The increasingly demanding requirements of a number of military applications mean that there is a need for more energy dense power sources that is unlikely to be satisfied with conventional battery chemistries. A high temperature electrochemical power source employing carbon as a fuel has been identified as a technology offering a step change in available energy density. Direct carbon conversion is an approach being pursued by several groups in the US. This paper discusses the state-of-the-art in this technology, and describes work carried out at Dstl and St. Andrews University to establish a new carbon-air semi fuel cell concept. This forms part of a four-year programme to develop a 50 W, 500 Wh demonstration unit. Crown Copyright (c) 2005 Published by Elsevier B.V. All rights reserved.