ANALYSIS CENTER PAPERS by Robert P. Haffa, Jr. and James H. Patton, Jr. 1 June 2002 In Brief The U.S. Department of Defense plans to invest hundreds of billions of dollars in stealthy aircraft over the next several decades. Will low-observable (LO) capabilities incorporated in military aircraft such as the B-2 bomber, the F-22 air superiority fighter and the F-35 joint strike fighter prove as successful and enduring as submarine stealth? To address that question, this paper briefly explores antisubmarine warfare, examines the development and fielding of low- observable aircraft, and suggests analogues between stealthy platforms in the sea and in the air. When those analogies are drawn, many of the same reasons the submarine has proven so difficult to detect, track, fix, and destroy also pertain to stealthy aircraft. The friction of combat, the platform operators’ ability to modify their tactics, the technology of denying more than fleeting contacts, and the problem of looking for small things in large volumes all apply. The submarine’s long-term success suggests that properties inherent in low-observable combat platforms provide an enduring competitive military advantage to those who produce, maintain and continually improve them. It stands to reason, therefore, that stealthy aircraft should maintain an enduring edge over anti-aircraft defenses, providing their sponsors constantly study and exploit the environment, and take prompt and sustained corrective actions to negate enemy countermeasures. Stealth Analogues of 1 This paper adopts the same title and thesis presented in an article the authors published a decade ago, but explores the issues quite differently. See “Analogues of Stealth” in Comparative Strategy (Vol. 10, No. 3) pp. 257-271. Copyright 1991, Taylor and Francis. Now, as then, we acknowledge James G. Roche for encouraging us to examine the similarities between stealthy submarines and aircraft. We would also like to thank our colleagues in the Northrop Grumman Analysis Center for their assistance, especially John Backschies, Mary Hubbell and Adam Siegel.

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Page 1: Analogues Stealth



Robert P. Haffa, Jr. and James H. Patton, Jr.1

June 2002

In Brief

The U.S. Department of Defense plans to invest hundreds of billions of dollars in stealthy aircraft over the next several decades. Will low-observable(LO) capabilities incorporated in military aircraft such as the B-2 bomber, theF-22 air superiority fighter and the F-35 joint strike fighter prove as successfuland enduring as submarine stealth? To address that question, this paper brieflyexplores antisubmarine warfare, examines the development and fielding of low-observable aircraft, and suggests analogues between stealthy platforms in the seaand in the air.

When those analogies are drawn, many of the same reasons the submarine hasproven so difficult to detect, track, fix, and destroy also pertain to stealthy aircraft. The friction of combat, the platform operators’ ability to modify theirtactics, the technology of denying more than fleeting contacts, and the problemof looking for small things in large volumes all apply. The submarine’s long-termsuccess suggests that properties inherent in low-observable combat platformsprovide an enduring competitive military advantage to those who produce,maintain and continually improve them. It stands to reason, therefore, thatstealthy aircraft should maintain an enduring edge over anti-aircraft defenses,providing their sponsors constantly study and exploit the environment, and takeprompt and sustained corrective actions to negate enemy countermeasures.

StealthAnalogues of

1 This paper adopts the same title and thesis presented in an article the authors published a decade ago, but explores the issuesquite differently. See “Analogues of Stealth” in Comparative Strategy (Vol. 10, No. 3) pp. 257-271. Copyright 1991, Taylorand Francis. Now, as then, we acknowledge James G. Roche for encouraging us to examine the similarities between stealthysubmarines and aircraft. We would also like to thank our colleagues in the Northrop Grumman Analysis Center for their assistance, especially John Backschies, Mary Hubbell and Adam Siegel.

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Introduction: Analogues of Stealth

Recent claims regarding the detection and vulner-ability of low-observable aircraft like the B-2bomber are reminiscent of similar reports issuedover the years postulating the demise of the sub-marine’s stealth. Comparing submarines and aircraft employing stealth—low-observable technologies and tactics—results in several analo-gies useful in refuting these claims: • Each system operates in a three-dimensional

environment facilitating low observability: vaststretches of sea and sky.

• They can use terrain features (ocean trenches,mountain ranges) to mask their presence fromsensors.

• They can vary their immersion within theenvironment (depth, altitude) and use its char-acteristics (i.e., temperature, weather, or dark-ness) to add measures of stealthiness.

• They can reduce to varying degrees theirobservable signatures (through sound-deaden-ing techniques, infrared shielding, or cooling).

• They can avoid or attack active means ofdetection (sonar, radar) and make themselvesless detectable by spoofing or jamming thosesystems.

• Finally, owing to these properties stealth pro-vides, they each enjoy the tactical advantage ofchoosing when to engage the adversary incombat.

With these analogies in mind, this paper exploressimilarities between low-observable submarinesand aircraft with the purpose of examining thestaying power of stealth.2 To accomplish that, wefirst briefly review the history of anti-submarinewarfare (ASW)—a story of the search for coun-termeasures against a platform that from the out-set was designed to use the environment to maskits presence. Yet, ever since submarines enteredmilitary operations, claims have emerged thatsome new technology will make them obsolete.Time and again those claims have proved base-less. With continued modernization and modifi-cation, the submarine’s signature has beenreduced to the point where the “noisy” nature ofits operational environment hides its position anddramatically reduces or neutralizes the effective-ness of various detection means. Indeed, everynuclear-powered U.S. submarine was quieter, thatis, more stealthy, when decommissioned thanwhen it was launched.

It is our contention that low-observable aircraft,when they reach the end of their service life,should also be retired in a more stealthy condi-tion than that of their first flight. Seeking to sup-port that contention, the paper next outlines thedevelopment and employment of airbornestealth. Although the story of air defense beginswith observers on the ground and in the air, sinceWorld War II air defenses have relied primarily


2 There are differences as well, most notably that the submarine achieves its stealth primarily by submerging, while a stealthy aircraft operates in the same medium as non-stealthy planes. We believe the comparisons far outweigh the contrasts, particularly with regard to the mutual need to counter detection technologies and the operationaladvantages that accrue to stealthy combat platforms whether in the sea or in the air.

SSBN GeorgeWashington


SSBN Ethan Allen(608)

SSBN Permit(594)

SSBN Permit(594)

SSBN Lafayette(616)

SSBN Sturgeon(637)

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SSBN Ohio(726)

US Attack Submarines


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SSBN GeorgeWashington


SSBN Ethan Allen(608)

SSN Permit(594)

SSN Skipjack(585)

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SSN Nautilus(571)

Merchant Ship

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DieselSubmarineon Battery

1965 1970 1975Year

1980 1985 1990 1995 2000

Adapted from Tom Stephanic,Strategic Anti-Submarine Warfare and

Naval Strategy (New York: Lexington, 1987), p. 278.

Figure 1. This estimate of total radiated sound levels for US nuclear submarines suggests a noise reduction of 60 dB over45 years. Modern submarines emit about one-millionth of acoustic energy as did their predecessors.

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survive, must be accorded the attention and theresources it deserves.

Anti-Submarine Warfare: CounteringUnderwater Stealth

Attempts to degrade the submarine's inherentstealthiness through ASW have evolved throughnumerous techniques and technologies. Initially,ASW relied on a submarine compromising itsstealth by operating in a non-submerged mode orraising its periscope above the ocean’s surface.Before World War II, technological innovationsled to active means of detection (e.g., sonar) tosearch for submerged submarines. During WorldWar II, ASW exploited the nonstealthy aspects ofa submarine's behavior by employing radar whenthe sub was required to operate on the surface,

and by using direc-tion-finding equip-ment when subma-rine transmissionsbroke radio silence.Finally, since WorldWar II, more sophis-ticated detection

techniques have emphasized passive detectiontechnologies, such as listening for the sounds of asubmarine, detecting its metallic hull, or pickingup the trail it leaves behind.

