A European government that needs a patented technology to sustain or expand defence production may face a proprietor who will not license on acceptable terms, or who cannot supply the volumes required. In December 2025 the European Union adopted a regulation creating a Union compulsory licence for patents in a crisis, but it expressly excluded defence-related products. The question is therefore answered by national law. In the United Kingdom, Germany and France statute allows the state, or a supplier acting under state authority, to use an invention without the proprietor’s consent, and each system attaches its own compensation rules. A patent, however, is a right to exclude, not a production line. The legal power to practise an invention does not on its own supply drawings, process data, software, tooling, trained staff or the acceptance of a design authority, and the statutes concerned are largely silent on those matters. The question that matters for European rearmament is whether government patent-use powers give states usable industrial access when a supply chain is blocked, or whether they remove only one obstacle on a critical path that is governed mainly by other constraints.