The 2001 Lithuanian general census found the population of Stašėnai, a dot-on-the-map village whose existence is barely perceptible amid flat and verdant farmland northwest of Vilnius, to be 66 souls. By the next census, a decade later, the figure had fallen to 45. Earlier this week the population of Stašėnai and the fields around it swelled, suddenly and temporarily, to hundreds of soldiers from 11 NATO countries.

At 10 a.m. on Tuesday staff cars rolled up to a tent and disgorged a dozen dignitaries, including the President of Lithuania, Dalia Grybauskaitė, and the Secretary General of NATO, Jens Stoltenberg. A few minutes later the crowd, which included a multinational throng of journalists decked out in bright yellow MEDIA vests, crossed the street to observing stands on the bank of the meandering Neris river.

This is still a residential neighbourhood, albeit sparsely populated, so a few families left their farmhouses to peer curiously at what came next, which was a low-key but unmistakable show of force.

Seven M3 amphibious rigs, ungainly vehicles that can drive on roads or float on water, had joined together to form a bridge across the Neris. Three of the rigs were operated by the U.S. Army, four by the German Bundeswehr.

On a signal delivered by a signal flare, heavy vehicles started rolling across the land bridge: armoured personnel carriers, tanks, motorized heavy equipment. Eventually dozens of vehicles had crossed the makeshift bridge. Combat helicopters hovered overhead. At one point a boat appeared, motoring up the river toward the bridge. This obliged the M3 operators to halt the motor traffic that had been rolling across their rigs, dismantle the bridge within a few minutes and chug upriver separately, allowing the boat to pass. Then two of the rigs returned to the landing and, operating together this time as a raft instead of a bridge, carried the last two tanks across the river.

In the final minute of the exercise, a roar in the eastern sky announced the arrival of an American B-1 bomber, which flew over the site of the exercise at low altitude. The amphibious bridges and tanks, their crews armed with weaponry ranging from personal sidearms to cannon, can deliver a certain amount of havoc and destruction. That single bomber could, if needed, deliver many multiples of the same. The point having been made, everyone repaired to white tents for news conferences and canapés.

The river crossing was a highlight of Day 9 of Multinational Exercise Iron Wolf, the summer’s major NATO training effort in Lithuania. Iron Wolf in turn is one part Exercise Saber Strike 17, a month of exercises across Poland and the Baltic countries, designed to build “interoperability” among 20 armies with widely varying capabilities, equipment, lore and traditions.

Saber Strike in turn is a bigger version of exercises that have been taking place with increasing frequency and intensity across Europe in recent years: Six Allied Spirit exercises since 2015. Atlantic Resolve exercises operating almost continuously. The immense Anaconda war game last year in Poland, the largest since the Cold War with 31,000 troops.

NATO has been adding muscle and stepping up its exercise tempo since 2014, when Russian-backed troops and irregular fighters invaded Eastern Ukraine and annexed Crimea. Those operations took a giant step forward last summer: NATO heads of government met in a Warsaw soccer arena for a summit meeting at which they decided to set up multinational battlegroups across the region.

Those battlegroups are now in place. Canada commands the battalion in Latvia, with troops and equipment from Spain, Italy, Poland, Albania and Slovenia. The battlegroup in Poland is led by the United States; Great Britain commands the force in Estonia; and Germany is in charge of the battlegroup in Lithuania.

These soldiers, 4,530 in total as the spearhead of a 29-nation alliance, have set up shop with a clear mission. In the aftermath of Russia’s invasion of parts of Georgia in 2008, and parts of Ukraine in 2014, it has never been clear whether Vladimir Putin wants to take back any more of the territory that used to be part of the old Soviet Union. The most obvious targets are the Baltic countries, Lithuania, Latvia and Estonia. For a generation they were constitutionally part of the USSR. When they asserted their independence in late 1990, even so mild a Soviet ruler as Mikhail Gorbachev tried briefly to block their departure, sending tanks into Lithuania.

Unlike Georgia and Ukraine, the Baltic countries and Poland are members of NATO, whose central tenet is that an attack against one member will meet a response from all of them. But by 2014, almost a quarter-century after the Cold War ended, it was hardly obvious what that might mean in concrete terms, on NATO’s home turf in Europe: A response from whom? With what manpower, equipment, doctrine and strategy?

In Warsaw the heads of government concentrated long enough to sketch answers. Now their soldiers are filling in the details. And soldiers tend to be attentive to detail. Iron Wolf was all about detail.

The exercise began with the American-led battlegroup rolling up from its base in Orzysz, in northern Poland, into Lithuania. That involved getting to know a crucial bit of real estate in intimate detail. The land bridge between the two countries is narrow, only 105 km of open land between the authoritarian-ruled country of Belarus and Kaliningrad, an isolated pocket of Russian jurisdiction on the Baltic Sea. This stretch of land is called the Suwalki Gap, after the Polish town in the middle of it.

If Russian troops, working alone or in concert with Belarusians, managed to seize control of the Suwalki Gap, the Baltic region would be cut off and vulnerable. So in part, Iron Wolf was about getting to know this crucial neighbourhood, learning how invaders might try to take it, and how defenders might need to cross it under fire.

After the bridge crossing show, the commander of the U.S.-led battlegroup that had come up from Poland, Lt.-Col Steven Gventer, 47, paused to discuss the mission with reporters. A broad-shouldered former high-school teacher, wearing camouflage face paint and with a 9mm pistol strapped to his chest, Gventer described in intricate detail the web of interactions his troops have already had with their colleagues, German, Lithuanian and other.

