- NATO invoked Article 5 for the first time in its history after the 9/11 terrorist attacks against the United States.
The 9/11 terrorist attacks
The United States was the object of brutal terrorist attacks on 11 September 2001. The Alliance's 1999 Strategic Concept had already identified terrorism as one of the risks affecting NATO’s security. The Alliance’s response to 9/11, however, saw NATO engage actively in the fight against terrorism, launch its first operations outside the Euro-Atlantic area and begin a far-reaching transformation of its capabilities. Moreover, it led NATO to invoke Article 5 of the Washington Treaty for the very first time in its history.
An act of solidarity
On the evening of 12 September 2001, less than 24 hours after the attacks, the Allies invoked the principle of Article 5. Then NATO Secretary General Lord Robertson subsequently informed the Secretary-General of the United Nations of the Alliance's decision.
The North Atlantic Council – NATO’s principal political decision-making body – agreed that if it determined that the attack was directed from abroad against the United States, it would be regarded as an action covered by Article 5. On 2 October, once the Council had been briefed on the results of investigations into the 9/11 attacks, it determined that they were regarded as an action covered by Article 5.
By invoking Article 5, NATO members showed their solidarity toward the United States and condemned, in the strongest possible way, the terrorist attacks against the United States.
Taking action
After 9/11, there were consultations among the Allies and collective action was decided by the Council. The United States could also carry out independent actions, consistent with its rights and obligations under the United Nations Charter.
On 4 October, once it had been determined that the attacks came from abroad, NATO agreed on a package of eight measures to support the United States. On the request of the United States, it launched its first ever anti-terror operation – Eagle Assist – from mid-October 2001 to mid-May 2002. It consisted in seven NATO AWACS radar aircraft that helped patrol the skies over the United States; in total 830 crew members from 13 NATO countries flew over 360 sorties. This was the first time that NATO military assets were deployed in support of an Article 5 operation.