This paper consists of two parts, modeling of passive sequential strut and modeling of 8-DOF high mobility tracked vehicle incorporating the strut.In first part, a tunable passive, sequential, heavy-duty hydro-pneumatic mono-tube strut is discussed to achieve variable damping for a tracked vehicle suspension. The hydro-pneumatic strut is modeled as a nonlinear dynamical system incorporating nonlinearities due to orifice flow, gas spring and pressure relief mechanisms. The shock and vibration isolation performance of hydro-pneumatic strut are evaluated and compared to the vehicle model employing a constant orifice strut. It is shown that the vehicle ride performance is improved considerably using an adequately tuned sequential hydro-pneumatic strut.In second part, a twelve-road wheel high mobility tracked vehicle, is modeled as an 8 degrees-of-freedom in-plane non-linear dynamic system incorporating bounce and pitch motion of the sprung mass and bounce motion on six road wheels. Ride response characteristics of non-linear vehicle model are studied for different ground inputs.