In the 13 weeks since launching a long-anticipated counteroffensive along several axes in southern and eastern Ukraine, the Ukrainian army has lost just five of its 71 Leopard 2 tanks. Many more of the German-made tanks—at least 10—have suffered damage. But the Ukrainians are repairing the damaged tanks at depots in Poland and Germany and returning them to the front. The fundamental toughness of the 69-ton Leopard 2 means tanks might take damage, visit a repair depot, return to the fighting then again take damage and head out for repairs. So on and so forth. The Leopard 2 lends itself...