The Sidewinder Story / The Evolution of the AIM-9 Missile (2024)

The AIM-9L/M seeker used theaerodynamic design of the AIM-9H with a new all aspect InSb baseddetector . The example is carried by an RAAF Hawk (© 2009 Dr CarloKopp; Fuji S5600).

The ubiquitous AIM-9 Sidewinderis without doubt the most important heatseeking missile of the lastthree decades, seeing service in every engagement between Westernpowersand their adversaries since the 1950s. Shamelessly copied by theCommunists as the K-13/AA-2 Atoll, the Sidewinder has had a profoundinfluence on the design of modern heatseekers and is much the yardstickagainst which such missiles are judged today.

Thecollapse of the agreement between the US and EEC nations on the ASRAAM,the planned successor to the AIM-9, has seen further life injected intothe humble Sidewinder, with the US at the time of writing electing tocontinue the development and production of the weapon for its ownservices.

TheAIM-9 has had a colourful history and has evolved considerably sincethefirst of its kind left a missile rail in the distant fifties. It isstory of technical ingenuity as much as operational application andmorethan anything underscores the fundamental soundness of the basicairframe and system design, which has seen ongoing evolutionarydevelopment since the fifties.

The AIM-9 traces its earliest ancestry to the US Naval Weapons Centerat China Lake, in the Mojave Desert. THe NWC initiated, in the earlyfifties, a program to design a heatseeking air intercept missile fortheintercept of bombers by naval interceptor aircraft, until then armedwith either .50 cal or 20 mm guns. The fledgling missile was aptlynamedafter the Sidewinder, a desert rattlesnake which detects its prey bysensing the animal's heat emissions.

Theresult was a compact lightweight cruciform canard weapon, which used asolid propellant rocket motor, a fragmentation warhead and an uncooledoptical seeker.

TheSidewinder's seeker used an ingeniously clever optical arrangement,witha Cassegrainian mirror fitted with a tilted secondary mirror. Thesecondary mirror rotated in unison with a reticle, projecting the wholeinstantaneous field of view of the mirror through the reticle onto afilter/detector assembly. Because the mirror secondary was tilted,rotating it about the missile's axis swept the cone of the mirror'sfield of view about the missile's axis in a fashion analogous to aconical scanning radar seeker (see diagram).

Themissile used a 2.5" glass dome nose window, transparent to 1 micronbandradiation, providing with the gimballed seeker for a 25 degree seekerfield of view. The mirror assembly provided a 4 degree instantaneousfield of view (IFOV), projected on to a PbS (Lead Sulphide) uncooleddetector. Because of the design of the optical system, the AIM-9B wasstrictly a tail aspect weapon, as it was blind to anything cooler thanatailpipe. The modest 11 deg/sec seeker tracking rate limited the weaponto non-maneuvering targets. All seeker electronics were built fromvacuum tubes. A hot gas generator provided actuator power for the nosecanards, and was limited to a 20 sec burn duration before exhaustion.Unlike other missiles of the day, the Sidewinder did not employ activeroll stabilisation (via gyros and differential control input), insteademploying rollerons, ie slipstream spun metal discs embedded in thetrailing edge of the wingtips, which acted as four tiny gyrosstabilising the missile mechanically. The engineer who thought of thatcertainly earned his paycheck.

TheAIM-9B used a fragmentation warhead triggered by a passive infraredproximity fuse. The Thiokol Mk.17 solid propellant rocket delivered8,200 lb-sec of impulse with a burn duration of 2.2 seconds.

While by modern standards the AIM-9B is a very limited weapon, it hadnoserious competitors in its day and was soon adopted by the USAF andNATOas a standard weapon, with no less than 40,000 guidance units built byFord Aerospace, the prime contractor. The RAAF also adopted themissile,fitting it to the CAC Avon-Sabre, and subsequently the Mirage.

NATOrounds were mainly built by West Germany's FGW, who evolved an improvedsubtype designated the AIM-9B-FGW Mod.2. This AIM-9B used solid stateelectronics, carbon dioxide seeker cooling, a new nose dome and betteroptical filtering, the latter providing for much better seekersensitivity.

