French troops don their gas masks while manning a trench, 1915 (c)

Photograph, World War One, Western Front, 1915 (c).

The Germans first used gas against the French during the capture of Neuve Chapelle in October 1914 when they fired shells containing a chemical irritant that caused violent fits of sneezing. In March 1915 they used a form of tear gas against the French at Nieuport. These early experiments were but a small taste of things to come and as the war progressed all sides developed ever more lethal gases including chlorine, phosgene and mustard gas.