This explainer provides a breakdown of the S-400 ‘Triumf’ missile system that India recently bought from Russia. We will look at its key building blocks, its place in India’s air defence network, the advantages it brings to the table, its weak points, and how it might be overpowered. To keep things simple, we will mostly steer clear of technical minutiae and performance specifications. They are not that important, and tend to draw attention away from how it all works.
Integrated Air Defence System Basics
Before we jump into the structure of an S-400 set, it is important to have a basic understanding of how an Integrated Air Defence System (IADS) works and how its various parts interact with each other.
Simplified structure of an Integrated Air Defence System (IADS). The areas shaded in light colour show the scan angles of the radars, i.e. the area that they can “see”. The portions shaded in dark colour show the position of the radar beams at a given moment. Imagine the beams oscillating back and forth within the coverage area.
The basic building blocks of an IADS are a series of radars and command posts. At the highest level are long-range air search radars. These are usually operated at the national or sector level. In the Indian case, the long-range surveillance system is underpinned by THD-1955 radars that can see out to more than 1,000 km. While they possess great range, they are also slow, inaccurate, and prone to obstruction by geographical features. So the network is supplemented with “gap filler” radars for better coverage.
If the radars form the eyes of an IADS, then a series of “operations centres” or “nodes”, form the brains. An operations centre controls all air defences in its assigned sector. It takes in data from several sources (long-range radars, AWACS, observation posts, and others), deconflicts it, generates a consolidated picture of the airspace, prioritises targets, and issues instructions to various fighting units under its command. Multiple operations centres report up to a national headquarters.
Situated one level below the operations centre are individual air defence units. We shall use the term “unit” to describe a self-contained formation that is capable of operating all by itself. The Indian Air Force (IAF) calls this a “Squadron”, the Indian Army calls it a “Group”, and the Russian Armed Forces call it a “Regiment”.
A unit is centered around a command post and a surveillance radar. The radar is similar to the long-range air search radars mentioned above, but is more compact. In the old days, surveillance radars were large devices, and fixed in place. Nowadays, they are more mobile, and can be mounted directly onto trucks or towed platforms. They provide extended range coverage, and are often the first to detect enemy aerial activity. The command post exercises control over its subordinate units—particularly surface-to-air missile (SAM) batteries; but there is other stuff too, like transport vehicles carrying additional missiles, engineering equipment, communications gear, and more.
The surveillance radar passes preliminary data on intruding enemy aircraft to a Target Acquisition Radar (TAR). TARs are generally shorter in range, but capable of more precision than a surveillance radar. They take the contacts acquired by the surveillance radar and develop precise target tracks.
The next grouping in the hierarchy is a “battery”, which the IAF calls a “Firing Unit” or “Flight”. Russian Forces call it a “Battalion”. It consists of an engagement radar, also called a Fire Control Radar (FCR), and several missile launchers. An FCR is capable of extreme precision; enough to guide missiles towards individual enemy aircraft. Older FCRs could engage only one contact at a time, but with contemporary sets, around four to eight targets can be simultaneously engaged.
In this structure, TARs are extremely versatile. With modern hardware and processing, they can substitute for surveillance radars as well as fire control radars, to the point that they are now called multifunction radars. As such, they can be deployed anywhere in the network. At the unit level, they work with the surveillance radar to generate target. At the battery level, they supplement the engagement radar and grant the battery more autonomy. The Indo-Israeli MR-SAM/Barak 8 system showcases this versatility rather well. Instead of dedicated radars for surveillance, target acquisition, and engagement; it uses a single sensor, called the Land-Based MF-STAR, for everything.
Finally, we come to the missiles themselves. Like radars, they come in all ranges, sizes, and types; but unlike radars, they are not distributed throughout the command chain. They are always assigned to batteries, and directed by the FCR towards individual targets.
