A SPICE 2000 kit with a Mk 84 HE bomb

Why IAF used 907-kg 'penetrator' bombs to target Jaish terror camp

by Sameer Joshi

At around 3.30 am on 26 February, Mirage-2000s of the Indian Air Force made shallow incursions inside Pakistan and targeted Jaish-e-Mohammed camps at Balakot, along with Muzaffarabad and Chakothi (in Pakistan Occupied Kashmir). The strike on the Markaz Syed Ahmad Shaheed madrasa complex located on Jaba hill-top in Balakot was the most significant amongst them, especially considering that the Indian Air Force had struck a target inside Pakistan for the first time since the 1971 war. The strikes were a direct response to the attack by the Pakistan-based terror proxy – JeM – on a CRPF convoy at Pulwama on 14 February in which over 40 Indian jawans had lost their lives.

The IAF used the Israeli made SPICE-2000 stand-off glide bomb to target Balakot. The SPICE-2000 is a glide bomb kit, fitted on a 2000 lb (907 kg) bomb. The IAF uses both the SPICE 1000 and 2000 kits. As per Indian Air Force sources, 5 x SPICE-2000s were utilised to target Balakot, while one bomb was brought back. These bombs fell within 2 metres of their designated mean points of impact (DMPI) in the targeted area. The Indian Air Force has publicly stated that it has synthetic image radar (SAR) imagery of the post-strike battle damage analysis, which confirms its claim that all targets were accurately hit.

Meanwhile, Pakistan has denied any damage or casualties at Balakot, and said that the Indian payloads landed in the nearby forest, missing the targets completely. International satellite experts based on their reading of data available with private satellite networks post-strike, have ridiculed Indian claims that the bombs fell anywhere on the target. This has been widely supported by a large section of the western media, who have been sceptical about the accuracy of the attack. Pakistan, on its part, has completely sealed the targeted camp in Balakot, discouraging any independent verification of the damage.

What has baffled the world is why the 2000 lb bombs, which hit the madrassa complex, did not cause widespread explosive damage over the target. George William Herbert, an international weapon’s expert, tweeted a few days ago that a 2000 lb/907 kg bomb like the Mk 84 made of 428 kg trinitol high explosive core and a 479 kg of metal casing, would have obliterated the building, destroying it completely due to the shock wave travelling at over 1.83–2.13 km/s. Typically, it would double the pressure inside a standard three-storey building around 25 meters wide, further contributing to the damage.

Latest OSINT data reveals that while at least two of the targeted structures are still standing – with dark smudges or holes visible on the rooftop of the biggest target — they also suggest that SPICE bombs have indeed penetrated the building. While the imagery is synonymous with SPICE strikes seen in Syria, this does not match up to the damage assessment for an Mk 84 or an equivalent bomb carried as part of the SPICE-2000 glide kit as brought out by George Herbert. Also, suspected use of Fuel Air Explosive (FAE) through the SPICE-2000 mission, supported by dark smudges seen in the target area imagery, is also seen as a possibility by some experts. In addition, there is indication of a deep penetration SPICE bomb hit north of the big hall, where a seeming heap of soil is present, which suggests that either the building collapsed after being targeted or the Pak Army has razed it to the ground post strike to hide the damage.

Post Strike Analysis of the target | Col Vinayak Bhatt | ThePrint

IAF sources have recently confirmed that the Mirages had used the ‘penetrator’ version of the SPICE-2000 glide bomb, which has a 907 kg hard metal reinforced casing with an embedded ‘low mass’ TNT warhead of 70–80 kg of net explosive quantity (NEQ). This version is designed to target reinforced concrete installations like C2 centres, penetrating deep before carrying out a low mass explosion to eliminate all with shrapnel and a blast over pressure wave, and not necessarily collapsing the targeted installation. The IAF is confident that this is what has happened at Balakot. This theory is reinforced by the statement of Maulana Ammar, the younger brother of the JeM boss Masood Azhar, that the madrassa complex at Jabba top has indeed been hit by Indian bombs; as well as through discreet interviews with eyewitnesses in the area amid a media clampdown by the Pakistani army, which confirms witnessing at least 35 bodies of killed JeM militants and ISI operatives being taken out post-strike. Indian intelligence had estimated more than 250-300 individuals active inside the camp before the strike. Details of actual number of casualties remains sceptical as of now.

However, rather than being taken at a face value, this revelation has been further given an unwarranted spin within the media and intersecting theories. This is because even a 70–80 kg low mass TNT explosion would send shrapnel and corresponding shock waves upward of 1 km/s as dictated by the Gurney equation out to around 14 meters, enough to cause very significant damage to the targeted structure. Let’s hence diagnostically analyse the usefulness of the penetrator version of the SPICE-2000 as the bomb used by the IAF in its strike at Balakot.

The Right Deal For The Job At Hand?

