The United States has repeatedly debated whether to adopt a nuclear no-first-use (NFU) pledge. Advocates for such a pledge emphasize its potential advantages, including strengthening crisis stability, decreasing hostility, and bolstering nonproliferation and arms control. But these benefits depend heavily on nuclear-armed adversaries finding a U.S. NFU pledge credible. A new theory based on the logic of costly signals and tested on evidence from NFU pledges by the Soviet Union, China, and India suggests that adversaries perceive such pledges as credible only when: (1) the political relationship between a state and its adversary is already relatively benign, or (2) the state's military has no ability to engage in nuclear first use against the adversary. Empirically, these conditions rarely arise. More typically, hostile political relations combined with even latent first-use capabilities lead adversaries to distrust NFU pledges and to assume the continued possibility of being subject to first use. The implication is that changes to U.S. declaratory policy alone are unlikely to convince adversaries to disregard the prospect of U.S. nuclear first use without changes in these countries’ political relationships or U.S. nuclear force posture. The beneficial effects of an NFU pledge are therefore likely to be more minimal than advocates often claim.

The military implications of Chinese control of Taiwan are understudied. Chinese control of Taiwan would likely improve the military balance in China's favor because of reunification's positive impact on Chinese submarine warfare and ocean surveillance capabilities. Basing Chinese submarine warfare assets on Taiwan would increase the vulnerability of U.S. surface forces to attack during a crisis, reduce the attrition rate of Chinese submarines during a war, and likely increase the number of submarine attack opportunities against U.S. surface combatants. Furthermore, placing hydrophone arrays off Taiwan's coasts for ocean surveillance would forge a critical missing link in China's kill chain for long-range attacks. This outcome could push the United States toward anti-satellite warfare that it might otherwise avoid, or it could force the U.S. Navy into narrower parts of the Philippine Sea. Finally, over the long term, if China were to develop a large fleet of truly quiet nuclear attack submarines and ballistic missile submarines, basing them on Taiwan would provide it with additional advantages. Specifically, such basing would enable China to both threaten Northeast Asian sea lanes of communication and strengthen its sea-based nuclear deterrent in ways that it is otherwise unlikely to be able to do. These findings have important implications for U.S. operational planning, policy, and grand strategy.

Could a conventional war with the United States inadvertently prompt Chinese nuclear escalation? The military-technical threat that such a war would pose to China's retaliatory capability—combined with wartime perceptual dynamics that might cause China to view this threat in an especially pessimistic light—could lead to reasonable Chinese fears that the United States might be attempting conventional counterforce, or considering or preparing for nuclear counterforce. China might see several forms of limited nuclear escalation as its least-bad response to this sort of threat to its nuclear deterrent, notwithstanding the country's no-first-use policy. This finding, derived from a more general framework about the military-technical and perceptual drivers of potential nuclear escalation in response to conventional counterforce, has broader ramifications for U.S. policy and military strategy, and it illustrates recurring dilemmas that the United States may face in conventional wars with other nuclear-armed adversaries.

How might Iran retaliate in the aftermath of a limited Israeli or U.S. strike? The most economically devastating of Iran's potential responses would be closure of the Strait of Hormuz. According to open-source order of battle data, as well as relevant analogies from military history and GIS maps, Iran does possess significant littoral warfare capabilities, including mines, antiship cruise missiles, and land-based air defense. If Iran were able to properly link these capabilities, it could halt or impede traffic in the Strait of Hormuz for a month or more. U.S. attempts to reopen the waterway likely would escalate rapidly into sustained, large-scale air and naval operations during which Iran could impose significant economic and military costs on the United States—even if Iranian operations were not successful in truly closing the strait. The aftermath of limited strikes on Iran would be complicated and costly, suggesting needed changes in U.S. force posture and energy policy.