WASHINGTON (AP) — About 100 Ukrainian troops will head to Oklahoma’s Fort Sill soon to begin training on the Patriot missile defense system, two U.S. officials said Tuesday.

Ukraine has long sought the Patriot surface-to-air guided missile defense system because it can target aircraft, cruise missiles and shorter-range ballistic missiles. During his late December visit to the U.S. Ukrainian President Volodymyr Zelenskyy said the battery would make a significant difference in bolstering Kyiv’s defenses against Russia’s invasion.

The number of Ukrainians coming to Fort Sill is approximately the number it takes to operate one battery. Kyiv’s decision to take troops off the battlefield to training across the Atlantic in the U.S. is unusual, although it has sent forces for short-term training at European bases for other more complex systems it has received, such as on the longer-range High Mobility Artillery Rocket System.

The U.S. pledged one Patriot battery in December as part of one of several large military assistance packages it has provided Ukraine in recent weeks. Last week Germany pledged an additional Patriot battery.

Each Patriot battery consists of a truck-mounted launching system with eight launchers that can hold up to four missile interceptors each, a ground radar, a control station and a generator. The Army said it currently has 16 Patriot battalions.

The Patriot batteries will complement a variety of air defense systems that both the U.S. and NATO partners have pledged to Ukraine, as it faces an evolving barrage of missiles and drones against its civilian population and infrastructure from Russia in the now 11-month old conflict. In the last few months Germany has pledged four IRIS-T air defense systems; the U.S. has also pledged eight mid-range National Advanced Surface-to-Air Missile Systems, or NASAMS and Avenger air defense systems.