WASHINGTON — NATO officials at the Madrid summit revived a Cold War-era concept of spelling out which alliance countries are responsible for securing specific, vulnerable European members situated closer to Russia.

The idea is wrapped up in a shift in the alliance’s force posture that walks a fine line between filling countries from the Baltics to Romania with actual combat forces and the mere promise of shipping them there quickly in the event of an attack.

“We need to understand that these forces, of course, will be paid and organized by the different NATO allied countries, so they will be based in their home countries but they will be pre-assigned to specific territories, to specific countries and territories, to be responsible for the protection of these territories,” Secretary-General Jens Stoltenberg told reporters in Madrid this week.

The new emphasis on pre-assigned forces comes with a plan for more prepositioned equipment that arriving troops could quickly access from storage. In addition, static capabilities, like air-defense weapons, are to be moved closer to the would-be front lines with Russia.

Many details of the posture plan have yet to be sorted out, with specifics still obscured by an arithmetic of wishful thinking under which the alliance tends to count force packages from member nations as highly ready to fight simply by saying so.

But the focus on divvying up smaller geographic areas of responsibility along the eastern flank is here to stay, according to analysts. Rooted in NATO’s enhanced forward presence concept, enacted after Russia’s annexation of Crimea from Ukraine in 2014, the plan envisions, for example, a French brigade-sized formation focusing on Romania, while the Germans would increase their commitment to Lithuania and the British would take responsibility for Estonia.

The posture change aims to move the character of NATO’s eastern deployments from that of a tripwire force, by which invading Russian forces would be held up long enough for help to arrive, to more of a “brick wall” at the border that would deny them any gains at all, said Kelly Grieco, a senior resident fellow at the Atlantic Council think tank.

“But the devil is in the details,” she said. Would the forces in western Europe and North America be tasked with anything other than their mission of defending their assigned eastern flank regions when needed, for example, she asked.

It’s also unclear if the larger member nations will be able to sufficiently fill prepositioned stocks in their assigned areas, a key ingredient in NATO’s surge calculus, Grieco added.

Jim Townsend, a former Pentagon official on Europe and NATO now with the Center for a New American Security, said the the summit plan amounts to a half-step toward the permanent alliance presence eastern European allies have been seeking since 2014 annexation. While the Baltic states felt American boots on the ground would provide extra deterrence against Russian aggression, Pentagon leaders saw the expense of basing troops and their families in Eastern Europe as too high, he said.

“I think what they’re trying to do is have it both ways: They’re going to have the familiarity with a region that you would have if you were permanently deployed, but they’re going to get that as rotational forces,” Townsend said.

Kremlin officials have said in recent days they see NATO preparing for war with Russia. Townsend thinks the new moves, which include home-porting two U.S. Navy destroyers in Rota, Spain, will stoke fear and respect in Moscow.

“For sure it’ll be perceived as a provocation, and they’ll make a big deal out of it in Moscow, but I think they’ll respect it too because it shows we’re serious, that we’re putting our money where our mouth is,” Townsend said. “Certainly the Russians will notice that we didn’t pull back on the throttle.”

Still, the new force model is “quite restrained on the part of NATO,” said Sean Monaghan, a former British defense official now a visiting fellow with the Washington-based Center for Strategic and International Studies.

That’s because the idea of true “forward defense,” as the eastern member states wanted, exists only as an ambition, he told Defense News.

“The question is, will that provide a credible enough deterrent to Russia,” he asked.

According to Grieco, there are political pitfalls wrapped up in the emphasis on pre-assigned forces from the West. “Europe could become a first responder that way,” she said. But having American troops on their territories is ultimately considered more valuable for many vulnerable NATO members, she added.

Sebastian Sprenger is associate editor for Europe at Defense News, reporting on the state of the defense market in the region, and on U.S.-Europe cooperation and multi-national investments in defense and global security. Previously he served as managing editor for Defense News. He is based in Cologne, Germany.

Joe Gould was the senior Pentagon reporter for Defense News, covering the intersection of national security policy, politics and the defense industry. He had previously served as Congress reporter.

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