For my twelfth (and last?) contribution to ABC New England's Road to War series, I spoke about what was undoubtedly the most important battle to take place in late April 1915, the Second Battle of Ypres in Flanders. The reason why this was so important is because it opened with the first successful, large-scale poison gas attack in the history of warfare (the first unsuccessful attack had been at the Battle of Bolimov on the Eastern Front at the end of January). I looked how the particular gas used by the Germans, chlorine, worked in chemical, biological and military terms, the role played by Fritz Haber in developing it, the shattering effect it had on the French lines, and the unreadiness of the German army to do much to exploit its success. I also noted briefly the prewar laws against the use of poison gas and its subsequent career in the war and after, including in the present Syrian civil war.
Image source: Imperial War Museum.