Two F-117s on the ramp at Al Jaber AB, Kuwait, ready for a mission in support of Operation Southern Watch in 1998. Photo: TSgt. James Mossman
The existence of a new technology called “stealth” was announced by Secretary of Defense Harold Brown at a Pentagon news conference Aug. 22, 1980.
The special contribution of stealth was that it could reduce the radar cross section of an aircraft to approximately that of a bird, enabling a bomber to penetrate deep into enemy airspace without being detected or intercepted.“It is not too soon to say that by making existing air defense systems essentially ineffective, this alters the military balance significantly,” Brown said.
What he did not say was that a stealth fighter prototype—which would lead eventually to the F-117 Nighthawk—had been test flown in 1977, or that a forerunner of a stealth bomber—the future B-2 Spirit—was already on contract.
Stealth was developed and fielded under tight secrecy. Despite occasional leaks and glimpses, the stealthy aircraft would not appear in the open for almost 10 years. The public rollout of the B-2 was in November 1988. The F-117 was publicly revealed in April 1990, four months after its combat debut in the Panama invasion of 1989.
The immediate reaction to Brown’s announcement in 1980 centered on politics. Critics said the reason for the disclosure—coming three months before the elections in November—was to take the heat off President Jimmy Carter for having canceled the nonstealthy B-1 bomber in 1977. Carter and Brown were also accused of recklessly releasing a critical defense secret for political purposes.
Republican presidential candidate Ronald Reagan, who would defeat Carter in the election, joined in the criticism. Upon taking office, though, Reagan decided on a two-bomber approach, reinstating the B-1 but proceeding concurrently with what would become the B-2. Development of the stealth fighter, concealed by even greater classification than the B-2, continued apace.
Stealth came under severe attack in the 1990s by those who wanted to cut defense spending. The harsh judgments were not lessened appreciably by the outstanding performance of the F-117 in the Gulf War in 1991 and that of the B-2 and the F-117 in regional conflicts later in the decade. Production was sharply curtailed for both aircraft.
THE STEALTH ADVANTAGE
Looking back from the perspective of 40 years, the significance of stealth has been enormous. No major countermeasures have emerged to negate it. The United States maintained its monopoly on the technology well into the 21st century.
Stealth, also known as “low observable" technology, still conveys an overwhelming combat advantage. It reduces exposure by a full range of signatures—electromagnetic, infrared, visual, and acoustic—but the main one is radar.
Stealth makes an object seem smaller on the radar screen by diffusing the reflection of the beam instead of bouncing it directly back to the radar receiver. Fighters and bombers with low radar cross sections can get close to their targets before they are detected. Nonstealthy aircraft pitted against stealthy opponents will almost certainly be shot down.
USAF’s F-15 Eagle, for example, was introduced in the 1970s as the world’s premier air superiority fighter. However, its radar cross section is 5,000 times greater than that of the F-35. Radar can pick up the F-15 more than 200 miles out, whereas the F-35 gets within 21 miles before it can be detected.
In recent years, the Chinese and the Russians have begun flying stealth fighters. US allies in Europe and the Pacific are partners in the stealthy F-35 Joint Strike Fighter program. For its stealth fighter needs, the US Air Force will rely on a mix of F-35s and a smaller number of older but even more capable F-22 Raptors. A new stealth bomber is in development.
Depending on budgets and politics, the Air Force anticipates a steady increase in the percentage of stealth aircraft in its combat units.
Secretary of Defense Harold Brown. Photo: Frank Hall/DOD
The roots of stealth can be traced to experimental aircraft of the 1940s, particularly Jack Northrop’s fabled YB-49 flying wing, which had smooth surfaces and rounded edges but no tail or fuselage. The all-wing configuration generated a relatively small image on radar screens, but that was of no great interest at the time, and the YB-49 was canceled in 1949.
In an obscure technical paper in the 1960s, Russian physicist Pyotr Ufimtsev theorized that electromagnetic waves bouncing off a flat surface could be calculated and used to estimate the return on radar. His findings were ignored by everyone, including the Russians.
By the 1970s, bombers and fighters were increasingly vulnerable to radar-controlled air defenses. In 1974, the Defense Advanced Research Projects Agency and the Air Force began a major effort to develop combat aircraft with low radar signatures.
Two of the principal aircraft companies, McDonnell Douglas and General Dynamics, were occupied on the new F-15 and F-16 fighters so the tasking for stealth fell to Lockheed and Northrop. Both of them were awarded contracts in 1975 to build static models for the Experimental Survivable Testbed (XST).
Lockheed and Northrop took distinctly different approaches in their development of stealth. Ufimtsev’s paper on calculating radar refraction had been translated by the Air Force Foreign Technology Division in 1971, and Lockheed engineer Denys D. Overholser blended it into his own work for a computer program called “Echo 1.”
