This paper presents the results of numerical simulations applied to an impact penetration test with the simulation code equipped with the capability to evaluate the strain rate effects on the material strength. The aim of this study is to obtain the designing tool for the protective walls to ensure the safety of operators and equipments around the engine room of a ship, in the case of an accidental explosion. First, an impact penetration test is carried out to evaluate the protective capability of a plate against the perforation failure. The test is performed with a powder accelerator to shoot the mild steel plate with a simulated cylindrical fragment at the speed of 403 m/s. Speeds of the fragment and a plug after perforation are measured by strain gauges and a high speed cinematograph during the test. Deformation of the fragment is also measured after the test. Next, numerical simulations are carried out to reproduce the experiment. DYNA3D is used for the numerical simulations of the test. The elastic-plastic model with failure is employed to express fracture phenomena occurred during the test. The function to evaluate strain rate dependency of material strength is added to this model to refine the accuracy. The fragment and the wall plate are simplified to an axially symmetric model. The edges of the wall plate are fixed and the initial speed is applied to each grid of the fragment model. The speeds of the fragment and a plug after perforation, and the radial and axial deformation of the fragment, are compared with the simulated values, changing parametrically the mechanical properties of the fragment and the wall plate. The effects of the mechanical properties on the measured values are obtained. As a result, a set of reasonable material properties is obtained by the numerical simulations. The expeimental results are shown to be reproduced well by the numerical simulations with this set of material properties. The numerical simulation method is shown to be an efficient way to estimate the protective capability of a steel plate against the penetration caused by high speed fragments. A seies of numerical simulations is carried out to reproduce five experiments with the same material set. The critical perforation speed and the deformations of fragments after perforation are compared with the experimental results. The estimated critical perforation speed gives 11% less than the measured value. The deformation of fragments show fairy well correlation with the measured values.