TheSidewinder was by the early sixties the principal heatseeker in Westernservice and as such first drew blood over North Vietnam, there used bythe USAF and USN. Its early combat record was not spectacular, as theseeker performance limitations were exacerbated by the poor reliabilityof the tube electronics and the inexperience of its users, who untilthen trained for intercepts rather than dogfights. Kill probabilitieswere in the tens of percent, very sensitive to how well the launchaircraft was positioned. Designed to intercept lumbering bombers, theAIM-9B was ill suited to knife-fights with MiG-17s at low level. Itslaunch load factor limit of 2G hampered aircrew, while its seeker veryoften locked on to the sun or clouds, subsequently sending the missileballistic. The range limit of 2.6 NM meant that the launch aircraft hadto be quite properly positioned for a shot, and the pilot very carefulabout closure rate and range.

Nevertheless, no less than 28 MiGs were killed for 175 launches between1965 and 1968, by USAF F-4C/D aircraft, an aggregate P[k] (killprobability) of 16%.

The US Navy recognised the limitations of the AIM-9B during the earlyfifties, and soon proceeded with the development of a follow-on subtypewith improved performance. Thus was born the first of a series ofdedicated naval Sidewinders, a split in the family tree which persiststo this very day.

Themost important change in the AIM-9D was the use of a Nitrogen coolingsystem for the PbS detector element, coupled to a redesigned opticalsystem. The new optical system retained the tilted cassegrain of theearlier subtype, but was more compact, fitting into a ogival nosesection, and spun at a higher frequency of 125 Hz, rather than the 70Hzof the B-model. The IFOV was reduced to 2.5 degrees, while the seekerFOV was slightly increased to beyond 25 degrees. The glass nose domewasreplaced by a much smaller Magnesium Fluoride dome, which providesbetter transparency to longer wavelength (cooler) infrared emissions.

TheNitrogen coolant was contained in a 6 litre bottle in the Navy LAU-7launcher, and provided for 2.5 hrs of seeker cool down.

Theseeker changes provided a higher target tracking rate of 12 deg/sec,andthis was further assisted by an improved actuator system, whichdelivered up to 100 lb.ft of torque. Both of these measures improvedmissile manoeuvrability, while a longer gas generator burn provided fora 60 second usable flight time. The rocket motor was changed to aHercules Mk.36, with more impulse and longer burn.

Changes were also introduced to the fusing, with the option of aninfrared fuse or a radio-frequency proximity fuse, which fired a newcontinuous rod warhead. Continuous rod warheads have a casing oflengthwise rods welded together at alternate ends, on detonation therods expand into a circle about the missile before breakup, upon whichatorus of fragments is produced about the axis of the weapon. These rodsare like knives which chop into the skin and structure of the target.

Incomparison with the AIM-9B, the AIM-9D had a much wider engagementenvelope, was more manoeuvrable and hence offered a better P[k]. TheAIM-9D entered production in the late fifties, and Ford Aerospace builtabout 1,000 systems.

TheAIM-9D was succeeded by the very similar AIM-9G, which employed SEAM(Sidewinder Extended Acquisition Mode), a facility which slews theoptics through a search pattern to acquire the target (most likelyusinga rosette scan), or allows slaving of the optics to radar or a helmetsight. The latter was used extensively by Navy F-4s during theseventies, before the deployment of the F/A-18.

TheAIM-9D/G was used extensively by the Navy in Vietnam, accounting formany kills of manoeuvrable adversaries such as the nimble MiG-17 andMiG-19, engaging Navy aircraft at low altitude. Most Navy kills werescored with this weapon.

Thelatter phase of the Vietnam war, the Linebacker campaigns, saw thefirstapplication of the subsequent naval Sidewinder, the AIM-9H. The Hotelsaw some radical changes resulting from experience with the D/G, whichsuffered reliability problems due the intolerance of vacuum tubes torepeated 20 ft/sec sink rate recoveries on aircraft carrier decks. TheAIM-9H was the first solid state Sidewinder, with the complete guidancepackage built with semiconductors. In redesigning the electronics, theGoptical system was essentially retained, but the tracking rate wasfurther increased, to complement the more powerful 120 lb.ft actuators.

While few of the AIM-9H were fired in combat due shortages of supply,they are reported to have scored a much higher kill rate per launchthanany other Sidewinder in the campaign. Over 3,000 were built.

The AIM-9H was by far the best of the earlySidewinders and distinguished itself in Vietnam achieving the best killrate of any missile in the campaign. Using a solid state seeker with aNitrogen cooled Lead Sulphide detector, and a more powerful actuatorsystem, the AIM-9H was the most manoeuvrable of its kind. ThesubsequentAIM-9L was directly derived from the AIM-9H.

