This study focuses on the theoretical analysis, design, development and testing of a magneto-rheological fluid (MRF) damper for a high-mobility multi-purpose wheeled vehicle (HMMWV). A MRF damper is designed to provide an enhanced performance over the original equipment manufacturer (OEM) damper while keeping the geometric parameters, such as outer diameter and stroke, the same as the OEM damper. The theoretical analysis is developed using a fluid mechanics model and a three-dimensional electromagnetic finite element analysis. The MRF damper is designed as a fail-safe damper, which retains a minimum damping capacity in the event of a power supply or electronic system failure. The damper is designed to achieve non-symmetrical force characteristics, i.e., different force responses in rebound and compression. This is achieved by using shims. Experimental results show that the MRF damper for the HMMWV has an improved performance than the OEM damper. Theoretical and experimental results agree well and are presented for the force-displacement and force-velocity performance of the damper under different input motions, various input magnetic fields, and different MR fluids.