war on the rocks

The Need for SEAD Part II: The Evolving Threat

June 7, 2016

Editor’s Note: This is the second part of a 2-part series called “The Need for SEAD”, which advocates the restoration of the defense suppression enterprise that carried the Joint Force from Vietnam until Desert Storm. Part I covered the need for the restoration of the “electronic combat triad” once covered by specialized, well-trained crews in the F-4G, EF-111A, and the EC-130. 

 

Since the Gulf War, the air defense environment has changed radically. American electronic warfare capabilities savaged Iraqi air defenses. The F-117A was able to slip relatively easily through an Iraqi air defense built upon Soviet systems that had been fielded between 1955 and 1970. The F-117’s stealthy design proved to be more than a match for Iraq’s beleaguered air defenders, but this advantage was transient. In Operation Allied Force, the U.S. Air Force suffered its first combat loss of a stealth aircraft, shot down by a Serbian surface-to-air missile (SAM) battery with a pair of vintage radar systems dating from before the Vietnam War — systems the Iraqis also had in their inventory almost a decade earlier. The cloak was slipping.

Once the United States showed its hand, Russian and Chinese scientists knew exactly what the American defense industry had done and why — and set about trying to counter it. They knew the physics and fully understood that by shifting the frequency of their radars downward, they could negate a great deal of the U.S. advantage in radar stealth.

As I’ve discussed in previous War on the Rocks articles, the U.S. Air Force is caught in a trap of its own making. Having largely abandoned its combat-proven electronic warfare capabilities to fund acquisition of stealth aircraft, the world’s largest air arm finds itself without a robust electronic combat capability just as its advantage in stealth is eroding. The vanishing of its electronic combat triad caused an attendant loss of experienced personnel, leaving few operators in the force who have combat experience with the long-retired F-4G and EF-111A. As a result, the Air Force has been slow to recognize that it has been technologically outmaneuvered. Combined the hollowing of its fighter force due to a quarter century of neglect and underfunding, the Air Force is at risk of returning to the dark days of 1965, when it faced unprecedented losses from a threat it should have seen coming in the skies over Vietnam. The threat has evolved, and the days of stealthy aircraft providing a decisive overmatch are gone. In almost every respect, the relative balance between U.S. capabilities and the threat is worse than it was 25 years ago. Understanding that is a necessary step to restoring a defense suppression capability capable of enabling air operations in the face of a modern air defense threat.

The Good Old Days

Radar emerged as a means of detecting and engaging aircraft (and ships) in World War II. It works by bouncing a radio wave off a target that is reflective in the radiofrequency part of the electromagnetic spectrum. As soon as radar systems were fielded, scientists began working on methods to counter them. One of those methods was stealth — reducing the amount of radar energy that scattered back from a target. The United States reaped the advantages of early adoption of stealth for a very small portion of its combat aircraft. In 1991, there were 3,926 conventional fighter/attack aircraft in the Air Force, including reserve and Air National Guard aircraft, compared to 55 stealthy F-117s. Those 55 aircraft were appropriately considered a niche capability unmatched anywhere in the world, but analysts at the time anticipated this advantage to be short-lived. In 1985, the Central Intelligence Agency (CIA) published a special national intelligence estimate entitled Soviet Reactions to Stealth that predicted the likely direction of Soviet counter-stealth research. It wasn’t a hard call by the CIA — the theoretical physics involved were well understood by Soviet scientists. The CIA reported:

We are aware that the Soviets are developing higher powered early warning and intercept radars with the better resolutions necessary to come to grips with the low-signature and Stealth detection and tracking problem. Soviet Radar designers are likely to incorporate VHF and UHF frequencies, increased pulse repetition frequencies, and improved signal processing in their next generation of radars.                                                 

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Figure 1:  The EM Spectrum. (http://www.radartutorial.eu)

