What is Article 5 of the NATO treaty?

Russian missiles reportedly struck Poland, a NATO member, with missiles on Tuesday, setting off a frenzy over the Western alliance’s mutual defense mechanism known as Article 5.

Article 5 of the North Atlantic Treaty, NATO’s founding document, says that any attack on a NATO member in Europe or North America “shall be considered an attack against them all.”

Once a member invokes the principle of collective self-defense under the treaty, NATO can come to its defense with “such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.”

But that doesn’t mean any attack on a NATO member automatically triggers a state of war.

“It’s not like a trigger mechanism. It doesn’t mean that tomorrow every single country in NATO responds with a full military invasion of Russia,” Joel Rubin, a former deputy assistant secretary of State, said.

The diplomatic nature of an Article 5 invocation is by design. It allows the alliance the necessary pause and diplomatic toolkit to respond to an aggression on its own terms.

“If you think about it, if [it’s a trigger mechanism], you’ve given Russia all control over the battlefield. They decide when there is a war. They decide whether or not we get involved. No. We have control. We have agency over what our actions are,” Rubin said.

“Article Five is an incredibly powerful diplomatic tool. So it gives options for a  Polish response. That’s what it does. It gives options. It doesn’t give requirements,” Rubin said.

The Russian missile attack in question came amid a barrage against Ukraine’s energy infrastructure.

While Polish officials did not immediately confirm that missiles landed in their territory, U.S. officials said the possibly errant missiles killed two people on the Polish side of the border.

Polish Prime Minister Mateusz Morawiecki convened his security Cabinet on Tuesday to study the explosions near the Ukrainian border.

Story continues

Moldova, a small country wedged between Ukraine and Romania, reported widespread blackouts as a result of the attack but no direct hits on its territory. Moldova is not a NATO member but has friendly relations with the alliance.

Given the attack on its soil, Poland will first have to investigate why the Russian missiles overshot Ukraine.

“It’s quite possible that they were hitting Ukraine as much as they could. Russia’s military — they are not always precise,” Rubin said.

But the attack could also be a direct provocation or a Russian testing of the waters to gauge NATO’s resolve.

“The first step is to figure out why this happened and figure out whether it’s a beginning salvo or a test and then calibrate the response to that,” Rubin said.

The North Atlantic Treaty’s Article 4 says all the members will collectively study whether a specific member’s security or territory is being threatened.

Whether the missile strike was a mistake, an attack or a test, it could become the second invocation of Article 5 in NATO’s history.

The first happened on Jan. 12, 2001, when then-NATO Secretary General George Robertson informed the United Nations that NATO allies would come to the defense of the United States following the 9/11 attacks.

That Article 5 invocation led to a series of actions, ranging from intelligence sharing to diplomatic actions to direct military action, all undertaken as a response to the terrorist strike.

Under a Polish invocation, NATO would be free to design its own collective response, whether diplomatic, economic or military, under the umbrella of the principle of collective self-defense allowed by the United Nations Charter.

For the latest news, weather, sports, and streaming video, head to The Hill.