When high-velocity projectiles penetrate an enclosed fluid-filled structure, the projectiles transfer the kinetic energy to the surrounding structure through the fluid and cause excessive structural damage. This process is referred to as a hydrodynamic ram (HRAM) . The HRAM can be divided into five phases: penetration, shock, drag, exit, and cavity oscillation. The HRAM phenomenon has been studied analytically [2,3], experimentally [4–7] and numerically [8–10]. However, few studies have been performed on the hydrodynamic ram caused by multiple penetrators. In the present work, a previously validated numerical model was used to analyze the differences of hydrodynamic rams caused by one and two projectiles impacting water-filled containers.