Let’s Talk About The Missiles Behind S-400’s Extraordinary Capabilities

S-400 launcher
A launcher unit of S-400 air defense system. By Соколрус – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=40082350

The S-400 has been in the news for various reasons, like its deployment in Syria by Russian forces, Turkey’s decision to purchase it leading to it’s kicking out of the F-35 program, or its purchases by other countries like China, India and Saudi Arabia. And considering that it is a relatively new system, we will be hearing about it for some time to come. To most people, the S-400 is also enigmatic. With undisclosed abilities and claims of being capable of shooting down stealth fighters. Considering its fabled capabilities and its history of controversies, its worth while to do an objective assessment of the S-400 system, especially its missiles, based on what ever open source information we can find about it.

The System

S-400 is an air defense system developed by Russia’s Almaz Antey, to defend against aircraft of all kinds, drones, cruise missiles and short to medium range ballistic missiles. S-400 is not a single weapon. It is a complex consisting of a variety of radars and other sensors feeding information to a command and control system, which in turn controls launchers that can launch three different types of medium to long range surface to air missiles. Short range air defense systems like the Pantsir can also be integrated with the S-400. And it can also receive data from other sources like AWACS and reconnaissance aircraft. In other words, it is a system of systems. But let’s have a look at the basic components that make up an S-400 battery. The video below shows an S-400 battalion being setup and its missiles being test launched.

At 0:18 mark in the video, you see the sight most people associate with the S-400- he missile launcher itself. Each of these launchers can carry four missiles each. One S-400 fire unit consists of 9 such launchers, and 120 missiles. The spare missiles are carried by support vehicles that load them on the launcher using a crane. These missiles are encased in air tight canisters (the four green tubes you see on the launcher), that significantly  reduce their maintenance requirements. They can essentially be stored in these canisters for a long period without requiring any maintenance.

From 0:40 to 1:40 mark, you can see the missiles being launched. We will come back to this sight a while later. At 1:50 mark, you see the 91N6E Big Bird radar. This is an S band panoramic acquisition and battle management radar system with  maximum detection range of 600 km. It can track 300 targets at a time. At 0:42 mark, you see it being set up. At 2:00 mark, you see the 92N6E radar. This is a multi functional radar with a range of 400 km, and can track 100 targets at a time. From 4:00 mark onward, you see multiple units of this radar being setup.

At 2:12 mark, you see the 55K6E command and control system, which processes information from the above two radars, as well as additional radars and other sources, and gives launch command to the launchers. One S-400 battalion comprises of one 55K6E command and control system, one 91N6E Big Bird acquisition and battle management radar and up to eight fire units. Each of the eight fire units comprises of one 92N6E Gravestone engagement and fire control radar, and up to 12 launchers, with each launcher carrying 4 missiles.

Let's Talk About The Missiles Behind S-400's Extraordinary Capabilities 1
Core components of an S-400 battalion. Image courtesy: Ria Novosti / Sputnik

There are also other, optional sensors that can be integrated with the S-400 system. These include the 96L6E acquisition radar, 59N6 Protivnik GE and the 67N6 Gamma DE radars that operate in the L band, the 1L119 Nebo SUV radar that operates in S band and the multiband Nebo M radar system. The 96L6E acquisition radar can complement the 91N6E Big Bird radar. There is just one Big Bird radar per battalion, but each of the 8 fire units in the battalion can have a separate 96L6E radar, so that if the Big Bird radar is taken out by the adversary, the individual fire units will still have some ability to independently scan the sky.

Nebo M system consists of three different radars and a command post that fuses and analyses data from all three radars. Nebo M system can reportedly scan upto a range of 1800 km and an altitude of upto 1200 km. There is also the 40V6MR mobile mast, on which a radar like the 92N6E Gravestone can be fixed. This places the radar at a higher altitude, allowing it to operate in heavily forested or mountainous terrain and also extending its horizon.

In this context, the ability of S-400 launcher to launch missiles vertically is also useful, as it allows missile launches from the middle of forests or built up areas. In contrast, a system like Patriot launches missiles at an angle, requiring an area free of trees, buildings and other obstacles in front, so that the missile has a clear path.

