NATO Articles 4 and 5: Understanding Alliance Obligations Amid Recent European Drone Incursions

Drone activity was detected overnight Wednesday across Northern Denmark, causing significant disruption to aviation operations.

Denmark announced Thursday it was considering invoking NATO's Article 4 following drone incursions that temporarily closed two airports and affected military facilities in the western Jutland region overnight.

Defence Minister Troels Lund Poulsen characterized these incursions as "hybrid attacks" intended to generate fear, though he could not identify the responsible parties.

Earlier, Prime Minister Mette Frederiksen connected similar drone activities that briefly shut down Copenhagen airport overnight into Tuesday with suspected Russian drone incursions and disruptions occurring across Europe. Moscow has denied any involvement in these incidents.

INCIDENT DETAILS

Billund airport, Denmark's second largest, was closed for one hour, while Aalborg airport, which serves both commercial and military flights, remained closed for three hours due to drone incursions late Wednesday, according to Danish police. Both airports had resumed operations by Thursday.

Drones were also observed overnight near airports in Esbjerg and Sonderborg, as well as Skrydstrup airbase, which houses some of Denmark's F-16 and F-35 fighter jets, and over military facilities in Holstebro, police confirmed to Reuters.

All affected locations are situated on the Jutland peninsula in western Denmark.

Danish authorities explained they decided against intercepting any drones in their airspace due to safety concerns, despite the significant disruption to air traffic.

UNDERSTANDING ARTICLE 4

Article 4 stipulates that NATO members will consult together whenever any member believes the territory, political independence, or security of any alliance member is threatened.

Under Article 4, discussions within the North Atlantic Council - NATO's principal political decision-making body - could potentially lead to joint decisions or coordinated action.

The Danish government is conducting internal discussions and consulting with NATO regarding the possible invocation of Article 4, according to Defence Minister Poulsen.

If Denmark proceeds, it would mark the second such invocation this month. Polish Prime Minister Donald Tusk invoked Article 4 on September 10 after Poland shot down drones in its airspace following what he described as a "large-scale provocation" by Russia.

Russia's defence ministry stated its drones had targeted military facilities in western Ukraine but denied planning to strike any targets in Poland.

Several European officials described that incursion as deliberate and indicative of Russian escalation.

Article 4 was previously invoked in February 2022 when Bulgaria, the Czech Republic, Estonia, Latvia, Lithuania, Poland, Romania, and Slovakia requested consultations following Russia's invasion of Ukraine.

UNDERSTANDING ARTICLE 5

If Russia were determined to have attacked the territory of a member state, attention would shift to Article 5, the cornerstone of NATO's founding treaty.

The alliance was established in 1949 with the U.S. military as its powerful foundation, primarily to counter the Soviet Union and its eastern bloc satellites during the Cold War.

The charter states that "the Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all."

"They agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defense recognized by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area."

UKRAINE WAR AND ARTICLE 5 IMPLICATIONS

Since Ukraine is not a NATO member, Russia's full-scale invasion in February 2022 did not trigger Article 5, though the United States and other member states rapidly provided military and diplomatic assistance to Kyiv.

However, experts have consistently warned about potential spillover to neighboring countries on NATO's eastern flank that could compel the alliance to respond militarily.

Such actions by Russia, whether intentional or accidental, have raised the risk of widening the conflict by directly drawing other countries into the war.

ARTICLE 5 ACTIVATION PROCESS

Following an attack on a member state, other NATO members convene to determine whether they collectively agree to regard it as an Article 5 situation.

There is no time limit for such consultations, and experts note the language provides flexibility for each member to decide how far they will go in responding to armed aggression against another member.

Article 5 has been activated only once before – on behalf of the United States, following the September 11, 2001, terrorist attacks on New York and Washington.