Estonian soldiers take part in NATO military exercise Hedgehog 2015 at the Tapa training range in Estonia May 12, 2015. (Ints Kalnins/Reuters)

A year ago, Russian President Vladimir Putin seized Ukraine’s Crimean Peninsula because he said he feared NATO’s expansion. This week, U.S. tanks were cutting up the Estonian countryside just 65 miles from the Russian border in response to local fears about Russia’s expansionism.

From destroyers in the Baltic Sea to paratroopers over Georgia’s skies to camouflaged reservists in Estonia’s birch forests, drills across the former Eastern Bloc this past week were a stark new sign of worries about Kremlin aggression. Estonia in recent days held its biggest military exercises since the end of the Cold War, and other nations adjoining Russia have taken forceful steps to avoid Ukraine’s fate.

Training efforts have swept the region, and in the past week alone separate exercises took place in Poland, Lithuania, Georgia, Estonia and the Baltic Sea. Military planners said they were a practical attempt to drill new lessons about how Russia wages war. But they were also intended as a warning that unlike in Crimea, where Ukrainian forces surrendered without firing a shot, the Kremlin would face stiff resistance if it tried its tactics anywhere in NATO territory. U.S. military trainers are also in Ukraine trying to strengthen that nation’s fighting forces even as a war burns in the eastern part of the country.

Although the exercises could bolster military preparedness, they might also antagonize Putin, some critics say. They are part of a rapid militarization on both sides of the Russian frontier. The burst of training came as Russia celebrated the 70th anniversary of the defeat of Nazi Germany this month with a vast military parade in Moscow’s Red Square that included powerful new tanks and antiaircraft missiles.

“This new security situation is here for the long haul,” said Estonian Defense Minister Sven Mikser, who presided over the exercises this past week in the tiny Baltic nation that is wedged between Russia and the sea. “If we try to be overly conciliatory and take deescalatory steps unilaterally, that’s when Putin senses weakness and indecision, and rushes to fill the vacuum.”

Fighters from Lithuania's army rapid reaction unit attend the Zaibo Kirtis (Lightning Strike) joint anti-riot drill in Svencioneliai, Lithuania. (Ints Kalnins/Reuters)

After Russia seized Crimea last year, NATO nations announced that they would deploy troops on a rotating basis to Poland and the three Baltic countries of Estonia, Latvia and Lithuania. Those are the NATO members whose borders with Russia are poorly defended.

President Obama followed up on the pledge with a visit to the Estonian capital of Tallinn in September.

“An attack on one is an attack on all,” Obama said. “So if, in such a moment, you ever ask again, ‘Who will come to help?’ you’ll know the answer — the NATO alliance, including the armed forces of the United States of America.”

Companies of U.S. troops have been rotating through the countries ever since, drilling alongside their host nation’s military. NATO warplanes have also stepped up patrols in the skies of the Baltics, intercepting Russian jets hundreds of times in the past year.

In the past week’s exercises in Estonia, more than 13,000 troops practiced how to respond to an invasion from the fictional nation of Aslavia, a stand-in for Russia. In a country of 1.3 million people that is smaller than West Virginia, Operation Siil, or “Hedgehog,” had a broad-ranging impact, emptying reservists out of workplaces and dominating local news coverage. A contingent of U.S. and British troops also took part, providing air support with A-10 Warthog attack jets and playing the part of the aggressors with four tanks on the ground.

The exercises covered a wide swath of Estonian territory, pulling ordinary residents into the proceedings, at least as observers, as armored vehicles crisscrossed highways. Howitzers and machine guns rang out near back yards and across blooming farmland.

Estonian defense officials said the exercise had been planned for three years, well before the start of the conflict in Ukraine. But the Ukrainian fighting gave the operations a sharp urgency, and it spurred reservists from around the world to fly back to Estonia to take part.

“Ukraine and Crimea had some kind of impact to change our society’s mainstream thinking a bit,” said Estonian Lt. Col. Aron Kalmus, who led the exercises. If Estonia ever needs to respond to an invasion, he said, its citizens “ will come to protect whichever corner of the Estonian landscape they are” in.

Estonians are particularly nervous about the town of Narva, which is pressed against the Russian border and is more than 80 percent ethnically Russian. U.S. tanks took part in an Estonian independence day parade there in November; Russian military exercises have taken place not far away on the other side.

The U.S. soldiers who participated in the exercises said they had grown to enjoy their Baltic sojourns, which last three months.

“Some soldiers might not have known where Estonia was on a map a year and a half ago,” said Capt. Timothy Keilty, an officer in the 173rd Airborne Brigade who led the U.S. opposition forces in the training exercises. “They certainly know where it is now. And they know the significance of U.S. forces, U.S. paratroopers, U.S. tankers being here in the country.”

Other Eastern European nations are also nervous about their future. Lithuania’s military this week held exercises designed to counter the threat of so-called little green men, the unmarked Russian special forces troops who surprised Ukraine when they fanned out over Crimea. Lithuanian leaders have also distributed a guide to its citizens about what they should do if they are invaded. Polish lawmakers conducted special combat training of their own.

And outside the protective shield of NATO, U.S. paratroopers fluttered down this week on Georgia, which had a brief war with Russia in 2008. U.S. military trainers are in western Ukraine, away from the front lines of the conflict there, to try to bolster the combat skills of the Ukrainian military and national guard.

Baltic security officials acknowledge that no matter how hard they train, they will never be able to prevail alone over a determined Russian assault. But one part of deterrence is showing in advance that they are willing to put up a fight, officials say. And part of their strategy is to be able to hold out long enough for NATO forces stationed elsewhere to arrive if there is a conflict.

The Baltics “are very much like the West Berliners during the Cold War,” living in a territory that is nearly impossible to defend from a determined aggressor, said Artis Pabriks, a former Latvian defense minister who is now a member of the European Parliament. “For us, it’s an existential threat.”

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