When Polish radar detected a mass of Russian drones entering the country's airspace on the night of 9/10 September, the reaction was swift but also alarming for the entire alliance.
Poland shot down several aircraft, and the rest were monitored by the Allies. It was the first time that a NATO member had shot down Russian drones in its own airspace during the war in Ukraine.
This incident prompted the Alliance to officially launch a new activity – Eastern Sentry – to increase presence, surveillance and response speed on the eastern flank.
Secretary General Mark Rutte announced the Eastern Sentry on 12 September in Brussels, stressing that it is not an ad hoc gesture but a long-term mechanism.
The Supreme Allied Commander Europe (SACEUR), General Alexus G. Grynkewich, added that the new activity is intended to show how NATO's defence is equally linked in peace and in crisis.
Behind the message is a clear signal to Moscow – the Alliance will not allow its borders to become grey zones for testing Russian drones or missiles.
Balancing deterrence with avoiding direct escalation
The Polish public and political elite perceived the incident as a deliberate test of NATO's readiness and reaction speed on its own border. The Ministry of Defence declared that it was an attempt by Moscow to test NATO's ability to respond.
Immediately, the government tightened the flight regime, introduced restrictions along the eastern border, and temporarily closed several airports. According to available reports, around 20 Russian drones entered Polish airspace (estimates range from 19 to 23).
The statement from Washington was somewhat more cautious, stating that it was possibly a "navigational error." However, it also stated that "every inch of NATO territory will be defended." This difference in tone shows how carefully the allies are balancing deterrence with avoiding direct escalation.
Poland's decision to shoot them down signals a willingness to apply the rules of engagement consistently, even risking escalation
Eastern Sentry is planned as a multi-domain activity: it combines aircraft, air defence systems, sensors, cyber capabilities, and logistics. In contrast to previous "air policing", which primarily consisted of continuous patrols by fighter aircraft, Eastern Sentry has a greater range and a faster rhythm.
It can be flexibly expanded or reduced depending on the situation and is not tied to fixed schedules. In the first phase, fighter aircraft from Denmark, France, Germany and the UK were deployed, as well as a Danish frigate covering the Baltic Sea.
In practice, aircrews and command centres make real-time decisions about shooting down enemy aircraft. Small radar silhouettes, low altitude and the ability to carry explosives make drones a dangerous target that cannot be ignored.
Poland's decision to shoot them down signals a willingness to apply the rules of engagement consistently, even risking escalation. For NATO, it was a sign that it needs to improve its procedures because similar incidents will occur more and more frequently.
A thin line between the military and civilian spheres
The incident also raised the question of the safety of civilian transport. European airlines fear that repeated incursions could disrupt air traffic along the eastern border.
Temporary restrictions and NOTAM (Notice to Air Missions) notices have already led to diversions and additional costs. This has shown how thin the line is between the military and civilian spheres and how one night can affect the economics of air travel across Europe.
If NATO demonstrates weakness on the Polish border, it would call into question the entire concept of Article 5
The political dimension is equally important. While Mark Rutte publicly condemned the incident and emphasised solidarity with Poland, the US administration left room for an assessment of intent.
This raised the question of whether a united tone can be maintained within the alliance. Almost all European capitals sided with Warsaw, as it is clear that this is a test of collective defence.
If NATO demonstrates weakness on the Polish border, it would call into question the entire concept of Article 5.
Testing the defence plans
What Eastern Sentry changes is not just the number of flights or soldiers, but the routinisation of procedures. Instead of treating each intrusion as a one-off incident, the new activity builds a continuous network for detection, communication, and response.
This means that even a small drone is detected and registered within the joint system, and the decision to shoot it down does not depend on improvisation. In this respect, Eastern Sentry is more than a military exercise – it is the transition to a new permanent preparedness system.
This has practical significance for Poland, but also for Ukraine. Polish officers are intensifying consultations with their Ukrainian colleagues, but the Polish Ministry of Defence has specified that operational training and joint exercises will take place on Polish territory.
Thus, the border of the alliance will become a classroom for the exchange of experience in the fight against Russian drones, and NATO will expand its capabilities by indirectly strengthening Ukraine.
Eastern Sentry is also a test for the new defence plans adopted at the Vilnius Summit in 2023. At that time, the members adopted detailed plans for the deployment of armed forces in the event of a crisis.
Russia often takes the opportunity to deny or disavow the incidents by claiming that the drones got lost or did not cross the border at all
Now these plans are being tested in practice – from response time to interoperability and logistics. For NATO, this is a way of demonstrating that its commitments are not just political rhetoric but sophisticated military-technical procedures.
The most important innovation lies in the documentation and exchange of data. Russia often takes the opportunity to deny or disavow the incidents by claiming that the drones got lost or did not cross the border at all.
Therefore, Eastern Sentry establishes a data chain that allies can share and use publicly, thereby enhancing the legitimacy of any attack decision. At a time when information is as important as military response, this is a crucial innovation.
The economic consequences cannot be overlooked. Any disruption in the East Wing impacts insurance, transport and energy prices. Unsafe air corridors increase insurance costs and divert freight and passenger traffic. This affects entire supply chains and shows how border security is also an economic issue.
A new threshold for collective defence
In the coming weeks, Eastern Sentry will be further developed, with faster patrols along the Polish and Baltic borders, occasional sensor deployments in the south, and a more intensive engagement with Ukrainian capabilities.
The very fact that Eastern Sentry has been launched shows that NATO understands that the border cannot be protected without a permanent and coordinated response
All these developments will occur without the formal declaration of a new mission, as the Alliance aims to demonstrate flexibility and prevent escalation.
But the very fact that Eastern Sentry has been launched shows that NATO understands that the border cannot be protected without a permanent and coordinated response.
Eastern Sentry therefore represents a new threshold for collective defence. It is a system where defence is measured in minutes and dates, not just in the number of aircraft or soldiers.
Its aim is to deter Russia from further testing and to show that the Alliance has the strength and political will to respond without delay.
If it proves effective in the coming months, it will be a signal that NATO can modernise its mechanisms and that collective defence is not a static doctrine but a living system ready for new challenges.
