PABRADE, Lithuania On a desolate plain where Soviet tanks once prepared for a possible invasion of Western Europe, American troops are training to deter Moscow from another invasion.

Through a dense smokescreen, soldiers of the Second Cavalry Regiment advance amid intense gunfire on the imaginary positions of a NATO enemy. On their flanks are fellow NATO soldiers from Lithuania where the war game is being held who just a quarter century ago would have been enemies, as Lithuania was one of the fifteen republics of the Soviet Union.

The U.S. and NATO are ramping up their deterrence capabilities against any Russian threat to Europe's borders and this joint exercise is aimed squarely at Russia. NATO is drawing a red line in the three Baltic states, all of them alliance members, with a message to Moscow: "Don't cause trouble here and don't try to invade!"

American Stryker armored vehicles speed across the churned ground; later this year they will be replaced in Lithuania by Abrams main battle tanks and another rotation of American troops will arrive.

U.S. Army Capt. Russell Moore, who is leading the troops involved in the current exercise, said the war games show not just that the "the U.S. is willing to stand with all of its NATO alliance partners It shows that we're strong, Europe is strong and there's a collective defense ready to defend against any foreign aggression."

Lieutenant Evaldas Milkintis, his Lithuanian comrade, agrees.

"We feel safer training together," he said. "We're trying to be ready to react to any threat from outside."

Lithuania has good reason to feel threatened. It was ruled by Moscow for decades until the end of the Cold War and doesn't want to be ruled by Vladimir Putin now. That's why the small nation has watched with growing alarm as Ukraine's borders were torn up by Moscow-backed fighters.

To its west is the Russian enclave of Kaliningrad, home to Russia's Baltic warships. And in the skies above the Baltic Sea, it watches Russian warplanes test NATO's responses.

Lithuania has become one of Russia's main adversaries because it has sent military help to the Kiev government.

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Tanks and Tactics: NATO Exercises Send Message to Putin