When then U.S. Secretary of Defense Donald Rumsfeld was making this statement: "Today we lack metrics to know if we are winning or losing the global war on terror," the RAND journal Studies in Conflict and Terrorism was already attempting to address his concern. Wars are composed of battles, so presumably the war on terror is composed - at least in part - of battles against terrorist cells. But how can one tell if those battles have been won? How can we measure that? In this monograph, the author lays out a mathematical model for answering these questions. Although not meant to be all inclusive, he shows through his examples, some uses, details and suggestions for possible improvements in current processes. If one accepts the formalism of the model, with a few additional and reasonable assumptions, one can ask, "What is the structure of the 'perfect' terrorist cell? Which terrorist cells are most robust? Which cells are least likely to be disrupted if a certain number of its members have been captured or killed?"