Stealth technology Stealth technology also termed LO technology ( low observable technology ) is a sub - discipline of military tactics and passive electronic countermeasures , which cover a range of techniques used with personnel , aircraft , ships , submarine s , missiles and satellites to make them less visible ( ideally invisible ) to radar , infrared , sonar and other detection methods . It corresponds to camouflage for these parts of the electromagnetic spectrum . Development in the United States occurred in 1958 , where earlier attempts in preventing radar tracking of its U - 2 spy planes during the Cold War by the Soviet Union had been unsuccessful . Designers turned to develop a particular shape for planes that tended to reduce detection , by redirecting electromagnetic waves from radars . Radar - absorbent material was also tested and made to reduce or block radar signals that reflect off from the surface of planes . Such changes to shape and surface composition form stealth technology as currently used on the Northrop Grumman B - 2 Spirit " Stealth Bomber " . The concept of stealth is to operate or hide without giving enemy forces any indications as to the presence of friendly forces . This concept was first explored through camouflage by blending into the background visual clutter . As the potency of detection and interception technologies ( radar , IRST , surface - to - air missile s etc . ) have increased over time , so too has the extent to which the design and operation of military personnel and vehicles have been affected in response . Some military uniforms are treated with chemicals to reduce their infrared signature . A modern " stealth " vehicle is designed from the outset to have a chosen spectral signature . The degree of stealth embodied in a particular design is chosen according to the predicted threat capabilities . History . The concept of camouflage is known to predate warfare itself . Hunters have been using vegetation to conceal themselves perhaps as long as people have been hunting . In England , irregular units of gamekeepers in the 17th century were the first to adopt drab colours ( common in 16th century Irish units ) as a form of camouflage , following examples from the continent . Diffused lighting camouflage , a shipborne form of counter - illumination camouflage , was trialled by the Royal Canadian Navy from 1941 to 1943 . The concept was followed up , but for aircraft , by the Americans and the British : in 1945 a Grumman Avenger with Yehudi lights , reached from a ship before being sighted . This ability was rendered obsolete by radar . The U - boat " U - 480 " may have been the first stealth submarine . It featured an anechoic tile rubber coating , one layer of which contained circular air pockets to defeat ASDIC sonar . Radar absorbent rubber / semiconductor composite paints and materials ( codenames : “ Sumpf " , " Schornsteinfeger ” ) were used by the Kriegsmarine on submarines in World War II . Tests showed they were effective in reducing radar signatures at both short ( centimetres ) and long ( 1 . 5 metre ) wavelengths . One of the earliest stealth aircraft was the Horten Ho 229 flying wing . It included carbon powder in the glue to absorb radio waves . Some prototypes were built , but it was never used in action . During the 1950s , the Avro Vulcan , a British bomber , had a remarkably small appearance on radar despite its large size , and occasionally disappeared from radar screens entirely . In 1958 , the CIA requested funding for a reconnaissance aircraft to replace the existing U - 2 spy planes , and Lockheed secured contractual rights to produce it . " Kelly " Johnson and his team at Lockheed ' s Skunk Works were assigned to produce the A - 12 ( or OXCART ) , the first of the previously top secret Blackbird series , which operated at high altitude of 70 , 000 to 80 , 000 ft and speed of Mach 3 . 2 to avoid radar detection . Radar absorbent material was used on U - 2 spy planes , and various plane shapes designed to reduce radar detection were developed in earlier prototypes , named A1 to A11 . In 1964 , an optimal plane shape taking into account compactness was developed for another " Blackbird " , the Lockheed SR - 71 . This aircraft surpassed prior models in both altitude ( 90 , 000 ft ) and speed ( Mach 3 . 