This chapter documents the ways in which an aggressively modern war took shape in language in World War One, yielding, in Clark’s notebooks, a real-time engagement with the fleeting diction of vernacular geography at the front, the weapons of industrial warfare, and the diverse taxonomies of mud or sound. It explores the emergence of trench warfare, and its own distinctive patterns of use (and variability), alongside the reconceptualization of fundamental terms such as battle and battlefield. Here, too, is a shifting language of attack and resistance and of ‘them’ and ‘us’, in which air warfare, or amphibious warfare, or gas warfare, or the brief efflorescence of Turpiite, offer striking lexical fertility alongside their new capacities for destruction.