Whether a ‘Brexit’ would threaten the United Kingdom’s national security has become a central theme in the run-up to the in/out referendum on EU membership. Although national security has been a central facet of both the ‘Remain’ and ‘Leave’ campaigns thus far, there has been little mention of the implications of a Brexit for UK defence industries or defence procurement, let alone formal debate or analysis. The article addresses this gap by analysing the potential implications of a Brexit for defence procurement and industries in the UK and the EU member states. The first section analyses the policy context for a Brexit by exploring existing levels of EU defence procurement integration in the UK’s and Europe’s defence industries. The second section draws on Jozef Bátora’s ‘institutional logics’ framework to identify two pro-Brexit and two pro-Remain narratives, each employing differing assumptions on the relative benefits of national sovereignty and closer EU integration The final section analyses the way in which these ‘logics’ or narratives will be deployed by their advocates in the run-up to the UK’s EU referendum. The article concludes that the national security battleground in the 2016 referendum will be fought over competing narratives and arguments, partly because there is a dearth of data and evidence concerning UK and EU defence procurement and industries, which renders this crucial area of national security vulnerable to the politics of spin.