A projectile that passes through a moving shock wave experiences drastic changes in the aerodynamic forces as it moves from a high-pressure region to a low-pressure region. These sudden changes in the forces are attributed to the wave structures produced by the projectile-shock-wave interaction and are responsible for destabilizing the trajectory of the projectile, consequently leading to a loss of projectile stability and control efficiency. A computational study was performed here using a moving-grid method to analyze the effects of the projectile overtaking a moving shock wave on the projectile aerodynamic characteristics. A one-dimensional analysis was also carried out to identify the projectile overtaking criteria. The analytical results show that the projectile overtaking flowflelds can be in a subsonic or supersonic flow regime, based on the relative projectile Mach number. However, it is found that the actual flowflelds in the present computations cannot be distinguished with the relative projectile Mach number only, because the blast-wave strength is diminishing with time and space. The aerodynamic characteristics of the projectile are hardly affected by the overtaking process for smaller blast-wave Mach numbers, as the blast wave will become weak by the time it is overtaken by the projectile. The projectile drag coefficient is more greatly affected by the unsteady flow structures through which the projectile travels in the near field than by the overtaking process. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.