Potential terrorists/adversaries can exploit a wide range of airborne threats against civilian and military targets. Currently there is no effective, low-cost solution to robustly and reliably detect and identify low observable airborne vehicles such as small, low-flying aircraft or cruise missiles that might be carrying chemical, biological or even nuclear weapons in realistic environments. This paper describes the development of a forward-based fence that contains a multi-modal mix of various low cost, low power, netted sensors including unsophisticated radar, acoustic and optical (Infrared and visible) cameras to detect, track and discriminate such threats. Candidate target (Cessna, Beech Craft, crop duster, and cruise missile) signature phenomenologies are studied in detail through either theoretical, numerical simulation or field experiment. Assessments for all three modalities (Radar, acoustic and IR) indicate reasonable detectability and detection range. A multi-modal kinematic tracker is employed to predict the location, the speed and the heading of the target. Results from a notional, template based classification approach reveal reasonable discrimination between different aircraft tested in the field experiments.