Canadians in a reserve position attach detonators to Mills bombs. The sign advertises that small-arms ammunition and bombs are available at the "store." Infantry companies would usually receive an allotment of grenades when they moved into the front-line trenches. Grenades were robust weapons that could withstand considerable jostling, but there were many cases of grenade pins working themselves loose and detonating grenades in the trenches.
George Metcalf Archival Collection