The longest ranged missiles are large, expensive, and unwieldy—the farther away a target is, the harder it is to find and shoot down. So, they are reserved for “high-value targets” that operate well behind the frontline—AWACS aircraft, refueling tankers, electronic warfare platforms, and the like. They may also be fired to “scare” the enemy, scatter carefully planned formations, and perhaps score a few lucky kills. Medium-range missiles bring attackers under accurate fire, and are intended to shoot down enemy aircraft before they can release their payloads. Short-range missiles, also known as quick-reaction missiles, provide a third layer of protection. While they are unable to prevent the system from being penetrated, they are invaluable in protecting key facilities and nodes from attackers that filter through the first two layers of defence.
The arrangement appears slow and clumsy, but it isn’t. It is largely automated, datalinked for seamless communication, and can function like a well-oiled machine when operated by well-trained personnel. An IADS is neither impregnable, nor meant to secure every inch of friendly airspace all the time; but when designed and used properly, it can be lethal and can whittle down an enemy over long periods of fighting.
Enter The S-400
Having understood the structure of an IADS, it becomes easier to decipher the S-400 and its various components. The first thing to note is that the S-400 is not a “SAM”, but an entire family of radars, command posts, missiles, and support elements that can be assembled into combat units to protect large patches of airspace. Developed by Russia’s Almaz Central Design Bureau, it was inducted into service in mid-2007, and has been exported to China, Turkey, and India.
Configuration of a typical S-400 regimental set/squadron. Emphasis on “typical”. Exact numbers may vary. Each squadron can contain up to four batteries, with each battery supporting up to twelve launch vehicles.
The central element of an S-400 unit is a surveillance radar—the 91N6E ‘Big Bird’. It is paired with a command vehicle, the 55K6E, which houses operator consoles from where an air battle is managed. Together, the Big Bird and the 55K6E form a command post called the 30K6E. The Big Bird can double up as a target acquisition radar, but the 96L6E ‘Cheese Board’ is available if a dedicated device is needed.
A command post can manage as many as eight individual batteries (also known as firing units), although two is more common. Each battery is equipped with a 92N6E ‘Grave Stone’ radar for target acquisition as well as fire control, and can be supplemented with a Cheese Board for surveillance and tracking. A single battery usually consists of four missile launch vehicles, but is capable of supporting up to twelve. Each launch vehicle has four tubes containing ready-to-launch missiles. Four different missile types are available, capable of engaging targets flying at various ranges and altitudes.
Apart from this, there are support vehicles to store, transport, and reload missiles; site survey vehicles, engineering equipment; electronic sensing measures (ESM) equipment; power generation stations; and other gear.
The radars, operator cabins, and command posts are all connected to each other via secure datalink. The battle management system automates all routine functions like assessing targets, deconflicting data, building and presenting a tactical picture of the airspace, and so on. Human input is generally limited to command-and-control functions.
The entire setup is road-mobile and its components can be packed up for relocation within minutes. It can also be airlifted and redeployed across the length and breadth of the country on short notice. The radars are modern electronically scanned arrays, designed to resist enemy jamming and to prosecute stealthy targets. On the whole, the system is designed to repel airstrikes as well as ballistic missile salvoes; all while maintaining a high degree of survivability against a Suppression of Enemy Air Defences (SEAD) campaign.
One Part of a Whole
Information in the public domain suggests that the S-400 is a highly capable system; possibly the most capable in the world at this time. It has been designed with the lessons of Operation Desert Storm in mind, and advertised as being able to fend off the type of offensives that destroyed the Iraqi IADS in a matter of days.
For India, however, the S-400 will be a small part of a much larger whole. And that “whole” is itself in the middle of a mini-revolution.
The IAF’s command, control, and communications (C3) backbone being extensively modernized, with a pronounced emphasis on enhancing situational awareness and streamlining communication. A key piece of this upgrade is a network-centric air defence environment called the Integrated Air Command and Control System (IACCS). The IACCS soaks up information from a multitude of sources (Army and Navy radars, the civilian radar network, as well as the IAF’s own systems) and fuses it together to generate a comprehensive tactical picture of the battlespace. This information is distributed to Air Defence Control Centres (ADCCs), which direct the larger air battle by issuing orders to individual air defence units and fighter squadrons. When the Pakistan Air Force struck back at India in February 2019, air defence operations were directed from an ADCC in Barnala, Punjab.
