Target Hardening and Terrorist Signaling: The Case of Aviation Security

In this article, we examine the relationship between hardening a target and the value that a terrorist group derives from attacking it. We use a simple expected value framework to compare how the expected value of attacking a hardened target varies between a violence-based approach, where terrorists are presumed to be maximizing the physical damage done to the target, and a signaling-based approach, where terrorists are presumed to be maximizing the symbolic value of their attack. We argue that, if it is proper to understand terrorist attacks as costly signals of terrorist strength or determination, hardening a target actually increases the expected value of attacking a target (relative to its value before hardening), even if the attack fails. We go on to examine the evolution of aviation security, and trace how al-Qaeda's views of airplanes and airports as targets have changed since 9/11. As aviation targets were hardened with increasingly onerous security measures, al-Qaeda began to see even attacks that did not result in detonation as successes, in large part because of what they signaled about al-Qaeda's abilities, and the ability of al-Qaeda to impose costs on the U.S. and other countries even in the absence of explosions.