Article 5 is a vague consultative mechanism

Article 5 of the Washington Treaty is not literally 'an attack on one is an attack on all'; it is a consultative mechanism, deliberately written vaguely by the US after WWII to avoid automatic commitment to another European war, requiring only 'such measures as it deems necessary, including the use of armed force,' so the US could satisfy the letter of Article 5 by sending a single AWACS plane if part of Estonia were annexed, making the guarantee far softer than most policymakers assume.