The billions of dollars in military aid the United States has sent Ukraine includes some of the most advanced and lethal weapons systems in the world. But Ukraine has also scored big successes in the war by employing the weapons and equipment in unexpected ways, and jury-rigging some on the fly, according to military experts. From the sinking of the Moskva, Russia’s Black Sea flagship, in April to the attack on a Russian air base in Crimea this month, Ukrainian troops have used American and other weapons in ways few expected, the experts and Defense Department officials say. By mounting...