A chemical weapon is generally defined as a toxic chemical contained in a delivery system, likely a shell or a bomb. In World War !, chemical weapons were used, first by the Germans, and subsequently by other countries, in as an effective method to attack defending soldier who were fighting from trenchers. In trench warfare, direct attack was often fraught with difficulties, and incurred many casualties. Chemical warfare, initially, proved to be an effective way of attacking defending soldiers without direct contact, or, in turn, direct risk. A cloud of gas could be launched towards a line of soldiers sheltering in a trench without danger for the attackers. Although, defenses against chemical weapons quickly developed, initially chemical weapons were highly dangerous.