In recent years, it has become increasingly clear to many observers that the Department of Defense must better communicate to the officers at the tactical end of the nuclear mission a rationale for nuclear weapons and deterrence, the critical role that they play in the post-Cold War strategy of the United States, and the value of nuclear weapons to the security of the American people. This report tracks the changing conceptual and political landscape of U.S. nuclear deterrence to illuminate the gap in prioritizing the nuclear arsenal and to build a compelling rationale for tactical personnel explaining the role and value of U.S. nuclear weapons.

For decades, the United States has led the effort to stem the spread of nuclear weapons, both among potential adversaries and among its allies and partners. The current state of deterrence and of the nonproliferation regime, however, is open to many doubts. What happens if the nonproliferation regime should break down altogether? What happens if extended deterrence should fail, and allies no longer believe in the credibility of the U.S. nuclear umbrella? What happens when the world has not 9 but 11, 15, 18, or even more nuclear powers? This study explores how such a world might function and what it would mean for our present conceptions of deterrence, for the place of the United States in the international order, and for international order itself.

This study identifies five alternative strategies and, using CSIS's Force Cost Calculator, builds a cost-capped force structure, modernization program, and readiness profile for each strategy. It then stress-tests each strategy against four sets of simultaneous conflict scenarios, which the authors devised. The study explores potential ways to mitigate the fiscal pressure forcing these strategic tradeoffs. It concludes by making recommendations for the FY 2017 defense budget and the next Quadrennial Defense Review (QDR).

Project Atom is a forward-looking, "blue-sky" review of U.S. nuclear strategy and posture in a 2025-2050 world in which nuclear weapons are still necessary. The report highlights and addresses the current deficit in national security attention paid to the continued relevance and importance of U.S. nuclear strategy and force posture, provides a new open-source baseline for understanding the nuclear strategies of other countries, and offers a credible, intellectually tested, and nonpartisan range of options for the United States to consider in revising its own nuclear strategy.

This report defines a set of strategy options, each with associated capabilities, gleaned from other leading think tank reports as well as the study team's analysis. The report identifies capability priorities for the 2021 and beyond security environment and recommends a force structure for a 2021 affordable military.

CSIS undertook a study in support of Office of the Secretary of Defense (OSD) Strategy and the 2014 Quadrennial Defense Review (QDR) to explore using U.S. military power in new ways to achieve high-priority strategic ends (derived from the 2012 Defense Strategic Guidance).The project was informed by a series of in-depth interviews and a Core Working Group with experts from outside the U.S. government, including former government officials, current foreign government uniformed and civilian defense officials, global business strategists, and individuals knowledgeable in humanitarian assistance and disaster relief."