Ukraine's counteroffensive in the northern Donbas, codenamed Operation Vivaldi, has forced Russia onto the defensive along one of the most important axes of the war, with Kyiv claiming the surrender of more than 250 Russian soldiers in a single operation and independent analysts assessing that Moscow lost more ground in September than it gained.
The fighting, concentrated around Lyman in Donetsk region, matters because it threatens Russia's approach to Slovyansk and Kramatorsk — two cities that form part of Ukraine's so-called fortress belt and remain among the Kremlin's principal objectives in the east. After three months of small but steady Russian advances, the momentum in this sector has reversed.
Robots dropped behind the lines
What distinguishes Vivaldi from earlier Ukrainian counterattacks is how heavily it relies on unmanned systems. According to Andriy Biletskyi, commander of Ukraine's Third Army Corps, Ukrainian forces airdropped armed robotic systems more than 10 kilometres behind Russian lines during one assault — the first known time ground robots have been smuggled behind Russia's defensive positions in this way.
Controlled remotely from command centres inside Ukrainian-held territory, the ground drones then attacked Russian troops from an unexpected direction. Ukrainian forces have also converted old Soviet-era armoured personnel carriers into unmanned explosive vehicles, packed with explosives and driven into Russian fortifications — vehicles Kyiv's military has taken to calling "Trojan" carriers.
The results, Ukraine says, included mass surrenders. Video shared by the Third Army Corps this week showed long columns of Russian prisoners walking in single file through forest before being counted by their captors. Some prisoners said they had surrendered after running out of basic provisions. CNN said it could not independently verify the footage, but noted that prominent pro-Kremlin military bloggers have complained publicly about command failures and supply shortages in the sector.
September in numbers
The Institute for the Study of War (ISW) calculates that Russian forces seized about 175 square kilometres in September while losing roughly 256 square kilometres elsewhere — a net loss of around 81 square kilometres. ISW attributes nearly 150 square kilometres of recaptured territory to Vivaldi alone, and assesses that Russian forces have lost a net 293 square kilometres across the front since March.
President Volodymyr Zelensky has put the Vivaldi figures higher, saying 176 square kilometres have been recaptured and 5,000 Russian troops killed or wounded since the operation began. The Ukrainian General Staff separately reported that Russia suffered 46,230 casualties in September, its highest monthly total of 2026, while Western intelligence estimates put Russian losses at roughly 40,000 troops a month — around 340 casualties for every square kilometre gained.
Rybar, one of Russia's most prominent pro-war military bloggers, has warned that Russian troops will now have to reorganise their logistics and slow their advance on both Slovyansk and Kramatorsk. ISW has calculated that at the current pace, Russian forces would not complete the capture of the remaining Donbas until 2032, if they can manage it at all.
What it means for the fortress belt
None of this ends Russia's offensive capacity. Moscow continues to pummel Ukrainian cities from the air, exploiting Kyiv's shortage of air-defence interceptors, and President Vladimir Putin claimed at the Valdai forum this week that Ukrainian resistance could collapse within 18 to 24 months. Russian forces also retain the ability to regenerate manpower, with Putin expanding the army's authorised strength again this autumn.
But Vivaldi has demonstrated something Ukraine's partners had begun to doubt: that Ukrainian forces can still plan, conceal and execute a multi-month counteroffensive — one built around drone supremacy and robotic systems rather than massed armour — and take ground back from Russia in the process. For the soldiers holding the fortress belt, that buys the one commodity Ukraine needs most this winter: time.
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