U.S. soldiers and equipment arrived in Poland on January 12, greeted by many in Eastern Europe as a boost to security but viewed by Moscow as a "threat" on its doorstep.
Some residents waved American flags and cheered as the first of about 3,500 U.S. troops crossed the border from Germany, headed toward Zagan, where they will be based before fanning out across seven countries in the region.
"This is the fulfilment of a dream," said Michal Baranowski, director of the German Marshall Fund think tank in Warsaw. "And this is not just a symbolic presence but one with a real capability."
The Obama administration ordered the deployment in 2014 to reassure regional allies after Russia’s moves against Ukraine.
Russia has been highly critical of the deployment.
"These actions threaten our interests, our security," President Vladimir Putin's spokesman said on January 12. "Especially as it concerns a third party building up its military presence near our borders."