Very large airplanes using alternative fuels are examined in the context of existing and possible future U.S. Air Force missions. Synthetic jet fuel, liquid methane, liquid hydrogen, and uranium (i.e., aircraft nuclear propulsion) are the fuel alternatives selected for detailed analysis. Conceptual designs of airplanes using each of these fuels were developed and estimates were made of their life-cycle cost and life-cycle energy consumption. Mission analyses were performed to determine the effectiveness of the alternative airplanes in strategic airlift specifically and in the station-keeping role in general. Results indicate that for most military applications airplanes with gross weights in excess of one million pounds promise to be superior to any contemporary airplanes in terms of cost effectiveness and energy effectiveness. From both cost and energy viewpoints, a conventional hydrocarbon jet fuel, whether manufactured from oil shale, coal, or crude oil, remains the most attractive aviation fuel for future Air Force use.