resilient against a wide variety of terrorist attacks. This is akin to a “capabilities-based” approach to defense planning.4

In the face of massive uncertainty, a common impulse is to think of across-the-board defense improvements. But given our finite wealth, time, and ability to concentrate, we must make choices. Doing so requires using probability estimates or other methods for dealing with uncertainty. If probabilities are used—e.g., the probability of a given type of attack, of an installation’s vulnerability, or of the capacity to rebuild or substitute for a damaged node—they typically cannot be obtained from empirical frequency distributions; the events are too uncommon or hypothetical. Instead, the probabilities must be derived using a combination of modeling, gaming, and analysis—all with a good deal of subjectivity. Further, the probabilities should change over time as our experience grows and our knowledge improves.

The Threat System to Be Weakened

In parallel with strengthening defenses, we can reduce the likelihood of various threats by destroying terrorist organizations where possible and, in some cases, by deterring elements of the terrorist organizations’ larger systems. A terrorist network has numerous parts, each with different vulnerabilities and receptiveness to influence. A Bin Laden may not be deterrable, but other parts of the system—for example, an organization’s financiers and state supporters—may well be. The segments of society from which the terrorists are drawn could be influenced by international actions and by attacks on terrorism ideology and tactics. Within the United States, those who assist terrorists may be dissuaded or caught. Finally, the terrorist actors themselves are often concerned about operational risk—they may be willing to risk their lives, but not in futile attacks. Thus, better defensive measures can help to deter or deflect.5

A Simple Game-Structured View

The overall system the committee is describing is dynamic. U.S. actions affect the terrorist system, and terrorist actions affect the United States. It is thus appropriate to view the problem analytically as a game, a simple version of which is shown in Figure 10.2. (It is simple by virtue of its not treating other countries or organizations explicitly.)

The state of the real world changes as both sides take actions and have

4  

See Rumsfeld (2001).

5  

For recent discussions of terrorist behaviors, see Lesser et al. (1999), Talbott and Chanda (2001), Tucker (2000), Moodie (1998), Roberts (1997), and the Monterey Institute’s online bibliography at <http://cns.miis.edu/research/cbw/biblio.htm#terror>.



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