Echo 1, which computed the radar cross section from various angles over a range of wavelengths, was the enabling step to stealth for Lockheed. The catch was that the best available computers of the day could handle results only from flat surfaces. Thus, the calculations were spread out over hundreds of facets. The results were then combined to determine the radar cross section of the aircraft as a whole.
By contrast, Northrop relied on modeling of compound curves and shaping of the edges to achieve stealth. When the B-2 bomber was subsequently revealed to be a flying wing, the popular assumption was that it descended directly from Jack Northrop’s YB-49. Corporate heritage and culture no doubt played a part, but the engineers insisted that they started with a clean sheet of paper.
The XST models were mounted on poles and bombarded with electromagnetic waves to compare their radar cross sections. Northrop’s shaping approach worked well enough in deflecting radar beams from head on but was less effective than the Lockheed faceting when results from the sides and rear were considered.
Lockheed won the “pole off” and was selected in 1976 to proceed with a technology demonstrator to validate the pole test results.
In a separate venture—but with the additional objective of preserving Northrop’s stealth experience in the defense industrial base—DARPA in 1978 awarded Northrop a contract to design the Battlefield Surveillance Aircraft (BSAX). It was part of a broader program called “Assault Breaker,” intended to repel a massive tank attack in Europe. BSAX had to be stealthy enough to operate close to the forward edge of battle.
China's J-20 displays its weapons bay during an air show in 2018. Another Chinese fifth-gen fighter, the J-31, is an F-35 lookalike and could be operational soon. Photo: Emperornie
INTO THE AIR
The Lockheed fighter was at least five years, sometimes more, ahead of the Northrop bomber in the stealth timeline. The next step after the XST pole tests was “Have Blue,” Lockheed’s manned technology demonstrator that entered flight testing in April 1977.
Have Blue was a sharp-nosed single-engine aircraft with swept wings and stark planar surfaces. It was 60 percent the size of the F-117 fighter, which would come afterward. The facets, set at unusual angles, scattered the incoming radar beams.
The F-117 made its first flight in June 1981. Strictly speaking, the F-117 was an attack aircraft rather than a fighter. It was intended to drop bombs, not engage in aerial combat. However, Gen. Robert J. Dixon at Tactical Air Command believed that an “F” (for fighter) designation would be more attractive to the best pilots better than would an “A” (for attack).
Northrop’s BSAX demonstrator, “Tacit Blue,” made its first flight in February 1982. It was one of the strangest-looking aircraft ever built. For reasons needful to testing of the surveillance radar it carried, Tacit Blue was essentially a box with low-observable features wrapped around it. As Northrop acknowledged, “Tacit Blue’s shape looked like a butter dish with wings.” Between 1982 and 1985, Tacit Blue made 135 test flights.
Northrop had been announced in 1981 as winner of the contract for the Advanced Technology Bomber, which would be designated the B-2 in 1984. The Tacit Blue test results built confidence in Northrop’s approach to stealth.
In the interval since Lockheed’s Have Blue, computing power had increased exponentially, and it was no longer necessary to estimate radar cross section by figuring the results for individual panels one by one. The faceting route to stealth was largely abandoned.
The B-2 would not make its first flight until July 1989, only six months before the F-117 Nighthawk flew its first combat mission.
THE STEALTH REGIME
Stealth imposed penalties and trade-offs—chiefly in speed and aerodynamics—on the F-117 and the B-2. They had no afterburners and were limited to subsonic speeds. Supersonic flight would have undercut the benefits of stealth by announcing the presence of the aircraft, with both a sonic boom and a big thermal signature from the hot-burning engines.
Mach speeds would also have consumed more fuel, already at a premium since internal carriage of the engines did not leave much space for additional fuel tanks. Gas-guzzling afterburners would have diminished the operational range.
The early stealth airframes were aerodynamically unstable. Flight was made possible by digital “fly-by-wire” technology that employed computers to constantly adjust the flight controls.
Stealth designers addressed seven types of observable signatures: radar, infrared, visual, contrails, engine smoke, acoustic, and electromagnetic. Reduction of the critical radar cross section was achieved with 90 percent by shaping of the aircraft and 10 percent by radar-absorbent materials.
The radar-absorbent coatings were fairly thick in places and added weight to the aircraft. Repairing the coating and applying fresh material after each mission was expensive and time consuming.
SHOTS IN THE DARK
Seeking to defuse criticism that his announcement of stealth had been for political gain, Defense Secretary Brown said in 1980 that because of leaks about stealth “in the last few days” to the press and television, “it is not appropriate or credible for us to deny the existence of the program.”
Indeed, there had been several recent leaks—at least one of them by a high Pentagon official and presumably with Brown’s blessing—but they were not the first disclosures of stealth.
The first public mention of stealth was in May 1975 by Defense Daily, a trade publication, which reported a design study for a “high Stealth-2 aircraft.” Under the heading “Lockheed ‘Stealth Fighter’, ” the 1977-1978 edition of Jane’s All the World’s Aircraft said that the Lockheed Skunk Works at Burbank, Calif., was building “a small ‘stealth fighter’ of which a primary feature will be low radar, infrared, and optical signature.”
