Abstract: This invention concerns a navigation system of the type utilizing proportional navigation guidance laws to guide an aerodynamically controlled body tracking a target, and particularly relates to a navigation system mechanization wherein necessary body-to-target line-of-sight rate-of-change information with respect to an inertial reference is developed implicitly, in part by using system optics and detector elements that are fixed to the guided body rather than to a body-mounted, inertially stabilized platform, to obtain stabilized guidance system tracking.