Abstract: In an improved target detector, echo signals received from the same range range bracket on successive scans of the same angular direction are stored. Different combinations of elements from said echo signals are sampled and integrated, each combination being chosen to include elements indicative of a target moving with a particular velocity. Different combinations are indicative of different target velocities, or of targets situated at different initial ranges, and means are provided for signalling an alarm when the integral of any combination exceeds a threshold.