It was the dead of night, and the Ukrainian infantryman was writhing in a tree line from serious injuries to his legs, shoulder and lung.

His unit had told him by radio that they could not send anyone to evacuate him. The road to their base in the nearby city of Kostiantynivka had become a kill zone. “There were too many drones flying around,” recalled the infantryman, Oleh Chausov, as he described the experience.

Instead, he was told, the brigade would try to get him out with a small, robot-like tracked vehicle remotely operated from miles away and less visible to Russian drones than an armored carrier.

When the vehicle arrived, Mr. Chausov dragged himself aboard, his wounded legs dangling. But within 20 minutes, the vehicle hit a mine and blew up, he said. Miraculously, Mr. Chausov survived, crawled out and took shelter in a nearby trench.

He was back to square one, still trapped on the battlefield.