In 1915, World War One introduced a weapon that changed warfare forever. Chemical gas attacks were first used on a massive scale, starting at Ypres in Belgium. Clouds of chlorine and later mustard gas drifted silently across battlefields. Soldiers had no warning. Many inhaled chemicals that burned their lungs from the inside, leaving no visible wounds. Some survived the battlefield itself, but suffered permanent damage to their breathing, eyesight, and health for the rest of their lives. Gas war