“We start to run into one another over and over again,” he said. “So as large as NATO is—geographically, militarily—we are a small community that gets to know one another through these exercises. And that provides us with the common operating picture that we’ve already developed. That provides us with secure FM comms”—dependable radio frequencies—“that we’ve already trained. That allows us to use our fires capability” — army jargon for the ability to find and hit targets — “across international lines. For a sensor from the United Kingdom, a scout out front, to identify a target; call it through a U.S. battlegroup headquarters, who call it and clear it through a brigade fire direction centre that might be Italian or Lithuanian or Polish; and then call it right back down to guns that might be Polish, United States, it doesn’t matter; and those guns reach out and put effects on the target.”

“Putting effects on a target” is another way to talk about destroying it, but what Gventer was really discussing was an extended and methodical effort to iron the bugs out of a gigantic fighting machine.

NATO is starting to see “the fruit of that long-term relationship that we start to build across national lines,” he said. “An understanding of what each other’s capabilities are. But also our weaknesses. The United States comes to the fight, at a battalion level, without air defence. But the Romanians provide us air defence. The United States doesn’t necessarily have bridging capability”—the river-crossing equipment that was the focus of the day’s demonstration—“to the extent that we might want. But the U.K., the Italians, the Germans have bridging capabilities.”

Gventer was turning into the best kind of source, the kind that talk a lot, so I googled him on my phone while he kept talking. He has had an eventful career. In 2004 he was in Sadr City, a violent Baghdad district, when an insurgent shot him through the calf with a machine gun. Two weeks later a rocket-propelled grenade hit a wall behind him and sent shrapnel into his shoulder.

“It was a great time to be a commander, and to learn the trade, I guess,” Gventer said when I asked him about his Iraq experience.

Now here’s the thing. After the decade and a half the alliance has been through since 9/11, most of NATO’s military leadership in central and eastern Europe has personal experience fighting under fire in Afghanistan or Iraq.

At Camp Adazi in Latvia I was surprised to learn that I know the commander of the Canadian-led battlegroup there. He came up to say hello. His name is Lt.-Col Wade Rutland, a red-haired guy with a ready smile. These days he is the commanding officer of 1st Battalion, Princess Patricia’s Canadian Light Infantry, based in Edmonton. In 2010 I spent two days visiting Rutland and the 200 soldiers he commanded inside a Soviet-built mountain fortress at Sperwan Ghar, in one of the most inhospitable corners of Kandahar province in Afghanistan.

Iraq and Afghanistan were deeply frustrating work for many of the soldiers who were deployed there. Every soldier I asked has already watched War Machine, the highly entertaining new Netflix movie that stars Brad Pitt as a lightly fictionalized version of the disgraced U.S. army general Stanley McChrystal. Some have seen it two or three times, and recited lines from the movie with relish. It’s a parable about the futility of command in an environment where victory may not be possible. So these guys aren’t naive about the limitations of their craft.

But they also grew up in an environment where combat is not hypothetical and where small mistakes in the battlefield can kill. They did not grow up in a world of weekend passes. They are used to taking serious work seriously.

“This is a much bigger fight,” Gventer said when I asked him to compare Iraq to central Europe. “The artillery capability of the enemy there was limited to rockets, very uncoordinated. What they lacked in accuracy they made up for in the number of rockets they would fire. But that said, the enemy didn’t have the ability to counterbattery” — that is, to use sophisticated equipment to discern the origin of incoming fire and send accurate fire back to destroy the launchers. “The enemy didn’t have air forces. This enemy does. Large amounts of artillery and counter-artillery, those are the things that we now would be concerned about.”

In Iraq, in other words, Gventer was fighting determined and inventive irregulars armed, for the most part, with what they could carry. Here in Stašėnai he was preparing to fight people whose methods and equipment much more closely match his own. “A near-peer or peer template,” as he put it.

There are other differences. In Iraq and Afghanistan, a near-permanent base would serve as the starting point for short-haul expeditions and raids. Whatever else soldiers went through, they would normally return to familiar surroundings each night. Now, “we don’t prepare to fight out of a base,” Gventer said. “We’re gonna leave that base very quickly if we have to fight.”

One reporter pointed out that the American battlegroup in Poland is the only one of the four new battalions that doesn’t have tanks with it. That’s because the Poles have plenty of their own, unlike the armies of the smaller Baltic countries, Gventer said. “The Polish bring a lot of armour. What they need is our ability to put light infantry in the woodline, near that armour, and destroy enemy armour forces coming towards them. We love having their armour; they love having our light infantry and our anti-tank capability. It’s not a match made in heaven, but it’s close.”

The goal of all of this deployment and training — and even, to a great extent, of the coverage of it, of all those reporters in yellow MEDIA vests at Stašėnai — is to make a great show of readiness so that if does have any thoughts of further military adventures, he will decide against them. In itself, the drum-beating carries its own risks of provocation and escalation.

NATO insists its plans are purely defensive, and every part of the Saber Strike maneuvers is designed to refine techniques for defending NATO territory within the confines of NATO territory. But one effect of the maneuvers was to send hundreds of tonnes of materiel into action in a ring of territory around Kaliningrad, an outpost Russia guards jealously. And NATO is not the only entity that has gotten into the relationship-building business: this month a three-ship Chinese convoy has been conducting exercises with the Russian navy in the Baltic Sea. So on the long list of nightmare scenarios here, one is that Western exercises designed to fend off a Russian attack could provoke one, or at least serve as a pretext for one. No part of this business is without serious risks.

But to Gventer, Rutland and the other battle-hardened soldiers leading the newly augmented NATO effort in Europe, there is no better way to avoid armed conflict than to prepare for it diligently. As Gventer put it: “If the deterrence doesn’t work, God forbid, then we’re capable to defend and we’re capable to be lethal in order to preserve the borders of NATO.”