On February 2, 2018, the Pentagon released the new Nuclear Posture Review (NPR), stating that it rests “on a bedrock truth: nuclear weapons have and will continue to play a critical role in deterring nuclear attack and in preventing large-scale conventional warfare between nuclear-armed states for the foreseeable future.” The global landscape is already filled with simmering nuclear tensions, as well as other serious issues of conflict. Stressing the role of nuclear weapons is not merely unhelpful but is likely to increase these tensions.
In a complex and dangerous international environment, the difficult relations between the United States and Russia and China, as well as the other states named in the NPR (North Korea and Iran), can be worsened by any provocative nuclear policy, leading them to strengthen their reliance on nuclear weapons. The expansion of the role of nuclear weapons risks triggering another round of the nuclear arms race, dramatically increases the risks of their use, and makes the road to a nuclear weapons free world even more difficult.
Besides pursuing the modernization of all the elements of the Triad (strategic bombers, ICBM, SLBM), the NPR foresees projects to develop new types of nuclear weapons tailored to different adversaries and scenarios, and “flexible” enough to respond to a variety of current threats. Increasing the number and the possible role of (smaller) tactical nuclear weapons is a recipe for a disaster. Tactical nuclear weapons can make nuclear war more likely through de-facto lowering the threshold between a conventional and a nuclear conflict. As compared to the previous NPR, this NPR appears to have taken backward steps. For example, the assertion that nuclear weapons have a role in deterring significant non-nuclear attacks reverses the prior statement that the US will not use nuclear weapons to deter chemical or conventional attacks.
We believe that this latest development of US nuclear weapons policy will serve only to increase the saliency and attractiveness of nuclear weapons, and will certainly not enhance international security, let alone prospects for progress in bilateral and multilateral disarmament and non-proliferation efforts.
Sergio Duarte, President of Pugwash
Paolo Cotta-Ramusino, Secretary General of Pugwash
 Secretary James Mattis, Preface to the 2018 Nuclear Posture Review, https://media.defense.gov/2018/Feb/02/2001872886/-1/-1/1/2018-NUCLEAR-POSTURE-REVIEW-FINAL-REPORT.PDF