We present a highly interactive large-scale visualization environment for performing the tasks of detection and classification of sonar contacts in a low signal to noise environment. The system described deals with simulated passive sonar data from an advanced towed array system, chosen for both the amount and high dimensionality typical of the data produced. Our prototype application employs a semi-immersive 3D display system, multiple and mixed modalities of interaction and feedback, and state-of-the-art volumetric visualization and abstraction techniques. Our two-stage approach seeks to use human talents, experience and intuition to leverage and direct high-performance computing resources. The first stage (search&detect) aims at providing advanced visualization and human/machine interface techniques to enable sonar operators to quickly and confidently detect contacts in low signal-to-noise dataspaces. In the second component (analyze&classify), we utilize a highly interactive volumetric representation of the tactical SensorSpace that the operator can interrogate using various visual and auditory cues. This presentation describes the application scenario, approach and implementation of the visualization environment and concludes with experiences, lessons learned, and future directions from both the interactive large-scale visualization as well as an application point of view.