Patriot missile defense system is seen at Sliac Airport, in Sliac, near Zvolen, Slovakia, May 6, 2022
The Ukrainian personnel arrived Sunday evening at Fort Sill in the state of Oklahoma for training at the US Army Air Defense Artillery School, Colonel Curtis King of that facility said in a video posted on Twitter.
Washington promised a Patriot battery, it fires missiles to take out missiles -- to Ukraine late last year to help counter relentless aerial attacks by Moscow.
This was a significant victory for Kyiv, which had repeatedly pushed the United States for the system as the war launched by Moscow almost a year ago grinds on.
King did not say how many Ukrainian troops are in Oklahoma, but the Pentagon said earlier this month that 90 to 100 would come to America to learn how to operate and maintain the Patriot system in a course lasting several months.
Air defenses have played a key role in protecting Ukraine from strikes and preventing Moscow's forces from gaining control of the skies.
But as Russia faced increasing setbacks on the ground, it began systematically targeting critical infrastructure in Ukraine in attacks that have disrupted electricity, water and heat to millions of people.
It has also hit purely civilian structures.
A Russian missile strike Sunday on an apartment building in Dnipro in central Ukraine killed at least 40 people. Russia denied it was responsible for one of the deadliest single attacks since the war began.
Made by Raytheon, the MIM-104 Patriot is a surface-to-air missile system initially developed to intercept high-flying aircraft.
It was modified in the 1980s to focus on the new threat of tactical ballistic missiles, and was used in combat against Iraq's Russian-made Scud missiles in the first Gulf War.
The Patriot has been proven effective in Saudi Arabia against Iranian-designed ballistic missiles fired from Yemen.
Raytheon says the system has intercepted more than 150 ballistic missiles in combat since 2015.