And, in all but one case it looks as if the 'fire missions', in modern parlance, were i direct fire - harassment and interdiction, on enemy areas, so some chance that no one actually died as a direct result of all that ammunition expended. I read an account recently of one incident in which three MGs were kept firing continuously for 18 hours in a long range, indirect fire, role against a piece of ground hundreds of yards away behind German lines . The expenditure of rounds was in the tens or even hundreds of thousands of rounds - I've forgotten the exact number but it was staggering.
In fact, supply trains and columns supplied ammunition, fodder for the horses and food in that order, I believe. Hospital trains full of wounded were sixth or seventh on the priority list and often spent days on sidings waiting for clear lines. A sign of someone's priorities.