Let's Talk About The Missiles Behind S-400's Extraordinary Capabilities 2
Nebo M Radar System; Image courtesy: ausairpower.net

In addition to these radars, S-400 can also take data from ground based emitter locating systems like Topaz Kolchuga M, LRTP-91 Tamara and 85V6 Orion. These are vehicle mounted systems that detect the radar and radio communication  emissions of enemy aircraft. This helps locate an enemy aircraft without using the S-400’s radars if the situation so demands. They can also make it easier to locate stealth aircraft. The way they do this is by placing three such emitter locating vehicles spaced several tens of kilometres from each other.

When an enemy aircraft emits a radio signal to communicate with other friendly aircraft through datalinks like Link 16, this radio signal is detected by all three emitter locating vehicles. The time the radio signal takes to reach each of these vehicles is different, and depends on the distance of each vehicle from the enemy aircraft emitting the radio signal. This difference can be used to locate the enemy aircraft via a process called triangulation.

Kolchuga-passive-sensor maks2009.jpg
Kolchuga Passive Sensor System By Allocer – Own work, CC BY-SA 3.0, Link

The Interplay

Before we come to the missiles that make S-400 so potent, let’s unzip the claims about S-400’s capabilities and the counter arguments that question their validity. One of the most impressive things about the S-400 is its extraordinary ability to hit aircraft up to 400 km away. To put this in perspective,  an S-400 battery in London could theoretically track and shoot down an aircraft flying to the south of Paris. The first thing we need to consider when thinking about a surface to air missile system detecting, tracking and hitting an air borne target 400 km away is the earth’s curvature.

If you have ever observed a ship approaching you from far away in the sea, you know that the mast of the ship is visible first and only a while later you observe the rest of the ship. This is, in fact, one of the most easily available proofs that the earth is round (sorry flat earthers). And when you take off in an aircraft near the sea, far away clouds that were not visible from land suddenly become visible. This is because as your altitude increases, so does the horizon. And just like you can’t see an object beyond the horizon, a radar can’t either. You can calculate how far away horizon would be from you by entering your altitude in this horizon calculator.

Now, lets look at the service ceiling of one of the aircraft that S-400 is designed to engage at a range of 400 km. For reasons I will come to later, its likely that 40N6E, the 400 km range missile of S-400, is designed to take out large, unmanoeuvrable aircraft like AWACS, refuelling tankers and strategic bombers, and not small, manoeuvrable aircraft like fighters. As per Wikipedia, the service ceiling of an E3 Sentry, the AWACS aircraft used by USAF, is 12,000 meters. At this altitude, the horizon extends to 391 km. This is well within the 400 km range of 92N63 radar and the 600 km range of 91N6E radar.

Hence, an E3 operating at its service ceiling will have to be more than 391 km away from an S-400 site if it doesn’t want to be detected by its radars. The limits of this horizon apply not just to S-400 radars but to the E3’s own search and track radar as well. So aircraft and missiles flying at tree top level won’t be detected by E3 operating at its service ceiling, if they are beyond 391 km. But as their altitude increases, so does the range at which E3 can detect them.

As per Wikipedia, E3’s radar can detect targets flying at low altitude (but higher than tree top level) at around 400 km, and targets flying at medium or high altitude at a range of 650 km (of course, the shape and size of the target also matters here). This means that if an E3 stays more than 391 km away from an S-400 site located near the border of enemy territory, it can still peep roughly 291 km into enemy airspace looking for medium and high altitude targets, while staying undetected by the S-400’s radars.

But this is exactly one of the advantages S-400’s range confers. It would force AWACS aircraft like E3 to stay almost 400 km away, not letting it peep too deep into enemy airspace. Moreover, while S-400’s ground radars can’t detect AWACS aircraft if they are beyond horizon, the radar emissions of the AWACS can be detected by enemy ELINT (Electronic Intelligence) aircraft flying safely within their own airspace. One such aircraft is the Boeing RC-135 Revit Joint.

Again, from how far these ELINT aircraft can detect the emissions of an AWACS depends on their altitude. But an ELINT aircraft can detect the radar emissions of the AWACS much further away than this aircraft can be detected by the AWACS radar. This is because an ELINT aircraft just needs to detect radar waves coming straight out of the AWACS, but the AWACS needs to detect radar waves that have traveled all the way from the AWACS to the ELINT aircraft, reflected off its surface, and than traveled all the way back to the AWACS. Radar waves loose a lot of their strength during this long journey. So if an ELINT aircraft is networked with S-400, it could send the location of the AWACS to S-400 site while staying outside the detection range of the AWACS.

