ABOARD A US MILITARY AIRCRAFT (AP) — The first class of 635 Ukrainian fighters has finished a five-week advanced U.S. training course in Germany on sophisticated combat skills and armored vehicles that will be critical in the coming spring offensive against the Russians, the Pentagon said Friday.

Pentagon press secretary Brig. Gen. Pat Ryder said that additional training is already underway at the Grafenwoehr training area, and will involve about 1,600 more Ukrainian troops. The completion of the first class coincided with a visit to the base by Defense Secretary Lloyd Austin, giving him his first chance to see Ukrainian soldiers training there.

The first group of Ukrainian forces arrived at the base on Jan. 15 and was put through an intense course that prepared them to take Bradley fighting vehicles and M109 Paladins into battle. The Bradleys and Paladins are two of the many armored vehicles and tanks that the U.S. and allies have pledged to the Ukrainians to help them punch through entrenched Russian troop lines. The Paladin is a self-propelled howitzer that runs on tracks rather than wheels.

Ryder said another battalion of Ukrainian troops began training on the Bradley fighting vehicle two weeks ago, and a field artillery battalion started instruction on the Paladin. Those two units total about 710 troops. Another field artillery unit and a Stryker battalion will start training next week, involving about 890 troops. That will be the first Ukrainian battalion to get training on the Stryker, an armored personnel carrier.

Defense leaders have called the latest training program key to expanding Ukraine’s ability to launch a coordinated offensive, teaching its military to effectively move and coordinate its company- and battalion-size units in battle, using combined artillery, armor and ground forces.

Ukrainian President Volodymyr Zelenskyy has continually pressed Western allies to hasten their military support. Speaking at a major international security conference in Munich on Friday, Zelenskyy said delays would play into Russia’s hand as the war approaches its first anniversary.

During a visit to the Grafenwoehr training base last month, U.S. Army Gen. Mark Milley, chairman of the Joint Chiefs of Staff, said the new skills will better prepare Ukrainian troops to counter any surge in Russian attacks.

“This is not a run of the mill rotation,” he said when meeting with U.S. commanders there. “This is one of those moments in time where if you want to make a difference, this is it.”

The training, which is being done by the 7th Army Training Command, includes classroom instruction, field work and larger combat exercises.