Bits and pieces of the stealth story appeared intermittently in the 1980s. In particular, George Wilson of the Washington Post had good sources. In May 1982, he reported that the stealth bomber “is shaping up as a radically advanced flying wing.” That was confirmed in 1985 by Sen. Barry Goldwater (R-Ariz.), who had seen a model of the airplane.
Secrecy about the F-117 was tighter than that surrounding the B-2, and the guesswork was less accurate. There was scattered speculation that the stealth fighter would be the “F-19.” That designation was used on a plastic model kit marketed by Testor in 1985. The picture on the box was a gracefully rounded delta shape. The forward fuselage resembled an SR-71. It attracted attention, but nothing about it was correct.
Testing of the F-117 was conducted at the Tonopah Test Range in the Nevada desert. Every week for eight years, pilots and ground crews from Nellis Air Force Base at Las Vegas flew up to Tonopah on Monday and returned home on Friday. Operations at Tonopah did not begin until an hour after sunset.
Security at Tonopah was breached in July 1986 when an F-117 on a night mission crashed near Bakersfield, Calif. Within a month, Wilson and the Washington Post reported that the crashed airplane was one of 50 stealth fighters flying out of Tonopah.
The Pentagon, deciding in 1988 that it could no longer justify the cost and effort to keep a total lid on the program, released a grainy photo of the F-117 but deliberately blurred its features to avoid revealing too much about the design. Wilson in the Post pronounced it “awkward looking.”
The stealth aircraft were developed in secrecy—the F-117 as a “black” program and the B-2 as a “gray” one—and were not subjected to much criticism during their formative years. That changed with the rollouts of the aircraft.
Relaxation of security on stealth coincided with the end of the Cold War and top-to-bottom reductions in the defense program. The stealth aircraft, especially the B-2, were favorite targets for defense critics in Congress and the news media.
Strong performance in the Gulf War and in regional conflicts in the Balkans did not make a difference. Only 59 F-117s were delivered to the Air Force, and the B-2 total was capped at 21.
The next generation of stealth arrived with the Lockheed Martin F-22 Raptor, an air-to-air fighter that first flew in 1997. The radar cross section of the F-22 is sometimes described as comparable to that of a golf ball, at other times as equal to that of a bumblebee.
The Lockheed Martin F-35 Joint Strike Fighter—designed for both aerial combat and ground attack—flew in 2006. It has a single engine and is smaller than the twin-engine F-22.
Improvements in technology allowed the new stealth aircraft to escape some of the limitations of their predecessors. Supersonic speed is now an available option. The F-22 can reach Mach 2 and for the F-35 Mach 1.6.
The Air Force initially planned on 750 F-22s and 1,763 F-35s, but the F-22 program was terminated at 187 aircraft, and USAF so far has taken delivery of fewer than 200 F-35s. At present, stealth aircraft account for less than 20 percent of the fighter forces of US services.
The successor to the B-2 will be the Northrop Grumman B-21 Raider. It will enter flight testing in 2021, but the number to be built is not yet decided. It is the fulfillment of the Long-Range Strike Bomber program, and in concept drawings, it has a strong family resemblance to the B-2.
The US monopoly on stealth could not last forever, and it didn’t. Both the Russians and the Chinese flew stealth fighters in tests in 2010.
The Russians have 10 flyable prototypes of the Su-57—also known as the T-50, its internal name at manufacturer Sukhoi—at various stages of test and evaluation. Reports say the program is “troubled” and behind schedule, but Sukhoi claims that the first operational Su-57s will be delivered soon to the Russian air force.
The Chinese are well ahead of the Russians and have two stealthy fighters. The first was the J-20, which has some features akin to those of the F-22 and F-35 and draws heavily on technology presumed to be stolen from the United States. The J-31 has been called “an F-35 look-alike” and may soon be ready for mass production. The Chinese are reported to be working on a J-31 variant that could fly from an aircraft carrier.
In addition, the Chinese have a stealth bomber, the Xian H-20, in development. The predicted range would be sufficient to target US bases on Guam.
A significant source of stealth proliferation is the US itself. The F-35, operational with the Air Force, Navy, and Marine Corps, will be operated by a dozen US allies in Europe and on the Pacific rim, and also Israel. About half of them have already begun receiving airplanes.
In a study for the Air Force Association’s Mitchell Institute in 2017, Maj. Gen. Mark A. Barrett and Col. Mace Carpenter concluded that stealth has become an “imperative” in the digital age. “The capability to significantly reduce the range and effectiveness of modern radars and other threat sensors is now a basic requirement for aircraft survival,” they said.
John T. Correll was editor in chief of Air Force Magazine for 18 years and is a frequent contributor. His most recent article, “The Counter Revolution in Military Affairs," appeared in the July/August issue.
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