The drones attacks that have filled the skies over Ukraine and Russia the past few weeks have not only cemented a new era of warfare, they have also shown Western countries how ill-prepared they are for it.

On Sunday, Ukraine launched hundreds of drones it had smuggled into Russia to strike air bases there, damaging or destroying as many as 20 strategic aircraft thousands of miles apart. That sent defense officials in some NATO nations rushing to assess whether they, too, could be vulnerable, if an adversary using drones could severely hobble a big military power — be it Russia, China or even the United States.

“This is more than an isolated incident — it’s a glimpse into the character of future conflict, where war won’t be confined to neatly drawn front lines,” said James Patton Rogers, a drone warfare expert at Cornell University. He said the urgent question for NATO, after “an impressive attack by Ukraine,” is to determine the vulnerabilities of its own air bases, bombers and critical infrastructure.

Before the Ukrainian barrage, Russia had intensified a near-daily deluge of long-range drones to attack military and civilian targets across Ukraine, demonstrating an ability to launch thousands of uncrewed aircraft as quickly as they are built, experts said. By comparison, defense manufacturers in the United States and Europe have struggled for more than three years to ramp up weapons production.

NATO knows it has much to learn.

Earlier this year, NATO opened a joint training center with Ukrainian forces in Poland to share lessons from Russia’s invasion. Ukraine’s military is the largest (aside from Russia’s) and most battled-tested in Europe, even if it is struggling to maintain territory in its border region.