Abstract: 1. In a proximity-controlled bomb adapted to be dropped upon a target and adapted to reach a fixed velocity, a fixed/radio-frequency control mechanism comprising a continuous wave radio transmitter and receiver operating at a fixed frequency and having a fixedly tuned network in common, an antenna coupled to said network, a detector coupled to said network for deriving a difference-frequency signal by heterodyning the transmitted wave and the wave reflected from said target, and means coupled to said detector and responsive to signal amplitudes derived only when said bomb and target reach a predetermined proximity.