Poison gas was probably the most feared of all weapons in World War One. Poison gas was indiscriminate and could be used on the trenches even when no attack was going on. Whereas the machine gun killed more soldiers overall during the war, death was frequently instant or not drawn out
A poison gas attack meant soldiers having to put on crude gas masks and if these were unsuccessful, an attack could leave a victim in agony for days and weeks before he finally succumbed to his injuries.
It is assumed that gas was first used by the Germans in World War One. This is not accurate. The first recorded gas attack was by the French. In August 1914, the French used tear gas grenades containing xylyl bromide on the Germans. This was more an irritant rather than a gas that would kill.
Poison gas (chlorine) was used for the first time at the Second Battle of Ypres in April 1915. Armies quickly produced gas masks that gave protection as long as sufficient warning was given of a gas attack. Soldiers also used make-shift gas masks if they were caught in the open without a gas mask during a gas attack - cloth soaked in their own urine and placed over the mouth was said to give protection against a chlorine attack
The international community banned the use of chemical and biological weapons after World War I and reinforced the ban in 1972 and 1993 by prohibiting the development, production, stockpiling and transfer of these weapons.