In this paper, a controllable electrorheological fluid suspension system (ERSS) is proposed for a tracked vehicle. After identifying the Bingham properties of an electrorheological fluid, a double-rod-type ERSS is devised, and its damping characteristics are evaluated with respect to the intensity of the electric field. Subsequently, the governing equation of motion of a tracked vehicle featuring the ERSS is established followed by the formulation of a linearized state space model. An optimal controller integrated with Kalman filter is then designed in order to suppress unwanted vibrations of the tracked vehicle subjected to bump and random road excitations. Control performances such as vertical acceleration at the centre of gravity are evaluated in both time and frequency domains.