Dual use technology has been advocated as the solution for the twin problem of maintaining a high tech defence technology base and improving economic competitiveness. The concept of dual use technology turns out to be rather imprecise representing a multitude of different meanings. This paper focuses on one important aspect, notably the co-operation between civilian and military actors in developing a new technology, by analysing the evolution of a socio-technical network related to the development of an advanced battery in The Netherlands. The analytical framework used for interpreting the empirical case builds on theories of socio-technical networks and on two previous and complementary analyses in Research Policy on dual use technology. Our analysis of the dynamics underlying the evolution of the ‘battery network’ shows how the emerging notion of the battery’s duality became a window of opportunity for a co-operation strategy of either joint or concurrent development of the battery for both civilian and military applications. The interactions within the evolving network are steered by the search for expertise and funding. In view of the difficulties of realising civilian–military integrated joint development projects, the establishment of ‘dual capacity networks’ is suggested as part of a possible strategy towards an integrated civilian–military technology and industrial base.