During WWI, poison gas was used as a type of chemical warfare to attack large armies. The gas was delivered either by using the wind to carry the poisonous gas to the enemy's front line or by placing the gas into artillery and aerial bombs and firing them at the enemy's front lines.
The Germans first successfully used lethal poison gas during WWI in 1915, when German soldiers fired ammunition shells filled with xylyl bromide at Russian troops at Bolimov. Due to the cold temperatures, most of the gas froze before hitting the Russian troops. Despite this, Russians reported the loss of more than 1,000 men as a result of this new weapon. The Germans also attempted to use tear gas on French soldiers nearly a year earlier, but the attempt was unsuccessful.
Despite the fact that the Germans were the first to use lethal gas during WWI, it was the French army that started chemical warfare. The first account of chemical warfare happened in 1912, nearly three years before the Germans' first successful attempt, when the French used tear gas on the battlefield. However, this tear gas was more of an irritant than anything deadly. After witnessing this type of warfare, the Germans started the development of their own chemical weapons.