On the screen of a thermal imaging camera, the Russian armored personnel carrier disappeared in a silent puff of smoke. “What a beautiful explosion,” said First Lt. Serhiy, a Ukrainian drone pilot who watched as his weapon buzzed into a Russian-controlled village and picked off the armored vehicle, a blast that was audible seconds later at his position about four miles away. “We used to cheer, we used to shout, ‘Hurray!’ but we’re used to it now,” he said. The war in Ukraine has been fought primarily through the air, with artillery, rockets, missiles and drones. And for months, Russia...