Traditional deductive recognition-based methods – whether model-based or anomaly-based – are not appropriate to the counter-piracy application. Both threats and normal activity are often extremely difficult to model. Furthermore, an intelligent adversary can be expected to maximize ambiguity and exploit the defence response cycle. Rather than a deductive recognition-based approach, we recommend a diagnostic (abductive) one: (a) focus on potential victims rather than potential pirates, (b) detect and diagnose potential encounters and estimate time-to-go, and (c) manage assets for situation resolution and interdiction, based on assessed encounter impact, likelihood, available and required time to respond, and confidence in these factors. An interactive situation management concept is presented, in which the operator is able to visualize the predicted evolution of the maritime situation, together with the predicted evolution of the system's state of knowledge and of response opportunities.