Ukraine launched ATACMS missiles at Russian forces on Tuesday, marking the first time that the U.S-provided weapons have been used in the conflict in Ukraine.

A small number of the missiles have been secretly sent to Ukraine in recent days, where they will augment Kyiv’s capability to carry out long-range strikes at Russian forces during an important stage of its counteroffensive, according to people familiar with the matter.

Ukraine has long sought ATACMS, a surface-to-surface missile that can strike well behind Russian lines and that can be fired by the Himars, or High Mobility Artillery Rocket System launchers, the U.S. has provided the country.

On Tuesday, the Ukrainian military’s communication department said on the Telegram messaging app that it “made well-aimed strikes on enemy airfields and helicopters near the temporarily occupied Luhansk and Berdyansk.”

The ATACMS models that were provided have a range of about 100 miles.

The U.S. decision to send the ATACMS, which stands for the Army Tactical Missile System, has been long in the making. Ukraine repeatedly said the missiles were essential to its war plan, giving it the range it needed to strike targets behind the front lines in Russian-held Ukrainian territory.