The Brest Arsenal is a collection of military buildings on the northeastern coast of France. Munitions for the war were made there. Keep in mind that when Germany was stopped in 1914, the area that they occupied was an industrialized area. This helped the Germans commandeer French manufacturing and helped the German war effort beyond its own capabilities.
I sometimes write that WW1 was a war that straddled eras. The below picture captures it. The automation we envision with manufacturing modern weapons was partly there but partly not yet arrived. The photo below shows individuals hammering shells back into shape to be reused.