By Ben Aris
September 20, 2026
Defense
The Armed Forces of Ukraine (AFU) have scored a major strategic victory with Operation Vivaldi and liberated hundreds of square kilometres in the Donbas, just as Russia’s forces looked poised to take the two remaining “Fortress Belt” cities that Russian President Vladimir Putin has demanded to end the war in Ukraine.
That goal suddenly looks beyond Russia’s reach – a stunning reversal from the outlook on a few weeks ago. Ukrainian gains north of the strategic city of Lyman have made Russia’s plan to encircle the Donbas fortress belt unfeasible, the Institute for the Study of War assessed on September 15.
Ukraine’s Third Army Corps commander, Brigadier General Andrii Biletskyi, disclosed the operation, codenamed Vivaldi, on the same day after weeks of what he called maximum information silence. The corps said it had cleared 75 square kilometres of Russian infiltration groups and retaken a further 10 sq km, along with the village of Serednie. Novoselivka, Oleksandrivka, Yarova and the outskirts of Korovii Yar were cleared in the same phase.
A second season followed on September 20. Biletskyi said the corps had taken another 40 sq km, liberating Shandryholove and Derylove and putting Drobysheve under full control, which brings the two phases to 125 sq km recovered, of which 50 sq km is ground formally de-occupied rather than cleared of infiltrators, Ukrinform reported.
He put Russian losses at about 800 men in the second season and more than 3,000 across both, figures that have not been independently verified. The corps’ deputy commander, Petro Horbatenko, had said the day before that further settlements were cleared and liberated whose names could not yet be disclosed for tactical reasons, nv.ua reported.
The salient was the northern half of one arm through Dobropillia from the south, another through Lyman and Sviatohirsk from the north, the two meeting at Barvinkove in Kharkiv oblast, far behind the four cities of the fortress belt – Sloviansk, Kramatorsk, Druzhkivka and Kostiantynivka.
Biletskyi argued that encirclement would be less costly for Russia than frontal assaults. Putin has reportedly ordered his army to seize the whole of Donetsk oblast by the end of 2026.
How much ground has actually changed hands is disputed. Open-source analyst Clement Molin put the area at more than 200 sq km; Konrad Muzyka of Rochan Consulting assessed that Russian forces had lost control of about 240 sq km; and milblogger AMK Mapping counted 151 sq km.
Most of the area Kyiv announced was cleared of infiltration groups rather than ground that had fully left Ukrainian hands, the Kyiv Independent reported. Its September 15 report said milblogger DeepState had recorded no changes in the area. The conflicting accounts require reconciliation. DeepState has since moved closer to the Ukrainian account, mapping Shandryholove and Derylove as de-occupied on September 20.
ISW’s September 16 assessment said the full extent of the Ukrainian advances and the shape of the front line in the area “remains unclear, due to limited open-source evidence.”
ISW went further in its September 19 assessment, saying Russia’s defence ministry had tried to deny Ukrainian successes in the Lyman direction “by presenting an inaccurate picture of the battlefield that denies the ample evidence provided by Russian milbloggers, Ukrainian sources, and geolocated footage.”
On ISW’s reading, Moscow’s account conflicts with reports from Russian military bloggers. Open-source trackers have contradicted Russian capture claims in the Donbas before.
Russia’s defence ministry said on September 18 that its Southern grouping had taken Viroliubivka and its Centre grouping Zolotyi Kolodiaz, both in Donetsk oblast, Interfax reported. Neither claim carries Ukrainian or independent confirmation. ISW’s assessed-control map for the key city of Pokrovsk, that was taken by Russia in December, was drawn the previous day and places Zolotyi Kolodiaz inside an area of the Ukrainian counterattack rather than under Russian control.