3 ) . The SR - 71 included a number of stealthy features , notably its canted vertical stabilizers , the use of composite materials in key locations , and the overall finish in radar absorbing paint . During the 1970s the U . S . Department of Defence launched project Have Blue , with the aim of developing a stealth fighter . There was fierce bidding between Lockheed and Northrop to secure the multi - billion dollar contract . Lockheed incorporated into its bid a text written by the Soviet / Russian physicist Pyotr Ufimtsev from 1962 , titled " Method of Edge Waves in the Physical Theory of Diffraction " , Soviet Radio , Moscow , 1962 . In 1971 this book was translated into English with the same title by U . S . Air Force , Foreign Technology Division . The theory played a critical role in the design of American stealth - aircraft F - 117 and B - 2 . Equations outlined in the paper quantified how a plane ' s shape would affect its detectability by radar , its radar cross - section ( RCS ) . This was applied by Lockheed in computer simulation to design a novel shape they called the " Hopeless Diamond " , a wordplay on the Hope Diamond , securing contractual rights to produce the F - 117 Nighthawk starting in 1975 . In 1977 Lockheed produced two 60 % scale models under the Have Blue contract . The Have Blue program was a stealth technology demonstrator that lasted from 1976 to 1979 . The success of Have Blue led the Air Force to create the " Senior Trend " program which developed the F - 117 . Principles . Stealth technology ( or LO for " low observability " ) is not a single technology . It is a combination of technologies that attempt to greatly reduce the distances at which a person or vehicle can be detected ; in particular radar cross section reductions , but also acoustic , thermal , and other aspects : Radar cross - section ( RCS ) reductions . Almost since the invention of radar , various methods have been tried to minimize detection . Rapid development of radar during WWII led to equally rapid development of numerous counter radar measures during the period ; a notable example of this was the use of chaff . The term " stealth " in reference to reduced radar signature aircraft became popular during the late eighties when the Lockheed Martin F - 117 stealth fighter became widely known . The first large scale ( and public ) use of the F - 117 was during the Gulf War in 1991 . However , F - 117A stealth fighters were used for the first time in combat during Operation Just Cause , the United States invasion of Panama in 1989 . Increased awareness of stealth vehicles and the technologies behind them is prompting the development of means to detect stealth vehicles , such as passive radar arrays and low - frequency radar s . Many countries nevertheless continue to develop low - RCS vehicles because they offer advantages in detection range reduction and amplify the effectiveness of on - board systems against active radar guidance threats . Vehicle shape . The possibility of designing aircraft in such a manner as to reduce their radar cross - section was recognized in the late 1930s , when the first radar tracking systems were employed , and it has been known since at least the 1960s that aircraft shape makes a significant difference in detectability . The Avro Vulcan , a British bomber of the 1960s , had a remarkably small appearance on radar despite its large size , and occasionally disappeared from radar screens entirely . It is now known that it had a fortuitously stealthy shape apart from the vertical element of the tail . In contrast , the Tupolev 95 Russian long range bomber ( NATO reporting name ' Bear ' ) appeared especially well on radar . It is now known that propellers and jet turbine blades produce a bright radar image ; the Bear had four pairs of large ( 5 . 6 meter diameter ) contra - rotating propellers . Another important factor is internal construction . Some stealth aircraft have skin that is radar transparent or absorbing , behind which are structures termed re - entrant triangles . Radar waves penetrating the skin get trapped in these structures , reflecting off the internal faces and losing energy . This method was first used on the Blackbird series ( A - 12 / YF - 12A / SR - 71 ) . The most efficient way to reflect radar waves back to the emitting radar is with orthogonal metal plates , forming a corner reflector consisting of either a dihedral ( two plates ) or a trihedral ( three orthogonal plates ) . This configuration occurs in the tail of a conventional aircraft , where the vertical and horizontal components of the tail are set at right angles . Stealth aircraft such as the F - 117 use a different arrangement , tilting the tail surfaces to reduce corner reflections formed between them . A more radical method is to eliminate the tail completely , as in the B - 2 Spirit . In addition to altering the tail , stealth design must bury the engines within the wing or fuselage , or in some cases where stealth is applied to an extant aircraft , install baffles in the air intakes , so that the compressor blades are not visible to radar . A stealthy shape must be devoid of complex bumps or protrusions of any kind ; meaning that weapons , fuel tanks , and other stores must not be carried externally . Any stealthy vehicle becomes un - stealthy when a door or hatch opens . Planform alignment is also often used in stealth designs . Planform alignment involves using a small number of surface orientations