This paper investigates numerically the enhancement of impact resistance of multiplayer steel armor to rigid and blunt projectiles. The monolithic armor always possesses higher ballistic resistance than the multilayer one of the same weight and areal density. In this work, the monolithic Weldox 460E steel armor is divided into three layers. The front and rear layers have the same thickness and they are thinner than the middle one. The thicker middle layer is prestressed by applying initial compressive strain. Then, the yield point of the middle layer is raised and the overall impact resistance of the prestressed multilayer armor is increased. The prestressed armor is impacted by a high-speed armor piercing (AP) blunt and rigid projectile. The impact resistance is macroscopically measured as the percentage reduction in the kinetic energy (KE) of the AP projectile. The percentage reductions in KE are calculated for the monolithic armor, equal and different thicknesses three layers armors with and without prestressing their middle layers. According to the presented computations, the maximum reduction in KE corresponds to the different thickness three layers armor having its thicker middle layer been prestressed.