Why Layered and Tiered Defence in Air Defence

Issues Details: 
Vol 10 Issue 4 Sep - Oct 2016
Page No.: 
Sub Title: 
Why the need for layered and tiered defences in building an dynamic and robust Air Defence System
Brigadier MKK Iyer, SM
Monday, October 3, 2016
Many of my friends have always questioned me on one aspect of air defence, especially the air defence of the army, as to why are there are so many varieties of equipment and that too from different sources and where is the need for so much complication. Well the answer is not as difficult or complicated as the question seems. The issue can be simply explained by giving an example of the employment of troops in anti-infiltration role on the borders. Let’s take the border with our Western neighbor into consideration. If we take the border fence as one layer of defence, it has to have a subsequent layer (made up of men) guarding it since the fence left unguarded can be breached at a time or place of their own choosing by the infiltrators.  The entire area behind the fence cannot be physically occupied hence; there is a need for the area to be controlled or dominated with weapons, patrols etc. In spite of the first two layers, there would still be some infiltration and the infiltrators would have to be neutralized in the hinterland. For this there is need to deploy another tier of troops deployed making the grid three layered. Similar analogies are equally applicable for troops occupying defences during war. There is a need to have defence in depth to be able to effectively deal with the enemy.
Similarly, in the case of air defence, the task is only tougher since the air space cannot be separated by any fence and therefore, to protect important assets we need to guard them with a variety of weapons of various ranges and capabilities. The entire mechanism of the air defence battle commences with the eyes or the sensors which are the radars. These could be airborne sensors like AWACS, balloons fitted with radars, long range, medium or short range radars. Alternately these could even be spotters who are deployed ahead to warn against enemy incursions. The next task is to convey the identity of the aerial object which involves the process of identification. This aspect is important from two angles. The first is to ensure that there is no fratricide or blue on blue engagement and the second is to use an appropriate weapon to engage the enemy intrusion. This is carried out by an elaborate control and reporting chain with a good communication system. Thereafter the shooters are designated;these could be the defenders aircraft or ground based air defence weapon systems (GBADWS) to destroy the aerial threat.
An air defence battle consists of various stages as shown below pictorially.
The next aspect that will help understand the need for a layered defence is the threat envelope. When slow moving aircraft were the only threat from the air, the ack ack guns of the Second World War were considered par for the course. But today we consider the aerial threat in terms of a threat envelope. A typical threat envelope can be described as threat manifestation in terms of varying ranges, height or altitude and speed of the aerial threat. Hence, there would be a need for engaging the threat before the aerial threat releases its weapons. Alternately there would be a requirement to engage the weapon itself like destruction of missiles. This would naturally require a family of weapons or GBADWS consisting of systems from long range missiles to close in weapon system like the guns. 
The lowest portion or Low/Medium Level (upto a height of 5 Kms and a range of 60 Kms), and closest to the Vulnerable Point (VP) is the area where the threats are the maximum from nap of the earth flying attack helicopters and fighters. Therefore, the threat in this area is the closest and most dangerous with minimum reaction time to the air defence gunners. It is obvious therefore that this area has to be covered by the VSHORADS and radar controlled close in weapon systems (CIWS) using high rate of fire guns with precision ammunition. It should be clearly understood that long range radars have the disadvantage of minimum range due to technical reasons of the curvature of the earth and therefore, to cater for early warning against suddenly appearing helicopters, radar controlled CIWS is the best answer. The area above and further from the VSHORAD (very short range air defence system) engagement area or High Level/Extended Level (at a height of 15 Kms and upto 90 Kms) is the area where the air threat is the most from fighters, UAVs (both armed and unarmed) and precision guided missiles (PGMs). Consequently, this is the area for engagement of the aerial objects with Short Range Surface to Air Missiles (SRSAM) or its quick reaction version (QRSM) utilized in support of the mechanized forces. Further away and in the extended zone in the threat envelope, the threat emerges from UAVs and fighters capable of engaging our assets from longer distances using PGMs. This zone therefore, is the engagement zone for the MRSAMs (medium range SAMs). The higher zone in the threat envelope belongs to Ballistic Missile Defence (BMD) engagement zone against Tactical Ballistic Missiles (TBMs) and SRBMs. It must be remembered that the air threat gets pushed from low to high altitude and vice versa by effectiveness of air defence. 
Let’s now discuss the prevalent practice of the concept of layered air defence in the case of an air field protected by the air force and the carrier battle group (CBG) of the navy. Although it can be argued otherwise, air threat to an airfield and a CBG is lesser than that to the forward assets in the tactical battle area (TBA). This is purely due to the distance of these assets from the enemy air fields. In the case of an airfield, the air defence is provided by fighters in air defence role, MRSAM, SRSAM, VSHORADS and CIWS. The CBG is protected by fighter and air defence aircrafts, Long range SAMs, SRSAM, VSHORADS and CIWS. 
The layered concept of air defence is not peculiar to the Indian air defence but is followed by the most advanced armies in the world. Let’s now have a look at the weapon systems used by four advanced armies of the world.
Similarly there is a lot of talk on a theatre grid concept. Although we do not have it in the present context, the US forces and others have already implemented a theatre grid concept of air defence. Emphasis is on one/two/three layered air defence in a grid as per terrain and assets in a geographical location. There is a shift from point to area air defence and point defence. Point defence is given to only critical VPs only.
The area where the army air defence functions is where the threats emanate from low level flying objects including ammunition as a threat vehicle. The radar horizon limitations force differing surveillance and tracking requirements in terms of radars and the GBADWS cannot be tasked to engage all threat platforms. As a target gets down to the low level, the detection by a MRSAM or LRSAM radar also gets reduced in terms of range. Further, the detection to tracking, identification, system reaction time and engagement time also needs to be catered for. For example, the S-400 System radar needs to pick up a target at 135 to 140 Kms for engagement at 70 Kms. Therefore, there is a need for a family of air defence weapons on ground from radar controlled guns with precision ammunition to long range missile systems to be deployed in a tiered and layered fashion. The CIWS with the VSHORADS is the last bastion of defence and can overcome the effect of electronic counter measures by engaging the missile or the ammunition itself. This also caters for unconventional threats like drones, large caliber rockets, micro lights and balloons too.
Military Affairs