You speak of "Plunging fire" and now it's called "Indirect fire". Now means simply a target being engaged when you can't see it by direct line of sight because of obscuration by smoke, fog or slight rise in ground. The days of raining ammunition down into trenches was over when static warfare ended. It wasn't as lost as it was outdated. The theories of plunging fire were still in the machine gun book before the C6 (MAG 58) came into CDN service.