The U.S. Army is currently participating in the large-scale military exercise Saber Striker throughout the Baltic nations and Poland. The annual exercise, which aims to increase international interoperability throughout the region in an effort to deter Russian aggression, has 18 national participants and sees U.S. troops working alongside some 18,000 troops from various other nations.

These types of exercises are often led by the United States, but an embarrassing setback in the early days of the exercise resulted in 15 American soldiers being sent to a Lithuanian hospital after their four M1126 Stryker Combat Vehicles collided near the city of Prienai.

The soldiers and vehicles all hailed from the 2nd Squadron, 2nd Cavalry Regiment — none of the soldiers suffered serious injuries and have since been returned to full duty.

“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, told reporters.

The incident took place at approximately 11:00 A.M. local time and according to Wrenn’s statements, involved no civilian vehicles and resulted in no appreciable damage to private property. An investigation has been launched into the cause of the crash, and thus far, U.S. officials are declining to comment on what may have caused the incident.

More than a thousand Strykers are taking part in Sabre Strike 18 overall, split between two routes that take a sizeable portion to a mock engagement in Prague and the other through Germany toward Poland. The two elements will then meet in central Poland as the training exercises progress.

Although all the soldiers involved in the collision were returned to full duty, the incident itself comes amid increasing calls from U.S. military leaders to improve upon the European defensive forces response to a Russian incursion into the Baltic region. Although NATO forces outnumber Russian troops in total, it has become increasingly apparent since the Russian military annexation of Crimea in 2014 that NATO forces could not counter a full scale Russian incursion into the region, particularly in the narrow stretch of land between Poland and Lithuania known as the Suwalki Gap.

This narrow stretch of land measures only about 60 miles between Russian ally Belarus and the Russian enclave of Kaliningrad and divides Poland from Lithuania. If Russia were to capture this small area, it would effectively cut the Baltics off from their NATO allies, meaning getting reinforcements or supplies into the besieged nations extremely difficult.