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TheRulesofStealthTheB-2bomberfirstflewonJuly17,1989.Thirtyyearson,Americacountsonlowobservablestealthmorethanever. Everyday,theB-2sprovidenucleardeterrenceandconventionalbomberpresencefortheUnitedStates.TheB-2hasalsoproveditselfincombatinfiveseparateaircampaigns.YettheriseofgreatpowercompetitionrequirestheUSmilitarytoprepareforfacingoffwithRussia,China–andthemilitaryhardwaretheysell.Inthepastfiveyears,RussiahassolditsadvancedS-400surface-to-airmissilesystemstoChinaandothernations,andbeguntestsofitsnext-generationS-500missilesystem.BothRussiaandChinahaveincreasedfighterandbomberflightsinAsiaandotherareas.Somesaythevalueofstealthisfadinginthefaceofthesethreats.

It’sfairtoask:canAmericanstealthstillruleairwarfare? StealthandtheElectromagneticSpectrumTherulesofstealthbeginwithlowobservableshapingtoeluderadartracking.Everycombatairplaneisagroupofgeometricshapes,thinksthestealthbomberdesigner.Wings,verticaltails,engineinlets,weaponshangingunderthewing,cockpitbubble,fuselage:alltheseareshapesthatreflectradarwavesbacktoenemyairdefensesonthegroundorintheair.

RadarcameintowidespreaduseinWorldWarIIwhencommandandcontrolcentersonlandandaboardshipsusedittodetectincomingformationsofattackingaircraft.Bythe1960s,radar-guidedsurface-to-airmissilesguardedtargetsfromMoscowtoHanoi.Electronicwarfare

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attemptedtoartfullyblastbackenergytofuzzuptrackingradarsorturntheirsignalsagainstthem.ButVietnamlossratesshowedtheedgeshiftingtothedefenders.

Then,inthe1970s,researchonlowobservableshapesforaircraftyieldedthefirststealthfighterdesigns.Stealthworksonamarveloussetofprinciples.Radar“sees”thereturnedwaves.Theareareflectedbyradarcanbemuchlargerorsmallerthanthephysicaldimensionsoftheaircraftitself.Specialequationspredicthowradarwavesbehave.Analyzeacombatplaneasagroupofshapesandthesumistheradarcrosssection.

Astealthaircraft’sdesignreducestheradarcrosssection.It’snoteasy.Radarwavesmirrorbackfromverticalsurfaces,bounceofftails,travelalongedges,scatteraroundcavitiesanddiffractfromwingtips.Anglethesurface,andtheradarwavereflectsoffandawayfromthetrackingradar.Putalltheseprinciples–andmore–intoplaceandwithenoughmathematicsandsimulation,engineerscancalculate,predictandcontrolradarreturn.

Thenetresultis“lowobservables”orstealth.Alowobservableaircraftrendersradardetectionandtrackingmuchlessefficient.Thefirstpurpose-builtstealthaircraftwastheF-117.Theflatplatesandanglesshowedclearlytheideasdrivingfirst-generationstealth.Toimproveitsstealth,theF-117carriedweaponsinsideabombbayinsteadofunderthewings.

In1981,theAirForcecommissionedtheB-2bomber.Withrevolutionarylowobservabletechnology,theB-2couldeludetheSovietUnion’sairdefensebatteriesandoutfoxfighterinterceptors.

Lowobservablesareoptimizedtoworkagainstthemostdangerouselementofenemyairdefenses:thefire-controlradars.Theseradarsemitalowfrequencyradarwave,thekindwithabigwavelengththatflowsoveranyshape.Thelowfrequencywavecandetectsomethingoutthere,briefly,thenit’sgone.Trackingfastcombataircraftonanattackprofilerequiresmorefrequent,shorterwavelengthpingsoperatingatcloserranges.

TheB-2bombertookstealthtoanewlevelbyintroducinglarge,curvedsurfacesassistedbycomplexcomputer-aideddesign.Anditaddedrangeandpayload.DefeatingIntegratedAirDefensesStealthdeliverssurprise.PicturetheB-2sattackingtargetsinSerbianairspacein1999.Pilotsreportedtheeeriequiet.Lightswerestillonincitiesbelow,withflashesofothercombatengagementsvisibleatloweraltitudes.NeitherintegratedairdefensesnortheSerbianairforceMiG-29sandotherfightersinterruptedthestealthB-2sontheirbombingruns. Lowobservablesdeliversurvivabilitybydrasticallyloweringthenumberofaccurateshotstakenbyenemysurface-to-airmissiles.Steponeisreducingdetectionrange.As

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discussed,thelowerradarcrosssectioncutsdownthedistanceatwhichenemyradarscandetect,trackandengagetheaircraft.Reducetheradarcrosssectionbyafactoroftenandthedetectionrangeofaradariscutby44%,accordingtotheradarrangeequation.