Sviatohirsk logistics
Russian forces seem to be getting ahead of themselves as their hold on the contested town slips. Putin said on public TV on September 1 that the town of Sviatohirsk had been captured but six days later the Ukrainian commander Biletskyi filmed himself on his phone standing in the town centre and told the Russians to “take off your clown noses”. He said his corps’ 60th Mechanised Brigade held the place. Zelenskiy has also made this gesture several times, travelling to contested towns to take selfies of himself in the centre of the town.
The counteroffensive has now pushed the nearest Russian-held ground more than 20 km from Sviatohirsk, according to AMK Mapping. The milblogger argues that this reduces the town’s exposure to barrel artillery and puts it more than twice as far from Russian positions as Sloviansk and Kramatorsk.
AMK Mapping says every ordinary bridge over the Siverskyi Donets at Lyman has been destroyed and that the town had been supplied only across pontoons or by drones. Sviatohirsk can now work as a rear logistics hub, with roads running in from Kharkiv oblast, providing considerable relief to the AFU troops, and easing the pressure on Sloviansk to the south and Borova to the north, making Lyman itself far easier to hold.
Drones ahead of the infantry
Ukrainian forces spent the run-up to Vivaldi hunting Russian drone operators, building the drone overmatch the advance then needed, ISW reports on September 19. The corps’ own account of
the method has strike drones, artillery and aviation coordinated against the units running Russian surveillance and reconnaissance and against their launch sites, until the Russians could no longer watch the ground in front of them, with electronic warfare and air defence covering the infantry as it moved up.
“During assault operations, UAVs and ground robotic systems always move ahead of the infantry,” said Biletskyi, who claimed the Third Army Corps was the first in the world to deliver ground robots to the front by air. The operation drew in the corps’ brigades, Ukraine’s Special Operations Forces, the border guard and the military intelligence unit Artan under a single tactical command, and ran for months under an information blackout before it was disclosed.
A soldier of Artan who fought at Lyman, using the callsign Derun, said the hardest part was prising Russians out of positions built well enough that the defenders saw every approach. “The hardest is to knock him out of there, because when a position is competently prepared, they see everything,” he said. An assault group has to cross open ground under observation and gets fought at a distance; the opening comes when the defenders stop watching. “When Russian troops are distracted, it can play into our hands: we can approach under cover, when he does not see us, and work him from close range,” he said, in an account Euromaidan Press carried on September 19.
Russian armour and drone support are moving to the Dobropillia direction for mechanised assaults this autumn, ISW reported on September 17, with roughly 1,200 drone crews from Russia’s Rubikon centre working the sector. Moscow has been fighting for Kostiantynivka since October 2025 and has taken none of the four cities.
Ukraine’s Third Army Corps says Vivaldi destroyed Rubikon’s logistics, stores and launch positions and forced the unit out of the Lyman-Borova sector, an account Ukrainska Pravda carried on September 18 that has not been independently corroborated.
Two seasons still to run
The Vivaldi operation has suddenly made the Russian capture of the rest of the Donbas significantly more difficult. For Biletskyi the pay-off is that Moscow is left without a cheap way in.
“Then they will have to storm the Sloviansk-Kramatorsk and the Druzhkivka-Kostiantynivka agglomerations head-on,” he said in a television interview reported by Euromaidan Press on September 17, “and storming these cities head-on is a far more painful and costly business for them than trying to envelop them and effectively take them without a fight.”
He said his troops were fighting for better defensive lines rather than for territory as such, and that Vivaldi has four seasons, of which two have now been disclosed.
Milblogger Russia Matters lists average monthly Russian gains over the past year equivalent to roughly 170-190 sq km, based on ISW and DeepState data. Its ISW monthly average does not reconcile with the annual total in the same table, and the disputed Lyman estimates do not support a single equivalent number of weeks. Ukraine also faces manpower constraints: it has to
draft at least 30,000 men a month simply to hold the army it already has, and its 2027 draft budget puts defence and security at 43.8% of GDP and faces an estimated $32.6bn external financing shortfall.