BRUSSELS — EU officials in Brussels conducted simulations in early May to operationalize Article 42.7 of the Lisbon Treaty, the European Union’s mutual defense clause. The clause, which provides security guarantees to member states, is textually similar to NATO’s Article 5.

European Commission President Ursula von der Leyen stated, "The time has come to bring Europe’s mutual defense clause to life," at the Munich Security Conference in February. In early May, EU ambassadors began simulations to implement the provision, described by EU’s top diplomat Kaja Kallas as "mapping what we have done, what the possibilities are, who does what in what case, and how we are all working together."

These efforts follow Russia’s full-scale invasion of Ukraine, which EU officials describe as the most acute security threat to the bloc. EU member states have been targeted by state-sponsored attacks attributed to Moscow, including Russian drone incursions that have violated European airspace. Additional gray-zone actions have targeted European critical infrastructure at sea and in cyberspace.

In March, drones from the Middle East struck Cyprus, hitting a British military base on the island. EU countries in the Eastern Mediterranean could be vulnerable to further drone strikes by Iran or its proxies, according to security assessments. Cyprus, Ireland, Malta, and Austria are EU members that do not belong to NATO, making the EU’s mutual defense clause particularly relevant for their security planning.

NATO’s Article 5 states that an armed attack against one or more NATO members in Europe or North America shall be considered an attack against them all, obligating members to assist the attacked party by taking “such action as it deems necessary, including the use of armed force.” The EU’s response to Russia’s invasion of Ukraine—including military, financial, and humanitarian assistance—is proposed as a model for how Article 42.7 might be activated in future crises.