The weapon to target matching suggests that the IAF was specifically looking to carry out a precision strikes and avoid large area collateral damage. As described after strike by the Indian Foreign Secretary, the ‘non-military preemptive strikes’ was aimed at targeting the JeM cadre while avoiding civilian and Pakistani military casualties. Hence the ‘penetrator’ version of the SPICE-2000, with a low mass TNT warhead was the right fit for the mission as compared to the high mass Mk 84 bomb equivalent version, which would have inflicted significantly more area damage. The SPICE-2000 is an all-weather 1000 kg glide bomb kit, which uses 12 control surfaces to achieve a definitive range of 60 kilometres. It navigates with the help of IN/ GPS and approaching the target reduces the GPS errors using its Electro optical/ infra-red terminal attack sensor. This matches what it sees with pre-loaded satellite/ drone imagery of the target through ‘scene matching’, rapidly reducing the margin of errors and impacting the target within a CEP of less than 3 meters.

The SPICE-2000 used by the IAF has an advanced electrical fuse, which accurately predicts the impact sequence and delay required to activate. This is especially useful when penetrating multiple floors of a building, before exploding on the right level. A microphone embedded with a microcontroller in the smart fuse is used, with the microphone measuring the number of impacts and the microcontroller counting the floors, until the bomb breaks through the desired number of floors. Used extensively by the Israeli Air Force in Lebanon and Syria against tactical battlefield targets and in urban areas, the SPICE-2000 has a near perfect operational reliability record. These fuses would be critical in penetrating the various targeted buildings with at least 2 levels.

The focus of SPICE-2000 strike was the madrasa complex at the north edge of Jaba top, dominated by a huge 30 meters (length) x 30 meters (width) x 8 meters (max height) white/gray main Madrassa building, used mostly for imparting lessons by the instructors to their trainees. This would possibly be the target for a solitary SPICE-2000 bomb. Connected to this main hall is a set of buildings. Another concrete structure with two storeys 12 meters (length) x 10 meters (width) x 8 meters (height) is located to the north of the big hall, which housed the under-training ab-initio cadre of the JeM. This building would have been targeted with a SPICE-2000 bomb. There was a twin storey mosque to the right of this building and a shed further to the north. To the south of the big hall, across the training ground was a robust ‘U’ shaped concrete structure with sloped roof, housing the instructors, senior trainees and a guest house in each component. One SPICE-2000 bomb each, would certainly have been earmarked for the Guest House, the Instructor’s quarter and the senior trainee accommodation. The last target was the house of Umar Ghouri, the local JeM boss, who lived across the dirt track. This would be a certain target for a single SPICE-2000 bomb. It is believed that one of the SPICE-2000s malfunctioned and could not be launched by the Mirage-2000s. Hence in all probability, one of the targets out of the GH, instructors and senior trainee buildings would not have been engaged.

Pre-strike vintage images of the buildings show thin metal roofs, with light concrete layer and two storeys. The walls would be a mix of concrete, local bricks and mortar, reinforced by rough iron pillars and concrete for support as is common in the construction characteristics found in Balakot region. While viewing historic satellite imagery of the place, it’s interesting to note the camp mostly survived the 2005 Balakot earthquake which caused widespread devastation in the area.

Possible targets for IAF in the JeM Camp | Sameer Joshi

Post-strike imagery analysis done from the images available, has revealed that all the bombs impacted the roofs of the various targets at near vertical position. This would have been tactically planned by the IAF to achieve maximum penetration, before the bombs exploded. This may also explain the reason behind the IAF’s shallow incursions in Pakistan Occupied Kashmir, aiming to fire the SPICE-2000 well within its launch envelope to achieve the optimal vertical trajectory over the target, rather than launch it at the fringe range of 60 kilometres from Indian territory.

To Be Or Not To Be…

Let’s analyse the science of what happened post impact on 26 February at Jabba top, Balakot. If we compare the Israeli made SPICE-2000’s penetrator casing volume and weight; it is closest to the USAF’s BLU 116 penetrator used on the GBU 24/27 series 2000 lb bunker busting munition. As per information, the BLU 116 can penetrate 3.4 meters of reinforced steel (or 15 meters of earth) using a nickel cobalt steel alloy core. The SPICE-2000 penetrator bomb has similar capabilities. Assuming that the SPICE-2000 hit the target at a near nadir point, it would have easily sliced through the thin metal/ light concrete roof and at least one semi concrete floor to hit the base floor with a decent foundation in the ground, which is largely made up of Bafliaz volcanic rock in the Balakot region. For the sake of calculating the impact force on a bunker class target, we will assume the SPICE-2000 is able to penetrate at least 3 meters of 500 PSI reinforced concrete (a figure which is certainly less than the actual) and 10m of earth.

We reverse calculate the average impact force on a reinforced concrete target as follows –

Average impact force = mgh ÷ d
m — Weight of the penetrator (907 kg)
g — Acceleration due to gravity (9.81 m/s)
h — AGL height where the bomb transitioned from glide mode to vertical drop trajectory (a minimal 500 metres estimated for the Balakot attack)
d — Depth of penetration

Therefore, Average impact force of SPICE-2000 on reinforced concrete is 1474 kN and on earth is 442 kN. Incidentally, the more a bomb penetrates into the ground, the lesser will be its average impact force. The Bafliaz volcanic rock at Balakot is composed of at least three quarters of alkaline basalt, which has a density of 2.8 g/cm3. The approximate density value for 500 PSI reinforced concrete is 2.9 g/ cm3, which is close to basalt. Taking the margins in error and chemistry of basalt, it can safely be assumed that after penetrating the roof and another possible floor, the impact value would have increased from the 442 kN on the roof and the first level to (taking an approx. 15 percent jump within margin of error) to 508 kN. However, with the penetrator intact and no major loss in momentum, the same 15 % error margin can be applied to the 1474 kN standard 500 PSI reinforced concrete penetration figure, this time reducing the average impact force to 1253 kN, giving us a penetration distance of 3.5 meters in the Bafliaz rock geology at Jaba top.