in the shape of the structure . For example , on the F - 22A Raptor , the leading edges of the wing and the tail surfaces are set at the same angle . Careful inspection shows that many small structures , such as the air intake bypass doors and the air refueling aperture , also use the same angles . The effect of planform alignment is to return a radar signal in a very specific direction away from the radar emitter rather than returning a diffuse signal detectable at many angles . Stealth airframes sometimes display distinctive serrations on some exposed edges , such as the engine ports . The YF - 23 has such serrations on the exhaust ports . This is another example in the use of re - entrant triangles and planform alignment , this time on the external airframe . Shaping requirements have strong negative influence on the aircraft ' s aerodynamic properties . The F - 117 has poor aerodynamics , is inherently unstable , and cannot be flown without a fly - by - wire control system . Ships have also adopted similar methods . The Skjold class patrol boat was the first stealth ship to enter service , though the earlier Arleigh Burke class destroyer incorporated some signature - reduction features . Other examples are the French La Fayette class frigate , the German Sachsen class frigate s , the Swedish Visby class corvette , the USS " San Antonio " amphibious transport dock , and most modern warship designs . Similarly , coating the cockpit canopy with a thin film transparent conductor ( vapor - deposited gold or indium tin oxide ) helps to reduce the aircraft ' s radar profile , because radar waves would normally enter the cockpit , reflect off objects ( the inside of a cockpit has a complex shape , with a pilot helmet alone forming a sizeable return ) , and possibly return to the radar , but the conductive coating creates a controlled shape that deflects the incoming radar waves away from the radar . The coating is thin enough that it has no adverse effect on pilot vision . Non - metallic airframe . Dielectric composites are more transparent to radar , whereas electrically conductive materials such as metals and carbon fiber s reflect electromagnetic energy incident on the material ' s surface . Composites may also contain ferrites to optimize the dielectric and magnetic properties of a material for its application . Radar - absorbing material . Radar - absorbent material ( RAM ) , often as paints , are used especially on the edges of metal surfaces . While the material and thickness of RAM coatings can vary , the way they work is the same : absorb radiated energy from a ground or air based radar station into the coating and convert it to heat rather than reflect it back . Radar stealth countermeasures and limits . Low - frequency radar . Shaping offers far fewer stealth advantages against low - frequency radar . If the radar wavelength is roughly twice the size of the target , a half - wave resonance effect can still generate a significant return . However , low - frequency radar is limited by lack of available frequencies - many are heavily used by other systems , by lack of accuracy of the diffraction - limited system s given their long wavelengths , and by the radar ' s size , making it difficult to transport . A long - wave radar may detect a target and roughly locate it , but not provide enough information to identify it , target it with weapons , or even to guide a fighter to it . Noise poses another problem , but that can be efficiently addressed using modern computer technology ; Chinese " Nantsin " radar and many older Soviet - made long - range radars were modified this way . It has been said that " there ' s nothing invisible in the radar frequency range below 2 GHz " . Multiple emitters . Much of the stealth comes from reflecting radar emissions in directions different than a direct return . Thus , detection can be better achieved if emitters are separate from receivers . One emitter separate from one receiver is termed bistatic radar ; one or more emitters separate from more than one receiver is termed multistatic radar . Proposals exist to use reflections from emitters such as civilian radio transmitter s , including cellular telephone radio towers . Moore ' s law . By Moore ' s law the processing power behind radar systems is rising over time . This will erode the ability of physical stealth to hide vehicles . Ship ' s wakes and spray . Synthetic Aperture sidescan radars can be used to detect the location and heading of ships from their wake patterns . These may be detectable from orbit . When a ship moves through a seaway it throws up a cloud of spray which can be detected by radar . Schlieren Signature . Anything that disturbs the atmosphere may be detected ( Schlieren Photography ) because of the Schlieren effect caused by that atmospheric disturbance . This type of MASINT detection falls under the category of Electro - optical MASINT . Quantum interference . Principles from quantum interference have been proposed for the detection of stealth aircraft . The overall approach relies upon devising a gravimetric radar system for detecting moving massive objects based on the time variation that these objects produce in the local gravitational field measured by several detectors . Acoustics . Acoustic stealth plays a primary role in submarine stealth as well as for ground vehicles . Submarines use extensive rubber mountings to isolate and avoid mechanical noises that could reveal locations to underwater passive sonar arrays . Early stealth observation aircraft used slow - turning propellers to avoid being heard by enemy troops below . Stealth aircraft that stay subsonic can avoid being tracked by sonic boom . The presence of supersonic and jet - powered stealth aircraft such as the SR - 71 Blackbird indicates that acoustic signature is not always a major driver in aircraft design , although the Blackbird relied more on its extremely high speed and altitude . One possible technique for reducing helicopter rotor noise is ' modulated blade spacing ' . Standard rotor blades are evenly spaced , and produce greater noise at a particular frequency and its harmonics . Using varying degrees of spacing between the blades spreads the noise or acoustic signature of the rotor over a greater range of frequencies . Visibility . The simplest stealth technology is visual camouflage ; the use of paint or other materials to color and break up the lines of the vehicle or person . Most stealth aircraft use matte paint and dark colors , and operate only at night . Lately , interest in daylight Stealth ( especially by the USAF ) has emphasized the use of gray paint in disruptive schemes , and it is assumed that Yehudi lights could be used in the future to mask shadows in the airframe ( in daylight , against the clear background of the sky , dark tones are easier to detect than light ones ) or as a sort of active camouflage . The original B - 2 design had wing tanks for a contrail - inhibiting chemical , alleged by some to be chlorofluorosulfonic acid , but this was replaced in the final design with a contrail sensor from Ophir that alerts the pilot when he should change altitude and mission planning also considers altitudes where the probability of their formation is minimized . In space , mirrored surfaces can be employed to reflect views of empty space toward known or suspected observers ; this approach is compatible with several radar stealth schemes . Careful control of the orientation of the satellite relative to the observers is essential , and mistakes can lead to detectability enhancement rather than the desired reduction . Infrared . An exhaust plume contributes a significant infrared signature . One means to reduce IR signature is to have a non - circular tail pipe ( a slit shape ) to minimize the exhaust cross - sectional volume and maximize the mixing of hot exhaust with cool ambient air . Often , cool air is deliberately injected into the exhaust flow to boost this process . Sometimes , the jet exhaust is vented above the wing surface to shield it from observers below , as in the B - 2 Spirit , and the unstealthy A - 10 Thunderbolt II . To achieve infrared stealth , the exhaust gas is cooled to the temperatures where the brightest wavelengths it radiates are absorbed by atmospheric carbon dioxide and water vapor , dramatically reducing the infrared visibility of the exhaust plume . Another way to reduce the exhaust temperature is to circulate coolant fluids such as fuel inside the exhaust pipe , where the fuel tanks serve as heat sink s cooled by the flow of air along the wings . Ground combat includes the use of both active and passive infrared sensors and so the USMC ground combat uniform requirements document specifies infrared reflective quality standards . Reducing radio frequency ( RF ) emissions . In addition to reducing infrared and acoustic emissions , a stealth vehicle must avoid radiating any other detectable energy , such as from onboard radars , communications systems , or RF leakage from electronics enclosures . The F - 117 uses passive infrared and low light level television sensor systems to aim its weapons and the F - 22 Raptor has an advanced LPI radar which can illuminate enemy aircraft without triggering a radar warning receiver response . Measuring . The size of a target ' s image on radar is measured by the radar cross section or RCS , often represented by the symbol σ and expressed in square meters . This does not equal geometric area . A perfectly conducting sphere of projected cross sectional area 1 m ( i . e . a diameter of 1 . 