Abstract: A switchable privacy display comprises a spatial light modulator with output polariser, a reflective polariser, a polar control liquid crystal retarder and an additional polariser. The electrodes of the polar control liquid crystal retarder are patterned with a mark. In wide angle and narrow angle operational modes, the electrodes of the liquid crystal retarder are driven such that the mark is not visible. In a mark display state, the electrodes are driven to provide visibility of the mark in reflected light to an off-axis observer.

Abstract: A method and apparatus for passively detecting, locating and tracking submerged or waterborn objects which generate acoustic radiation as they move through the water, includes a hydrophone array which is linked to a monitoring station by cable or radio transmitters. The apparatus at the monitoring station includes a hydrophone selector for individually monitoring the output of each hydrophone, a band pass filter, a db meter and visual display apparatus. The db meter is provided with indicia to convert the difference in intensity in db for the hydrophones to a range or distance ratio from the hydrophones to the noise source. A fix on the noise source can be obtained by plotting range ratio circles or using a tactical display scope. Once the noise source is located, the db meter is calibrated to read directly the range from the hydrophones to the object.