This collaborative work investigates the unfolding catastrophe that the unleashing of chlorine against the Allied positions meant for individual soldiers and civilians. It describes the hesitation on the German side about the effectiveness, and hence impact on combat operations of the weapon whilst reflecting on the lack of Allied response to the many intelligence pointers that something significant was afoot.It goes on to describe the massive transformation that societies were undergoing as a consequence of industrialisation, science and technology, and the impact these trends were to have on the emergence of what we know today as 'total war'. Chemical warfare pitted the brightest minds from the various belligerents against each other and in some ways this competition revealed early thinking about intellectual superiority that was to define the decades after the Armistice. The ability to survive in a chemically contaminated environment was proof of a higher level of achievement. In simple terms, chemical defence equalled survival of the fittest.