As a reminder, the higher the frequency of a radar, the shorter the wavelength. High frequencies were often preferred for fire control radars, because the beams could be made narrower and the shorter wavelengths provided tighter range information. The tradeoff was clear — low-frequency radars (2000 MHz and below) could travel further and packed more power, but they couldn’t locate targets precisely enough to shoot them. So radars were effectively separated by function — the early warning radars detected aircraft at long ranges and then handed them off to more precise high-frequency fire control or target-tracking radars. It was these target-tracking radars that U.S. stealth designs focused on, because those were the radars that were going to direct weapons. It was the low-frequency radars that offered the best chance of detecting aircraft, but if they couldn’t shoot (and they couldn’t), then the air defenses suffered. Oversimplified, air defense requires basic detection (early warning) of enemy aircraft before weapons (SAMs and AAA) can be guided by higher-fidelity fire control radars that more accurately track the target.

The radio bands referred to as “very high frequency” (VHF) and “Ultrahigh Frequency” (UHF) are, oddly enough, relatively low-frequency bands. In 1978, when the decision was made to produce the Senior Trend (F-117A) aircraft, there were four operational Soviet surveillance radar systems that operated in the VHF band, two of which had been copied by the Chinese. The Flat Face UHF band radar was in widespread service. Yet none of these radars had any height-finding capability, and their resolution was poor in both angle and range. Called 2D radars, they were the last generation of radars developed without any digital signal processing. In short, they were incapable of providing the precision necessary to guide a surface-to-air missile (SAM). Without a VHF height finder (of which there were none), these low-frequency early warning radars could not even determine the altitude of any stealthy aircraft that a very alert and skilled radar operator might have otherwise detected. Soviet air defense operators (and their Iraqi clients) were therefore not equipped to locate the F-117, a fact that became painfully obvious in 1991.

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Figure 2: Operational Low Frequency Early Warning radars in 1978

But Soviet designers were not asleep. By the Gulf War, the Soviets had already fielded two modern 3D early warning radars in the VHF band. Tall Rack, which was referenced in the 1985 CIA study, was operational before the F-117, and the Soviet Box Spring and Chinese Type 408C radars were fielded before the Gulf War.

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Figure 3:  VHF Early Warning radars fielded between the start of SENIOR TREND and the Gulf War

Today, the Russians and Chinese have built a half dozen new VHF systems, upgraded older systems, and fielded a dozen new systems in UHF- and L-bands. Some of these capabilities, particularly the upgraded older radars, have been widely exported. Like the air defense systems that they support, these newer systems are mobile, and in some cases (Vostok-E) can be on the move in as little as eight minutes from shutdown. The good old days wherein stealth fighters could rely on a sparse environment of early warning radars are not only gone — they have been gone for two decades.

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Figure 4:  Adversary air defense surveillance radars with “low” operating frequencies below 2000Mhz fielded since the debut of the F-117A in the Gulf War.  Most of these are still in service.

Discounting the Threat

Low-frequency radars are not primarily used as a counter-stealth solution; they are widely utilized where long range is necessary and fire control solutions are not.  Numerous reports have emerged that the F-22 can be seen on civilian Federal Aviation Administration (FAA) air traffic control radars. These reports are typically dismissed by Air Force officers as being of little import because radars in this band are not associated with fire control, a categorically false assertion. The FAA’s ASR-9 and ASR-11 radars operate in the same S-band used by the Vietnamese FAN SONG B/F (SA-2) and FIRE CAN (AAA) radars. Between 1965 and 1971, SA-2s downed at least 130 U.S. aircraft. The number of aircraft downed by the Fire Can or SA-2B/F from 1972 to 1973 is not entirely clear. The lower bands can and do detect aircraft with low radiofrequency (RF) signatures, and they can and have killed fighter aircraft.

Even if an early warning radar can’t guide a missile, it can still guide fighters or cue other sensors possessing the precision necessary to fire a SAM. Modern air defense radars have fairly small uncertainty volumes, capabilities granted with complex waveforms and digital signal processing. The greatest value of radar stealth is the ability to avoid detection in the first place. Once detected, much of that value is lost. It may be true to say that the early warning radars cannot immediately take a shot on a detected aircraft, but it is also irrelevant. Those radars can hand off detected aircraft to someone else who can take a shot or direct a shooter to move into position. Russian and Chinese radar designers have thought this through in detail over many years. In a dense air defense system like those possessed by China or Russia, a shot will be coming.

