By RD Misal, RL Saini & Rohitendra Bhandari
The perpetual fight between tank armour designer and anti-tank ammunition designer is going on ever since tanks appeared on the battlefield in the First World War. The former is concentrating on applying better systems with better materials to enhance protection levels of tanks keeping the weight of the tank as a constraint and the latter is trying to increase the lethality of the projectiles with better designs to counteract the improved armours keeping the same armament and stowage system as a constraint.
The technologies that have emerged and are emerging in the armour field include the development of composite armour systems, ERA, Heavy ERA and Active and Reactive protection systems. To counteract the continuous improvements in the armour field, the ammunition designers have come up with novel concepts, be it in system design, materials, and applications, along with in almost every aspect which goes into the design of ammunition.
Tank ammunition is traditionally classified as chemical energy ammunition & kinetic energy ammunition. Chemical energy ammunition achieves the defeat of the target by utilizing the energy interlocked in the chemical structure of the explosive. Whereas K.E ammunition utilizes its kinetic energy to neutralize the target. Each class has a variety of ammunition in its family. As chemical energy ammunition, an army has high explosive Anti-Tank (HEAT), High Explosive Squash Head (HESH), High Explosive (HE), Anti-Tank Guided Missile (ATGM), Penetration-cum-Blast (PCB), Thermo Baric (TB) as various alternatives to choose from, depending upon the battlefield scenario.
The kinetic energy tank ammunition has seen the development from the World War I origin Armour Piercing (AP) ammunition to Armour Piercing Discarding Sabot (APDS) ammunition in World War II & Fin Stabilized Armour Piercing Discarding Sabot (FSAPDS) Ammunition- presently being used by all armies world over. AP & APDS ammunition were spin-stabilized in comparison to fin stabilisation used for FSAPDS ammunition.
Indian Army (IA) is having a large fleet of Main Battle Tanks (MBTs), due mainly to its long land borders adjoining Pakistan and China. Indian Army has at present three varieties of MBTs operational, the Russian origin T-72 & T-90 MBTs with 125 mm smoothbore gun as their main armament and indigenous MBT Arjun with 120 mm rifled bore gun. Considering the fleet size, the requirement for tank ammunition is enormous.
Armament Research & Development Establishment (ARDE), Pune is a premier institution of Defence Research & Development Organisation (DRDO). ARDE has been in the field of indigenous development of tank ammunition of calibres 105 mm, 120 mm & 125 mm, over the past three decades in collaboration with sister laboratories High Energy Materials Research Laboratory (HEMRL) Pune, Defence Metallurgical Research Laboratory (DMRL) Hyderabad & Proof & Experimental Establishment (PXE) Balasore.
In the current battlefield scenario, FSAPDS is considered as the primary tank ammunition, because of its superior lethality, excellent first-round kill probability and immunity against any form of active, reactive, or passive tank armour. As the name suggests, FSAPDS consist of a high-density core, called a penetrator, generally of Heavy Alloy (HA). The penetrator is assembled with a fin tail unit for stabilization. On impact at the target, the high-velocity penetrator pierces the target, in a phenomenon called Hydrodynamic Penetration.
The target along with the penetrator suffers erosion and the residual length of the penetrator, along with a plume of molten fragments of the penetrator and target material, emerge out in the inside of the tank compartment. The Behind Armour Debris (BAE) is sufficient to completely neutralize the tank and tank crew. With the high momentum, stability, and inertia of the penetrator as well as the absence of any electronic module, it is almost impossible for the current generation active, reactive and passive armours to defeat or deflect the FSAPDS projectile.
The basic design philosophy for the design of the FSAPDS projectile is to have a maximum Length to Diameter ratio (L/D ratio) of penetrator and a maximum density of penetrator material to have an optimum penetration. However, the design should also have sufficient structural strength for satisfactory in-bore performance. At sufficiently high strike velocities, the penetration is hydrodynamic in nature, where target and projectile, both can be taken as fluids and modified Bernoulli’s equation is applicable.
Then, the penetrator & target strength don’t play many roles and only the length and density of the penetrator and target materials are of concern. However, the typical ordnance velocities are lower than the cut-off limit for it to qualify as hydrodynamic penetration. Here, the material strengths also play a role and there are several established empirical formulations, which predict the penetration performance with reasonable accuracy.
In past, ARDE has gained enough expertise and skills for the development of FSAPDS ammunition through various ammunition development programs, viz, 105 mm APDS, 105 mm FSAPDS, 125 mm FSAPDS steel Core & 125 mm FSAPDS hardcore ammunition. Utilizing the experience gained through these developments, ARDE has developed 120 mm FSAPDS ammunition- Mk-I and 120 mm FSAPDS ammunition Mk-II for MBT Arjun. 120 mm FSAPDS Mk-I ammunition has been produced in large numbers and serving the fleet of MBT Arjun for a long period.
To keep pace with global developments, the Mk-II version has been developed as an improvement. 120mm FSAPDS Mk-II ammunition has lethality equivalent to the best of tank ammunition available worldwide. The performance of the ammunition was demonstrated in terms of functionality, serviceability, toxicity, lethality, consistency, accuracy, and safety.
ARDE has also developed 125 mm FSAPDS Mk-I ammunition and the same was produced in large numbers. To enhance the lethality, ARDE is now developing an advanced version of 125 mm FSAPDS ammunition, and the ammunition will be offered for trials. The ammunition, once inducted, will enhance the penetration capability of T-72 & T-90 tanks.
Looking at the large fleet of T-72 & T-90 tanks, the requirement of ammunition for training is quite large. The service ammunition, being costly and penetrator material not available freely, cannot be utilized for crew training. Considering this aspect, ARDE has come up with 125 mm FSAPDS Practice ammunition. The ammunition is considerably cheaper and matches the ballistics of in-service ammunition. The barrel wear is also considerably less with Practice Ammunition, making it a feasible alternative for crew training that has been recommended for induction into service. Production has been established at DPSUs.
Coming to the family of chemical energy ammunition, a 120 mm HESH, secondary ammunition, for MBT Arjun. The shell houses a high explosive formulation of RDX & Wax and is initiated with a base fuze on target impact. The shell thickness is kept bare minimum to achieve an optimum scabbing effect, at the same time, it is sufficient to ensure structural integrity inside the bore of the barrel. The ammunition produces excellent scabbing performance against armour and demolished secondary targets like bunkers & field fortifications.
In addition, 120 mm Penetration-cum-Blast (PCB) & Thermo Baric (TB) Ammunitions has been designed and developed. PCB Ammunition has toughened nose, which enables for initial penetration into the target and then the high explosive formulation initiates causing an explosion inside the target for achieving maximum damage.
On the other hand, TB Ammunition generates a long duration thermal impulse, in addition to blast impulse. This makes TB ammunition effective against soft targets, especially those hidden in enclosed spaces like bunkers, tunnels, underground hideouts etc. The performance of PCB and TB ammunitions has been demonstrated. Thus, a wide variety of Secondary Ammunitions for MBT Arjun are available today as options.
The development of other varieties of tank ammunition, viz, 125 mm High Explosive (HE) & High Explosive Anti-Tank (HEAT) Ammunitions is also underway. Completing these developments will not take much time and multiple novel concepts in the field of tank ammunitions are being experimented with for a new generation of ammunition.
To do all this world-class testing infrastructure and test methodologies are in place to take up any challenge in future.
About The Authors
The authors, RD Misal is Scientist ‘G’ at ARDE, Pune, RL Saini is Scientist ‘F’ & Rohitendra Bhandari is Scientist ‘D’ there