Seeking nonstealthy signatures. Although someobservers anticipated the submarine’s militarypotential before World War I, a more typicalopinion was that the submarine was a cowardlyweapon employed only by weak naval powers.Even after three British cruisers had been torpe-doed and sunk in a matter of minutes by aGerman U-boat on September 22, 1914, themedia coverage about the event concluded thatthe submarine threat was likely to be short lived.“Mining harbors, torpedo nets, better armor,careful lookouts (including aircraft) and highspeeds and frequent course changes” were seen ascountermeasures likely to negate any advantagesthe submarine could achieve by wrapping itself inthe cloak of the sea.3

The 1918 British development of sonar, forSOund Navigation And Ranging, strengthenedthe belief that the submarine would become


on radar to detect, track, and subsequentlyengage hostile aircraft. That said, optical detec-tion is still pursued, as are detection techniquesseeking other aircraft signatures such as heat,radio communications, and even turbulent wakesin the atmosphere.

Although the atmosphere provides some naturalhiding places for aircraft, such as clouds anddarkness, an airplane’s signature must be loweredto survive in a hostile environment. Using stealthtechnology, aeronautical engineers reduce an air-craft’s susceptibility to radar detection and miti-gate its observable infrared, electromagnetic, visu-al and acoustic signatures. Indirect or passivemeasures diminish the contrast between an air-craft’s profile and its physical or electromagneticsurroundings. For example, camouflage paintallows an aircraft toblend into the back-ground, while aircraftthreat-warning systemsenable search radar eva-sion. Countermeasuresinclude presenting anincoming anti-aircraftmissile with a false signature to lead it astray,using focused light, flares or lasers to lure aninfrared seeker, and employing active jamming ordeploying a towed decoy to deflect radar terminalguidance. Using these multi-spectral signaturereduction techniques, low-observable aircraftdeny current detection methods to a degree com-parable to the modern submarine’s ability tocounter anti-submarine warfare capabilities.

Finally, we draw analogies between the game ofmeasure and countermeasure characterizing thehunt for stealthy platforms in the air and beneaththe sea, speculate on future challenges, and con-clude with some implications for the long-termcompetitive advantage stealth provides. A themethroughout the paper implies that those forecast-ing the impending demise of low-observable aircraft may be falling into the same sort of trapsas those who wrongly predicted the degradationof the submarine’s stealth. But we hasten to warnthat maintaining a combat platform’s stealth isneither a naturally occurring nor a self-sustainingphenomenon. As a proven and essential capabilityof future U.S. power projection forces, stealth, to

3 “Modern Submarine Warfare: Methods of Guarding Against the Latest Form of Underwater Attack,” Scientific American, November 1914, pp. 376-77.

…stealth, to survive, must beaccorded the attention and the

resources it deserves.

allows an aircraft toblend into the back-ground, while aircraftthreat-warning systemsenable search radar eva-sion. Countermeasuresinclude presenting anincoming anti-aircraft

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increasingly detectable by its armed adversaries.Sonar apparatus generates a pulse of acousticenergy in the water and utilizes directional listen-ing for the signal’s return when it bounces off thesubmarine’s hull. However, submariners had dis-covered that near-surface temperatures increasefrom sunlight late in the day, creating a refractivelayer in the water. Like a prism, this layer directssound downward and adversely affects the hori-zontal ranges of sonar detection. Tactics weredeveloped to take advantage of these refractivelayers, including those well beyond the depth ofdaily solar heating, thus directing the sound awayfrom the receiver and making it difficult for sonaroperators to hear the submarine's return echo.

Despite these early stealth-enhancing tactics, thesubmarine’s military utility was questioned dur-ing the inter-war period. If the Naval Institute’sProceedings journal can be considered as a bell-wether for fleet perceptions, experienced navalofficers regarded the submarine's capability asextremely limited, owing to its perceived vulnera-bility to a growing antisubmarine threat. Betweenthe World Wars, the conventional wisdom amongthe Navy’s leadership was that the submarinewould ultimately prove to be vulnerable in combat.4

Active submarine detection. When airborne radarsets became operational in mid-1942, Germansubmarines deploying into the Atlantic andreturning on the surface became vulnerable tosudden and unexplained attack in the Bay of

Biscay. Admiral Doenitz, com-mander of the German U-Boatfleet, deduced properly that thesubmarines were being detectedby radar, and his U-boats wereoutfitted with a radar receiverfed from an improvised anten-na consisting of wire wrappedaround a wooden frame.Among the first pieces of elec-tronic support measures equip-ment, this “Biscay Cross” per-mitted the detection of a threatsignal in more than enoughtime for a submarine to sub-merge before the transmittingplatform could locate and

attack it. When the British later decided to con-vert terrain-profiling air force radar to ASW use,the Biscay Cross could not intercept that frequen-cy, and losses resumed.

By early 1944, the snorkel (a mast-mounteddevice allowing the submarine to ingest air fordiesel engine operation while at periscope depth)returned stealth to the submarine. The exposedportions of the snorkel mast were also coatedwith radar-absorbent material (RAM), reestab-lishing stealth as a defense and allowing the U-boats to operate in the English Channel again.An unexpected benefit of these submerged tran-sits was, since submarines then had to surface totransmit radio messages, their physically enforcedradio silence deprived the Allies of their mostproductive source of detection and localization.

Despite technological advances in underwaterstealth, the most successful ASW applications inboth World Wars came from surface tactics—convoys escorted by numerous ASW ships—negating those improvements. Because a subma-rine could attack only one ship in the convoy at atime, it exposed its position to the ASW ships,which formed a concentrated and effectivedefense. The German tactical response to convoysin World War II was the “Wolfpack”—attackingthe convoys with multiple submarines in a coor-dinated, swarming assault. Massing stealthy plat-forms, however, creates the risk of multiple expo-sure, and while the submarines were successful in


4 See “Submarine Capabilities and Limitations,” Naval Institute Proceedings, Aug. 1925, pp. 1398-1407.

The German U-14 heads out to sea during World War I.

Page 5: Analogues Stealth




sinking ships, they also suffered major losses fromcounterstrikes. This experience influenced U.S.Navy strategy and force planning through theCold War, generating requirements for largenumbers of surface ships to escort trans-Atlanticconvoys.5

The development of nuclear-powered submarinesduring the Cold War altered the balance betweensurface and sub-surface combatants. By greatlylimiting their vulnerability through stealthy tac-tics and technologies, nuclear attack submarines(SSNs) gained the initiative against surface shipsunder almost all circumstances. The U.S. Navy,having invested significantly in the fielding andpractice of ASW, found that SSNs successfullyattacked surface ships in exercise after exercise.Thus, from the 1960s on, it was generallyacknowledged that the only consistently effectivedefense against a submarine attack was anothersubmarine defending the force, and submarinebarriers in the Greenland-Iceland-UK gapbecame important additions to the forces defend-ing Atlantic convoys.

Acoustic and non-acoustic ASW. Sound and sonarhave been the primary focus of efforts to counterthe submarine’s stealth since World War II.Acoustic technology improved the capabilities ofactive sound measurement and led to the devel-

opment of whole new systems based on passivetechniques. Sophisticated sonobuoys, bottomplaced sound arrays, towed sonar systems, andhelicopter-dropped arrays were deployed to detectsubmarine-generated noise. Sonar systems grewlarger, longer and more powerful to seek outincreasingly quieter submarines. However, U.S.submarines were able to respond to and counterthese threat improvements and retain theiracoustic advantage by using sonar to providethreat information, reducing equipment-radiatednoise, and employing various types of hull coat-ings analogous to RAM (inasmuch as theyreduced the strength of a submarine’s sonarreturn). Tactics also helped to defeat sonar detec-tion, or to break the kill chain linking that detec-tion to an effective attack. Thus, the submarine,alerted to a momentary breach in its low observ-ability, might deploy a noisemaker or launch adecoy to confuse the source trying to track andengage it.

