A mobile sonar surveillance system having a fully populated circular shapedorizontal receiving array steered in edgefired directions with overlapping coverage of beams. The array has a plurality of hydrophones randomly spaced and mounted on a series of parallel lines in the same horizontal plane and is suitable for towing by a single small ship. For alignment of a received signal one or more single beams suitable for rotation can be steered azimuthally with the proper set of synchronized variable delays. These beams will retain approximately the same parameters as they rotate.