Unlike the USN which was focussed on the tactical air battle, the USAFhad diluted its resources into several AAM programs and thus lagged inthe development of their own Sidewinder subtypes. Vietnam saw theAIM-9Bperform questionably, and the USAF sought improvements to the design toenhance performance against fighter type targets. The result was theAIM-9E.

TheAIM-9E saw the adoption of a similar low drag nose to the Navysubtypes,but using a conical rather than ogival profile, a distinguishingfeatureof this family to this very day. A Magnesium Fluoride dome was adopted,a more compact optical assembly was used, with a faster 100 Hz reticlerate, and a 16.5 deg/sec tracking rate. The canards were changed to thecharacteristic squared tip double delta planform, adopted to improvecanard behaviour at higher angles of attack. Significant changes weremade to the internal wiring harnesses.

Themost significant design change was the adoption of a cooling for thePbSdetector element, the USAF opting for Peltier thermoelectric cooling.This arrangement has the advantage of unlimited cooling time on thelaunch rail, subject only to the availability of electrical power. Theseeker improvements expanded the weapon's acquisition envelope andincreased its P[k], although not dramatically. Over 5,000 rounds wererebuilt from AIM-9Bs.

TheAIM-9E was deployed to SEA in the late sixties, and saw considerableuseby the USAF. Because most USAF engagements were flown at higheraltitudes, the weapon was used far less often than the Sparrow, and atshort ranges the USAF F-4E nd F-105D/F/G tended to rely on the internalM-61 gun, therefore the AIM-9 accounted for only 14% of USAF kills.Arguably this environment produced less pressure for improvements inUSAF AIM-9 performance, resulting in the use of less capable versionsincomparison with the Navy, whose F-4Bs were armed solely with missiles.

Aninteresting idiosyncrasy of the Vietnam period Sidewinders was how theykilled their targets, as they invariably pursued their targets and inmost instances flew up the tailpipe, bisecting the MiG aft of the wingupon warhead detonation. Much interesting gun camera footage exists.

AIM-9J launch from US Air ForceF-4D Phantom (US Air Force image).

Thefollow-on version to the AIM-9E was the AIM-9J, which was rushed intothe SEA theatre in July, 1972. The Juliet model saw incrementalimprovements to the AIM-9E design, with hybrid electronics using a mixof solid state and tube technology, and an improved control systemusinga longer burning gas generator for a 40 sec flight time, and morepowerful actuators delivering 90 lb.ft torque to the canards. 6,700 ofthis subtype were eventually built or rebuilt from AIM-9Bs.

In1973, Ford began production of an enhanced AIM-9J-1, later redesignatedthe AIM-9N. The November model employed a similar configuration to theJuliet, but the three main printed circuit boards were substantiallyredesigned to improve seeker performance. Close to 7,000 of thisversionwere built. The Hercules-Aerojet Mk.17 rocket motor was retained.

AIM-9 EARLY SUBTYPECOMPARISON TABLE

Author's note:

This table wascompiled from a wide range of sources, many of which do notspecify the exact conditions under which the statedperformance figures apply. Therefore caution must be exercised ininterpreting the figures. Since newer variants are stillcurrent in service, detailed figures for these are hard to acquire.

The lessons of Vietnam and the Yom Kippur clearly indicated thelimitations of the established Sidewinder subtypes, which did notperform well at low altitudes due background infrared emitted by theearth's surface and reflected by clouds, and were limited to tailhemisphere engagements due to the spectral range of the PbS detectorelement used. The need for all aspect capability against agile targetsdictated changes in both detector material and proximity fuse, as thepassive IR fuses used to date relied on sensing the target's exhaust atclose range. Much debate took place in the mid-seventies as to thesuccessor to the Sidewinder, with a USN proposal for a modified AIM-9Heventually adopted as offering the lowest risk. A West German proposalto fit a fully gimballed seeker to the AIM-9H airframe, creating theALASCA (all aspect capability) missile was dropped.

TheAIM-9L is essentially an AIM-9H with a new optical system, new fuse andnew cooling system. The Cassegrain system of the H was retained, but anew FM reticle was adopted, necessitating some fundamental changes tothe guidance electronics. A new 4 micron band Indium Antimonide (InSb)detector was used, enclosed with an optical filter in a cryogeniccontainer. This optical system allows acquisition and tracking oftargets from all aspects, due the longer wavelength sensitivity of theInSb, with the filter employed to reject shorter wavelengths. Argon gasis used to cool the detector, with the coolant tank embedded in themissile's seeker to allow use with arbitrary physically/electricallycompatible launchers.

