Which military missions for unmanned undersea vehicles (UUVs) appear most promising to pursue in terms of military need, operational and technical risks, alternatives, and cost? To answer this question, the authors assess risks associated with using UUVs for advocated missions, identify non-UUV alternatives that may be more appropriate for such missions, and analyze potential costs associated with UUV development and use. They conclude that seven missions: mine countermeasures, deployment of leave-behind surveillance sensors or sensor arrays, near-land and harbor monitoring, oceanography, monitoring undersea infrastructure, anti-submarine warfare tracking, and inspection/identification - appear most promising. Among other recommendations, the authors suggest that the U.S. Navy consolidate its unmanned system master plans and establish relevant priorities in coordination with the Office of the Secretary of Defense. Increased emphasis on the use of surface platforms rather than submarines as host platforms is recommended.