Apart from ELINT aircraft, over the horizon radars can also help detect an aircraft even if it is beyond the horizon. These radars are capable of such a feat because their radar waves get reflected back to earth after hitting the ionosphere. Russia has multiple over the horizon radars installed at various locations. However, the disadvantage of these radars is that owing to their large size, they are not mobile, with their coordinates fixed and well known. So they would be easy targets on the very first days of a conflict.

The Missiles

S-400 system utilizes a range of missiles with varying ranges and features to deal with the full spectrum of aerial threats, ranging from precision guided munitions and small UAVs to medium range ballistic missiles. At the low end is the 9M96E missile, with a range of 40 km and maximum speed of mach 2.6. This missile uses active radar homing, but there are versions with optical and infrared homing as well. Stealth targets can be engaged with this missile through optical and infrared homing with assistance from long wavelength radar . In this conformation, they can be guided to the general area of the stealth fighters that would be known by long wavelength ground radars, and once in the general area, they would attempt to locate the stealth targets with their on board optical / infrared seekers.

9M96E is maneuverable enough to take down highly maneuverable targets like fighter jets. Besides shooting aerial targets, 9M96E can be used for marksmanship for low flying targets that are beyond radar horizon. In other words, it can use its on board radar to detect targets that are beyond the horizon of the S-400 ground radar, or are behind a terrain masking feature like a mountain, and send its location to the S-400 ground control. This helps the S-400 system deal with low flying cruise missiles. An advanced version of the 9M96E is the 9M96E2 missile, with a range of 120 km and maximum speed of mach 2.9. This is a highly maneuverable missile, with a load factor of more than 20g at an altitude of 30 km. This enables it to intercept short to medium range ballistic missiles.

96M6E and 96M6E2 missiles are small enough for four of them to fit in a single canister of an S-400 launcher. So a standard S-400 launcher with four canisters can carry a total of 16 96M6E or 96M6E2 missiles. The 9M96 missiles are also used in the S-350 Vityaz air defence system, which can be integrated with the S-400 system. These two missiles together give S-400 the same capabilities that the Patriot air defense system has. For example, the maximum range of Patriot (that of the PAC2 variant) is 160 km, comparable to the 120 km range of 96M6E missile. And just like 96M6 missiles, the missiles of the PAC3 variant of Patriot are small enough for 16 of them to be carried by a single launcher with four canisters.

Above the 96M6 family comes the 48N6E family of missiles, consisting of three varients, namely 48N6E2 with a range of 200 km, and 48N6E3 and 48N6DM, with a range of 250 km. All three variants have a maximum speed of mach 5.9 and are guided by semi active radar homing. These missiles, therefore, fill the range gap between the 96M6 and the 40N6E missiles.

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Source: ausairpower.net

But it is 40N6E, the third missile, that has made S-400 such a talked about weapon system. This missile is believed to have a range of 400 km and a maximum speed of Mach 12. At this speed, it would cover its maximum range of 400 km in just over 100 seconds. But that’s if it flies at this speed from the start to finish of its journey which is something we will come back to in a while.

There is something about such high speeds that the general public is not aware of. As the speed of an object flying within the atmosphere increases, its push on the air ahead of it also increases. The increase in this push or friction manifests itself in the form of increased temperature of the object’s surface as well as temperature of the air surrounding the object. At low speeds, this effect is too small to notice. But beyond the speed of sound, especially at hypersonic speeds, it is very visible and makes a hell lot of difference.

For example, the shooting stars, or meteors that you often see on a clear night glow because of friction with atmosphere. The lowest speed at which meteors hit atmosphere is around 11 km/sec. But meteors are often known to enter the atmosphere at speeds as high as Mach 209. That’s 72 km/sec! At such speeds, the friction with air is so high that the meteor gets engulfed in flames, or plasma. This glowing plasma surrounding the meteor is what makes it visible in the night. You can also imagine from this, the incredible kinetic energy with which the asteroid that wiped out the dinosaurs must have hit earth.

