Indian Defence Review

B-2 Bombers

Stealth is the defining attribute of fifth-generation fighter aircraft and it has a two-fold appeal. First, stealth aircraft are far less vulnerable to engagement by hostile interceptors and ground defences, because radars can’t “see” the stealth platforms. Second, a low-observable jet has an excellent chance to detect and kill a non-stealth adversary because it can close in and strike, sometimes before the target aircraft even realises it is under threat. Only one stealth aircraft has been lost in 30 years of combat operations – an F-117 brought down by a surface-to-air missile over Yugoslavia in 1999. This has given stealth aircraft in general and the USAF in particular, an aura of invincibility. However, this seeming invulnerability is now under threat.

During the Gulf War of 1991, the Lockheed F-117 Nighthawk, operated by the United States Air Force (USAF) flew approximately 1,300 sorties. This constituted the first widespread use of a combat aircraft specifically designed to avoid detection using a range of technologies that reduce reflection or emission of radar, Infra-Red (IR), visible light, Radio-Frequency (RF) spectrum and audio. These technologies are collectively known as stealth technology or low-observable technology. Since then, the USAF has operated three other stealth aircraft – the Northrop Grumman B-2 Spirit, the Lockheed Martin F-22 Raptor, and the Lockheed Martin F-35 Lightning II. And wherever the USAF has deployed stealth aircraft in combat, for instance in Iraq and Syria, the results have been spectacular.

Stealth is the defining attribute of fifth-generation fighter aircraft and it has a two-fold appeal. First, stealth aircraft are far less vulnerable to engagement by hostile interceptors and ground defences, because radars cannot ‘see’ the stealth platforms. Second, a low-observable jet has an excellent chance to detect and kill a non-stealth adversary because it can close in and strike, sometimes before the target aircraft even realises it is under threat. Only one stealth aircraft has been lost in 30 years of combat operations – an F-117 brought down by a Surface-to-Air Missile (SAM) over Yugoslavia in 1999. This has given stealth aircraft in general and the USAF in particular, an aura of invincibility. However, this seeming invulnerability is now under threat.

Stealth’s Gradual Decline

For one thing, a military advantage is most significant when the adversary doesn’t have the same technology. The USAF’s dominance of stealth is now being challenged by China, Russia and other countries. China’s People’s Liberation Army Air Force (PLAAF) is on the cusp of a transformative shift in its war-fighting capabilities with the commissioning of its first fifth-generation fighter – the Chengdu J-20A. This single-seat twinjet, entered military service in September 2017, becoming only the third operational stealth fighter in the world, and the first in Asia. Meanwhile, Russia’s Sukhoi Su-57 stealth fighter is planned to enter service next year. A more significant reason why the USAF’s free run seems set to end is the determined pursuit of counter-stealth technologies by practically every major nation, including India. Sooner or later, stealth’s ‘invisibility cloak’ is likely to be pierced by razor-sharp Air Defence (AD) radars.

How Does Stealth Work?

The development of a credible counter to low-observable aircraft requires a clear understanding of what the technology involves. Before stealth, there was electronic jamming but effective jamming required precise knowledge of the adversary’s sensors. Stealth on the other hand, is more broad-based. Stealth depends on reducing the detectability of an aircraft so that it either cannot be picked up or appears only as a faint and intermittent target. This is done mainly by moulding aircraft into particular shapes that reduce detection by scattering or redirecting electromagnetic waves away from their source. In order to reduce an aircraft’s radar signature, it helps to lessen or eliminate sharp edges, other easily detectable features and weapons or equipment mounted on pylons. Even if the hostile radar receives a return signal, it should be of an entirely different character from the actual aircraft, perhaps like a bird or an insect.

Radar-Absorbent Materials (RAM) reduce or block waves that would otherwise be reflected from the surface. RAM coatings contain carbon black particles or tiny iron spheres that avoid reflecting radar and thus help conceal the aircraft, so every surface must be coated with two feet or more of RAM. Obviously, this is easier to do on a large and heavy bomber aircraft rather than on a small fighter aircraft. Heat emissions are also reduced to the extent possible to make it difficult for heat-seeking missiles to lock on. However, stealth is not an all or nothing capability. It is an intelligent combination of signature reduction and operational tactics and is most effective when employed in close coordination with other specialist aircraft. Stealth degrades the defender’s ability to detect the intruding aircraft. By ensuring delayed detection, it permits the attacker to engage even heavily-defended targets and leave before the defender can react effectively.

