Historians of World War I have often dismissed the important role of poison gas in the battles of the Western Front. In this text, the author aims to demonstrate that the serious threat of gas did not disappear with the introduction of gas masks. By 1918, gas shells were used by all armies to deluge the battlefield and those not instructed in a sound anti-gas doctrine left themselves exposed to this new chemical plague. Using primary sources such as letters, diaries and the official archival record, Cook aims to illustrate the horror of gas warfare for the average trench soldier. In response to this threat, the Canadian Corps developed an anti-gas doctrine, a process which Cook describes in full. In all, the book poses a challenging re-examination of the function of gas warfare in World War I, including its important role in delivering victory in the campaigns of 1918 and its curious post-war legacy.