But coming back to missiles, the fastest objects ever developed by humans to travel inside the earth’s atmosphere are space shuttles and Intercontinental Ballistic Missiles, or ICBMs. The re-entry vehicle of an ICBM, carrying its deadly nuclear payload inside it, enters the atmosphere and streaks towards its target at speeds between Mach 20 and Mach 25, which is around 8 km/s. In the video below, you can see re-entry vehicles from a Russian ICBM streaking across the atmosphere glowing just like meteors, engulfed in plasma generated due to their extreme speed.

Now, as it happens, this generation of plasma due to friction with air can happen at Mach 10 as well. Sprint was an American anti-ballistic missile that was designed to intercept the re-entry vehicles of ICBMs within the atmosphere. But unlike the re-entry vehicles, the Sprint’s maximum speed was Mach 10. Intercepting a re-entry vehicle travelling at double that speed was a humungous task that required phenomenal performance. To achieve this feat, Sprint achieved its max speed within seconds of launch, and instead of trying to directly hit the re-entry vehicle, it would detonate a nuclear warhead in the vicinity of the re-entry vehicle.

The huge radius of destruction of the nuclear warhead meant that Sprint did not need to be very accurate to destroy the re-entry vehicle. The two videos below show the Sprint missile being test launched. In the first video you see the missile being launched, and at around 0:05 mark, you see the even faster ICBM re-entry vehicle streak by. In the second video, at around 0:24 mark, you can see the Sprint missile’s body going white hot and getting engulfed in plasma as it accelerates to Mach 10.

Now, if a missile travelling at Mach 10 gets engulfed in plasma, so could the 40N6E, that travels at Mach 12. But there lies a problem for 40N6E. This plasma a high speed missile gets engulfed in, prevents it from communicating with ground control and also prevents its radar from working, if it carries one. With ICBM re-entry vehicles, this isn’t a problem as they don’t need a radar or external guidance. They just need to travel towards a large, unmoving target like a military base or city, and detonate their nuclear payload over it, which doesn’t require them to be super accurate.

The Sprint did need external guidance as it needed to hit a tiny, flying target moving at double its own speed. Sprint didn’t have its own radar as the plasma surrounding it at Mach 10 would have rendered any on board radar useless. But a ground-based radar tracked the re-entry vehicle, and this data was transmitted to Sprint mid flight through a ground-based radio station. The radio signals from this station had to be extremely powerful to penetrate the plasma surrounding the Sprint and reaching its receiver.

The 40N6E, however, doesn’t have this option, as unlike Sprint that had to intercept the re-entry vehicle within the horizon of the ground radar and radio station, 40N63 might have to engage a target beyond the horizon of the S-400 ground radars, and therefore will need its own, on board radar. Moreover, the radio station that guided Sprint could be huge and powerful enough to penetrate the missile’s plasma because it was a fixed instillation. The S-400’s radars and command centers on the other hand, are mounted on vehicles, and hence are unlikely to send signals powerful enough to penetrate plasma, although technological advances making this possible cannot be ruled out.

However, the generation of plasma around the missile depends on one more factor apart from the missile’s speed. This factor is air pressure. The thicker the air through which the missile is travelling, the higher will be the friction with the missile, and easier will be the generation of plasma. But air pressure steadily decreases as the altitude increases, as the figure below shows.

At an altitude of 12000 meters, the altitude at which 40N6E is supposed to engage targets like AWACS aircraft, air pressure is far lower than it is close to sea level. And while an ICBM re-entry vehicle travelling at Mach 25 might get engulfed in plasma even in the thin air at 12000 meters, the 40N6E travelling at Mach 12 might not. This would allow the missile to locate and hit its target using its on board radar. Targets flying at low altitude however, will be out of its reach as it will be engulfed in plasma as it descends into lower, denser layers of atmosphere.

Air - altitude in meters and atmospheric air pressure in kPa
Image courtesy: engineeringtoolbox.com

However, there are ways in which 40N6E could locate and hit low flying targets too. Firstly, by executing S or corkscrew manoeuvres, the missile could gradually reduce its speed, preventing plasma generation and enabling the radar to work. Secondly, as this article shows, Chinese scientists have been working on a solution to enable radio communications between ground stations and spacecraft re-entering atmosphere at Mach 25. They are trying to use the plasma layer itself to amplify the radio signals instead of blocking them, using a phenomenon called resonance.

