Addressing the well-established need for accurate cyber situational awareness on military vehicles and weapons platforms, we developed a well-tested, robust Intrusion Detection System – Fox ShieldTM – currently rated TRL-8. The system is described and the lessons learned during its development are discussed. The basic principles of our anomaly detectors are outlined, and the details of our innovative warning-aggregating Fuser are presented. Many attack detection examples are presented, using a publicly available CANbus dataset.