Thefirstchartshowsadetectionrangeforfournotionalaircraft,startingwitha1-metersquareradarcrosssectionandreducingdowntoverylowobservablelevels.Verylowobservableradarcrosssectiontruncatestheenemyairdefenseradar’seffectiverange.Atthelowestshapedisplayed,thestealthaircrafttakesawaymostoftherangetrackingadvantage.Hereiswheresurvivabilityincreasessignificantly.

Asdetectionrangedrops,thenumberofaccurateshotstakenbyenemyairdefensesalsogoesdown.Thishappensinpartbecausethestealthaircraftspendmuchlesstimeinsidetheeffectivethreatradiusofthesurface-to-airmissilesystem.Thisnextchartassumeseachofthefournotionalaircraftisflyingat400mphandwilllaunchaJDAMatadistanceof15nmawayfromthetarget.Thestealthiestshapeasdepictedingreenwillbedetectedonlyat18milesaway.Asaresult,theaircraftmustflyjustthreemilesintotheeffectivethreatring,whichtakesless

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thanoneminuteatthegivenspeed.Incontrast,theaircraftwiththelargestcrosssectioninredisdetectedearlierandspendmoretimeinazoneofvulnerability.Lessshotsequalsmoresurvivability.

Stealthincludesmorethanshapingforlowobservablesagainstradar.TheB-2designalsoworkedtocontrolelectronic,infrared,acousticandvisualsignatures.Forexample,theB-2’sfourenginesarenestedinsidethebomberwithspecialductingthatreducesdetectionofengineexhaustheat.ThesawtoothtrailingedgeoftheB-2helpscreateshedvorticestomixhotandcoolair.TheB-2’sdesignalsominimizesmajorsourcesofsoundfromtheenginesandairframe.UpdatestoStealthStealthisnotstatic.Whiletherulesofstealthapply,thereisnoquestionthatthethreatenvironmenthaschanged.Today’smilitarydoctrinecentersonmulti-domainoperationsandtacticsforgainingtemporaryairsuperioritytocarryoutmissionsindeniedairspace. Stealthismoreimportantthanever.Thesinglebestproofcomesfromthenationalinvestmentintwomajorfighterprograms,theF-22andF-35.Bothaircraftdesignscenteronlowobservablesandradarcrosssectionreduction.In2015,theAirForce’sdecisiontobuildtheB-21Raiderstealthbomberforthemid-2020sshowedagainthatstealthisexpectedtobeadominantforceinaircombatfordecadestocome. However,inthesametimeperiod,RussianandChineseairdefensesystemshaveimprovedinqualityandnumberssincetheoriginaldesignoftheB-2.Regionalconflictscenariosoncepicturedpunchingthroughairdefenses.Now,theAirForcethinksofpenetratingcorridorsamongdensethreatsthatmayremainactive.Adversaryfighterswithlong-rangemissilesandsophisticatedradarswillbeintheair.Stealthinthisenvironmentreliesmorethaneverontactics,andinparticular,onnewtechnologiesforthreatemitterlocation.

TheB-2fleetisintheprocessofreceivingamajorDefensiveManagementSystemupgradetoimprovethethreatemitterlocationsystemsonthebomber.Active,electronically-scannedradarscanassistwithfindingenemysurface-to-airmissilebatteriesandotherthreats.Forpilotsinthecockpit,knowingthethreatpictureletsthemadjustcourseandtactics,employelectronicwarfarewhenneeded,andimproveradarcrosssectionmanagement.CounterstoStealthTheresurgenceofRussianandChinesemilitarymodernizationhasalsotouchedoffanewroundofdebateonhowtocounterstealth.Notmuchhaschangedwithphysics.But,asitturnsout,thecounterstealthtalkisfueledbyhotrivalryamongaircraftcompanies,bothdomesticandforeign.

Russianmilitarysalesbrochuresaccountformuchofthecounter-stealthliterature.Here’sanexample.“Withauniquewideband“Kharchenko”squareringelementradiatorarrangedinadiamondlatticepattern,theVostokEradarisdesignedtoimproveitsfrequencyagilityagainstearliergenerationstealthfighters,”readthisone.“Evenwhenfacingmoreadvancedstealthaircraft,theVostokEcandetecttargetsfrom57kilometersawayandshootthemdownwiththeS-300surface-to-airmissile.ItisanewdesigntochallengetheaerialdominationofAmericanstealthaircraft,”orsothesalespitchsaid.

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ThisRussianwentontobragthat“VietnamwillprobablybecomethefirstnationtousetheradarsysteminanasymmetricwarfarestrategyagainststealthfightersfromChinaincludingtheJ-20andJ-31overthedisputedSouthChinaSea.”i

Counterstostealthtrytorestoresomeofthedetectionrangedeniedbylowobservableshaping.Sincelowobservablesconcentrateoncounteringtheshortwavelengthsforfirecontrolradar,onecounter-stealthtacticistoimprovelow-frequencydetection.Improvedcorrelationandanalysisoflong-range,low-frequencyearlywarningsignalsmightintheoryyieldbetterearlytracksofstealthaircraft.Networkedradarsandbettercomputingpoweraresupposedtohelpcompensateforwhatthelowfrequencysignalscan’tdeliver.

