1. A sentry system comprising: a remote operator station; a plurality of watchtowers and communication channels connecting the plurality of watchtowers to the remote operator station; a plurality of fixed cameras including at least one fixed camera located on each of the plurality of watchtowers to cover a local field of view in areas proximate to each of the plurality of watchtowers and to capture successive video images of the local field of view; a local data processor for the fixed cameras or cameras for each of the plurality of watchtowers including a video signal processor for processing the successive video images to detect objects within its local field of view; means for qualifying detected objects for tracking from the successive video images; the means for qualifying detected objects including a visual recognition data base of characteristic ranges for size, shape and trajectory through the field of view for detected objects; a steerable targeting camera on each watchtower which may be aimed by the local data processor to track a qualified detected object; a steerable energy projector located on the watchtower which may be aimed by the local data processor to direct an energy beam toward the qualified detected object; the communication channels including a bidirectional communication link between the local data processor and the remote operator station allowing an operator located at the remote operator station to direct aiming of an acoustic projector and to apply acoustic signals to the acoustic projector; and the means for qualifying further including means responsive to operator input for accessing the visual recognition data base for a watchtower allowing operator specification of characteristics of detected objects which mark them for initial automatic tracking.