Although GPS can support U.S. and allied military activities, it can at the same time create a dependency. Furthermore, enemy uses of GPS can threaten U.S. forces and broader security interests. This dual aspect of GPS -- its utility in American and allied hands, along with the risks of dependency and enemy use -- highlights a fundamental dilemma for decisionmakers seeking to maximize the benefits of GPS technology while minimizing its risks. To help policy- makers deal with this dilemma, this chapter sets forth the benefits and risks associated with military uses of GPS.
The first section considers U.S. military use of GPS. Because U.S. forces rely on GPS, we pay particular attention to potential vulnerabilities and threats that could prevent U.S. forces from taking full advantage of the system. The second section evaluates the threats arising from hostile use of GPS against U.S. assets or those of its allies. Rather than placing equal emphasis on all potential uses of GPS by hostile forces, this study considers those situations that appear to be the most threatening to U.S. forces. For example, the use of GPS by enemy navies appears much less serious than the enemy use of GPS on cruise missiles. It is our assertion that by examining the threats that appear the most significant, we can make a reasonable assessment of the overall risks associated with hostile use of GPS.
The third section of this chapter analyzes how GPS augmentation systems could be exploited by hostile forces. Third-party local- and wide-area differential GPS (DGPS)1 systems can be used by one nation to attack another. The fourth section examines the effectiveness of two signal modifications implemented by the U.S. government: selective availability (SA) and anti-____________________