As Europe faces evolving security challenges, the need for a unified and common approach to defence within the EU has never been more pressing. Yet the intergovernmental model of governance, with its emphasis on national sovereignty, significantly hampers the EU's ability to develop a cohesive defence ecosystem. This article investigates this issue from the perspective of interoperability, defined as the ability of different systems or actors to work together in an efficient and coordinated manner. Given the plasticity of this concept, it can be articulated in various ways, and in this case is tripartite in its institutional, material and strategic dimensions. Therefore, this paper dissects the impact of intergovernmental logic on these interoperability dimensions while highlighting the European Commission's emerging role in transcending these limitations through entrepreneurial political activities. In conclusion, this analysis highlights the critical interplay between national sovereignty and collective defence efforts within the EU.