For many years, SAM systems were designed to operate in higher frequencies. The SA-3, 5, 6, 10, 11, 12, 15, 17 and 20 target-tracking radars all operated in C- or X-bands, with the short-range SA-8 and SA-19 in the Ku- and K-bands. Given that these systems are widely proliferated, it seemed that low observability optimized for the higher frequencies would be a good investment.

But, like the early warning radars mentioned above, engagement radars have seen a similar change in operating frequencies, particularly in Chinese designs. In the past decade, no Chinese SAM radar has been fielded in the I-band (lower X-band) so heavily favored by Soviet designers. Instead, Chinese systems have been driven down in frequency, and the Russians have embraced frequency diversity. The Russian NEBO M system, unveiled in 2012, is intended specifically to detect and engage the F-35 using a set of three radars in VHF-, L- and X-bands. This is the first system designed as an integrated set rather than relying on external system integration using a linked command and control architecture, and it is designed to tie directly into a SAM array at the battery or (more likely) brigade level. Passive detection systems can likely be integrated into a Nebo M battery configuration. As the older SAM systems age out, so will the preference for the X-band radars.

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Figure 5: Nebo M system on high mobility vehicles (NNIIRT Image)

To add insult to injury, the Russians have developed an L-Band radar for the Sukhoi Su-27/30/35 Flanker fighters, a lower-frequency band normally used by ground radars. Seeking a solution to counter stealth fighters, Russian defense contractor Tikhomirov NIIP revealed an L-Band Active Electronically Scanned Array (AESA) in 2009. Installed in the leading edges of a fighter’s wings and tail, this was an aviation first. Previously, lower-frequency radars were only installed on airborne early warning systems such as the Israeli Phalcon and Gulfstream 550 Eitam, the Indian A50EI, the Australian Wedgetail, the Chinese KJ-2000, and the U.S. Navy’s new E-2D. In an assessment of the new radar from open source data, Dr. Carlo Kopp summarized the design imperative:

The only reason to pursue the L-band is thus if it can do something which cannot be done easily in the X/Ku-bands. That something is inevitably the ability to produce useful skin returns from targets which are difficult to detect and track in the X/Ku-bands.

Put simply: outfitting fighters with low-frequency radars is an explicit attempt to allow Russian fighters to take on U.S. stealth fighters such as the F-22 and F-35.

Fortunately, the U.S. Air Force has not had to learn about this threat the hard way — yet.  The United States has never faced a “double digit” SAM in battle. The SA-10 was fielded in 1980, but never exported to Iraq or Serbia. Consequently, the U.S. Air Force never had to deal with a highly mobile threat capable of engaging multiple targets simultaneously with hypersonic missiles. Today, long-range SAM systems are protected by short-range SAMs, which may themselves be defended by close-in weapons systems. Aside from radar, passive radiofrequency detection systems are becoming cheaper and better. You can buy a longwave thermal camera for your iPhone. Chinese scientists are exploring multispectral target detection techniques for the exhaust plume emitted by jet aircraft. The methods for finding aircraft are regaining a balance lost when the F-117 exploited its low-observability advantage. Lowering an aircraft’s signature always provides a survivability benefit of some kind, but those benefits come at a cost that may be unacceptable in combat. Consider the F-117, which had a marvelously low signature across various spectra, even beyond radar. It was very limited in payload, could not act cooperatively, possessed no air-to-air capability, and was fundamentally good only for hitting large fixed targets vulnerable to weapons in the 2000-pound class at relatively close range.

