Abstract: For many years now, explosive reactive armour (ERA) has been well proven in reducing the penetration of shaped-charge jets into MBT hulls. This kind of appliqué protection, however, is more suited to heavy vehicles than lightweight armoured vehicles. A numerical study using the explicit non-linear transient dynamic finite difference code AUTODYN-2D has been undertaken to examine the effect of a rear plate from an explosive reactive armour impacting lightweight armoured vehicle hulls at normal incidence. Four thicknesses of explosive reactive armour plate impacting high hardness steel armour and an aluminium alloy (7039) armour were simulated. The deformation of the vehicle hull and the measured strains are reported indicating critical areas around the fixings and the central region of impact. These results make clear the need for care in applying explosive reactive armour plates to lightweight hulls.