Thesecondapproachistoseparatetheradartransmitterandreceiverintoabistaticradarsystem.Mostradarsystemstransmitandreceivesignalsbackatasinglepoint.Thebistaticsystemtransmitsradarenergytoareceiverinasecondlocation,makingalineorbarrierforattackaircrafttoflythrough,likethelaserbeamscenesinMission:Impossible. Thenthereistheoldrivalrybetweenstealthandelectronicwarfare.Thisone’sreallyanantique,forthebesttacticsnowcombineboth.However,evenafewyearsagostealthwasgettingroughtreatmentinthehyper-competitiveworldofinternationalfightersales.Atonepublicevent,Boeingmarketeditsnon-stealthyF/A-18GGrowlerelectronicwarfarefighterwiththeadvertisementphrase“stealthisperishable;onlyaGrowlerprovidesfullspectrumprotection.”RecentlyBoeinghasadvertiseditsupgradedF-15shave“everythingbutstealth.”

Thiscritiqueisavariationonthelow-frequencyapproach.SAM(Surface-to-AirMissile)radarsareshiftingtheirfrequenciesintolowerfrequencybandswhereU.S.stealthislesseffective,”saidoneexecutive.ii

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Bomber,NotFighterYetanothersubcategoryofthecounter-stealthdebatespunofffromcriticism(byotheraircraftmanufacturers)oftheF-35JointStrikeFighter.AssertingthattheF-35focusedonfront-aspectsignaturereduction,rivalmarketerssuggestedagainthatonlyelectronicwarfarecouldhandlethethreat.Theydidn’tseemtonoticethatofficialDepartmentofDefensestrategyincludedadvancedelectronicwarfarecapabilitiesfortheF-35thataretestedandperformingwell.iii

Buriedinthemixisavalidpoint.RussianandChineseadvancedsystemshaveimprovedtheirlow-frequency,longwavelength.Advancedsystemscansharenetworkedinformationtohelprefineearlydetection.

Buttherulesofstealthstillapply.Stealthdegradessurveillanceradardetectionandshrinkstheeffectivecoverageoffire-controlradars.Thehand-offfromsurveillancetofirecontroltomissileshotsbreaksdown.Mostimportant,stealthstartswithlowobservablesandcombinestactics,electronicwarfare,networkedinformationflows,andreductionsininfraredtocreatethepackageofsurvivability.

Also,thefighterdebatedoesn’tapplytoassessingstealthfortheB-2.It’simportanttoremembertheB-2wasdesignedwithall-aspectsignaturereduction:meaning,specifically,thatit’snotlimitedtohead-onattack.AprimerequirementintheB-2designwasminimizingradarreturnfrom360degreesaroundtheaircraft.Successinall-aspectsignaturereductionwasoneofthereasonsNorthropwonthecontractoriginally.SignaturereductionisperhapsnotidenticalfromeveryanglebuttheholisticdesigngivestheB-2lowobservableswhetherflyingtowards,aroundorawayfromtargetareas.

TacticsoftheFutureBeginningwithOperationAlliedForcein1999,AmericanB-2crewslearnedtoflythe“blueline,”carefullyplanningandupdatingtheroutetotargets.Tacticsofthebluelinepointthebomber’sstealthiestsignatureaspecttowardthethreat.Byflyingtheblueline,thebomberstaysoutofdetectionrange.Altitudeaddsanotheradvantage.Flyinghighcanworkaroundthestrongestzonesofradarcoverage. TheB-2’sstealthreliesonmorethanonetypeoftechnology.Oneenemybreakthroughdoesn’tshatterstealth.

TheB-2andsoontheB-21canplayuniquerolesincampaignsofthefuture.Thestealthbombercandegradeenemyairdefensesandstrikeotherhigh-valuetargets.Byextension,thestealthbomber’sabilitytoattackanytarget,anywhere,isthefoundationofdeterrence.All-aspectsignaturereductiongivesbomberstheadvantageintheduelwithdefendingIADSandfighters.Onlystealthaircraftcanattackwithmaximumefficiencyagainstthemostimportanttargets.

“TheB-2bomber,imaginehavingthatcomeatyou,”remarkedAirForceChiefofStaffGeneralDavidGoldfein.iv

i“VietnamwillbuytheBelarus-madesurveillanceradarVostokEabletodetectstealthfighter,”armyrecognitioncom,July18,2013.iiDaveMajumdar“StealthVS.ElectronicAttack,”USNI,April21,2014iiiHouseArmedServicesCommittee,AirandLandSubcommittee,“MilitaryServicesFifthGenerationTacticalAircraftChallengesandF-35Program,”February16,2017.ivGen.DavidGoldfein,Remarks,RetirementCeremonyforSecretaryoftheAirForceHeatherWilson