-url= https://web.archive.org/web/20051113125550/http://fmso.leavenworth.army.mil/documents/zhawar/zhawar.htm |archive-date= 2005-11-13 |url-access= subscription }}</ref> while the Redeye fared somewhat better. The Strela-2 did better and claimed a number of victories in the middle east and Vietnam.<ref name="Arms-Expo.ru">{{cite web|url=http://www.arms-expo.ru/site.xp/049051049050124052050050.html|archive-url=https://web.archive.org/web/20110126065453/http://www.arms-expo.ru/site.xp/049051049050124052050050.html|archive-date=2011-01-26 |title="Стрела-2" (9К32, SA-7, Grail), переносный зенитный ракетный комплекс — ОРУЖИЕ РОССИИ, Информационное агентство |publisher=Arms-expo.ru |access-date=2013-08-24}}</ref>

A major upgrade program for the Redeye started in 1967, as the Redeye II. Testing did not begin until 1975 and the first deliveries of the now renamed [[FIM-92 Stinger]] began in 1978. An improved rosette seeker was added to the B model in 1983, and several additional upgrades followed. Sent to the [[Soviet–Afghan War]], they claimed a 79% success rate against Soviet helicopters,<ref>{{cite book |first1= Ray |last1=Bonds |first2=David l|last2=Miller |title= Illustrated Directory of Special Forces |date=13 February 2003 |url=https://books.google.com/books?id=FMgpdulJsGgC&pg=PA359 |page=359|publisher=Voyageur Press |isbn=9780760314197 }}</ref> although this is debated.<ref>{{cite web |first= Leonard |last= Leshuk |title= Stinger Missiles in Afghanistan |year= 2008 |url= http://europauniversitypress.co.uk/auth_article416.html |access-date= 2015-09-16 |archive-date= 2017-12-26 |archive-url= https://web.archive.org/web/20171226014714/http://europauniversitypress.co.uk/auth_article416.html |url-status= live }}</ref> The Soviets likewise improved their own versions, introducing the [[9K34 Strela-3]] in 1974, and the greatly improved dual-frequency [[9K38 Igla]] in 1983, and Igla-S in 2004.<ref name=":0" />