On a hilltop near the occupied southern Ukrainian town of Polohy, Russian forces set up an observation point that can spot Ukrainian soldiers more than 6 miles away. Four times, Ukrainian forces destroyed the Murom-M surveillance system, said Lt. Col. Oleksiy Telehin, of Ukraine’s 108th Territorial Defense brigade. Four times, the Russians promptly installed a new one. Ukraine successfully outmaneuvered Russia’s far larger invading forces last year, despite being outmanned, outgunned and vastly overpowered in the air. With a nimble approach, superior knowledge of the terrain and the efficient use of drones and digital technology, its units were able to...