The chemical first used at Ypres was chlorine gas, or phosgene. It was the brainchild of Fritz Haber, a German Jewish chemist who would became known as the “father of chemical warfare.” There's no more controversial or paradoxical figure in chemistry.
The German military launches the first large-scale use of chemical weapons in war at Ypres, Belgium. Nearly 170 metric tons of chlorine gas in 5,730 cylinders are buried along a four-mile stretch of the front. In the end more than 1,100 people were killed by the attack and 7,000 are injured.
In the years following World War I, Britain, France, and Spain used chemical weapons in various colonial struggles, despite mounting international criticism of chemical warfare. In 1925, the Geneva Protocol of 1925 banned the use of chemical weapons in war but did not outlaw their development or stockpiling. Most major powers built up substantial chemical weapons reserves. In the 1930s, Italy employed chemical weapons against Ethiopia, and Japan used them against China.
Poison gas was very deadly and effective, and it caused over 1 million casualties and about 100,000 deaths. It was effective because it was really hard to protect yourself from it, and it was usually used to surprise the enemy. The gas did not kill most enemies instantly, it usually took many days to kill you, so it was slow and painful.
Poison gas relied on weather, if it was windy or raining, the gas would not work. Sometimes if it was windy, the gas would blow back at the army who attacked, and it would kill there own troops. The US killed about 2000 of their troops from their own gas because of this
