Shaped charges have high penetration capability against all known armour materials due to the special penetration mechanisms (hydrodynamic penetration). This penetration is almost independent of the hardness of the target material. Explosive Reactive Armour is a suitable answer to this threat.
In order to provide safety against such threats with armour steel, one reaches quickly considerable weight. In the case of the ubiquitous charge of the well-known RPG 7V grenade, the penetration capability of about 320 mm would already require more than 2.5 tons of armour steel per square meter to be protected. The requirement for the Puma, however, is a 360° protection against shaped charges and other threats. Even special light-weight armour materials with high effectivity against shaped charges will not satisfy the weight limitations of the system. The total weight savings would be around 50 percent.
Also the so-called statistical armour such as nets or slat constructions are not suitable due to the high protection requirements.
Explosive Reactive Armour for AIFV Puma’s protection against shaped charges
Design and mode of operation
Explosive Reactive Armour (ERA) goes back to research work of Professor Manfred Held and has been known for some time. The principal design is relatively simple: between two plates (made of metal or of composite material) there is a layer of high explosive, and this sandwich, called cassette, is arranged at an angle toward the incident threat. When such a cassette is hit by the jet of a shaped charge, the explosive is initiated and the two plates are accelerated towards the back and towards the incoming jet. So the jet will always find material to penetrate, much longer than in the case of just a static sheet of metal. Also, the blast effect of the explosive contributes strongly to a massive disturbation of the jet particles. This mechanism leads to a drastic decrease of the penetration depth of the charge. The function of this principle is illustrated by the figure on the left side.
Working principle of the ERA in practice
The two X-ray flash photographs, triggered at two different time intervals after initiation, show the incoming jet and the massive disturbation of the jet due to the interaction with the plates and the blast effect. The highly dangerous tip particles are strongly influenced, and the massive parts from the rear of the jet are neutralised by the backing plate. This backing plate will also minimise blast effects of the approaching charge and the counter measure (ERA) on the vehicle. The geometry of the arrangement as well as the amount of explosives used depend on the penetration power of the shaped charges to be defeated.
In practice, the cassettes are stored in closed boxes, called tiles, where a certain number of elements (cassettes) are arranged in a suitable way to guarantee maximum coverage. The weight of such tiles is adapted to the needs of the crew of being able to mount or dismount the tiles without any major equipment.
Dynamit Nobel Defence GmbH in Burbach (DND) has been developing, testing and evaluating Explosive Reactive Armour for more than ten years. The development of ERA is often conducted in cooperation with vehicle manufacturers and users to guarantee system compatibility. First qualification of Dynamit Nobel Defence ERA was performed for the IFV Marder and recce vehicle Fennek of Krauss-Maffei-Wegmann (KMW). The experience from these tests formed the basis of the development and qualification of Explosive Reactive Armour for the AIFV Puma.
The weight of protection systems is characterised by the areal density of the system, i.e. the weight of a given armour with given thickness for one 2meter. This is illustrated in the figure below, giving the thicknesses and areal densities for steel plates to guarantee safety against various threats.
When using Explosive Reactive Armour, there is a weight saving potential of approximately 80 percent with respect to steel plates, including the so-called “parasitic weight” of fixing elements etc.
A Puma fully equipped with Explosive Reactive Armour will carry a considerable amount of explosives on the outside of the vehicle. Therefore, special safety considerations are necessary regarding occupants safety and system compatibility, meaning compatibility to all environmental loads the vehicle might carry. Explosive Reactive Armour requires highly insensitive explosives that will only detonate in case there is a direct hit by a shaped charge jet. In all other cases the cassettes will remain passive. This also holds true for firings from heavy machine guns and high-power KE rounds, such as e.g. 30 mm APFSDS. The insensitive explosive used for ERA purposes guarantees that there will be no sympathetic detonation of other elements in case of a hit by a shaped charge jet.
Additionally, ERA tiles have been tested with torch flames, hot exhaust fumes, angle grinders, drive-over by heavy tracked vehicles, etc. to prove that no such external influence can cause an unwanted detonation. The robustness of the systems against loads coming from driving in extreme situations and the safety aspects have been proven by tests conducted by authorities in Germany.
In Germany, the users were very reluctant to use Explosive Reactive Armour as they thought that there would be intolerable collateral damage. This is true if steel plates and steel bolts are used in the ERA which will indeed result in dangerous fragmentation. These fragments can wound or even kill people at a distance of several hundred metres. These reservations were overcome as plates as well as bolts made of composite materials were used. Such materials will decompose due to the effect of the explosive close to the vehicle under attack, and there will definitely be no dangerous fragments. Also, the additional amount of explosives to that of the grenade is proven to be not critical for the vehicle or the crew.
The protection was tested thoroughly in the labs, but also under operation conditions, such as driving in hot climate (Abu Dhabi) and cold climate (Norway winter trials).
DND’s Explosive Reactive Armour can be used without any limitation in all climatic surroundings that also apply to the vehicle. For transport and storage, the ERA is classified as 1.4S.
Growth potential of ERA
The ERA qualified for the Puma AIFV has intentionally been designed to react only to shaped charge jets. It is, however, possible to choose more sensitive explosives and use multiple-cassette designs thus enabling the protection kit to neutralise e.g. 120 mm KE round or at least mitigate effects considerably. There are examples for such ERA in Russia. Recent developments show that it is also possible to defeat tandem shaped charges such as fired from shoulder-launched weapons or from ATGM launchers. These upgrade options are under development at Dynamit Nobel Defence.
Explosive Reactive Armour has been in use for many years by many nations. In Germany, resentments were only overcome when composite materials were used for all flying parts, as well as a highly insensitive explosive specially designed for use in ERA. The ERA used on the AIFV Puma offers a lot of advantages when it comes to shaped charge defeat, regarding weight, handling, and safety.
The latter is guaranteed by the effect that only the event “shaped charge jet incoming” has the potential to initiate the detonation of the explosive. Furthermore, the ERA is very resistant to loads by operation under severe conditions, such as collisions with obstacles or trees when driving off-road.
The qualified Explosive Reactive Armour of DND fits smoothly into the so-called “harmonised overall protection system” of the AIFV Puma and also offers growth potential against stronger threats.