Many non-renewable land-based resources are becoming depleted and the search for alternative sources of raw materials is intensifying. This situation has lead to the involvement of a number of countries, especially those of the European Community, in heavily funded ‘Wealth from the Oceans’ projects. A significant element of the research being conducted under the auspices of these projects is concerned with the development of small unmanned and untethered autonomous underwater vehicles (AUVs). To carry out their intended autonomous missions these vehicles will need reliable power systems which have high energy densities. However, although research into navigation, control and command systems has progressed considerably under this development effort, only limited headway has been made in the development of power systems which could be readily integrated into these vessels.Electrochemical power systems have been used in underwater applications for a number of years but those presently available cannot meet the rigorous specifications demanded by AUV missions. Consequently high performance fuel cells and advanced battery systems are being developed which should be generally available within the next ten years. Until then, power systems based on the utilisation of the more mature heat engine technologies appear to offer the possibility of a quicker solution to the energy density problem.Of the heat engine types available the Stirling Engine, already proven in larger submarines, shows considerable promise. One of the main reasons for the selection of the Stirling engine is it's ability to utilise any heat source, such as radioisotopes, thermal energy storage and metallic fuels. In this paper a project is described in which the design requirements for a Stirling engine driven AUV have been examined together with the identification of the most suitable primary energy source for a specific mission. As part of this project a user-friendly PC-based computer program has been developed which allows rapid assessments of the use of different energy sources with a double-acting Stirling for user defined missions. The structure and use of this code is discussed.