TheFM reticle provides superior performance by reducing the effect of atarget's increasing size with decreasing range on the seeker errorsignal output, a factor which can affect the behaviour of AM seekers,while providing the potential for better countermeasures rejection. Inaddition, design changes were adopted to bridge the dead zone about themissile's immediate boresight, a characteristic of conventional reticleseekers. To widen the manoeuvre envelope, lambda compensation isemployed, a technique which prevents the seeker from reaching itsangular limit during the early phase of its flight. If a target canforce the seeker past its angular limit, lock is broken and the missilelost.

Thecontrol actuators of the AIM-9H were retained, but the canards wereredesigned to the characteristic pointed tip double delta. Thecombination of new seeker and canards results in much better manoeuvreperformance than any earlier subtype, while the new detector allowsacquisition of targets from any aspect at substantially greater ranges.

This 3SQN RAAF F/A-18 is armed with an AIM-9L, thefirst all aspectSidewinder to be deployed. The AIM-9L was a key factor in the RoyalNavy's Falklands success, achieving a kill probability in excess of 80%per launch. The AIM-9L uses the optical system of the AIM-9H, modifiedfor an FM reticle and fitted with an Argon cooled Indium Antimonidedetector element. With modified canards to enhance the manoeuvrabilityof the AIM-9H airframe, and an active laser fuse and annular blastwarhead, the AIM-9L was a highly effective dogfight missile (© 1995 Dr CarloKopp; M645/1000S with Sekor C 80 mm f2.8).

Theneed to engage dogfight targets required a better fuse and warhead. TheAIM-9L was the first subtype to introduce an active laser proximityfuse, the DSU-15A/B. This device uses a group of Gallium Arsenide(GaAs)solid state lasers which radiate a spoke-like pattern about themissile,each laser is paired to a Silicon (Si) photodiode. The lasers emit astream of pulses, which are reflected by an object which enters thefusepattern, and sensed by the photodiodes, triggering warhead detonation.The scheme is highly resistant to jamming.

Thewarhead is also more lethal, using an annular blast arrangement withtwolayers of rods, which are specifically designed to tumble at high speedto ensure that their effectiveness is not reduced by impact angle onthetarget, a limitation of the conventional continuous rod scheme.

TheLima entered service in the late seventies and first drew blood in1982,used in both the Falklands campaign and the Bekaa Valley air battle. Inboth campaigns the weapon was a star performer, achieving killprobabilities in excess of 80%. Royal Navy Harriers and Israeli F-15sslaughtered their opponents in head-on shootouts, the haplessArgentinesand Syrians never devising suitable evasive manoeuvres. Over 5,500rounds were built and were sold only to trusted allies, with licencedproduction by Bodenseewerk in Germany and Mitsubishi in Japan.

The AIM-9M is an improved AIM-9L, with a low smokemotor, better guidance and counter-countermeasures capability. TheAIM-9M is the principal dogfight missile used by frontline Western airforces, and also equips the FAF's F/A-18 force. The AIM-9M wasresponsible for all of the 10 Sidewinder kills scored during the Gulfconflict, with most kills scored by the longer ranging Sparrow due theIraqis' reluctance to engage in dogfights.

TheLima was followed in production in 1982 by the AIM-9M, which isessentially an improved AIM-9L. The Mike has improved backgroundrejection, counter-countermeasures capability and a low smoke motor toreduce the visual signature of the inbound weapon. The latest subtypesdue for deployment are the AIM-9M-8 (Navy) and AIM-9M-9 (USAF). TheAIM-9M is the RAAF's standard dogfight AAM, carried by the F/A-18 andF-111.

TheAIM-9M was deployed in large numbers during last year's Gulf war, butonly several kills were achieved as the Iraqi air force preferred toletit*elf be taken out with six o'clock Sparrow shots. Were they to havedone the proper thing and put up a serious fight, the the statisticsmayhave been different, albeit the eventual outcome identical.

While the AIM-9L fulfilled the role of the frontline all aspectdogfightmissile, a need still existed for a second tier weapon for use in lessdemanding situations, and also suitable for export to less thanabsolutely trusted allies. This requirement was fulfilled by the AIM-9Pfamily, derivatives of the AIM-9J/N.

TheAIM-9P-2 and P-3 were introduced in the mid seventies and use improvedguidance electronics, a new rocket motor and an active optical fuse.While not receiving the publicity of the AIM-9L, the success of theweapon is testified to by the fact that no less than 21,000 have beenbuilt, with substantial numbers in the USAF inventory.

