Abstract: An optical assembly is mounted in the nose of a missile, this assembly including an infra-red sensor for sensing the orientation of the missile relative to an infra-red illuminated target, and a visible sensor such as a vidicon for determining the orientation of the missile relative to a visible target. The infra-red and visible detectors may be used alternatively for acquiring and tracking a target, as the situation may demand. The optical unit is stabilized in space about the pitch and yaw axes thereof by means of a gyro stabilized platform unit which is separated therefrom and linked thereto by coupling rods which cause the optical assembly to accurately follow the stabilized platform in both yaw and elevation.