The Effects of Signature Reduction

Signature reduction is still worthwhile; all other things being equal, it does reduce the range at which an aircraft can be engaged by a particular threat. This matters more for some aircraft more than others. While using open source data to calculate detection ranges is a chancy business, the detection curves are all the same shape. Reducing the radar cross section (RCS, or an aircraft’s radar signature) from 10 square meters (F-4) to one square meter (B-1B) has a very large effect on the outer range of the detection envelope, but subsequent reductions in signature have progressively lesser effect on absolute detection range. Figure 6 illustrates the detection curves for a variety of Russian or Chinese early warning radars. Taking the highest curve (the SA-20’s Vostok E), the radar sees an F-4 at 400 nautical miles out, but only sees a B-1B at 230 nautical miles, thereby giving up 170 miles and about 21 minutes of warning time.

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Figure 6: Russian/PLA VHF Early Warning radars (Airpower Australia)

Figure 7 illustrates the curve for a modern short-range air defense system (SHORADS), the S1 Pantsir (SA-22). An aircraft with an RCS of 10 square meters (smaller than an F-4 Phantom, but bigger than a breadbox) can be seen by the radar outside the maximum range at which the scope will display (48 nautical miles). By the time the RCS gets down to 0.1 square meters (about the size of a carbon-fiber subscale target drone) the acquisition radar can detect the target about 30 seconds before it reaches maximum missile range. Against genuinely low-RCS target, the detection range is inside the missile range, meaning that by the time the aircraft is detected, the SAM has given up a lot of its engagement envelope — assuming it hasn’t seen the target on optical sensors, of course. The Pantsir’s 57E6 missile is command-guided and cares not a bit what the target’s RCS is, and the Pantsir’s guns are unaffected, as the practical detection range of the radar is still outside the gun range.

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Figure 7: Detection Curves for 96K6 Pantsir (SA-22) SHORADS system (Air Power Australia)
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Figure 8: 96K6 Pantsir SAM/Gun system (Vitaly V. Kuzmin)

Closing the Distance

The radar range equation is old news. There is no shortage of knowledge about the implications of radar signature reduction among U.S. adversaries, but the equivalent knowledge about threat developments faced by U.S. airpower is somewhat lacking. With the retirement of the electronic warfare fighters, the Air Force divested itself of a community of aviators who possessed in-depth knowledge of the adversary threat. This in turn led to an overreliance on radar stealth at the expense of other capabilities that can assist the penetration of defended airspace. The fundamental problem remains: Air Force tactical aviation must understand the threat better than it currently does.

For the most powerful SAM systems, unassisted radar stealth may not get an aircraft any closer than low-altitude flight. Over water, a fighter at 200 feet of altitude hits the Vostok E’s radar horizon at 25 nautical miles, which takes a massive amount of signature reduction to accomplish otherwise. For a fighter without standoff weapons, this is a fairly long way out from a defended target. But there are time-tested techniques that can further complicate the challenge for an air defender: to start, electronic attack (jamming) or lethal defense suppression using anti-radiation missiles. Regardless of the measures used to delay engagement, the need for SEAD is still a key attribute of the modern battlefield.

It should be clear to the Air Force by now that the unsupported medium-altitude approach envisioned by the partisans of stealth aircraft is simply infeasible against a threat array that is mobile, interlinked, and uses multiple sensor modalities for target detection, identification, and threat assessment. Current Department of Defense concepts for dealing with an anti-access/area-denial environment are light on execution details, widget-heavy, and operationally unexecutable. If the Air Force is to regain its ability to penetrate well-defended airspace with enough mass to actually achieve significant effects, it is going to have to embrace older techniques and recognize that the threat environment today is qualitatively different from the threat faced by the F-117A a quarter century ago. The threat evolved, and so must the Air Force.

 

Col. Mike “Starbaby” Pietrucha (Wild Weasel #2235) was an instructor electronic warfare officer in the F-4G Wild Weasel and the F-15E Strike Eagle, amassing 156 combat missions and taking part in 2.5 SAM kills over 10 combat deployments. He is the last “baby EWO” to graduate from the Wild Weasel School.  As an irregular warfare operations officer, Colonel Pietrucha has two additional combat deployments in the company of US Army infantry, combat engineer, and military police units in Iraq and Afghanistan. The views expressed are those of the author and do not necessarily reflect the official policy or position of the Department of the Air Force or the U.S. government.