AIM-9P-4 engages a QF-102Adrone(US Air Force).

The AIM-9P is a USAF sponsored development of the AIM-9J/Nfamily, to provide a missile for use in less demanding applications.The AIM-9P has evolved through the P-2, P-3 to the all aspect P-4, andthe P-5 with additional counter-countermeasures capability. Largenumbers of various AIM-9P subtypes are in use with the USAF and manyexport customers. The missile retains the conical nosecone andcharacteristic double delta canards first used in the Vietnam era USAFAIM-9E.

AIM-9P-3onF-15 Eagle (US Air Force)

TheAIM-9P-4 is an incremental development of the AIM-9P-3, with an allaspect seeker using some of the technology developed for the AIM-9L. Incomparison with its cousin, it is less agile but still a very effectivemissile. The AIM-9P-5 is further improved by the addition of acounter-countermeasures capability. The wide range of types which cancarry the P-3/4/5 suggest that the gas coolant is carried on board, aswith the L/M.

TheSidewinder family has spawned but one radar guided subtype, the US NavyAIM-9C semi-active radar homing missile. This weapon was designed toarmthe lightweight F-8 Crusader with an all weather missile, and used aconically scanning semi-active seeker. No records exist as to themissile's combat record and it was all but forgotten until the mideighties, when stocks of several hundred rounds were resurrected fromstorage to fulfill a Marine Corps requirement for a lightweightAnti-Radiation Missile for suppression of air defences.

TheAGM-122A Sidearm is essentially a rebuilt AIM-9C, in which the narrowband semi-active seeker electronics have been modified for the muchgreater bandwidth required to home in on a wide range of radars. Inaddition, the later DSU-15 active fuse was used, while the Mk.17 motorand WDU-17 warhead were retained. The control electronics were alsomodified to command an immediate pop-up after launch at low level, toprovide for a dive attack on the offending emitter.

TheAGM-122A was developed by the NWC and subsequent remanufacturingcarriedout by Motorola, the status of the program is at this time unclear. Theweapon in no way compares with serious ARMs such as the HARM and ALARM,and is easily seduced by countermeasures, but provides a useful meansofsuppressing unfriendly attention by systems such as the ZSU-23 or SA-8.No reports exist on combat use, the weapon was built to equip MarineAV-8s, A-4s and helicopters.

TheAIM-9R is the latest production Sidewinder, using an imaging seekerwhich is a fundamental departure from the established design. Developedby the Naval Weapons Center, the AIM-9R uses a modified AIM-9M controlactuator, while retaining the fuse, warhead, motor, wings and canardsofits predecessor.

Theimaging seeker is built around a focal plane array imaging device,analogous to the CCDs employed in modern television cameras. A focalplane array has a much greater instantaneous field of view than areticle seeker, and 'stares' at the target and its immediatebackground,tracking the target by means of a contrast lock similar to thatemployedby TV guided weapons such as Maverick or GBU-15. In this fashion, theseeker can account for the background contrast and reject it, whilealsoproviding the potential to discriminate between multiple targets andcountermeasures such as flares. Conventional pulse jammers have noeffect.

TheWGU-19 seeker uses a three gimbal stabilised platform mounting avisibleband focal plane array device, most likely a 256 x 256 element InSbarray, or a higher resolution PtSi device on a Peltier cooledsubstrate,to provide coverage down to the 4 micron band. The video signalproducedby the array is then digitised and processed by a software programmabledigital image processor, which tracks the targets and feeds theautopilot with data so it can send steering commands to the controlactuators.

The imaging AIM-9R is the latest naval Sidewinder,using the airframe, fuse and motor of the AIM-9M with a new digitalimaging seeker. The new seeker employs a focal plane array imagingdevice effective to visual wavelengths, mounted on a gimballedstabilised platform. The use of the imaging seeker has provided a vastimprovement in target detection range, off boresight angle, rejectionofbackground and ability to selectively aim for vulnerable areas of thetarget. Imaging seekers are immune to jamming techniques effectiveagainst reticle seekers.

TheAIM-9R provides a major increase in target acquisition range overestablished subtypes, with much better tracking performance, and theability to reject both background terrain and clouds. The total fieldofview of the seeker is much greater, allowing acquisition ofoff-boresight and manoeuvring targets, while the software provides forintelligent selection of an aimpoint when impacting a target. LoralAeronutronic, the manufacturer, claim effective counter-countermeasurescapability against known and postulated jamming or seduction techniques.