Eluding Radar

Radar is the sensor with the longest range and the greatest accuracy. Hence stealth is primarily meant to defeat radar rather than optical sensors such as IR or visible band imaging devices. But radars operate in many different bands and it is impossible to escape detection by all of them. Stealth designs are therefore optimised to defeat higher frequency radars that use the X (8-12 GHz) and S (2-4 GHz) bands, which are the most common for target acquisition. They usually cannot be made invisible to low frequency radars such as those in the VHF (50-330 MHz) or UHF (300-1,000 MHz) bands. Lower frequency implies longer wavelength. There is a ‘step change’ in an aircraft’s signature once the wavelength exceeds a certain threshold and causes a resonant effect. Typically, such resonance occurs when any feature on the aircraft is less than eight times the size of a particular wavelength, as happens with the tail-fin of a fighter.

Since reliable radar detection depends on a good signal-to-noise ratio, the trick is to reduce the signal using stealth and increase the noise using jamming. Following an analysis of the reasons behind the 1999 loss of the F-117 it became standard USAF practice to provide standoff jamming support to low-observable aircraft missions, thus combining stealth and Electronic Warfare (EW). For instance, a formation of tactical stealth fighters such as the F-22 or the F-35 is invariably supported by electronic attack aircraft such as the Boeing EA-18G Growler.

Counter-Stealth Radars and Techniques

Why are counter-stealth measures now proliferating all over the world? It is because whilst most countries cannot build their own stealth jets in a hurry, they can realistically aspire to at least defend themselves against a stealth attack. As already mentioned, V/UHF radars have good chances of detecting stealth aircraft. Since their wavelength (1-2 m) is of around the same magnitude as the prominent features on many stealth jets, their signal is echoed by a resonant effect that is unaffected by stealth shaping or RAM coatings. Radars of this type were always unpopular because they had poor resolution, picked up “noise” such as clouds and rain and were unsuitable for fire-control or terminal guidance. However, in view of their strong counter-stealth credentials, there is now renewed emphasis on perfecting such radars.

The best way to defeat stealth is probably a network of V/UHF Active Electronically Scanned Array (AESA) radar systems, all connected by high-speed data-links. Improved thermal sensors and visible band imaging devices can also provide useful inputs. Using advanced networking technology and high-speed computers, the data can be speedily collected, analysed and disseminated, to identify the presence of stealth aircraft and generate a weapons grade track. While radar-guided missiles may not be useful against stealth jets, interceptor aircraft could be vectored in by the AD radar and then launch their IR homing AAMs. As for the IR signature, even if the engine heat emissions are shielded from a particular angle, the heat generated by friction as the aircraft passes through the atmosphere, can help a heat-seeking missile to home on to the target. Most Russian combat aircraft are equipped with excellent IR detectors.

Stealth platforms are not optimised to produce the lowest signature from every angle – the emphasis is usually on the head-on aspect. So another defensive technique is to position several radars to illumine the target from the front, the sides and above using high-altitude surveillance Unmanned Aerial Vehicles (UAV) or Airborne Warning and Control System (AWACS) aircraft plus satellite surveillance and to then integrate all the data to obtain as accurate a track as possible.

Counter-Stealth Systems

Since the US has long enjoyed first-mover advantage over low-observable technology, its potential adversaries Russia and China have instead pursued counter-stealth systems. They have been exploring different avenues with varying degrees of success, including more sensitive, longer range radars and advanced digital signal processing and networking. Side-by-side they are developing more mobile and lethal SAMs and advanced fighter interceptors equipped with powerful AESA radars and Beyond-Visual-Range Air-to-Air Missiles (BVRAAM).

Although even the stealthiest aircraft will ultimately be spotted as it closes in, most current radars pick them up too late to react effectively. There is also a certain process, termed a ‘kill chain’ by the US military, between detecting a target and hitting it. It is a dynamic process that includes – Find, Fix, Track, Target, Engage and Assess (F2T2EA). The problem for both Russia and China is that while V/UHF radars will probably detect and even track a stealth fighter at adequate ranges, it is unlikely that they can plot its position accurately or provide an engagement quality track.

