Polish President Andrzej Duda and NATO Secretary General Mark Rutte took part in the unveiling of a U.S. missile defense base in Redzikowo, northern Poland on Wednesday.
The base, known as "Aegis Ashore," is part of the North Atlantic Treaty Organization (NATO)'s broader missile shield.
It can detect and intercept short- to intermediate-range ballistic missiles and will be under NATO command and U.S. European Command.
Moscow has pledged response. Russian media reported Wednesday, citing Kremlin spokesman Dmitry Peskov, that Russia will take necessary measures to maintain parity in response to the deployment.