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English: The simplest ERA designs entail explosives placed between two metal plates. To be most effective, the plates must be mounted at an angle to the incoming threat (see figure). Some designs use multiple plates at various angles to ensure coverage against threats from different attack angles. When the fast-moving jet of the shaped charge penetrates the outer metal plate, it sets off the inner layer of explosive. Designers are very careful in selecting the type of explosive to be used to ensure that it will not be set off by slower-moving threats or by routine impacts. Thus, they tend to use relatively insensitive explosives. However, later generations of reactive armor use more-sensitive explosives to make them effective against slower-moving EFPs. When the explosive between the plates detonates, the metal plates accelerate away from the explosive and into the shaped-charge jet. As the plates pass through the jet, they dissipate and disperse it, thereby reducing or even preventing the jet’s penetration of the vehicle. Typical reactive armor is made of small modules or tiles to provide coverage over the whole vehicle. Because the tile is destroyed in the process of protecting the vehicle, having many small tiles provides better protection against multiple hits scattered over the vehicle.