1. In an underwater-target direction-finding apparatus of echo- ranging type, in combination: receiver means, including a network tunable to resonance at echo signal frequency, for deriving, from received echo signals, command signals carrying echo-source direction information; target-recognition means for providing a gating signal only upon and during reception of an echo signal arising from a true target, and in time-coincidence with that echo signal; utilization means controllable by and in response to said command signals when applied thereto; and circuit means for placing said network in resonant condition in response to and only during occurrence of said gating signal, whereby to limit control of said utilization means to command signals stemming from true target echo signals.
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