What are NATO’s defence obligations under Articles 4 and 5 of its treaty?
While Article 4 triggers consultations, Article 5, NATO’s cornerstone, requires collective defense if a member’s territory is attacked.
Denmark is evaluating whether to invoke Article 4 of NATO’s founding treaty after a series of drone incursions temporarily shut down two airports and disrupted military installations in the western Jutland region, officials said on Thursday.
Danish Defence Minister Troels Lund Poulsen described the incidents as “hybrid attacks” intended to spread fear and uncertainty, though he did not confirm the perpetrators. “We have sent our forces to monitor and assess the situation. These incursions are deliberate and designed to unsettle us, and we will respond appropriately within NATO frameworks,” Poulsen said.
The drone activity affected Billund Airport, Denmark’s second-largest, which was closed for an hour, and Aalborg Airport, used for both commercial and military flights, which remained closed for three hours. Authorities also observed drones near airports in Esbjerg and Sønderborg, as well as over Skrydstrup Airbase and a military facility in Holstebro, home to Denmark’s F-16 and F-35 fighter jets. For safety reasons, Danish authorities opted not to take down the drones.
Earlier incidents linked to suspected Russian drone operations, including a temporary shutdown at Copenhagen Airport, have been reported across Europe, though Moscow has denied involvement. Prime Minister Mette Frederiksen connected the latest incursions to these broader disruptions.
What is Article 4?
Article 4 allows NATO members to consult collectively whenever any member believes its territory, political independence, or security is threatened. Such consultations at the North Atlantic Council can result in coordinated decisions or joint action.
If Denmark proceeds, it would mark the second invocation of Article 4 this month, following Poland’s request after downing drones in its airspace on September 10.
The distinction between Article 4 and Article 5
While Article 4 triggers consultations, Article 5, NATO’s cornerstone, requires collective defense if a member’s territory is attacked. Under Article 5, an armed attack against one member is considered an attack against all, compelling members to act, including military intervention if necessary.
NATO’s 1949 charter, with the U.S. military as a principal anchor, was designed to ensure security in Europe and North America, initially countering Soviet influence during the Cold War. Recent drone incursions highlight ongoing security challenges in the region, as European officials warn of deliberate escalation.
“The safety of Danish airspace and our military facilities is paramount,” Defence Minister Poulsen said. “We are coordinating closely with NATO to ensure all appropriate measures are taken.”