While acoustic techniques have remained thedominant means of locating submarines, theCold War saw attempts to exploit other phenom-enologies. Airborne magnetic anomaly detection(MAD) equipment was viewed as a great break-through in ASW when it was first used duringWorld War II. But, with very limited range andfrequent false readings, MAD proved to be a poor

search mechanism, andtoday serves primarily as alocalization device when anapproximate position of asubmarine is alreadyknown. The low altitudesneeded for MAD employ-ment also result in a cou-pling of the aircraft's noiseto the water, serving to alertany submarine around.

Technologists have alsodevised a number of systems in an attempt to detect the family of elements or compoundsshed, pumped, activated or

5 A typical force generation package for the escort mission included 10 surface combatants per convoy. Planning four convoys per month, and adding a carrier battle groupto each task force, could generate total ship requirements of 167 ships, not including submarines, just in the Atlantic.

Allied destroyer dropping twin depth charges in World War II.

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otherwise releasedfrom a modernsubmarine. Onedetection modeinvestigated aboardASW aircraft wasto detect hydrocar-bons released intothe atmosphere inthe exhaust of a snorkeling diesel-electric subma-rine. Although expectations mounted after limit-ed success under controlled conditions, open-ocean testing saw very high false alarm rates,especially in areas where other hydrocarbon-emit-ting shipping was present (a likely place forpatrolling submarines). As a result, this “sniffer”equipment had minimal operational impact.

Hydrodynamic principles, such as a Bernoulli“hump” or a Kelvin “wake,” offer other detectionmeans—sensing effects on the sea surface result-ing from a submerged, moving body. Most ofthese methods, enabled through radar- or laser-based scanning of the ocean’s surface, could theo-retically detect shallow, fast submarines. “Shallowand fast,” however, is a seldom-populated portionof the submarine’s total operating envelope.Although the Navy has expended significantefforts attempting to exploit these theoreticallyobservable phenomena, the “noise” surroundingthem remains significant in any kind of sea state,and there is little promise for future success whenthe submarine operates to optimize its stealth.Although several of these technologies are cur-rently lacking, the view of the submarine com-munity is to “expect the unexpected” and tohedge against the surprise threat that can’t imme-diately be countered. Such an approach supportsanalogous research in non-traditional areas tocounter emergent threats to airborne stealth.

Developing and Employing Airborne Stealth

Airmen appreciated the value of aircraft surviv-ability and tactical surprise—stealth’s primaryoperational benefits—long before the relativelyrecent advent of low-observable technology.

Although themantra chanted bysupporters of thestealthy F-22 airsuperiority fighteris “first-look, first-shot, first-kill,” theimportance of see-ing the opponent

first and completing an attack without beingdetected has long been the goal of would-be aeri-al aces.6 As far back as World War I, air combatdoctrine recognized that “the deciding element inair combat is usually surprise.”7 But in those daysof early combat aviation, when the primarymeans for detecting enemy aircraft was a visualsighting, there were few, if any, technological aidsto evasion. Rather, airmen of the time placed apremium on tactics to achieve surprise, such ashiding in clouds or approaching their adversaryfrom out of the sun’s glare.

From World War I through the inter-war period,visual observation—an inherently limited capabil-ity—remained the primary means of aircraftdetection. During this time, attackers retained,especially in air-to-ground engagements, a signifi-cant competitive advantage over defenders, givingrise to such absolute assertions of offensive air-power’s dominance as, “the bomber will always getthrough.” But this imbalance did not last. Eightyears later, radar’s operational debut as a primaryaircraft detection tool marked the beginning of apronounced tilt backward to the defender.

The Radar Game. RAdio Detection AndRanging, or radar, was developed in England inthe mid-1930s and is credited with giving theBritish an important competitive edge during theBattle of Britain in 1940. Later in the war, theGermans also exploited radar to gain a significantdefensive advantage, using it to inflict heavy loss-es on U.S. and British bomber formations.Tactics and techniques applied during World WarII opened a new era in air combat in which thesurvivability of an airborne force was now domi-nated by radar in the detection phase.8


6 See, for example, Bill Sweetman, Stealth Aircraft: Secrets of Future Airpower (Osceola, WI: Motorbooks International, 1986), p. 7. The advantage of a stealthy aircraft inan air-to-air engagement is that it provides an edge in situation awareness, proven to be the single most important factor in fighter duels. For a discussion of that, seeBarry D. Watts, Clausewitzian Friction and Future War (Washington, D.C.: NDU Press, 1994), pp. 96-104.

7 Rebecca Grant, The Radar Game (Arlington, VA:IRIS Independent Research, 1998) quoted William Sherman, “Tentative Manual for Employment of the Air Service,1919” printed in The U.S. Air Service in World War I, Volume I (Washington, D.C.: Office of Air Force History, 1978), p. 369.

8 Grant, p. 15.

…"first-look, first-shot, first-kill,"the importance of seeing the opponent

first and completing an attackwithout being detected has long been

the goal of would-be aerial aces.

otherwise releasedfrom a modernsubmarine. Onedetection modeinvestigated aboardASW aircraft wasto detect hydrocar-bons released intothe atmosphere in

Page 7: Analogues Stealth




After radar’s advent, U.S. aircraft designers wast-ed little time in pursuing counters to radar-baseddefenses. Indeed, the post-World War II periodushered in a fundamentally new approach to air-craft survivability—one in which aircraft weredesigned from inception to avoid detection. Bythe 1950s, radar-absorbing materials developed tomask antennas on submarines were being appliedto help shield conventionally designed aircraft fromradar detection. Thus, the Lockheed U-2, opti-mized for long range and high altitude based onan F-104 fuselage design, was later fitted with radarabsorbent paint and radar-scattering wire to ham-per detection by the improved early warning, track-ing and fire-control radars the Soviets were thenincorporating into their surface-to-air missiles.9

In addition to these quick fixes to conventional

platforms, there was a growing realization thataircraft could be designed to diminish the powerof the radar return, thereby allowing the aircraftto delay, or deny entirely, detection by radar. In1953, the U.S. Air Force specified that a newreconnaissance aircraft be designed to minimizeradar detection.10 The SR-71 later evolved from aseries of designs to replace the U-2 for the CIA,including a prototype “Blackbird” aircraft, desig-nated the A-12, the first production aircraft toincorporate a stealthy shape. The radar reflectivityof the SR-71, roughly that of a small private air-craft according to its designers, was “significantlylower than the numbers the B-1B bomber was ableto achieve twenty-five years later.”11 Key to thedesign of stealthy aircraft was the concept of “radarcross section” (RCS) that summed the majorreflective components of the aircraft’s shape, withmuch of the pioneering research being supportedby the U.S. Air Force Avionics Laboratory.12

9 See Ben Rich, Skunk Works (Boston: Little Brown, 1994), pp. 152-160.10 Grant, p. 22.11 Rich, p. 215.12 Mark A. Lorell and Hugh P. Levaux, The Cutting Edge: A Half Century of U.S. Fighter Aircraft R&D (Santa Monica: RAND, 1998). For an account of early Air Force

research on stealth technology see William F. Bahret, “The Beginnings of Stealth Technology,” IEEE Transactions on Aerospace and Electronic Systems (October 1993).

185-foot British “Chain Home Low” radar tower, circa 1940.

The Lockheed SR-71 Blackbird, above, was the first military aircraft designed from inception to minimize radar cross-section.

