A method of kinematic ranging for finding the range R of a jammer moving on a trajectory involves measuring the bearing of the jammer and the rate of change thereof using an airborne detector radar at a first position (24), causing the airborne detector radar to carry out a manoeuvre such that is it displaced in the horizontal plane by a displacement having orthogonal components Δx, Δy, and measuring the bearing of the jammer at a second position subsequent to the manoeuvre. By making an appropriate choice for the components Δx, Δy, the range R may be found with a desired relative range accuracy, and the error in R may be minimized.