Mustard gas has been used by Germany, Britain, France, Italy, Japan, Iraq, and ISIS across more than a century of warfare. Germany introduced it on the battlefield in July 1917, and it went on to cause more casualties than any other chemical weapon in World War I. Its use continued through multiple 20th-century conflicts and into the Syrian Civil War as recently as 2015.
Germany’s First Use in World War I
The German army first deployed mustard gas against British troops on the night of July 12-13, 1917, near Ypres, Belgium. Unlike earlier chemical weapons such as chlorine and phosgene, which were designed primarily to kill through suffocation, mustard gas was built to disable. It attacked the skin, eyes, and lungs, pulling soldiers out of the fight for weeks or months even when it didn’t kill them.
The weapon quickly proved devastating in scale. Among U.S. Army forces alone, 70,552 soldiers were reported as gas casualties during the war, roughly 31% of all battle injuries. When the type of gas was positively identified in American records, mustard gas accounted for nearly 75% of all cases, far exceeding phosgene (18.5%) and chlorine (5%). At least 27,711 U.S. troops were confirmed mustard gas casualties. Despite its enormous reach, mustard gas had a relatively low kill rate: of 13,691 American deaths from battle injuries treated during the war, 1,221 (about 9%) were attributed to all war gases combined.
After Germany introduced it, Britain and France developed their own mustard gas programs and used the weapon in the final stages of the war. By the Armistice, all major combatants on the Western Front had incorporated it into their arsenals.
Between the World Wars
Several nations used mustard gas in colonial and regional conflicts during the 1920s and 1930s. Spain deployed it against Rif rebels in Morocco in the 1920s. Italy used it extensively during its invasion of Ethiopia in 1935-1936, dropping mustard bombs from aircraft onto troops and civilians. Japan used chemical agents including mustard gas during its war in China throughout the late 1930s and into the 1940s.
During World War II, no major power used mustard gas on the battlefield, but every side stockpiled it. The consequences of those stockpiles became painfully clear in Bari, Italy, on December 2, 1943. German bombers attacked the harbor and hit the American cargo ship SS John Harvey, which was secretly carrying mustard bombs. The ship exploded, killing everyone on board instantly and releasing mustard agent into the air and water. More than 1,000 military and merchant marine personnel became casualties, with 628 confirmed mustard injuries and 69 deaths in the first two weeks. Civilian casualties in the surrounding area reached an estimated 1,000. Victims suffered burns, blisters, temporary blindness, swollen genitals, and respiratory damage, though most eventually recovered.
Iraq’s Extensive Use in the 1980s
The largest modern use of mustard gas came during the Iran-Iraq War (1980-1988). Iraq began limited chemical attacks early in the conflict, but by March 1985, it was using mustard gas and other agents extensively against Iranian soldiers on the southern and western fronts. Iran reported the attacks to international commissions as early as 1984, and in 1986, a United Nations observer team formally documented Iraq’s use of the agent.
Iraq didn’t limit its attacks to the battlefield. On July 27, 1987, Iraqi forces dropped four 250-kilogram bombs containing mustard gas on the Iranian city of Sardasht, injuring 4,500 civilians. In 1988, the last major chemical attack struck the city of Oshnaviyyeh, injuring 2,680 civilians. Tens of thousands of Iranian veterans continue to suffer long-term health effects from mustard gas exposure decades later, including chronic respiratory disease, eye damage, and skin conditions.
Iraq also used chemical weapons, including mustard gas, against its own Kurdish population, most notoriously in the 1988 Halabja massacre.
ISIS in the Syrian Civil War
The most recent confirmed use of mustard gas came from a non-state actor. The Organization for the Prohibition of Chemical Weapons (OPCW) concluded that ISIS deployed sulfur mustard using artillery during an attack on the town of Marea in northwestern Syria on September 1, 2015, wounding 11 people. The OPCW’s Investigation and Identification Team based its conclusion on the study of more than 20,000 files, 29 witness statements, and data from 30 environmental and biological samples.
An earlier incident in August 2015 in the Idlib governorate also likely involved sulfur mustard, sometimes combined with chlorine, based on the OPCW’s fact-finding mission. The broader Syrian conflict saw widespread chemical attacks using sarin and chlorine as well, with the Syrian Air Force held responsible for multiple chlorine attacks. But the confirmed mustard gas use was attributed specifically to ISIS.
How Mustard Gas Damages the Body
Understanding why so many nations and groups chose this weapon helps explain its persistent appeal. Mustard gas is a powerful alkylating agent, meaning it chemically bonds to and damages DNA, proteins, and fats inside cells. When it contacts skin, it reacts to form a highly reactive intermediate that attacks the genetic material in cells, creating crosslinks that prevent DNA from functioning properly.
The skin damage is particularly insidious because it’s delayed. Exposure typically produces no immediate pain, so victims often don’t realize they’ve been contaminated until hours later when blisters begin forming. The blistering happens because the agent specifically damages the deepest layer of skin cells, weakening the connections that anchor the outer skin to the tissue beneath it. The outer layer of skin essentially detaches, forming large, fluid-filled blisters. Eyes and lungs, which have similarly delicate tissue, are also highly vulnerable.
Current Legal Status
Mustard gas is classified as a Schedule 1 chemical under the Chemical Weapons Convention, the treaty’s most restrictive category, reserved for substances with few or no legitimate uses outside of weapons. The convention, which took effect in 1997, bans the development, production, stockpiling, and use of chemical weapons. As of now, 100% of the chemical weapons stockpiles declared by member states have been verifiably destroyed. The challenge that remains, as the Syrian conflict demonstrated, is enforcement against governments that hide their programs and non-state actors operating outside the treaty framework.