Established to mobilize science during the Second World War, the Office of Scientific Research and Development (OSRD) and its director, Vannevar Bush, created new weapons as well as a new relationship between science and government that helped shape Cold War America. Yet much about the partnership that emerged disappointed Bush, especially its uncontrolled expansion and the failure of civilian oversight. The failure, ironically, as this article explains, can be traced to the very approach that allowed Bush to mobilize rapidly during wartime, especially to an “associationalism” and contractual strategy that centralized the management of R&D in Washington while leaving its performance to private contractors. Forged in more conservative decades, the strategy facilitated the rapid exploitation of private-sector resources at the cost of promoting the uncontrolled proliferation of public-private arrangements that undercut Bush's postwar hopes.