As part of CNA's self-initiated project to examine potential issues associated with the upcoming defense review, the Director, Plans, Policy and Operations suggested we examine direct threats to the continental United States and what the contribution of naval forces would be in the defense. The report concentrates on three possible missions or threats: sea control, national missile defense, and non-traditional missions such as cross-border flows. The effects, likelihood, source, difficulty and Navy response are discussed for each mission.