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When the “Blackbird” aircraft were designed inthe late 1950s, only the gross effects of differentshapes on radar reflectivity could be assessed. Forexample, it was understood that a flat plane or acavity at right angles to an incoming radar wavewould produce a very large return. But the state-of-the-art in numerical design procedures in the1960s was not advanced enough to produce abalanced design, i.e., one in which a certain air-craft part did not produce a dominant (and thuseasily observable) return in one direction. By thenext decade, computer modeling had progressedto the extent that it was possible to design an air-craft with a reduced and balanced RCS, and fly-by-wire flight systems enabled control of the non-aerodynamic configurations mandated by stealth.Given these technologies, initial aircraft designsfor the F-117, B-2 and F-22 featured dramatical-ly reduced radar cross-sections.13

Despite design tradeoffs between aircraft per-formance requirements, cost, and radar cross sec-tion, there is little evidence of a leveling off in thecapability to continue to develop and producevery low radar signatures on aircraft. Clearly, continued growth in the computing powerrequired for stealthy aircraft design and develop-ment does not necessarily equate to proportionalreductions in RCS. However, government andindustrial test facilities reportedly now can meas-ure radar signatures as low as one ten-millionth

of a square meter—something like a speck ofdust. Thus, while today’s advanced stealthy air-craft can be detected at close range by the mostpowerful ground radars, continued advancementin RCS reduction should make future aircrafteven less detectable.14

Seeking other signatures. With emerging radaradvances unlikely to yield near-term, dramaticimprovements in detecting low-RCS aircraft,those interested in countering stealth must pursuecapabilities detecting other observable phenome-na. Here, the stealthy aircraft and submarineshare several properties susceptible to detection,including infrared, visual, acoustic, or electro-magnetic emissions.15 Although, historically, noneof these is as useful as radar for detecting low-observable aircraft, each must be minimized toensure that none can be used to obtain a defen-sive advantage. For example, a stray electronicemission could result in vectoring air interceptorsto a stealth aircraft’s general vicinity, increasingthe probability of close-in visual, infrared, orradar detection and tracking.

Infrared, or IR, is one of the most difficult signa-tures for a stealth aircraft to suppress. Aircraftgenerate heat in two basic ways: via the engine(both the engine exhaust and internal engine heatcoupling to the aircraft skin), and throughincreases in surface area temperatures resultingfrom atmospheric friction. To reduce engine-generated IR signature, subsonic stealthy aircraftsuch as the B-2 bury the engines within the air-craft fuselage and mix cold ambient air with theengine exhaust to lower its escape temperature.High-speed flight’s enhanced IR signatures poseadditional challenges to low-observability. Toreach supersonic speeds, stealthy fighters such asthe JSF must employ afterburning engines,


Figure 2. Radar Cross-Section: What the Radar Sees

Figure 3. Radar Cross-Section Size by Platform Type

13 These observations rely on “Fundamentals of Stealth Design,” a 1992 unpublished article by Alan Brown, program manager of the F-117. Brown is credited with thequote that the secret to stealth “was to design a very bad antenna and make it fly.”

14 Sweetman, Bill, “How LO can you go?” Jane’s International Defense Review, January 2002, pp. 22-23. See also J. Paterson, “Overview of Low Observable Technology andIts Effects on Combat Aircraft Survivability,” Journal of Aircraft, Vol. 36, No. 2, March-April 1999, pp. 380-388.

15 See John J. Kohout III, “Stealth in Context,” The B-2 Bomber: Air Power for the 21st Century (New York: University Press of America, 1995), pp. 141-144.

• Radar “sees” the area defined by the returned radar waves

• This can be much larger or much smaller than the physical area

• Radar cross section reduction shrinks the size of return field

• RCS is sum of return vectors

What the Radar SeesRCS

Source: Adapted from Grant, Rebecca.The Radar Game (Arlington, VA:IRIS Independent Research, 1998), p. 23

Source: Grant, The Radar Game, p. 27

-.0001Square Meters

-.001 -.01 -.1 1.0 10 100 1,000 10,000



The Stealth Zone Conventional Aircraft

-20 -10 0 10 20Fighters Bombers Ships

30 40

Page 9: Analogues Stealth




which, even with shielding, dramatically increasethe heat trail created by engine exhaust. Once atsupersonic speed, an aircraft’s surface heats upmarkedly owing to the increased friction betweenthe atmosphere and the skin of the aircraft. TheF-22, uniquely capable of flying at supersonicspeeds for extended periods in non-afterburning“supercruise,” must incorporate additional meas-ures, such as leading-edge cooling and special sur-face paints, to counter this phenomenon.16

Stealth critics and advocates alike point out thatlow-observable aircraft are not invisible, and ashundreds of thousands of witnesses at collegefootball games and parades will attest, they areeasily seen in conditions where a stealthy aircraft’smission is to show off. But visual detection hasbeen made more difficult by diminishing the aircraft’s size and shape, treating its surface withnon-reflective coatings, and minimizing the trailof engine smoke or condensation through tech-nology and operating procedures. Clearly, themost submarine-like tactic that a stealthy aircraftcan adopt is to operate under the cover of dark-ness to reduce the probability of visual acquisi-tion, and that concept of operations has been

used exclusively, thus far, incombat operations. How limit-ing a factor this is will dependon the mission’s purpose andpriority, as well as aircraft type.In part to give the B-2 bombera “24/7” capability during thefirst few days of an air cam-paign, for example, the AirForce developed the “GlobalStrike Task Force” concept ofoperations. Composed ofstealthy F-22s and B-2s, thisplan provides a stealthy daylightair superiority escort to defeatany enemy interceptors thatmight acquire the B-2 visuallybefore integrated air defensesare degraded. Given that con-cept of operations, any addedB-2 vulnerability resulting froman increased probability of visu-al detection would seem to

occupy a very narrow slice of the battlespace:enemy interceptors operating deep in their terri-tory beyond the F-22’s operating radius duringthe day in clear weather.17

The F-22 “Raptor” stealth fighter, above, has been outfitted with special technologies, such as leading-edge cooling and special surface paints, for infrared signature reduction at high-speeds.

16 Sweetman, “How LO can you go?” p. 22.17 See Christopher J. Bowie, “Destroying Mobile Ground Targets in an Anti-Access Environment,” Northrop Grumman Analysis Center Papers (December 2001), p. 9.

The B-2 “Spirit” stealth bomber, above, and the F-22stealth fighter form the lethal centerpiece of the Air Force’snew “Global Strike Task Force” concept of operations.

Page 10: Analogues Stealth

18 Kohout, p. 143.19 Office of the Secretary of the Air Force, Gulf War Air Power Survey: Operations and Effectiveness, Vol. II (Washington, D.C., U.S. Government Printing Office, 1993), p. 124.20 Chris Bowie, Untying the Bloody Scarf (Arlington, VA: IRIS Independent Research, 1998), p. 16.

1 0


As those same football fans watching a stealth fly-over would point out, when contrasted withfighters plugging in their afterburners the B-2 isdisappointingly quiet—and deliberately so. All-aspect stealth design includes diminishing theability of acoustic sensors to locate the aircraft. Inaddition, sound in the atmosphere is subject toirregularities similar to anomalies submarine-seek-ing sonar encounters owing to thermal layering inthe ocean. As one student of airborne stealth con-cluded, “Wind, ambient noise, atmospheric layer-ing, and rather rapid dissipation in the atmos-phere all combine to make sound a rather unreli-able and indeed expensive approach to detectingan attacking force.”18

Radio or radar signals transmitted by a stealthyaircraft could also give away its position.Therefore, techniques to decrease the probabilityof intercepting those signals, such as controlledand moderated electronic pulses that do notexceed the range of the target, and frequency-hopping radios and radars, are used to deny elec-tromagnetic detection. As in the case of the sub-marine, radio silence is the dominant concept ofoperation for stealthy aircraft, and the use of pas-sive receivers, including links from satellites, canprovide a comprehensive operating picture whileobviating external transmissions requesting navi-gation, targeting, or order-of-battle information.

Stealthy aircraft in combat. For many years,designers and builders of stealthy aircraft had tocontent themselves with computer-based simula-tions and flights over radar ranges to judge air-craft low-observability. Even the first combat useof the F-117 in Panama was against an adversaryill equipped to test conventional aircraft, muchless the stealthy Nighthawk. Since then, however,we have seen stealthy aircraft employed in hostileskies over Iraq, Serbia and Afghanistan. As aresult, we can conclude that airborne stealthworks.

On the first night of Desert Storm according tothe Gulf War Air Power Survey, “…the F-117sthat attacked the first targets in the capital…flewinto, over, and through the heart of the fullyoperating air defenses of Baghdad with no sup-

port from electronic countermeasures.”19 But theairmen planning that war’s first attack were notwilling to bet on unaided stealth technology, andrequested electronic jamming support in the formof three EF-111 aircraft over Baghdad. However,Iraqi air force activity forced one of the Ravens todivert, while the other two arrived later thanplanned and were forced to begin jamming wellbeyond the desired range.

