A government that wants to buy arms from a supplier of its own choosing, without opening the contract to bidders from across the Union, usually relies on one Treaty provision: the rule that a Member State may take the measures it considers necessary to protect the essential interests of its security in the production of and trade in arms, munitions and war material. Where that rule applies, the Union’s procurement directives cease to govern the award: there is no Union-wide notice, and competitors from other Member States need not be invited. The Court of Justice has long treated the provision as an exception to be read narrowly, and has placed on the government relying on it the burden of showing why its security interest could not have been protected within a competitive procedure. Governments that use the rule tend to explain their choices in terms of security of supply, interoperability or the protection of sensitive technology, objectives that a tender can sometimes accommodate and sometimes cannot. Recent practice in three Member States has produced a public record dense enough to examine: ministerial decisions, letters to parliament, programme reports, contractors’ statements and, in three cases, judgments of national courts. The question that record raises is narrow but consequential. When governments award defence contracts without a Union-wide tender, does national review hold them to the necessity standard the Court of Justice has set, or to something looser that the Treaty’s own wording invites?