Russia emphasises a tightly integrated AD network with several radars trying to paint the same aircraft from different directions and then sharing the data to obtain a track. It is unclear how successful its efforts have been. Meanwhile, China has been working for some years on advanced V/UHF radars.

Russia’s Almaz-Antey 55Zh6M Nebo M is a 3-D high mobility digital AESA radar system, with three individual networked radars. It is Russia’s primary counter-stealth radar, developed specifically to detect and track stealth jets, UAVs and missiles and provide tracking data to SAM batteries and interceptor jets. The importance Russia attaches to it can be gauged by the recent announcement that 100 Nebo M systems would be expeditiously procured for Russia’s AD forces.

The Russian S-400 Triumf designed by Almaz-Antey is widely recognised as one of the most capable and lethal long-range AD systems in the world. Its AESA radar is claimed to be extremely successful in detecting stealth jets. It can engage all types of aerial targets including aircraft, UAVs and ballistic and cruise missiles within a range of 400 km. It can fire four different types of missiles with ranges between 40 and 400 km.

China’s JY-27A is a VHF AESA long-range air surveillance and guidance radar system. It is highly reliable and mobile, resistant to jamming, and can easily detect stealth aircraft such as the US F-22 and F-35. China has also developed the JY-26 radar that works in the VHF and UHF bands. Both these radars have a claimed maximum detection range of 500 km.

China would, of course, love to neutralise the superior US stealth capabilities. That is why it has been making regular announcements of ‘breakthroughs’ in the development of radar systems capable of detecting stealth aircraft. Its latest announcement is that its scientists have mastered quantum radar technology. The country has long recognised the immense potential of quantum technologies and aspires to be a world leader in this new field. Western defence analysts however believe that quantum radar systems, based on quantum illumination (the process of isolating pairs of entangled photons) would have serious limitations even in a laboratory environment, while producing a reliable operational system would be next to impossible.

India’s Counter-Stealth Options

As is well known, the Indian Air Force (IAF) faces a severe shortfall of combat jets. It currently has just 31 squadrons (each consisting of 16 to 18 aircraft) against the assessed minimum of 42 necessary to engage China and Pakistan in a simultaneous two-front conflict. This situation is likely to get worse before it gets better. The IAF for many years enjoyed qualitative superiority over the PLAAF; but now the shoe is on the other foot.

With the recent induction of the J-20A fifth-generation fighter, the PLAAF threat to India has acquired an entirely new dimension. In around a decade from now, China will probably possess a significant number of stealth aircraft of various types and Pakistan is likely to get some too. The J-20A is China’s first operational stealth jet and since the PLAAF views stealth as a core capability, it won’t be the last. The Shenyang J-31 is another low-observable fighter expected to enter service in a year or two. And the country’s technologists are rumoured to be hard at work on the Xian H-20, a subsonic flying-wing stealth bomber with an anticipated range of 12,000 km and a maximum armament load of 20 tonne.

The J-20A’s performance has not been revealed, but its range is presumed to exceed that of the US F-35. It will probably carry a variety of AAMs for aerial attack, besides Precision Guided Munitions (PGM) for strikes against surface targets. By utilising inflight refuelling, J-20A jets would be able to attack various airfields, command and control centres and critical air defence nodes in North India and clear the way for sustained operations by non-stealth aircraft.

Some defence analysts have openly expressed scepticism about just how stealthy the J-20A is. But its low-observable characteristics would probably get it safely past India’s AD radars. Indeed, it presents a far more potent threat to countries in the Asia-Pacific region in general and India in particular, compared to the Russian-built Sukhoi Su-30MKK and Sukhoi Su-35S that are currently the spearhead of China’s air power. While Western air forces are reasonably confident that the J-20A pitted in combat against the F-35 or the F-22 would come out the loser, the same cannot be said of the J-20A versus the IAF’s Sukhoi Su-30MKI. The J-20A will probably detect the Su-30MKI well before the Su-30MKI picks up the J-20A and will therefore have the advantage in the resulting engagement.