You can read about the basic concept of resonance in this post by me, although there the phenomenon has been discussed in a very different context. Anyways, this technology, if successful, can be used to enable not just radio communications between spacecraft and ground stations, but also the radar of missiles travelling at hypersonic speeds. It could theoretically enable ICBMs fitted with radars and conventional warheads to locate and hit aircraft carriers even at Mach 25, enabling them to hit carriers thousands of kilometers away in a matter of minutes, at speeds so high that they would be practically impossible to shoot down.

Indeed, one of the intended uses of this technology by the Chinese could be to enable the DF-21 and DF-26 ASBMs to hit aircraft carriers, as these missiles cross Mach 10 in their terminal phase which leads to plasma generation, and have been claimed to have anti ship capability. And similarly, it could also enable a missile like 40N6E to locate and hit a low flying target even at Mach 12, despite being covered in plasma. However, there is no publicly available information that points to use of a technique like this in missiles like 40N6E. And even with the Chinese, it appears to be a work in progress.

If we assume that no such attempt has been made to enable 40N6E to hit low flying targets, then different types of targets can use low flying to escape the missiles to different extents. Fighter and transport aircraft like C-17 and C-130 can easily fly at altitudes so lo that even terrain masking becomes a protecting factor, as the video below shows. At altitude this low, its very unlikely that a missile fired almost 400 km away and travelling at Mach 12 could hit the airplane.

This low flying would not hinder the mission of a transport airplane, as it could fly high for much of its journey to conserve fuel, and go low as it approaches the S-400’s range. Non-stealthy bombers like B-52 and B-1 can similarly fly low. Moreover, with the advent of standoff weapons, they won’t need to get close to an S-400 site anyway. And the stealth bombers like B-2 and B-21 will anyway be difficult to target even at high altitude due to their stealth.

The airplanes most vulnerable to S-400 are the recon, petrol and command and control aircraft like E-3 sentry, Rivet Joint and P-8 Poseidon. You will probably never see an AWACS or ELINT aircraft flying at super low altitude like the C-17 in the video above. These airplanes need to fly at high altitude in order do their job, be it scanning the skies using an AWACS radar, or sniffing out radar and communication signals, or searching for sea, under sea or ground targets. Flying at low altitude will hinder these activities, as the curvature of earth will reduce the distance from horizon and terrain masking will further block signals.

Moreover, these airplanes might have no choice but to come within the range of an S-400 site to do their job. For example, as explained above, an AWACS like E-3 Sentry will have to come within 400 km of the enemy territory where S-400 hardware may be lurking, if it wants to look more than 200 km into enemy airspace. Similarly, a Rivet Joint might have to similarly come close to enemy territory to do recon. Moreover, these airplanes are large, non-stealthy, slow, unmaeuverable, and carry contraptions like the radar disk of AWACS, that likely increase their radar cross section even more. In other words, they sport every feature that makes it easy to shoot down an airplane.

And it is here that the true value of the 40N6E missile comes to the fore. These AWACS and ELINT/SIGNT airplanes are called high value low density assets. This means that they are available in low numbers due to their high price, but bring a huge difference to the war by enabling other platforms, like fighters, in doing their jobs more efficiently. And it is exactly these airplanes that S-400 will find the most easy to take down using the 400 km range 40N6E missile.

Most public debates pit S-400 against high density, small, agile and stealthy fighters like F-35. Some even bring up the 400 km range of 40N6E missile when speculating S-400’s ability to target F-35, despite the fact that as I described above, even non-stealthy fighters will likely be fairly protected from such missiles at that distance by flying at low altitude.

But take out the high value low density assets supporting these fighters with S-400, and suddenly they will find themselves in a lot more difficult environment to fight in. Usually, platforms like AWACS are shielded from enemy forces by a protective screen of fighter jets. But these fighters can shield the AWACS from enemy fighter jets, not long range, hypersonic missiles like 40N6E. With missiles like these, the enemy can directly hit the distant AWACS from ground, without having to send their own fighters for it, without having to worry about the fighter screen, and without even having to cross the border.

Using Anti Ballistic Missiles Against Surface To Air Missiles

In the situation described above, a platform like AWACS will be pretty much a sitting duck against the 40N6E. It could attempt to jam the missile’s seeker, but success isn’t guaranteed and 40N6E is claimed to be resistant to jamming. But there is one tactic, that could in future, potentially provide a viable defense against long range surface to air missiles.