It is not clear from available evidence whetherthat radar jamming aided the F-117s in avoidingdetection over Baghdad. We know that no fol-low-on F-117 strikes received direct jammingsupport, but we also can assume that these attackoperations benefited from the battlespace confu-sion generated by indirect jamming and other airattacks on Iraq’s integrated air defenses. As ChrisBowie has suggested,20 two principal conclusionscan be drawn from this combat use of stealth.First, the F-117s were able to penetrate relativelysophisticated air defenses without standoff jam-ming support, and did so repeatedly early in thewar. Second, although available electronic jam-ming may be desirable and planned to supportstealthy strikes, if that support is disrupted theattack can probably continue as planned withoutgreatly increasing the risk that the stealth aircraftwill be detected, tracked and engaged.


The F-117A “Nighthawk” stealth fighter, above, was thestar of the Gulf War air campaign.

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• Longer Early Warning

• More Time in Jeopardy

• Shorter Early Warning

• Less Timein Jeopardy

SAM Site

SAM Site

SAM Site

SAM Site


Source: Adapted from Grant, The Radar Game, p. 37


Non-Stealth Aircraft Stealth Aircraft

EarlyWarningRadar SAM Site

SAM Site

SAM Site

SAM Site




1 1



The B-2 stealth bomber’s performance overSerbia during Operation Allied Force mirrored theF-117’s success over Iraq. Because the B-2 wouldpenetrate uncorrupted air defenses on the war’sfirst night, mission planners constructed a rigidflight plan, known as the “blue line,” designed tooptimize both the B-2’s low-observable character-istics and the support available from jamming,defense suppression, and air superiority aircraft.21

As a precaution, and because the option existed atrelatively little cost, this approach to B-2 missionplanning continued throughout the campaign,and defensive support was provided when avail-able. Nevertheless, at least one B-2 mission wasexecuted autonomously during the conflict, whenbad weather forced the cancellation of all theplanned escort and support sorties in the theater.After the war, Air Force officials were quick tounderscore their confidence in the B-2’s ability toavoid detection on its own, while arguing thatproviding the stealthy bomber with available in-theater support was still a prudent, if conserva-tive, concept of operations.

Together, the B-2 and the F-117 put on animpressive display of offensive dominance duringOperation Allied Force. For most of the war theywere the only two aircraft to deliver direct-attackmunitions against heavily defended Belgrade.During the first eight weeks of the war, a total ofsix B-2s operating out of Whiteman AFB,

Missouri flew only three percent of the alliedcombat sorties but destroyed 33% of the targets.Using the Joint Direct Attack Munition (JDAM)and augmenting that weapon’s through-the-weather accuracy with its on board GPS-aidedradar, B-2s hit 84% of their targets on the firststrike and averaged 15 targets attacked per sortie.Not only were no B-2s lost; there is no evidencethat they were even detected, much less trackedand fired upon by Serbian air defense. The B-2

A B-2 bomber refuels under the cover of darkness beforeentering Serbian airspace during 1999’s OPERATIONALLIED FORCE.

Figure 4. Stealth Strike

21 Because the Air Force had retired its EF-111s after the Gulf War, the electronic jamming mission fell to the jointly operated EA-6Bs. Those aircraft not only providestandoff jamming, but also fire anti-radiation (HARM) missiles at any radar attempting to acquire a US aircraft. F-16 fighters equipped with HARM capability also con-tributed to defense suppression, firing their missiles in both reactive and preemptive modes. Finally, combat air patrol (CAP) air superiority fighters were available tothwart any enemy fighters.

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was judged by the air war’s commander to be the“superstar” of the Kosovo campaign.22

What, then, should be made of the Serbs down-ing an F-117 with a barrage of Russian-madeSA-3 surface-to-air missiles (SAMs)?23 Althoughan authoritative public accounting of the shoot-down is not available, numerous factors probablycontributed to the loss. Support assets may nothave been positioned properly, the missile sitewas either unknown or the SAM had been movedfrom a previously known location, the F-117 wasflying along a route repeatedly used to strike keytargets, (thus allowing the enemy to anticipatethe aircraft’s location based on dead reckoningfrom a known point and time), and some opera-tor error or technical malfunction may have keptthe bomb bay doors open longer than planned,providing a targetable radar return.24 In any case,the downed F-117 is a dramatic reminder thatstealth aircraft can be shot down, and that sur-vival against sophisticated defenses requires con-tinual attention to all-aspect low observabilityand innovative tactics. In this regard, stealthyaircraft are not much different from stealthy sub-marines, which have had their share of losseswhen stealth was compromised, however briefly.

In the air operations supporting OperationEnduring Freedom over Afghanistan, stealthy air-craft played a limited role for two reasons. First,the unavailability of land bases to support rela-tively short-range fighter aircraft meant that theAir Force fighter contribution to the battle,including the F-117, was minimal.25 Secondly,the very modest air defenses possessed by al Qaedaand the Taliban meant that stealth was notrequired after a brief “kick down the door” operation at the start of the air war to destroy air defenses, fighter aircraft and command andcontrol centers. Those strikes were executed by B-2s launched from their American bases. Afterthis enabling mission, they turned over the ensuing strike missions to the non-stealthy B-52sand B-1s.26

Drawing Analogies: (1) Future Challenges

What sorts of analogies are useful to drawbetween stealthy submarine and aircraft combatemployment and the wide range of countermea-sures deployed—or envisioned—to lessen theircombat advantage? Proponents of the military useof stealthy aircraft would not have wanted tosearch for analogies with the submarine at theend of World War I. At that time, the perceivedvulnerability of the submerged submarine, givenan accurate attack on it, was overemphasized.Overlooked was the fundamental element of thesubmarine’s defenses—its stealthy nature—thatreduced its susceptibility to detection and greatlydiminished the probability of such an attackoccurring at all.

Simply put, the true operational capabilities of astealthy platform in any media are not self-evi-dent when the system first appears, and adversaryand advocate alike misunderstand the technology.The adversaries apply traditional perspectivesoften mixed with a resistance to change, and failto appreciate the system’s potential. The advo-cates push their innovation, but often overlookthe range of applications and technologies likelyto reshape the strategies and tactics of warfare. Inthe case of the submarine, it first took theGerman snorkel-equipped U-boat during WorldWar II and, ultimately, nuclear power, before thegreatest combat leverage could be gained fromstealth. Today, low-observable technologiesapplied to reduce an airplane’s signature arealready comparable to those of the modern sub-marine, but the implications of that revolutionarytechnology are only just beginning to be includedin manuals of air combat.

What lessons might a low-observable aircraftadvocate have drawn from the use of the subma-rine during World War II? The first lesson wasthat a stealthy platform will perform best in amanner that preserves its low-observable proper-ties—working alone or in very small numbers27,

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22 Grant, p. ii.23 Lambeth, Benjamin S. NATO’S Air War For Kosovo: A Strategic and Operational Assessment (Santa Monica: RAND, 2001), p. 116.24 Sweetman, “How LO can you go?” p. 21.25 One report, quoting unpublished Pentagon statistics, stated that USAF bombers dropped 69% of the weapons over Afghanistan, Navy fighters launched from carriers

dropped 24%, and USAF fighters dropped 7% of the ordnance. See “Fly by Night,” Aviation Week and Space Technology, March 18, 2002, p. 23.26 See John A.Tirpak, “Enduring Freedom,” Air Force Magazine, February 2002, pp. 32-39.27 Some would argue that being in an environment where there are numerous other targets with strong returns, or when jamming is present, would improve the

survivability of a stealthy aircraft. But all those returns will also result in increased attention to that sector of the sky. See Paterson, p. 386. Submarines operating closelywith surface battle groups in the littorals would also seem more susceptible to detection.

