Answer
Fritz Haber proposed to use chlorine gas as a weapon during World War I. Chlorine gas was first used in combat on April 22, 1915, when German forces released 168 tons of chlorine gas at Ypres, Belgium. The attack killed over 1,000 French and Algerian soldiers and caused over 5,000 casualties. Chlorine gas is a highly toxic gas that can cause respiratory problems, blindness, and death.