World War I was the chemist’s war because it was the first time chemicals were used as a large scale weapon in war. During this period, many countries involved in the war raced to implement poisons into warfare and invent new ways to defend against those poisons. Not only were chemicals used as poisons on the battlefield, but new compounds were being implemented as explosives and shell propellant. Trinitro toluene or TNT was used as explosives. Mustard gas and chlorine gas were used as lethal chemicals. Cordite was used as shell propellent and was ignited by explosive mercury fulminate. While World War I was the first time these chemicals saw the battlefield, they existed and were understood even before the start of the war. Only after the war’s commencement countries began using these preexisting chemicals.Countries defended against these chemicals by building facemasks. After the Germany released chlorine gas on thousands of Allied soldiers in 1915, the British began developing a gasmask. One called the British Smoke Hood was made of a flannel bag soaked in alkaline solution and had a cutout for eyes. Because the British could defend against chlorine, the Germans mixed chlorine with phosgene, another lethal chemical. To combat this change, the British evolved the gasmask. One designed by chemist Edward Harrison was designed to not only defend against chlorine gas, but phosgene and other poisons as well. This back and forth behavior lasted throughout the war. Then, the Germans used one of the most lethal gases used in the war: mustard gas.In 1917, the only country to have mustard gas was Germany and its use was giving them the upper hand in the war. It was so lethal because of its lingering effects. While chlorine and phosphene disappeared after a few minutes, mustard gas stuck to clothes, horses, equipment, and foliage for days at a time. The oily agent caused blindness and blistering of lungs when exposed. When the United States entered the war that same year, American chemists worked on their own version of mustard gas, called lewisite. Winford Lee Lewis and his branch of the newly formed Chemical Warfare Service were directed to develop their own lethal chemicals. Thus, lewisite was created.Lewisite is a vesicant and caused similar symptoms to mustard gas; it caused blisters on the skin and bleeding in the lungs. While the Germans used sulfur-based mustard gas, Americans used arsenic-based lewisite. Both are able to linger in the air for days at a time. Overall, mustard gas was much more fatal, as it caused 40% of all World War I deaths. Lewisite’s development extended far after the end of World War I and was used in World War II. Today, other countries such as North Korea, Iraq and possibly Libya, have manufactured lewisite for use in modern wars.Chemicals were first used on the battlefield during World War I and have evolved since. Today, unconventional threats are classified into three categories: nuclear, biological, and chemical. Unconventional weapons have become more popular because it takes away risk from soldiers that would traditionally use force or physical contact against their enemies. They are in all forms, solid, liquid and gas. They are administered in a variety of ways: bomb explosions, aircraft, and wind. The United Nations recognizes and allows the use of 70 different chemical weapons in chemical warfare.In recent times, terrorist organizations have used modern chemical weapons against their enemies. Since 2014, the Islamic State of Iraq and Syria have used chemical weapons at least 52 times. Those weapons include less modern developments, such as mustard gas and chlorine gas. In September 2016, U.S. troops were attacked by ISIS with mustard gas in Iraq. Luckily, no soldiers were victim to the attack. While mustard gas was banned by the Geneva conventions after World War I, terrorist groups continue to utilize this dangerous and terrible substance. In conclusion, the use of chemicals in World War I was revolutionary. It began a trend of using unconventional weapons in warfare. Some unconventional weapons are still used and allowed today in the form of nuclear, biological, and chemical. The effects of lethal weapons are terrible, and their use is discussed in ethics debates. As future wars revolutionize the battlefield, countries can only continue to adapt to these changes.