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under mission-type orders, being given consider-able latitude in terms of time and space con-straints, operating with tactics that may seem toviolate traditional principles of force application,and with absolute attention to all aspects of oper-ational security. A second lesson is that sinceinsufficient resources require the pooling of assetsand a subsequent loss of low observability inemployment, stealthy systems must be acquiredin numbers adequate to get the job done.28

A third lesson is that a system able to commencean attack unobserved and to disengage at will hasa multiplier effect on required enemy defenses.

Analogies can also be drawn between post-WorldWar II ASW efforts and the hunting of stealthyaircraft. The search for a substitute for sonar asthe dominant ASW detection technique hasproved fruitless. Radar enjoys that same domi-nant position when it comes to finding airplanes,and other techniques provide only limited assis-tance under ideal conditions. Nevertheless, animportant similarity to be illustrated is that nei-ther the stealthy submarine nor the low-observ-able aircraft can be assured of its future surviv-ability. Each will continue to face challenges to itssuccessful combat operation. Each must continueto be improved.

Future challenges to underwater stealth. Active orpassive acoustic detection of submarines has longbeen the sine qua non of ASW techniques, andacoustic engineers continue to develop measuresto reduce vulnerabilities in these areas. For yearsit has been understood that, to minimize acousticenergy coupled to the environment, a submarine’spropeller should have an odd number of bladesto preclude reinforcement of the perturbationscaused when these blades intersect the turbulentflow behind an even number of control surfaces(rudders and stern planes). It was further under-stood that reducing the range to which suchacoustic events would propagate required moreblades rather than fewer. More recently, a Britishinnovation called a “propulsor” has been devel-oped to stabilize the flow from the rotatingblades. In this concept, a multi-vaned rotatingdevice is surrounded by a shroud containing fixedblades which “untwist” the flow from the rotating

blades, creating an axially stable thrust similar toexhaust from a jet engine. Other methods ofdamping acoustically detectable flow noise, suchas vortices from hull discontinuities, rely on formshaping—analogous to the stealthy design tech-niques of the F-22 and B-2.

Taking a lead from Russian innovations, hullcoatings have been developed to significantlyreduce a ship’s “target strength”—the acousticanalogue to RCS. These not only reduce the echoreturned from an active sonar but also have thesecondary effect of lessening the amount of struc-ture-borne vibration noise coupled to the ocean.

Some potential observables from a submarine,such as internal waves, thermal discontinuities orchemical/nuclear activation by-products, tend tostay at the depth at which they were generated,thus requiring a three- rather than two-dimen-sional search. Even with such a search, these sub-marine “footprints” dissipate quickly. For exam-ple, owing to the ocean’s immense thermal con-ductivity, temperatures can be restored to normaljust a few ship lengths behind a submarine dis-persing megawatts of heat energy into the water.On the other hand, internal waves or entrappedchemical/isotopic signatures persisting for days oreven weeks simply indicate that a submarine, atone time, passed through those waters.

Other theories of submarine detection suggestthat high-powered acoustic sources operating atvery low frequencies could illuminate thousandsof square miles under the ocean’s surface. Like anacoustic tomographic version of an MRI, theseemingly chaotic echoes from the entire areacould theoretically be collected by a large numberof geographically dispersed sensors, processed at acentral location, and correlated to develop a com-mon operational subsurface picture. Such a sys-tem is analogous to the bistatic radar challenge tostealthy aircraft discussed below. Submarine pres-ence could probably be detected by these multi-ple sensors and receivers, because it would beimpractical to apply the thick acoustic hull coat-ings required to reduce reflectivity from the longwavelengths associated with the low frequenciesinvolved. However, the technologies and resources

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28 Proponents of stealth in combat aviation argue that the U.S. has not capitalized on its substantial investment in stealth technology in its acquisition of limited numbersof aircraft. Only 59 F-117s were produced, and the B-2 buy was cut from a planned 132 to 21. The original plan to acquire 750 F-22s has been pared to less than 300,and the JSF is also facing program cuts.

Page 14: Analogues Stealth

necessary to put such a system in place arepresently well beyond the capabilities of credibleadversaries.

Since the late 1950’s Skipjack, single-hull con-struction has long been a characteristic of U.S.submarines–meaning that the entire pressure hullisn’t encased within a larger superstructure con-taining the main ballast tanks. Proposals to revertto a double-hull construction, allowing a muchgreater payload to be carried, are also being evalu-ated in terms of stealth. An included benefit ofthis change in shipbuilding philosophy, for exam-ple, would be a tripling of surfaces available forcoatings to further mitigate active/passiveacoustic signatures.

Non-acoustic detection vulnerabilities will alsoremain a challenge in the future. Many of theseare hydrodynamic in nature, either within thewater column or at the air-water interface. Thesubmarine force well understands these potentialdetection phenomena, and applies the tactics ofstealth to meet emerging ASW technologies.Thus, to keep “Bernoulli humps” or “Kelvinwakes” from being observable at the surface, theguidance might be: “Don’t go faster than XXknots if shallower than YYY feet and sea state isless than Z.” As sensor and processor capabilitiesimprove, and smaller signals are recoverable fromnoise, a constant review and modification ofdetection-free operating envelopes will remain anessential element of stealth.

As a rule of thumb, RF energy penetrates seawa-ter to only a small fraction of a wavelength. Anotable exception to this is at a small sliver of thespectrum in the blue-green visual domain. Thisphenomenon has long been a source of specula-tion and engineering, not only for detection, butalso for communication with submerged sub-marines. However, blue-green lasers have tended

to be either very inefficient or very expensive.Some recent solid-state advances have made theselasers more feasible and affordable, prompting therequirement for hull-borne early warning sensorsto provide advance warning.

In sum, there are numerous known detectionmodes for modern submarines, all of which arekept under very close scrutiny. The submarineforce must be the first to note a disruptive tech-nology and initiate efforts to counter or mitigateits impact. A continuing process of action-reac-tion has occurred in which potential upgrades inthreat capabilities are countered by improvementsin platform stealth. It is through these improve-ments that submarine survivability and effective-ness have been maintained.

Future challenges to airborne stealth. Stealthy air-craft such as the F-117 and B-2 have provedhighly successful in combat against current radardetection technology, monostatic radar, wherein asingle radar functions as both transmitter andreceiver. Although the B-2 is considered to be ageneration ahead of the F-117 in RCS reduction,both aircraft rely on the same principle of scatter-ing the reflection of incoming radio frequencywaves from the transmitter, thereby reducing thesize of their radar return when the transmitterand receiver are collocated. Theoretically, detec-tion of stealthy aircraft could be enhanced byseparating the transmitting radar from the receiv-ing antenna in a configuration known as bistaticradar. In this concept, the receivers, geographical-ly separated from the transmitter, must be prop-erly aligned to catch the radio waves scattered bythe low-RCS aircraft.

While simple in concept, bistatic radar detectionfaces significant technical and operational chal-lenges. Because stealthy aircraft are observableonly from a very small number of angle combina-tions, the aircraft will be reflected only if an idealalignment exists among transmitter, target andreceiver. Providing conventional radar the cover-age needed to ensure sufficient reception of thescattered signals might require placing radartransmitters every few miles—a cost-prohibitiveapproach. Coordinating the interception of mul-tiple radar beams and collecting and analyzingradar return data from a number of transmittersand receivers would also require massive computing

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The Virginia-class attack sub (SSN-774), above, will incorporate the latest in submarine stealth, along with awide range of new offensive capabilities, to support the littoral warfare mission.

