The problem of how to implement user-centred design (UCD) is well established as a research topic within HCI. Yet there are unresolved issues in order for UCD to actually be used in practice. This paper will present a case study within Sweden’s military defense organizations, concerning the introduction of UCD. The overarching goal of the research was to bridge the gap between work practices and systems development; focusing the efforts on introducing usability work in the procurement process. We concluded early on that we needed to develop and formulate an approach that is probably common in practice but not described or used in research. We call this strategy UCD guerrilla tactics, which entails to do the unexpected, to work pragmatically with change, and to use user centred methods to introduce UCD. Our main target group was future users and procurers of UCD methods. We aimed at demonstrating and involving them in the work through user centred activities. The tactics is also a reflexive and flexible approach based on continuous evaluation of what is feasible and potentially gives the largest outcome. This paper describes the guerrilla tactics, how it was applied in a case study and factors that should be considered when using it.