Earlier this year, India reportedly decided against going ahead with the joint Indo-Russian project to build an Indian Fifth Generation Fighter Aircraft (FGFA) based on the Sukhoi Su-57. The country’s stealth aircraft aspirations will now have to wait till its indigenous fifth-generation fighter known as the Advanced Medium Combat Aircraft (AMCA) becomes operational perhaps in the mid-2030s. Since the IAF cannot play the stealth aircraft deterrence card, it needs to bolster its current AD systems to include counter-stealth capability. It urgently needs to invest in advanced surface radar systems as well as Airborne Early Warning and Control (AEW&C) aircraft to add to its existing fleet of three Beriev A-50EI Phalcon and two Embraer EMB-145 aircraft.

However, this is easier said than done. Year after year, the defence budget is inadequate for its needs and the pace of hardware acquisition is glacial to say the least. On the other hand, China is investing heavily in advanced radars specifically designed to defeat US stealth and non-stealth aircraft. It is unlikely to face any problem in detecting and engaging the non-stealthy IAF aircraft.

The silver lining in this dark cloud is India’s impending deal with Russia, expected in the next few months, for five regiments of S-400 Triumf AD systems at a cost of approximately Rs 40,000 crore. They will mark an excellent first step in effectively countering the Chinese J-20A stealth threat.

State of Play

Are stealth’s glory days coming to an end? How long can it remain viable in the face of rapid advances in radar technology and computational power? Is it time to change tack rather than continue investing in costly stealth aircraft? The USAF, which has long been in the forefront of stealth technology and has invested hundreds of billions of dollars on stealth research, must be carefully considering these and other questions. An indication of its thinking will emerge once the contours of its next fighter aircraft, known as Penetrating Counter Air (PCA), become clear.

An opposing viewpoint is that the latest advances in radar technology make it harder for all aircraft, not just stealth jets, to avoid detection. Stealth will always be advantageous because advanced sensors will work even better against non-stealthy jets than stealthy ones. It is essential to employ stealth against heavily defended targets irrespective of the cost, because the alternative would be the loss of a number of aircraft. And, another argument goes, if China is so convinced that effective counter-stealth measures are just around the corner, why is it pursuing low-observable combat aircraft with such enthusiasm?

Another factor is that missions towards Suppression of Enemy Air Defences (SEAD) invariably form a key portion of the initial air campaign. Before any air force launches a major operation it makes determined efforts to suppress hostile AD facilities, including SAMs and related systems such as early-warning radars and Command, Control, Communication and Intelligence (C3I) facilities. Surface radars and sensors are a prime target for such SEAD missions. V/UHF radars which are claimed to be counter-stealth have large arrays with limited mobility and would be vulnerable to stand-off missile attacks. Similarly, any C3I system linked to a networked AD system would be deliberately targeted using electronic and cyber warfare. If such systems can be eliminated, stealth jets would again be difficult to detect.

The Eternal Cat and Mouse Game

Meanwhile, the mind games continue with nations in possession of stealth aircraft claiming that they can breach any AD system while their adversaries affirm the inevitability of detection and the impregnability of their defences. However, it is a truism that every weapon system eventually has a counter.

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Over the last 15 or 20 years, America’s mastery of stealth has not been seriously challenged because it has been used mainly against irregular forces, non-state actors and smaller nations. Meanwhile, Russia and China have focused their efforts on developing long-range sensors and weapons. They have also strengthened their Anti-Access/Area Denial (A2/AD) capability. They are now in a position to exploit their counter-stealth expertise and possibly impose unacceptable costs on intruding US aircraft. They have also invested heavily in military cyber and space capabilities. And all these technologies are cheaper and easier to develop than stealth aircraft which take many years to build and are exceedingly costly.

Stealth is now close to maturity and will become less of an advantage over time. In fact it has reached the stage of diminishing returns where even vast investments yield only limited increases in capability. On the other hand, counter-stealth technologies are on the ascendant and are steadily gaining advantage. They are becoming cheaper, more easily available and offer tangible benefits even for moderate investments. It is perhaps only a question of time before stealth loses much of its sheen of invisibility and invincibility.