Page 15: Analogues Stealth

power. Therefore, considerable skepticism existsthat a practical, stealth-detecting bistatic radarsystem will be deployed.29

Increases in computing power and the prolifera-tion of commercial radio waves as a by-productof the information revolution have given rise toanother challenge to stealthy aircraft. In the daysbefore cable, many television viewers could vouchfor the fact that an aircraft flying nearby couldmomentarily disrupt the antenna-generatedimage on their TV screen. That phenomenon isthe basis for a recent series of articles and inter-views alleging that “passive coherent location”(PCL) or “passive bistatic” radar systems usingTV, radio, or mobile phone transmitters, coupledwith sensitive receivers, could track stealthy air-craft. The theory behind this concept is that aradar system could be designed to exploit radiosignals already plentiful in the atmosphere ratherthan generating its own targeted beams. Systemsbased on cell phone signals as well as radio andtelevision waves have recently been touted asbreakthroughs capable of defeating airbornestealth.30

However, analysis and testing have determinedthat the performance and capability of such sys-tems are considerably less than that of commoncommercial and early warning radars. The U.S.Air Force does not regard PCL/passive bistaticsystems as possessing a “counter-stealth,” capabili-ty, notes the large number of false tracks thesesystems generate, and has concluded that jam-ming or other techniques could degrade the per-formance of passive detection systems even fur-ther.31

Perhaps the most problematic of counter-stealthtechnologies for airborne targets will be continu-ing improvements in infrared search and track(IRST) systems. Heat generated by engine andexhaust systems is one source of detection, andairborne IRST systems in fighter airplanes haveroutinely been able to detect afterburning enginesat a range of 30 miles. IRST systems that concen-trate in a higher range of the infrared spectrum to

detect surface heating resulting from atmosphericfriction may prove to be more effective, with themost advanced systems credited with picking upa conventional target at ranges up to 50 miles.Although IR-suppressing paint, exhaust shieldingand cooling, and heat tolerant fuels will all beused in lowering a stealthy aircraft’s thermal sig-nature, the plane’s surface will always be hotterthan that of its environment, and a temperaturedifferential as low as one degree may be sufficientto cue other sensors to look more closely.Nevertheless, the problem of searching large vol-umes of space for small differences in tempera-ture in varying atmospheric conditions stillapplies. According to the Air Force, the F-22 willhave a “low-aspect IR signature under sustainedsupersonic conditions.”32 Infrared detection ofstealthy aircraft is sure to remain a game of meas-ure and countermeasure.

Finally, there is the challenge of maintainingstealth logistically once it has been achieved oper-ationally. As stealthy air vehicles age, increasedLO maintenance is required to prevent signaturedegradation of unique design features. Both theF-117 and the B-2 have suffered from low “mis-sion capable rates,”—that is, the amount of timethat the aircraft is judged to be combat-ready—owing to excessive down times to replace andrepair LO-related structures and surfaces. Thoseproblems have been exacerbated by shortages inthe skilled labor force needed to do the work andthe training demands to fly the limited numberof aircraft acquired, thus postponing needed air-craft maintenance.

On the B-2, the application of alternate high frequency material (AHFM) now underway willresult in more durable and effective low observability,while dramatically reducing labor hours permaintenance action. Other actions to replacestealth treatments around windows and doorsand to deal with hot trailing edges and tailpipesare also essential to keeping the aircraft in a com-bat configuration. Despite these continuedimprovements in stealth technology, it seems cer-tain that the supersonic, aerobatic F-22 and the

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29 John Schaeffer, Understanding Stealth (Marietta Scientific: Marietta GA, 1997), p. 15.30 Bill Sweetman, “Stealth Threat,” Popular Mechanics, February 2002.31 Office of the Secretary of the Air Force, “USAF Analysis of Passive Coherent Location Systems,” Secretary of the Air Force Public Affairs, Washington, D.C.,

June 15, 2001.32 Sweetman, “How LO can you go?” p. 22.

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carrier-based F-35 will face environmental andlogistical challenges to maintaining their stealthwhen deployed forward.

We conclude that, as long as the submarine candeny the opponent an acoustic track and thestealthy aircraft can deny the opponent a radarlock, each low-observable platform will remainhighly survivable, even in the most hostile environment. Implicit in this assertion, however,is that the designers and operators of thesestealthy platforms will pay careful attention tothe status of disruptive technologies and willexercise tactical innovation, modify and updatesubsystems, and vary operational modes to mini-mize any emerging vulnerabilities. If left unim-proved, a stealthy system is likely to fall victim totechnological improvements in those sensorsfrom which they were designed to be secure.

Drawing Analogies (2): Conclusions andImplications

After World War II, the U.S. Navy concentratedon exploiting the submarine’s stealthy characteris-tics. Now the U.S. Air Force and the U.S. Navy,facing a new century with a new capability, couldbe on the threshold of leveraging low-observableaircraft with analogous tactics and technologies.

As they cross that threshold, they should ponderand seek to emulate the submarine’s success. Nonew or improved technologies have created the“transparent ocean.” The submarine’s ability toremain stealthy, and the potential for low-observ-able aircraft to duplicate that experience—despitethe enormous intellectual and monetary capitaldedicated to defeat stealth—can be attributed toone or more of the following considerations:

The real environment in which forces operatediffers significantly from the presumed or laboratory conditions in which new detectiontechniques are developed.

• Regarding ASW, enthusiasts lacked an appreci-ation for the geographic scale of looking forsmall things in large, noisy volumes.Furthermore, the superiority of properlyemployed stealth has never been a marginalissue, as in the “guns versus armor” case,where the relative advantage has periodicallyswung from one side to the other. There arefew technical or operational reasons to thinkthat this condition will change. In the end,when exploitable observables are reduced tonearly the background levels of the vastexpanses of sea and sky, the adversary is forcedto try to pull faint signals out of noise. Thephysics of such a problem are inherentlyskewed in favor of the stealthy platform.

• Similarly, critics of stealth aircraft are quick tonote that the aircraft is not likely to provecompletely invisible to some radars and fail toappreciate that there is sequence that appliesto airborne (or undersea) intercepts or attacks.To shoot down a stealthy aircraft, an opponentmust identify and track it with a long-rangesensor, then pass the target’s track to an air-borne interceptor or ground-based anti-aircraftsystem. That system must then locate, track,acquire and lock on to the aircraft. But thestealthy aircraft’s reduced radar detection rangemakes it difficult to launch and vector theattacking system before losing contact, andplaces demands well beyond the specifiedaccuracy and fusing parameters of missile seekerheads to the point where destruction is highlyunlikely. This required synergism of multiplesensors of varying granularity to derive intelli-gence is fully understood by any middle-agedperson wearing trifocals: a lens to drive to thelibrary, a second to find the book, and a third

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Carrier basing may pose environmental and logistical challenges to LO maintenance of the F-35 Joint Strike Fighter, shown above.

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to read the text. Remove or degrade the opti-cal system at any level, and the sequence nec-essary to get to the final solution is broken.

• For both stealthy submarines and aircraft, thesynergy in combining tactics and technologymakes defense doubly difficult. Although bothplatforms must sacrifice their stealth duringattack—launching torpedoes or opening bombbay doors—these events offer limited opportu-nities for counter-attack. Moreover, additionalaction can be taken by the stealthy platformduring the attack phase to further lower itssusceptibility to detection. Submarines, forexample, could launch a decoy, change courseand run in a silenced mode. Stealthy aircraftcould launch a defensive missile (such as aminiature air-launched decoy) or an offensiveone (such as an anti-radiation weapon) to con-fuse or suppress the adversary.

Operational or technical intelligence on newanti-submarine and anti-stealth techniques isavailable to submariners and aviators, allowingthem to modify their tactics to negate thosetechniques.

• The submarine has shown that stealth has asweeping impact because it goes to one of thefundamental success variables of warfare: theability to see the opponent (be it target orthreat) before being seen. In an operationalcontext, history has shown that this enabledthe submarine to evolve an entirely new set ofoperational tactics and doctrine, particularlythe ability to operate alone deep within enemyterritory for extended periods with minimumoutside support.

• Stealth provides the advantage that tactics canbe as useful as technology in achieving this all-aspect low observability. One can detect thethreat and maneuver around it or one canpresent the platform to the opponent in a waythat defeats his sensor.

