In a bunker near Lyman, in eastern Ukraine, a Russian drone flickers across a live-stream screen and the commanders watching it react at once. One, a cigarette in one hand and a radio in the other, orders a Ukrainian drone to bring it down and warns the infantry below. The danger is real: the soldiers are crossing open ground on foot, on their way out after three months at the front. Their rotation marks the end of a phase of Operation Vivaldi, a Ukrainian counter-offensive named for its four stages, like the seasons in the Italian composer's violin concerto.

Kyiv says the operation has liberated 277 sq km (106 square miles) of the Donbas region. Its strategic value, officials argue, lies less in the territory than in what it prevented: a Russian pincer movement that threatened to encircle the cities of the Fortress Belt, which Ukraine still holds. The contrast with the rest of the war is stark. This month Russia has pounded Ukraine from the air, crippling energy infrastructure and killing scores of civilians.

At the front, however, the momentum has recently moved the other way. Ukraine claims 8,000 Russian casualties in Vivaldi alone and close to 50,000 along the whole front in September, with few losses of its own. These figures are unverified and should be treated cautiously. Still, the Institute for the Study of War reports that pro-Russian military bloggers have acknowledged the advances and fear further setbacks.