On 17 March 2017, Syrian forces fired multiple S-200 missiles against Israeli airplanes in response to an Israeli airstrike. One of these S-200 missiles, after failing to hit its aerial target, continued to fly in a ballistic trajectory and entered Israeli airspace. Because of its ballistic trajectory, the Israelis thought it was a ballistic missile and fired an Arrow 2 missile to intercept it (its unclear in the media whether it was an Arrow 2 or Arrow 3, but I believe it was the former). What happened then was truly unprecedented. The Arrow 2 missile, despite being designed to intercept ballistic missiles, successfully intercepted the S-200 missile.

Arrow 2 launch on July 29, 2004, in Naval Air Station Point Mugu Missile Test Center, during AST USFT#1
Arrow 2 Anti Ballistic Missile; By Photographer’s name not specified – US Navy News Service, Public Domain, Link

This could be a sign of the things to come. S-200 was successfully intercepted by Arrow 2 because it was flying a ballistic trajectory. But this flight profile isn’t unusual for missiles. In fact, all long range surface to air and air to air missiles that don’t have an air breathing engine fly a ballistic trajectory, especially after they run out of fuel. Because this is the natural trajectory that any projectile that is no longer being self propelled takes.

Long range anti air missiles, in fact, make use of ballistic flight profile to maximize their range. Because according to the laws of physics, the range of a projectile is maximum if it is fired at an angle of 45 degrees, and decreases as the angle of fire is either increased or decreased from 45 degrees. To engage far away targets, a typical long range air to air missile like AMRAAM, after being fired, climbs up at altitude higher than that of the airplane, and at the apogee (the highest point of its ballistic trajectory), starts gaining further speed as the potential energy it gained by climbing at that altitude is converted into kinetic energy during its descent.

This extra kinetic energy maximizes its range and also helps it hit the target airplane. The 40N6E missile works similarly. It climbs up to its apogee, which is believed to be 40 km high, and then starts its descent, gaining kinetic energy. It is likely at this stage, and not right after launch, that the missile’s speed finally reaches Mach 12. This is further evident if you observe the first video in this post, of the S-400 missiles being launched, and compare them with the launch video of the Sprint missile.

The S-400 missiles are clearly not as fast right after launch as the Sprint, which was known to accelerate to Mach 10 within seconds of launch (although its not clear from the video whether the S-400 missiles being launched are 40N6Es or one of the other types). Anyway, having reached its apogee of 40 km, the altitude of 40N6E is almost four times that of platforms like AWACS, which typically fly at around 12,000 meters.

So, as it starts descending from its apogee, scanning the sky for its target with its on board radar, the 40N6E will be approaching the target aircraft from above, not below. In other words, the missile is following a ballistic trajectory with an apogee of 40 km, and hitting its target from above, pretty much like a surface to surface ballistic missile does.

And this is why the incident of the Arrow 2 missile shooting down an S-200 missile is relevant here. S-200 is basically the precursor to S-300 system, which in turn is the precursor to the S-400 system. S-200 has a maximum range of 300 km, comparable to the 400 km range of 40N6E, and just like 40N6E, S-200 was designed primarily to take out platforms like AWACS, strategic bombers and refueling tankers in enemy airspace. So, if the ballistic flight profile of S-200 enabled Arrow 2 to intercept it, the similar ballistic flight profile of 40N6E should in theory enable Arrow 2 to intercept 40N6E as well.

The problem though, is that while the maximum speed of S-200 is Mach 6, making it relatively easy to intercept by Arrow 2 whose maximum speed is Mach 9, 40N6E has a maximum speed of Mach 12. So a missile like Arrow 2 will have difficulty shooting it down. Arrow 3 missile is more advanced than Arrow 2, and although its maximum speed is not clear from publicly available sources, its almost certainly more than that of Arrow 2. Arrow 3, therefore, may find it easier to intercept missiles like 40N6E.

