Two-dimensional x-y addressed mosaic arrays of more than 12,000 lead-sulfide detectors (64 x 192 detectors in an active area slightly larger than 1/4 by 3/4 inch) have been successfully developed, tested, and demonstrated at Aerojet ElectroSystems Company. This paper describes the pulse-bias modulation concept used to operate the detectors and process their outputs, the design and fabrication techniques used to implement this concept, and the measured performance of these arrays, which was independently verified by the Naval Ocean Systems Center in San Diego.