Ukraine’s Operation Vivaldi foils Russia’s plan to encircle the Donbas, ISW analysis shows

In a new assessment, the Institute for the Study of War (ISW) concludes that Ukraine's Operation Vivaldi thwarted Russia's effort to encircle and occupy the Ukrainian-controlled Donetsk region in September. The operation, which targeted the "fortress belt" – a defensive and logistical network protecting Ukraine's portion of the Donbas – from Lyman in the north and Dobropillia in the southwest, was designed to link up near Barvinkove in the Kharkiv region.

Completing this encirclement would have brought Russia closer to its goal of occupying the entire Donetsk region. However, Ukrainian forces, including the 3rd Army Corps under Andrii Biletskyi, successfully dismantled the northern arm of the Russian pincer, liberating 176 square kilometres of territory. President Volodymyr Zelenskyy reported a range of 125 to 140 square kilometres, while ISW suggests the operation may have achieved even more than official reports indicate.

The defeat of the northern pincer forced Russia to abandon plans to advance on Sloviansk from the northeast and relinquish positions intended to threaten northern approaches to the fortress belt. This collapse also preserved key supply routes for Ukraine. While Russian forces retain limited gains around Kostyantynivka and east of Sloviansk, they have struggled to sustain their advance in these areas due to their reliance on infantry infiltration, drones, and bombardment, which do not provide the fast mechanized manoeuvres needed to break Ukraine's defenses.

Despite Russian claims that they occupied 1,301 square kilometres of Ukrainian territory in September – roughly two and a half times the figure reported in previous months – ISW argues that Russian units were pushed out of at least 80 square kilometres in September, resulting in a net retreat of 175.18 square kilometres. Ukrainian territory remains under Russian control for no more than 81% as per ISW's assessment.