Late in July the National Research Council released a report on a hitherto little-known, or perhaps unknown, U.S. capability: nuclear forensics. Nominally the report was a plea for more resources; too many skilled people trained during the Cold War were retiring, and too much equipment was becoming obsolete. However, the report was probably issued far more to disclose an important national capability. Nuclear forensics makes it possible to identify the source of a nuclear weapon based on evidence the weapon generates when it explodes. In effect it is a much bigger brother of the science that makes it possible to say where the explosive in a terrorist's bomb originated. The new disclosure may be associated with the Obama administration's view that nuclear proliferation must be curbed because of the threat of terrorists armed with nuclear or semi-nuclear weapons ("dirty bombs"). It could also be a response to the apparent failure of that initiative. In either case, the important news is that a nuclear explosion cannot be anonymous.