Atthe time of writing (1994) the AIM-9R had successfully flown livefiringtrials, and was in pilot production, with its long term future uncleardue ongoing defence cuts.

Thefollow on to the AIM-9M/R in joint service use is the AIM-9X, at thistime still very much a development exercise intended for deployment inthe late 1990s. (Author's note: this feature article predates the finalUS decision on the AIM-9X configuration, which is to use an SBRC 128^2InSb FPA seeker, digital autopilot, fixed forward canards, andsteerabletail surfaces and thrust vectoring, retaining the original motor).

TheAIM-9X has yet to be firmly defined, but reports indicate the weaponwill probably employ tail control with smaller or no canards. Twoairframe geometries will be used, a conventional layout for use byconventional aircraft, and a flat bottomed layout for conformalcarriageby stealthy fighters. The flat bottomed airframe is carried upside downand rolls itself upright after launch, a side benefit of this scheme isthe potential to use the shape for lifting purposes, if an active rollstabilising system is used.

Theseeker proposed is a focal plane array, possibly coupled to passiveradar homing for use as an ARM or semi-active homing weapon. The formerarrangement is used for instance by the GD RAM point defence SAM,interestingly enough itself using a modified AIM-9L/M seeker, and thelatest AIM-7 subtype, which also uses an AIM-9L/M seeker.

Raytheon, a second source for later model AIM-9s, have under USAFsponsorship expended three years of effort in developing a tailcontrolled canardless AIM-9 airframe. While most of the details areclassified, the weapon uses the standard 5" airframe of the existingAIM-9, with no canards, and a tail control system using a set of small11" span cruciform movable fins which are arranged in a 60 degree/120degree pattern, unlike the symmetrical tail of the existing AIM-9.

Thetail control missile is much faster due lower drag, and hasdemonstratedin tests higher peak speeds and load factors. A Raytheon designeddigital autopilot was fitted, providing for active roll control andreportedly resulting in better stability and manoeuvrability than theestablished design.

Livefiring tests carried out by the USAF 3245th Test Wing at Eglin inFlorida during the 1990/91 period saw eight launches, of which fiveweredirect hits, one a would be lethal near miss, one a miss and onecontrolsystem test flight without a target. These weapons employed standardAIM-9M seekers.

Muchof the USAF's interest in the tail control Sidewinder stems from theATFprogram, as the F-22 has small internal weapon bays unable to house thestandard Sidewinder.

TheNaval Weapons Center has also been working on modified AIM-9Ms undertheBoa-M program, in which a standard airframe was fitted with smallerAIM-9D canards and a smaller lower drag set of tail surfaces, and adigital autopilot. At least one test firing is known to have beencarried out, to the detriment of a QF-86 drone.

Boththe USAF and USN programs are aimed at size and drag reduction, andhigher agility by the use of artificial stability.

AIM-9 LATE SUBTYPE COMPARISONTABLE

Author'snote:

This table wascompiled from a wide range of sources, many of which do notspecify the exact conditions under which the statedperformance figures apply. Therefore caution must be exercised ininterpreting the figures. Since newer variants are stillcurrent in service, detailed figures for these are hard to acquire.

The Atoll traces its genealogy to the early AIM-9B. Numerous storiesexist on how the AIM-9 fell into communist hands. One suggests aturncoat German officer drove some friendly GRU agents to a Luftwaffebase and loaded an AIM-9 into a truck, subsequently transporting itacross the Iron Curtain. Another more probable story refers to adogfight between the Nationalist Chinese and Red Chinese over theFormosa straights in the early sixties, during which an AIM-9B embeddeditself in the fuselage of a Shenyang F-6 fighter where it failed todetonate.

Whichever way it transpired, the communists by the late sixtiesdeployed a missile which was very hard to distinguish from the AIM-9B.Many USAF aircraft in Vietnam fell to sniping tail aspect GCI hits byAtoll firing MiG-21s or F-8s, and the Atoll has since become the mostcommon heatseeking missile in Third World use.

Like the AIM-9B, the Atoll requires a skilled user to be effective atit* best, and therefore in Third World confrontations the weapon hasbeen of questionable usefulness. Well, at least it looks like aSidewinder !

The Sidewinder has stood the test of time, and spending 40 years at thecutting edge is a tribute to its original designers, who can be justlyproud of their basic design. While its newer derivatives may lookdifferent and use different guidance principles, they will all tracetheir ancestry to the Naval Weapons Centre's original fifties program.The Sidewinder must be acknowledged as the most successful heatseekingmissile design of all times.