The development of low-cost underwater acoustic array systems for the northern watch technology demonstration project is discussed. Developments since the end of the TDP project include upgraded quantization from 16 to 24-bits, an increased sampling rate range from a few Hertz to 240 kHz, reduction in power requirements for each node and the array controller (1.5W), improved digital bus structures with extra data and power pairs, and modernized interfaces including Ethernet and universal serial bus. The arrays for the Northern Watch project have been developed by Omnitech Electronics Inc. as prime under contract to DRDC. The arrays have undergone two prototype developments. The original array design was based on an absolute minimum cost and made extensive use of standard plastic piping and resin materials for the mechanical structure. The new array design also makes use of connectors to allow for hydrophone replacement.