The US Navy has been studying the technical and cost impacts associated with the availability and cost of fossil fuel contrasted with nuclear energy alternatives for surface combatants and amphibious warfare ships. Over the past two years these efforts have grown in maturity to examine the tactical and strategic implications of our Navy's dependence on fossil fuels from technical, economic, and military perspectives. This paper describes the NA VSEA evaluation of alternative propulsion methods in Small, Medium, and Large Surface Combatants performed during FY2005 in response to Chief of Naval Operations Guidance, and the efforts conducted during FY2006 directed by Public Law that added Amphibious Warfare Ships. Ship concepts were developed and analyzed in terms of acquisition cost, life-cycle cost, and operational effectiveness. Power and propulsion technologies including nuclear power, gas turbines, diesel engines, mechanical power transmission systems, hybrid power transmission systems, integrated power transmission systems, combined power plants (e.g., diesel and gas turbine), and various propulsor systems. Operational effectiveness in warfare, mobility and vulnerability areas are evaluated for alternative power and propulsion systems and associated architectures in non-program-of-record small (∼7,500 to ∼12,000 metric ton) and medium (∼21,000 to ∼26,000-metric ton) surface combatants and in amphibious warfare (∼34,000 to ∼38, 000-metric tons) ship concept designs. The techniques and models used in the studies are discussed, examples provided, and results presented. These results include a discussion of viable near term alternative power and propulsion system technologies and architectures, break-even cost of oil (where life cycle costs of nuclear and fossil powered ship concepts are equivalent), and correlation of alternative architectures with operational benefits.