Abstract: 1. A passive ranging system for use by a fighter in determining the dista along the line of sight between the fighter and a target travelling at constant speed; comprising in combination: a search and track system operable to generate signals proportional to the azimuth and elevation angles of the line of sight with respect to the fighter coordinate system, a stabilized platform normally slaved to said search and track system operable to generate signals proportional to the angular rate of rotation of the line of sight and signals proportional to the acceleration of the fighter in inertial space, resolver computer means coupled to said stabilized platform operable to resolve said angular rate and acceleration signals into terms of a reference coordinate system, algebraic computer means connected to said stabilized platform and said resolver computer operable to transform said signals into a voltage form representative of range between the fighter and the target.