Line drawing of a horse with a gas mask on.


By Susan Speaker ~

Cover page of "Defensive Measures Against Gas Attacks"
Cover of Defensive Measures Against Gas Attacks, 1917

World War I is notable for the size of the armies involved, the huge number of casualties, and the vast amount of national resources consumed. Unlike previous conflicts, it was carried out largely in trenches, and introduced motorized ground transport and aircraft to military operations; it also employed scientific medicine that controlled infectious diseases so that, for the first time, more soldiers died in combat than from camp illnesses. But one of the more remarkable aspects of the Great War was the large-scale application of science to military operations, both offensive and defensive, particularly to produce poison gases. Germany, then the world leader in scientific research and in chemical production, pioneered the development of chemical warfare.

On April 22, 1915, and again two days later, at Ypres, German forces introduced Allied troops to a terrible new weapon: chlorine gas, released from pressurized canisters into a wind that carried it into the Allied trenches and beyond. Caught entirely by surprise, and with no protection from the asphyxiating gas, some 5,000 died, and over 10,000 were injured. The Allies quickly determined that the gas was chlorine and began developing gas masks to protect against it. For the duration of the war the combatants would engage in a chemical arms race. Both sides recruited hundreds of chemists, engineers, and physiologists to serve in special military gas warfare services. These experts worked intensively to discover new toxic gases and delivery systems, and to develop defensive equipment, procedures, and medical treatments.

“The extensive use of poisonous gases was one of the most important developments of the World War; no innovation since the introduction of gunpowder has revolutionized warfare to such an extent.”

The Medical Department of the U. S. Army in the World War, Vol. XIV, Medical Aspects of Gas Warfare,1926, p. 25.

By September 1915, the British were able to launch their first chlorine gas attack against German forces. A more potent gas, phosgene, made its debut in December 1915, and for the next 18 months, chlorine and phosgene, together with several different tear gases, were used extensively. “Cloud” attacks, in which the gas was released from canisters, were superseded by artillery shells loaded with gas, starting in 1916. With the shells, armies could target attacks with little regard for the weather, and use a wider range of toxic chemicals.

“King of the battle gases”

The chemical weapons race was at a stalemate by spring of 1917, because improved gas mask technology kept troops safe from the asphyxiating chlorine and phosgene gases; casualties occurred only when they were caught off guard and exposed before they got masks on. German researchers broke the impasse that year with something new and different: dichloroethylsulfide, also called “mustard gas” (for its odor), “Yperite” (for the first place it was used), or “Yellow Cross” (for the marking on the shells.) It wasn’t actually a gas, but a volatilized oily liquid that could penetrate clothing and leather, and persist on buildings, equipment, and the ground for days. And within a few hours, it would produce incapacitating burns on any skin surface it touched, particularly the eyes and respiratory tract. The German army used mustard gas for the first time in July 1917, shelling Allied forces in the Ypres area repeatedly from July 12th to August 1st. As with the first chlorine gas attacks in 1915, the Allies were caught by surprise. The mustard gas (unlike chlorine) had no immediate irritating effect except to cause sneezing. Several hours later, however, many of the troops had developed painful blistering, including such severe eye inflammation that they were virtually blind and had to be led around by their comrades. (Lines of temporarily blinded soldiers outside the medical stations would become a common sight, captured in photographs and in John Singer Sargent’s well-known painting Gassed, 1919.) During those first weeks, over 14,000 cases of gas poisoning arrived at the British casualty clearing stations, and about 500 of them died.

Gas masks could protect the eyes and lungs from mustard gas, but everyone exposed to it had to get out of contaminated clothing, which had to be isolated and washed, and, then, ideally, wash with hot water, as well.

Floorplan for a large tent for groups of soldiers to use to move through a washing and cleaning process.
De-gassing Station in The medical department of the United States Army in the world war (Volume 14), 1926
An illustration of an extensive raw and damaged area of skin on a man's neck.
Mustard Gas Burn (Contact) of Neck in The medical department of the United States Army in the world war (Volume 14), 1926

Mustard gas exposure was a challenge for medical officers at several levels. Because “mustard” could remain active for days, medical staff had to get the clothing off wounded soldiers quickly without getting the stuff on themselves. Mustard gas burns took much longer to heal than ordinary chemical or physical burns, prolonging the soldiers’ time on sick leave, and increasing the chances of wound infection.

And mustard gas didn’t just dissipate with the wind, either—it settled on the ground, coated tents and equipment and structures. If weather was warmer, it would evaporate and the vapors would still be toxic. In cooler weather, it would persist on the ground for weeks. Troops had to decontaminate everything, usually using chloride of lime or other neutralizing agents. And it was hard to see, and difficult to smell (the mustardy odor is faint) so there was a real danger of soldiers tracking it around and exposing others to it. [See instructions for clearing mustard gas in “Defensive measures against gas attacks” in the gallery above] Thus, although mustard gas didn’t penetrate gas masks to any degree, it was an incredibly effective means of hampering enemy operations. It could inflict substantial long-term casualties, and complicated medical officers’ triage work. And it required many hours of clean-up and decontamination, along with extra supplies, including uniforms.

Several dozen chemical agents were developed as weapons between 1914 and 1918. Some, like chlorine and phosgene, were asphyxiants, which caused massive edema in the lungs and obstructed breathing. Many others were “lachrymators” (tear gas) or caused sneezing or vomiting. Vesicants such as mustard gas (and lewisite, developed by the U. S. late in the war) inflicted blistering burns. Chlorine, phosgene, and mustard were used most extensively, and sometimes mixed together for added effect. Over the course of the war, chemical weapons accounted for about 1,300,000 casualties, including 91,000 deaths. This was only about 5% of the war’s total casualties.

Chemical weapons were developed and used in the Great War despite several international agreements (in 1899 and 1907) that poisons would not be used in war. The Geneva Protocol, prohibiting the use of both chemical and biological weapons, was signed in 1925 and took effect in 1928. Nevertheless, most countries continued to develop, manufacture, and stockpile chemical weapons; expecting that some nation would fail to honor the agreement, they wanted to be prepared.

Through 2018, Circulating Now will periodically publish posts featuring NLM collections that illuminate the medical history of The Great War, which lasted from August 1914 to November 1918.

Susan Speaker, PhD, is Historian for the Digital Manuscripts Program of the History of Medicine Division at the National Library of Medicine.


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