The SPICE-2000 flight profile and penetration into the rocky surface explained | Sameer Joshi

The Science of the Blast

The smart fuse of the SPICE-2000 would have been set to explode after penetrating two layers as per the intelligence available before the strike. After digging deep 3.5 meters below the big hall, it would have triggered the explosion of 80 kilograms of TNT, with the Gurney equation estimating shrapnel release at nearly 1 km/ sec for an explosive equivalent of the TNT. At the same time, the expansion of the intensely hot gases at extremely high pressures in the fireball would have caused a shock wave to form, moving upward out of the dug in silo at nearly the same velocity out to an effective range of 14 meters. The main characteristic of this wave is that the pressure rises very sharply at the moving front, and falls off toward the interior region of the explosion. The variation of the pressure with distance from the centre of the fireball, at a given instant, is ideal for (instantaneously rising) shock front, which will eliminate any soft target in the region and cause significant damage to the structure and depending on the distance, will cause the structure to collapse.

Now let’s calculate the overpressure caused by the explosion of the 80 kg warhead — Overpressure in an enclosed space is determined using Weibull’s formula –

Overpressure Δp=2410(m/V) to the power 0.72 where: 2410 is a constant based on 1 bar (100 kPa; 15 psi); M = Net explosive mass calculated using all explosive materials and their relative effectiveness; V = Volume of given area (primarily used to determine volume within an enclosed space).

We have two zones to measure the overpressure, the first inside the 3.5 m silo created by the SPICE-2000 penetrator. This gives us a value of approx. 12631 kPA for the overpressure wave within the dug-up silo. This overpressure wave would have resonated through the rocky side, ejecting upward at a high velocity towards the single/ twin floors of the targets. Post expansion, the shrapnel and the overpressure wave would have killed all soft tissue targets and penetrated the walls and roofs with deadly effect.

But was that enough to collapse the buildings? As per experimental data, a minimal overpressure of around 14 kPA is required to cause the collapse of a non-concrete structure. Since the volume of the building was very large with two floors inside the building, the overpressure blast wave from the 80 TNT kg warhead, had it exploded at the base of the building (not accounting for the penetration to 3.5 meters), would be in the tune of 19.28 kPA. This overpressure would probably have brought down the buildings to implode and collapse. However, the explosion of the warhead 3.5 meters below the surface, with the rocky sides, walls bearing partial explosion and blast overpressure effects; will significantly drop the overpressure value inside the compartmentalised hall. What would also be noteworthy is that the foundation and support beams would have been dug in the solid basalt rock, hence will require a significantly greater charge to knock down core load bearing members, than the low mass 80 kg TNT of the penetrator version.

Though not basing assumptions on an empirical relationship and keeping well within the error margin, it can safely be assumed that the value of the blast overpressure wave would have fallen far below 14 kPA, which — while causing extensive kinetic energy based shrapnel and overpressure pressure damage to the roof and the sides, would not have been sufficient to break open or collapse the side walls with intermixed concrete, and the main roofs of the building. Compartmentalised damage would have occurred in the individual bomb’s sphere of influence.

Yes, there would be significant casualties within the confines of the targets due to shrapnel, intense heat and overpressure waves.

One piece of the puzzle is still not clear: why are multiple entry points visible on the roof of the big hall, when the building may have been targeted only by a single SPICE-2000 as per the data available on the number of bombs and the speculated targets? In all probability, these would be the result of inside to outside blast incursions.

One can, however, clearly see the result of the attack on the trainee accommodation north of the main hall (Refer Target 1), where the building has been destroyed with deep ingestion marks and a lot of loose soil unearthed, the classic tell-tale signs of a penetrator warhead entering the ground and making a mould of earth around it. This indicates that there was more sub soil present than basalt rock, underneath the structure as mentioned or a cover-up operation underway by the Pakistani Army post blast. Since the IAF points out that all the SPICE-2000 bombs hit within the CEP, impact points on the other targets would indicate clean penetration and deep explosions, which while killing all, would not be sufficient to get the complete buildings down as is seen at other locations.

Did the IAF SPICE-2000s strike at the target ?  Yes, they did. This assessment is based on the science of it all, which can be debated by explosive experts for its worth. The Indian Air Force has done its job; let’s not overreact to anything and everything of it. One day we will know what happened below that roof.

So, when the Indian Air Chief says ‘We hit the targets’, believe me, he means serious business!

The author is an former fighter pilot with extensive experience on the Mirage-2000 and MiG-21 aircraft of the IAF