U.S. naval forces must be prepared to respond to a broad array of threats. Of increasing importance are those from chemical and biological warfare (CW and BW). To help review its current state of preparedness, the Chief of Naval Operations asked the National Research Council (NRC) to assess the U.S. Navy's defense capabilities against CW and BW threats. In particular to what extent are they being developed to enable naval forces to sense and analyze quickly the presence of chemical and biological agents, withstand or avoid exposure to such agents, deal with contamination under a broad spectrum of operational conditions, and over what period will these capabilities be realized. This report presents the results of that assessment. It provides an overview of the potential threats, and an evaluation of the Navy's operations, non-medical programs, and medical countermeasures designed to confront those threats. The report also presents a series of general and specific findings and recommendations based on these assessments.