Consider that a century ago technology had advanced to the point where artillery could kill people that couldn't be seen. With a map and a slide rule, traject

Consider that a century ago technology had advanced to the point where artillery could kill people that couldn't be seen. With a map and a slide rule, trajectories over the horizon could be calculated with disturbing lethality. Of course the psychological impact of such artillery was almost as devastating as the lethal impact. Knowing that at any moment you could be killed without warning by a shell you'd never see coming, by a man over the horizon induced a great deal of PTSD.