Tens of thousands of drones have been employed across Ukraine to kill the enemy, spy on its formations and guide bombs to their targets. But this month the Ukrainian military began a program to use drones in a more unusual role: to guide Russian soldiers who want to surrender. The program had its genesis in late November, when the Ukrainian military released footage of a Russian soldier throwing his weapon to the ground, raising his hands and nervously following a path set out by a drone overhead, leading him to soldiers from the Ukrainian army’s 54th Mechanized Brigade. A few...