13 m ) will have an RCS of 1 m . Note that for radar wavelengths much less than the diameter of the sphere , RCS is independent of frequency . Conversely , a square flat plate of area 1 m will have an RCS of σ = 4π " A " / " λ " ( where " A " = area , " λ " = wavelength ) , or 13 , 982 m at 10 GHz if the radar is perpendicular to the flat surface . At off - normal incident angle s , energy is reflected away from the receiver , reducing the RCS . Modern stealth aircraft are said to have an RCS comparable with small birds or large insects , though this varies widely depending on aircraft and radar . If the RCS was directly related to the target ' s cross - sectional area , the only way to reduce it would be to make the physical profile smaller . Rather , by reflecting much of the radiation away or by absorbing it , the target achieves a smaller radar cross section . Tactics . Stealthy strike aircraft such as the F - 117 , designed by Lockheed Martin ' s famous Skunk Works , are usually used against heavily defended enemy sites such as Command and Control centers or surface - to - air missile ( SAM ) batteries . Enemy radar will cover the airspace around these sites with overlapping coverage , making undetected entry by conventional aircraft nearly impossible . Stealthy aircraft can also be detected , but only at short ranges around the radars , so that for a stealthy aircraft there are substantial gaps in the radar coverage . Thus a stealthy aircraft flying an appropriate route can remain undetected by radar . Many ground - based radars exploit Doppler filter to improve sensitivity to objects having a radial velocity component with respect to the radar . Mission planners use their knowledge of enemy radar locations and the RCS pattern of the aircraft to design a flight path that minimizes radial speed while presenting the lowest - RCS aspects of the aircraft to the threat radar . To be able to fly these " safe " routes , it is necessary to understand an enemy ' s radar coverage ( see Electronic Intelligence ) . Airborne or mobile radar systems such as AWACS can complicate tactical strategy for stealth operation . Research . Negative index metamaterials are artificial structures for which refractive index has a negative value for some frequency range , such as in microwave , infrared , or possibly optical . These offer another way to reduce detectability , and may provide electromagnetic near - invisibility in designed wavelengths . Plasma stealth is a phenomenon proposed to use ionized gas ( plasma ) to reduce RCS of vehicles . Interactions between electromagnetic radiation and ionized gas have been studied extensively for many purposes , including concealing vehicles from radar . Various methods might form a layer or cloud of plasma around a vehicle to deflect or absorb radar , from simpler electrostatic to RF more complex laser discharges , but these may be difficult in practice . Several technology research and development efforts exist to integrate the functions of aircraft flight control system s such as ailerons , elevators , elevon s , flaps , and flaperon s into wings to perform the aerodynamic purpose with the advantages of lower RCS for stealth via simpler geometries and lower complexity ( mechanically simpler , fewer or no moving parts or surfaces , less maintenance ) , and lower mass , cost ( up to 50 % less ) , drag ( up to 15 % less during use ) and , inertia ( for faster , stronger control response to change vehicle orientation to reduce detection ) . Two promising approaches are flexible wings , and fluidics . In flexible wings , much or all of a wing surface can change shape in flight to deflect air flow . Adaptive compliant wing s are a military and commercial effort . The X - 53 Active Aeroelastic Wing was a US Air Force , Boeing , and NASA effort . In fluidics , fluid injection is being researched for use in aircraft to control direction , in two ways : circulation control and thrust vectoring . In both , larger more complex mechanical parts are replaced by smaller , simpler fluidic systems , in which larger forces in fluids are diverted by smaller jets or flows of fluid intermittently , to change the direction of vehicles . In circulation control , near the trailing edges of wings , aircraft flight control systems are replaced by slots which emit fluid flows . In thrust vectoring , in jet engine nozzles , swiveling parts are replaced by slots which inject fluid flows into jets to divert thrust . Tests show that air forced into a jet engine exhaust stream can deflect thrust up to 15 degrees . The U . S . FAA has conducted a study about civilizing 3D military thrust vectoring to help jetliners avoid crashes . According to this study , 65 % of all air crashes can be prevented by deploying thrust vectoring means . References . 34 . “ Multiaxis Thrust Vectoring Flight Control Vs Catastrophic Failure Prevention ” , Reports to U . S . Dept . of Transportation / FAA , Technical Center , ACD - 210 , FAA X88 / 0 / 6FA / 921000 / 4104 / T1706D , FAA Res . Benjamin Gal - Or , Grant - Award No : 94 - G - 24 , CFDA , No . 20 . 108 , Dec . 26 , 1994 .