A constant hum of activity filled the underground bunker in eastern Ukraine. Soldiers shouted at each other as they monitored banks of screens showing live video feeds from the battlefield one morning last month. “Guys, let’s fight the war first and go about our business later,” shouted the commander, Yuriy Horobets, calming the room. “Our FPV is arriving now,” he said, pointing to a tiny, pale object, a first-person view drone, moving across the screen of a recognition signal. The drone, a remotely piloted quadcopter, was on its way to attack. His brigade, the 66th Mechanized Brigade, had multiple drones in the sky that day to attack Russian positions as his troops prepared to assault a tree line. The assault was the end of a months-long operation that recaptured a considerable portion of eastern territory. That operation, called Vivaldi, thwarted Russian efforts this year to encircle the last towns in Donetsk province, the prize Moscow insists it wants to end the war. After months of operational silence, the Ukrainian brigades involved have begun to reveal details of how they managed to turn a lost defensive fight against Russian forces into a successful offensive along parts of the front line. They allowed a team of New York Times reporters to join them for two weeks and see their work firsthand. Ukrainian troops had been losing ground to the much larger Russian army for the better part of two years. But the broader use of drones and remotely controlled vehicles, and changes to the command structure and culture within parts of the military, allowed Ukraine to change course. General Andriy Biletsky, commanding general of the operation, claimed that the tactics were so successful that his troops had annihilated the Russian 144th Motorized Rifle Division in fighting and reversed Russia’s gains for an entire year. “What we are seeing now looks more like desperate attempts to establish a defensive line, an agony, rather than organized and systematic military operations,” he told reporters at a briefing in October. Along with several of his commanders, he had gathered members of the media in a clandestine meeting. bunker to announce the end of Operation Vivaldi, whose main push he said began in May, and to summarize its results. In October, for the second month in a row, Ukraine gained more territory than Russia, and Russian forces suffered the highest monthly casualties (more than 54,000 dead or seriously wounded) of the war, according to the Institute for the Study of War. Lyman and an equal amount of territory on the Zaporizhzhia front line in southern Ukraine. The 66th Brigade was essential to that success. Their challenges were typical of many Ukrainian military formations, such as fighting with old equipment and shortages of personnel and resources. Many of his infantrymen are between 40 and 50 years old, like Horobets, 45, a battalion commander. Last year, the brigade, vastly outnumbered by the Russian forces opposing them, was steadily losing ground, Horobets said. Their supply routes were under fire, preventing them from bringing in ammunition and evacuating the wounded. But it was in the midst of that maelstrom, fed up with being destroyed by Russian firepower, that some battalion commanders said they took matters into their own hands. They took critical Russian positions on high ground above a village from where Russian troops were directing attacks against them. Once they controlled the heights and destroyed Russian communications, they discovered they had an advantage. Russian soldiers in the village did not know what had happened and could not replace equipment because Ukrainian forces were shooting down Russian supply drones and preventing vehicles from passing on roads, several commanders involved in the operation said. “At that time, we had superiority over the enemy both in terms of attack drones and aerial reconnaissance,” said Nazar Kinash, 25, acting commander of a mechanized battalion. The Russians “had been effectively blinded,” he said. The 66th Brigade began infiltrating soldiers into the village and setting up ambushes, Horobets said. Within a month, they had taken the village, and six weeks later, they had taken another. “For now, it’s quiet,” Horobets said as he pointed to a bank of video screens in his underground command post. “A month ago there was a terrible war here because the enemy was trying to regain its positions and counterattack,” he said. “But for now, they are sold out.” The operation is the first sign of a new direction under General Biletsky, who assumed command of the Third Army Corps in the summer of 2025, bringing unity of command and coordination among six brigades along their part of the front line, several battalion commanders said. Attuned for the first time to the units around them, commanders of the 66th Brigade said they had solved the problem of Russian infiltration, sealing gaps between units where Russian soldiers had been slipping through to establish positions behind Ukrainian lines. Drone warfare has transformed the front line in Ukraine into a miles-wide death zone, where vehicles are so easily targeted that soldiers move mostly on foot in small groups. The Russian military has largely abandoned frontal armored assaults in favor of stealthy advancement through the insertion of infantry soldiers. For months, the 66th Brigade pursued and destroyed every Russian position it could find, including isolated soldiers hiding in hideouts behind Ukrainian lines, infantry in trenches and drone pilots in bunkers, Horobets said. “Overall, it comes down to coordination,” he said. It showed two areas of overgrown forest outlined in red on a video screen. Russian soldiers were still entrenched there and were their target for the afternoon, he said. “First we will destroy the antennas, then we will destroy the generators,” he said. “It will turn out that we will also destroy the pilots.” As the Ukrainians began to advance, the value of their medium-range drone strikes became clear. The Third Army Corps attacked up to 50 Russian vehicles a day, sometimes as deep as 100 miles behind Russian lines, General Biletsky said. “It became normal for the enemy to unload 40 to 50 kilometers from the front line and then continue on foot,” he said. Sometimes a soldier carried a single artillery shell 20 miles, he said. “Their logistics have been effectively paralyzed.” Russian soldiers were running out of fuel, ammunition and food. Some began posting cardboard signs outside their positions, saying they were hungry and thirsty, several commanders said. Most critically, when Russian reinforcements were called in, Ukrainian drones attacked them as they descended from the vehicles miles before they could reach the front line, Horobets said. The broader use of robots on the battlefield to overcome Russia’s numerical superiority has grown steadily. A 27-year-old former Ukrainian stormtrooper said that since last fall he had been put in charge of forming a special battalion of remotely controlled attack vehicles. He asked to be identified only by his call sign, Makar, for security reasons and in accordance with protocol. The Ukrainians cannot outnumber the Russians in terms of personnel, he said in an interview. “But we can surpass them technologically,” he said, “in terms of quality and scale, if we consistently stay several steps ahead of them.” At this point, ground robots are vital. At several underground command posts our team visited, Ukrainian soldiers watched live video of footprints and brush as vehicles moved through the kill zone carrying cargo. Sometimes they brought out corpses of dead soldiers. Many of the vehicles broke down or were attacked by Russian drones, and their cameras showed the remains of other vehicles. But many of them make it through. General Biletsky said his brigades were delivering three times as much cargo to his soldiers on the front line as other brigades that recently came under his command. “That means a Third Corps soldier has considerably more resources and capabilities available – food supplies, ammunition, equipment, power sources, batteries, etc. – compared to a soldier elsewhere,” he said. They were even getting excavators to help build underground bunkers, he said. Makar said he had focused on using remotely controlled vehicles as attack tools. Soldiers from his unit, NC13, part of the 3rd Assault Brigade, were at the forefront of Operation Vivaldi, piloting such attack vehicles on the battlefield. The Times met with a group of them, 20-year-olds with nine months of Army experience, during a live-fire training exercise, in which they steered remotely controlled buggies armed with rocket-propelled grenades and a Browning machine gun. Another team piloted a reconnaissance drone to provide a constant video feed. The next day, his trainer, who uses the call sign Bar, was at the controls, guiding a robot vehicle into a tree line in an actual attack. The machine, visible in a video feed from a surveillance drone, moved clumsily back and forth, tangled in brush as it approached the entrance to a bunker. Then suddenly, the screen was filled with a cloud of smoke.
