Units from U.S. Army Europe are joining some 18,000 personnel from 18 other countries for Exercise Saber Strike 18, the eighth iteration of the exercise, taking place across Poland, Lithuania, Latvia, and Estonia in order to increase readiness and enhance interoperability between NATO allies and partner forces.

The exercise began on June 3 and runs through June 15, and one of the U.S. units involved has already encountered a setback.

Around 11 a.m. on Thursday, four Stryker armored vehicles from 2nd Squadron, 2nd Cavalry Regiment collided with each other during a road march near Prienai, a city in Lithuania roughly 50 miles from the border with Poland.

“Fifteen U.S. Army soldiers were transported to local hospitals by host nation ground ambulances for evaluation of injuries. Ten of those injured were held for overnight observation,” Don Wrenn, a U.S. Army Europe spokesman, said in an email. Earlier reports indicated 13 soldiers were taken to hospitals.

“All of the soldiers have been returned to duty” on Friday, Wrenn said, adding that there were no civilian vehicles involved or injuries reported and that an investigation into the cause of the accident was underway.

The 2nd Cavalry Regiment's road march from its home station in Vilseck, Germany, through Poland, the Czech Republic, Lithuania, and Latvia is one of the main components of Saber Strike 18.

The march includes more than 1,000 Strykers traveling two routes — one heading through the Czech Republic, taking part in an engagement in Prague, and another heading through eastern Germany toward Poland. The two routes converged on Powidz in central Poland.

From Powidz, the vehicles headed east to the Poland-Lithuania border, which they are scheduled to cross between June 5 and June 9, with most of the unit taking part in exercises in Lithuania and smaller drills in Latvia between June 9 and June 15. The unit is to return to Germany between June 16 and June 23, taking the same routes.

Related: US Tanks Just Marched Down German Roads For The First Time In 15 Years »

Other key elements of Saber Strike include bridging and river-crossing drills to support freedom of movement. The exercise also aims to integrate NATO command elements at multiple levels to practice coordination and command and control.

Moving personnel and equipment around Europe has been a particular concern for NATO in recent years, as growing tensions with Russia after its annexation of Crimea and intervention in Ukraine in early 2014 have brought renewed focus to the alliance's ability to respond to a potential conflict.

NATO internal report concluded in late 2017 that the defense alliance's ability to rapidly deploy around Europe had “atrophied since the end of the Cold War.”

Such a deployment would also face a tangle of bureaucratic regulations and infrastructure issues that complicate movements across borders — in January 2018, a convoy of U.S. Army Paladin self-propelled howitzers was halted by German police because the contractors transporting them had violated road regulations.

U.S. Army/1st Lt. Ellen Brabo

Army photo

A Stryker Infantry Carrier Vehicle from the 4th Squadron, 2d Cavalry Regiment completes an uncontested wet-gap crossing near Chełmno, Poland, June 2, 2018.

The report recommended setting up two new commands — one to oversee logistics on the ground in Europe and another to manage the movement of personnel and supplies across the Atlantic.

NATO said earlier this year that the European logistics command will based in the city of Ulm in southern Germany, while the U.S. has volunteered to host the Atlantic command in Norfolk, Virginia.

The focus on moving around Europe on the ground was apparent in exercises conducted earlier this year.

In late May, the U.S. Army's 1st Armored Brigade Combat Team from the 1st Cavalry Division arrived in Europe for a nine-month rotation, but rather than sailing to Poland and heading to it home station, it disembarked in Antwerp, Belgium, in order to practice traveling by road, rail, and barge across the continent.

In April, as the 2nd Armored Brigade Combat Team from the 1st Infantry Division prepared to end its nine-month deployment, it carried out a road march with over 700 vehicles on public roads in southeast Germany — the first time the exercise had been done at the brigade level in 15 years.

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