Seven radar aircraft. 830 crew members from 13 nations. More than 360 sorties.
That was Operation Eagle Assist, which ran from October 2001 to May 2002 and remains the most visible result of the only occasion on which NATO has called on Article 5 of its founding treaty.
The occasion was the September 11 attacks. On September 12, 2001, less than 24 hours later, the North Atlantic Council met in Brussels and agreed on a conditional finding. If the strike had been “directed from abroad against the United States,” it would “be regarded as an action covered by Article 5.” Investigators then pinned the attacks on Al Qaeda, and on October 2, 2001 the Council made the finding formal.
Eight measures for Washington
The allies did not announce a war. They agreed to eight specific steps. Intelligence on terrorism threats would flow more freely. American and allied facilities would get extra protection. Military aircraft received blanket overflight clearance, and ports and airfields opened to US forces. NATO also sent its Standing Naval Forces to the Eastern Mediterranean and its Airborne Early Warning aircraft to American skies.
A second operation, Active Endeavour, put those naval forces on patrol against terrorist activity in the Mediterranean. It started in October 2001 and ended in 2016.
Parliaments had a say
Berlin did not simply send troops. Germany went to the Bundestag first. On November 16, 2001, the parliament voted to commit 3,900 troops to Afghanistan, which the government counted as meeting its Article 5 obligations.
The treaty allows for this. Some members need legislative approval before armed forces cross a border, and the text says so.
What the words require
People often assume Article 5 forces every ally into combat. The wording is looser. Each member pledges to take “such action as it deems necessary, including the use of armed force,” to restore security in the North Atlantic area. The Brennan Center, in an explainer published in March 2022, read that as real discretion: an ally could ship equipment to the attacked country or sanction the aggressor instead of fighting.
The key sentence is brief. An armed attack on one or more members in Europe or North America “shall be considered an attack against them all.”
What counts as an armed attack has stretched since 1949. Allied leaders have said at recent summits that Article 5 may cover “attacks to, from or within space,” and that significant cyber attacks and other hybrid attacks may count as an “armed attack.”
Twelve founders, 32 members
Twelve countries signed the treaty on April 4, 1949: Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom and the United States.
Twenty more have joined over 10 rounds of enlargement, in 1952, 1955, 1982, 1999, 2004, 2009, 2017, 2020, 2023 and 2024. That makes 32 members as of March 2024. Finland entered in 2023 and Sweden in 2024, both turning away from military non-alignment after Russia’s 2022 invasion of Ukraine. Every newcomer needs consensus among existing members in the North Atlantic Council.
NATO describes the clause as a constant deterrent even though it has been formally used once. It rests on Article 3, which obliges members to “maintain and develop their individual and collective capacity to resist armed attack.”
Sources
- NATO's Collective Defence and Article 5
- NATO's Article 5 Collective Defense Obligations, Explained
- NATO member countries