These anti ballistic missiles might be relevant in this context because due to its 400 km range, 40N6E missile allows S-400 to be used not just for defense of home airspace, but for offensive operations in enemy airspace. If Syria had tried to shoot down an Israeli AWACS with S-400, the AWACS would have been flying well within Israeli airspace and the 40N6E fired to shoot it down would have followed pretty much the same flight profile as that of the S-200 missile that was shot down by Arrow 2. A missile like Arrow 2 or Arrow 3, or some other anti ballistic missile, could therefore be put to good use in this situation.

However, this does not mean such a tactic will render 40N6E useless. Far from it. Because a ballistic missile defense system trying to intercept 40N6E missiles streaking towards an aerial target will have to successfully intercept every single 40N6E missile to save the aerial target. The S-400 on the other hand, will need just one failed intercept by the ballistic missile defense system to take out the aerial target.

Moreover, the outcome of this contest between ballistic missile defense system and S-400 will also depend on the magazine depth of both systems. In other words, it will depend on how many anti ballistic missiles the ballistic missile defense system has for every 40N6E missile that S-400 has.

Usually, a ballistic missile defense system fires two or more anti ballistic missiles to take down a single enemy ballistic missile for assured destruction. This itself limits the number of targets the ballistic missile defense system can engage at a time. Moreover, an anti ballistic missile is typically much more expensive than the ballistic missile it is trying to shoot down. So between two countries with equal amount of resources, the side with the ballistic missile (or in this case, 40N63 missile) will enjoy an economic advantage over the other.

If the AWACS is over sea near enemy airspace, it could be protected from missiles like 40N6E by missiles like SM-3 carried by warships sailing in the vicinity of the AWACS. But here again, the same limitations of magazine depth, cost and need for 100 percent success apply. Moreover, when at war with a capable adversary, while the AWACS will be facing a volley of 40N6E missiles, the ship thats supposed to defend it with SM-3 missiles will itself be facing a volley of anti ship missiles. This means that the ship’s magazine depth with respect to SM-3 will be limited, as some of its vertical launch cells will have to carry missiles like SM-6, SM-2 and Evolved Sea Sparrow missiles for self defense.

Conclusion

Like any other weapon system, S-400 is no silver bullet, and it has its limitations. But its various features make it a truly formidable thing to deal with. Its 40 km and 120 km range 9M96 missiles, through their on board radar, enable it to locate aerial targets beyond the horizon of the S-400’s ground radars, and also low flying cruise missiles behind mountains, helping S-400 ground control deal with them. Their ability to carry optical / infrared seekers and be guided by long wavelength ground radars help them engage stealth targets. And their high maneuverability helps them intercept short and medium range ballistic missiles in their terminal phase.Their compact size also increases their magazine depth.

The 48N6 family of missiles fills the middle of the spectrum. And the 40N6E missile can be used against short and medium range ballistic missiles, as well as force multipliers like AWACS, petrol and ELINT/SIGINT airplanes. So, a force attacking an adversary armed with S-400 will be facing threats on multiple levels. Its AWACS, petrol and ELINT/SIGINT airplanes, despite being far inside friendly airspace and shielded by a screen of fighter jets, will be extremely vulnerable to the 400 km range 40N6E missiles, which will be streaking towards them at Mach 12 from an altitude of 40 km. The very knowledge of this possibility will keep the crews of these aircraft on edge every moment during their mission.

Contrary to popular belief, the 400 km range 40N6E missile will most likely not be used to hit fighter sized targets, which could easily escape it at those ranges. But the AWACS, petrol and ELINT/SIGINT aircraft and other high value low density assets that will either be shot down or kept away from the theater by this missile, will make the fight way more dangerous for the fighters. In the absence of ELINT/SIGINT aircraft, the electronic order of battle will not be clear, and it will be difficult for fighters going into enemy airspace to know the locations of threats and safe passages.

And without AWACS, the larger picture of the airspace will not be clear and fighters will most likely be forced to turn on their on board radars, giving away their location. The communications signals these fighters send through data links could be detected by passive radars feeding the information to S-400.

Moreover, even if they are stealth fighters, and manage to somehow stay electronically silent even in absence of AWACS, their general area could still be known through long wavelength radars, and 9M96 missiles fitted with optical / infrared seekers could be sent in that area. Anti ballistic missiles carried by ships or ground batteries could in theory be used to shoot down 40N6E, but they will have their own limitations, and are unlikely to prevent the most far reaching missile of S-400 from transforming the battlefield in very significant ways.

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