On April 19, 2007, the Preventive Defense Project convened a workshop of leading federal government civilian and military officials, scientists, policy experts, and journalists to address the actions that can and should be taken in the 24 hours following a nuclear blast in a U.S. city.

Through efforts like the Nunn-Lugar program, the U.S. government and many of the Day After Workshop participants, including us, have long sought to prevent nuclear weapons and fissile materials from falling into new and threatening hands, especially terrorists. But we all know that these efforts have not reduced the probability to zero. It is also a common refrain among policy thinkers concerned with the growing nuclear threat--again, ourselves included--to frame the issue of prevention in terms of a provocative question, "On the day after a nuclear weapon goes off in a U.S. city, what will we wish we had done to prevent it?"

But our Preventive Defense "Day After Workshop" asked a different question: "What will we actually do on the day after prevention fails?" What will we want to do? How can we prepare now to be able to do it? We asked the distinguished participants in the Workshop to catapult themselves vividly and concretely into the aftermath of a nuclear detonation on a U.S. city. The needed actions by government and the public on the Day After will fall into two categories: actions to recover from the first detonation, and actions to prevent a second detonation. The Workshop addressed both types of action in as much detail, including technical detail, as possible. Topics included emergency response, evacuation and sheltering, immediate radiation effects, follow-on threats to the first nuclear weapon, attribution and retaliation, and the long process of cleanup--especially the uniquely difficult problem of fallout and residual radioactivity.