The IACCS rides on a communications network called AFNet. This high-bandwidth network replaces the old radio communications infrastructure with a secure, jam-resistant, and high-bandwidth information grid. Together, the IACCS and AFNet are transforming what was once a collection of discrete sensors, command centres, and SAM units into a unified “system of systems”—an entity that is not only cohesive but also flexible and resilient enough to maintain that cohesion when degraded by enemy assault.
As the brains of the system are being overhauled, so are its eyes and fists. The air force’s obsolete land-based radar network is being steadily upgraded with a slew of homegrown radars to cover a vast range of duties and possibilities. A new generation of airborne sensors are also being acquired to help the IAF see farther out, and with greater precision than before. At the sharp end, the obsolete S-125 ‘Pechora’ and 9K33M2 ‘Osa-AK’ systems are being replaced with MR-SAM (medium-range), Akash (short range), and SpyDer (short-range/quick reaction) batteries. Even as these missile systems enter service, new blocks are under development—these being the XRSAM, Akash NG, and QRSAM.
It is within the ambit of this warfighting structure that the five squadrons of the S-400 system being acquired from Russia will operate. Each squadron will nominally be able to operate as an independent, self-contained fighting unit; but it will truly come into its own when melded with the IACCS—feeding data up the chain of command and receiving information/instructions from ADCCs.
Points of Failure
As it stands, the S-400 is expected to fill a major void in the Indian air defence umbrella by enabling air defence at extended ranges, well beyond the reach of the SpyDer, Akash, and MR-SAM systems.
However, there are limitations—affecting land-based air defences in general and the S-400 in particular. Land-based air defences are reactive, not very mobile, and unable to see beyond the curvature of the earth (called the radar horizon). Contemporary systems are designed to be quickly packed up and repositioned, allowing for a degree of concealment against attackers. However, they still remain relatively static in comparison to attack aircraft—they have to be fixed in position to operate. They are also fundamentally defensive assets, which naturally cede much initiative to the attacked. Recent history is littered with examples of SAM systems shattered by cyber and electronic offensives, decoys, radar-seeking missiles, stealthy aircraft/munitions, and low-level tactics.
Furthermore, surface-based systems have short radar horizons, which makes it difficult for them to engage low-flying targets. Terrain features like hills and valleys only compound this problem by creating voids that attackers can exploit. The S-400 and Akash systems partially address this problem by optionally mounting their surveillance radars on masts for improved coverage; but the utility of a mast varies depending on the geography. For example, a mast-mounted radar is still not high enough to see past obstacles in mountainous or hilly regions.
The S-400’s potential shortcomings are no less concerning. For one, it is a new system, untested in battle. This might not appear to be a major concern since very few modern weapons have seen combat against a peer-level threat. However, the S-400’s predecessor—the S-300—gave a poor account of itself in Nagorno-Karabakh conflict. One of Armenia’s S-300 batteries was successfully attacked by Azerbaijani drones and loitering munitions, and showed itself incapable of denying airspace to the enemy. The other, and more concerning problem is that the S-400 is a foreign system that has been sold to India’s adversaries. Its electronic and kinetic characteristics will be known to them, and they will use that knowledge to develop exploits against it.
At the end of the day, the S-400’s effectiveness in the Indian context will depend on its degree of fusion with the IACCS, which will help it overcome many of the challenges mentioned above, and also on how innovatively and aggressively it is used. There is little doubt that it is a very advanced system, and will prove to be a major enhancement to the IADS. However, it is not a silver bullet, and it can be countered by an intelligent adversary using the right tactics and technology.
Mihir Shah is a mechanical engineer who tracks military and aerospace issues closely. He contributes to to Livefist, Pragati Magazine, and Bharat Rakshak’s Security Research Review. Follow Mihir on Twitter here.