The purpose of this paper is to study the institutional logics of how and why two case units in the Finnish Defence Forces have reacted differently to external pressures originating from the State Audit Office to change their management accounting systems. The situation is made complex due to the fact that in military organisations, accountants' tasks have traditionally consisted of bookkeeping and financial reporting, while management accounting tasks especially (e.g. planning and control) have been performed predominantly by military personnel, who can be called hybrid accountants. The data for this study consists of project memos and interviews with people involved in designing and implementing enterprise-resource-planning (ERP)-linked cost accounting and reporting systems. In the case unit where management accounting and control had become institutionalised as a part of the uniformed officer's professional sphere, various resistance strategies (i.e. compromise strategy/pacifying tactics, avoidance strategy/buffering tactics and defiance strategy/dismissing tactics) were adopted. However, where this was not the case, the response was acquiescence. Despite the differences in responses to institutional pressure, the outcome for management accounting was the same. In the first case, demands for change were resisted, and in the second case, the old management accounting system was transferred into new information and communication technology (ICT) infrastructure without any significant change in content.