Something struck a group of Russian troops in Lgov, a town of 21,000 in western Russia’s Kursk Oblast, late Sunday or early Monday. “It’s terrible,” a bystander cried. “The guys are all in the bunker,” they added as the bunker burned. A Ukrainian official insinuated the fire was the result of a Ukrainian raid, which would make sense. Lgov lies just 30 miles north of the town of Sudzha, the anchor of the 250-square-mile salient that Ukrainian forces carved out of Kursk back in August. It’s a key road and rail node for troops and supplies supporting the two-month-old Russian...