Joint Acquisition as a Catalyst in EU Defence Policy: From Intergovernmental Hesitation to Supranational Momentum

Defence policy was historically shielded from supranational integration dynamics. However, Russian aggression against Ukraine brought a new focus to defence at the European level. Our research examines the decisions made in support of Ukraine — specifically the Joint Acquisition scheme of 155mm artillery shells, coordinated by the European Defence Agency (EDA) — and analyses how it challenged the historical reluctance to delegate defence competencies to EU institutions. Research indicates that the EDA’s role in coordinating joint procurement transcended technical coordination. It set the lessons and foundation for later policy proposals by the European Commission, which framed joint acquisition both as a crisis measure and as a mid-term industrial strategy for defence. This momentum reached its peak with the EDIP proposal, directly linking defence industrial policy to the broader goal of EU strategic autonomy. The article argues that this incident marks a silent but important change in the institutional balance of EU security governance. The EDA emerged as an enabling actor, while the Commission’s assertiveness in proposing budgetary instruments for defence suggests a functional expansion of supranational roles. This trajectory supports the idea that seemingly pragmatic and technical instruments, such as joint acquisition, can produce political and institutional consequences that reinforce EU integration. The research also emphasises the persistent reluctance of Member States to delegate supranational powers in a policy area intrinsically linked to national sovereignty. Despite its strategic relevance, this initiative has been largely neglected by the literature. This paper seeks to evaluate the effect of the EDA-led joint acquisition project on the institutional distribution of power within the EU, exploring whether and how this initiative may contribute to further integration in defence policy. Based on neofunctionalism (Haas, 1958; Schmitter, 1970) and liberal intergovernmentalism (Moravcsik, 1998), it addresses the competing theoretical interpretations of European integration. We especially value the concept of cultivated spillover (Tranholm-Mikkelsen, 1991), which helps to understand the entrepreneurial role of institutions such as the European Commission and its leadership — namely its president, Ursula von der Leyen, and the HRVP, Josep Borrell — in triggering policy innovation in crisis contexts. This theoretical framework allows for a broad understanding of the tensions between supranational ambition and intergovernmental sovereignty. Methodologically, we focused on primary sources, exploring direct discourse. We adopted a mixed-methods approach, combining qualitative and quantitative techniques. We conducted interviews with key institutional and governmental actors — both at the EU level and in selected Member States. Interviewees included senior figures from national governments at the ministerial level, permanent representatives in Brussels, and officials from the EU institutions involved in defence policymaking. We also analysed official documentation and conducted discourse analysis. The paper enhances the understanding of institutional change in the EU’s security architecture and offers an empirical case for studying policy innovation in times of crisis. It also provides insight into how defence policy — once a taboo in Brussels — is becoming central to the EU’s geopolitical positioning.