This weekend, an apparent Ukrainian rocket barrage reportedly blew up a rail bridge Russian workers were building south of Hranitne, 25 miles north of the Sea of Azov coast and 50 miles south of the front line in occupied southeastern Ukraine. It’s one of the biggest under-reported events in months in a grinding war where logistics are everything. In reportedly dropping the incomplete span over the Kalmius River, Ukraine sets back—indeed, makes a mockery of—Russia’s efforts to improve its supply lines to its beleaguered forces in and around Crimea in southern Ukraine. “The Ukrainians just shot a hole in a...