This brief is the second in the CSIS Project on Nuclear Issues (PONI) Deep Dive Debrief Series that explores emerging or contentious nuclear challenges. These briefs are based on a series of “deep dive” workshops convened by PONI that bring together next generation technical, operational, and policy experts from across the nuclear community to debate and discuss these nuclear challenges. This brief reflects discussion and insights from a deep dive workshop convened by CSIS PONI and the Royal United Services Institute’s (RUSI) UK PONI on September 15, 2020. It examines the debate surrounding the development of U.S. nuclear warhead capabilities and whether the United States is or is not creating “new” nuclear weapons. It discusses the expansion of U.S. nuclear warhead capabilities and its potential implications for U.S. relations with the United Kingdom and the North Atlantic Treaty Organization (NATO), warhead production infrastructure, and arms control and nonproliferation efforts. Read the full brief on CSIS.org.