i know that the vickers MG was used for indirect fire.
meaning it sits somewhere in a trench and fires on ranges it cant see but with bullet drop/forward spotters etc they could hit inside trenches etc
now imagine 500k russians with nagats all firing indirectly at some target 3000m away.
volley fire
(i dont think this is true but somewheat reminds me of that russian bomber with the 80 something downward facing ppsh smgs for starving runs.)
anyways most weapons have sight markings for ranges far beyond effective firing range, not sure why though.