Context

Among other things, Sikorski declined to elaborate on how NATO should respond to a lethal “hydrous attack” by the Russian Federation, but noted that Poland and Estonia had already resorted to the application of Article 4 of the Alliance's charter — request for high-level consultations — after the violation of airspace by Russian drones and fighters, hinting at the need for more decisive action.

It was used only once: it was done by the United States after the terrorist attacks carried out by Al-Qaeda on September 11, 2001.