The last great confrontation of the Cold War, the U. S. Strategic Defense Initiative (SDI), was a hyperbole, an overstatement of the entire conflict. It magnified the interdependence of technology and national security, which was manifest in foreign policy, domestic politics, and the economy. The ambiguous vision of an ultimate shield against nuclear attack was broadly interpreted and reinterpreted, celebrated, denounced, and continually revised. The ultimate shield became a distributed vision, subject to many interpretations, which the component technologies of SDI both reflected and enabled. How defense technology happens, how it interacts with the various national expectations, as magnified by SDI, is the subject of this chapter.