Despite the changes in warfare, Russian forces retain the ascendancy and are making slow but steady advances in the east and north of Ukraine. Russia has also caught up in UAV technology after falling behind early in the war, according to military analysts, and like its enemy is churning out drones domestically at a rate of millions a year.

Drone attacks for a third day on oilfields in Iraq's semi-autonomous Kurdistan region have slashed crude output by 140,000 to 150,000 barrels per day, two energy officials said on Wednesday, as infrastructure damage forced multiple shutdowns.