• A nearly universal truth is that the command-er of the stealthier platform always retains theinitiative to attack or not. A corollary to theseobservations is that a defender’s detection of astealthy platform can be considered prima facieevidence that an attack is in progress, becausethe attacker has obviously made a consciousdecision to risk that detection. Because of this,there is an extraordinarily high (and sometimes

frenzied) rate of ordnance expenditure in realcounter-stealth scenarios. For example, theRoyal Navy, faced with the threat of only onesmall coastal defense submarine off theFalklands, expended—fruitlessly—nearly theentire fleet’s inventory of ASW weapons.Against a stealthy aircraft, plagued by falsealarms and unable to precisely locate its adver-sary, ground-based air defenses have similarlyfired at extraordinarily high rates, as evidencedby CNN’s displays of anti-aircraft artillery inthe skies over Baghdad during the first nightsof Desert Storm.

Stealth provides a long-term competitive advantage.

• The existence of a stealthy force creates anenormous burden on the defense. Whether ornot the platforms are being employed, there isa major requirement for a prepared response,because the defender is never sure where orwhen the threat will surface. Stealth thus con-tributes to virtual attrition of enemy forces bycausing the adversary to maintain a high andexpensive level of readiness.

• The virtual attrition property of stealth sug-gests the opportunity cost of defending againstlow-observable platforms. During World WarII the allies invested in thousands of ships andhundreds of thousands of people in defendingagainst U-boat attacks. Theoretically, extreme-ly high concentrations of air defense systemscould provide some capability against stealthyaircraft, but the B-2 was designed to negatethat enormous investment made by the formerSoviet Union in air defenses. Any potentialU.S. adversary faces an enormous opportunitycost to develop a system to defend itselfagainst stealthy ships and aircraft whileattempting to engage the U.S. military inother arenas. Thus the U.S. investment instealth (an asymmetric advantage in its ownright) poses a significant allocation dilemmafor potential adversaries—invest enormousamounts to counter stealth (and neglect otherareas) or spend elsewhere (and remain vulnera-ble to stealth).

The submarine or aircraft, as a stealthy system,is a noncooperative target able to manipulate itsobservables and reduce its signature by constantlyreviewing and correcting emerging deficiencies.

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• Had the nature of the submarine threatremained constant, more might have beenexpected from ASW efforts over the years.However, stealthy platforms have strong operational forcing functions to evolve tech-nologies at a rate capable of maintaining theircovert nature in a relative sense, and have anintrinsic advantage of being able to “sense thesensor” (or the platform upon which it is car-ried), and respond accordingly.

• Another lesson is that true stealthiness involvesall aspects of a platform’s design and opera-tion. Decades of evolution, sometimes withhard lessons learned through losses, haveshown that every potential source of signaturemust be controlled. Reflections of the adver-sary’s energy (sonar or radar) have to bereduced; energy radiation from the low-observable platform (self-generated signature)has to be minimized; and operational practices(use of active vice passive radio communica-tions) have to be controlled.

• In submarine warfare, when complacency wasavoided, where counter-stealth R&D pro-grams were aggressively maintained, and whenoperational desires were not allowed toencourage nonstealthy behavior, stealth hasprevailed. The implicit issue here is that stealthwas the only variable judged immune fromdesign and development tradeoffs. The Navymight accept bigger, slower or shallower, buteach new class, or variant, had to have the sameor less radiated noise characteristics than thatof the preceding boat. All of these considera-tions are transferable to low-observable aircraft.

• It was noted earlier that every U.S. militarysubmarine, on decommissioning, left thewater stealthier than it entered. Indications arethat owners of stealthy aircraft have not yetlearned that lesson. LO modifications to theF-117 and B-2 have not been granted priorityin comparison with other upgrades, with anattendant decline in mission-capable rates.Even more troubling is a retreat from main-taining an aircraft’s stealth to enhance othercapabilities. Proposals to hang external ord-nance on the JSF or to turn it into a standoffelectronic jammer are illustrative of this trend,as are suggestions to stretch the F-22 anddiminish its stealth to give it an air-to-groundcapability. Clearly, tradeoffs will occur between

low observability and mission requirements,but related tactics and operational proceduresmust offset any stealth technology surrendered.


The analogies drawn between the stealthy sub-marine and low-observable aircraft suggest the following:

• Stealthy airborne platforms will maintain along-term edge over defenses, providing thatits sponsors continue to study and exploitenvironmental phenomena and opponents’countermeasures, and take prompt and sus-tained corrective measures.

• Continued operation of stealthy airborne plat-forms will prompt new tactics, techniques andprocedures markedly different from conven-tional concepts of operations. For example,the World War II bomber streams numberedin the hundreds of aircraft both for protectionand to muster the firepower necessary toaccomplish the mission; it was impossible toconceal such a signature. Similarly, the massivestrike packages into North Vietnam provideda wealth of warning to the opponent, andwere structured to smash directly throughenemy air defenses rather than to avoid them.Single-ship B-2 missions over Serbia andAfghanistan illustrate the value of stealth inavoiding these costly tactics. Converting theB-2 and the SSBN from their strategic nuclearroles to providers of long-range, precise con-ventional firepower may be one of the mosttelling analogies of all.

• Stealthy and nonstealthy aircraft will have todevelop special techniques for operating togeth-er, so that nonstealthy aircraft will benefit whilestealthy ones will not lose their inherent advan-tage. Working together, however, does not meancollocated in space or time. The submarineconducting forward offensive operations isworking with the approaching carrier battlegroup by destroying or diverting potentialattackers. The stealth aircraft, operating infront of a larger, nonstealthy force, defeats airdefenses to allow a greater penetration proba-bility for the following force, and frees up supporting resources (air superiority, escort,and electronic countermeasures aircraft) forother uses.

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• Numerous innovative countermeasures tostealthy aircraft will be proposed, but few, ifany, will have lasting impact even though theymay achieve momentary headlines.

• Low-observable aircraft, in which stealth hasbeen added to the intrinsic mobility of the air-plane, will prove as revolutionary as thenuclear submarine, where mobility was addedto inherent stealth.

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Analysis Center Papers are available on-line at the NorthropGrumman Washington Office Web site, Capitol Source, at www.capitol.northgrum.com. For substantive issues related to this paper, please contact Robert P. Haffa, Jr., [email protected], or call him at 703-875-0002. For copies, please call 703-875-0054.

About the Authors

Robert P. Haffa, Jr. and James H. Patton, Jr.

Colonel Robert P. Haffa, Jr., USAF Ret, is Director of the NorthropGrumman Analysis Center. He is a graduate of the U.S. Air ForceAcademy, holds an M.A. degree from Georgetown University and aPh.D. in political science from the Massachusetts Institute ofTechnology, and is an adjunct professor in the Security Studies program at Georgetown University. His active Air Force serviceincluded operational tours in the F-4 aircraft in Vietnam, Korea andEurope.

Captain James H. Patton, Jr., USN Ret., is founder and President ofSubmarine Tactics and Technology, Inc. in North Stonington, CT. A graduate of the U.S. Naval Academy, he holds an M.S. in ocean engineering from the University of Rhode Island. His Navy careerincluded service on seven nuclear submarines, including command ofa Sturgeon attack boat.

Analysis Center Papers are periodic publications of the Northrop Grumman Corporation, an $18 billion global defense company with its worldwide headquarters in Los Angeles.Northrop Grumman provides technologically advanced, innovative products, services andsolutions in defense and commercial electronics, systems integration, information technologyand nuclear and non-nuclear shipbuilding and systems. With nearly 100,000 employees andoperations in 44 states and 25 countries, Northrop Grumman serves U.S. and internationalmilitary, government and commercial customers.

© 2002 Northrop Grumman Corporation. All rights reserved.

Printed in the United States of America.

The Northrop Grumman Corporation established the

Analysis Center in 1977 to conduct objective analyses of

strategic trends, defense policy, military doctrine, emerging

threats and operational concepts, and their implications for

the defense industry. The Analysis Center works on the

leading edge in shaping US strategy and defining operational

requirements. The Analysis Center Papers present ongoing key

research and analysis conducted by the Center staff and its