“The Charged Vapor”

How tear gas went from a World War I weapon to police’s favorite anti-protester tool.

Police watch as tear gas is deployed during demonstrations in the aftermath of George Floyd’s death.
Tear gas, seen above in Santa Monica, California, has been a common sight during protests against George Floyd’s killing. Mario Tama/Getty Images

Over the past week, police across the country have responded violently to protests against the killing of George Floyd at the hands of Minneapolis police—with rubber bullets, with batons, and, in city after city, with tear gas. On Saturday, a college student lost his right eye after police allegedly shot a tear gas canister at his face during a protest in Fort Wayne, Indiana. At the same demonstration, a 3-year-old was also reportedly hit with a cloud of tear gas after getting caught in the crossfire. On Sunday, Massachusetts General Hospital had to set up a hazmat tent in Boston in order to treat tear gas victims, as did volunteers in Minneapolis. Tear gas, a class of substances that sting the mucus membranes of the eyes and irritate the upper respiratory tract, emerged largely as a wartime weapon a century ago. How did it find its way to police departments?

Tear gas made its debut in trench warfare during World War I as the first chemical agent to be used in the war, according to an article tracing its transition from a military to domestic technology in the journal Technology and Culture. There are some documented cases of the Paris police deploying gas cartridges on a small scale to root out barricaded criminals in the early 1910s, but the French army began using tear gas grenades on a much wider scale on the front lines in 1914. Tear gas was more effective at debilitating people in lower concentrations than toxic ones and forced opposing armies to wear heavy-duty masks, which caused discomfort and made soldiers much less efficient over an extended period of use.

The U.S. had been conducting research on tear gas throughout the war and eventually developed a powerful new agent using chloroacetophenone—but because this was right before the Armistice that ended the war, the weapon didn’t see much use on the battlefield. As a result, the U.S. Chemical Warfare Service, which was created during World War I to research gas munitions, still held a limited supply of the gas as the armed forces returned home. Over the next few years, the CWS received numerous requests for the weapon from police departments in cities like New York and Boston that were responding to a rash of civil unrest—from 1919 to 1921, there were 29 major strikes and riots that led to intervention from federal troops. Veterans of the war who became police officers were familiar with the gas and encouraged departments to seek it out. One such request, from the Department of Public Safety in Norfolk, Virginia, specifically mentioned that the gas grenades would be effective in subduing black people.

The CWS was eager to distribute tear gas to police, according to Technology and Culture. The agency was trying to convince Congress that it still deserved funding, and helping to put down domestic protests would prove that it could serve a purpose in peacetime. It also hoped that it could combat the public fear and abhorrence of chemical warfare that WWI had engendered by presenting tear gas as a more humane alternative to bullets and clubs in restraining mobs. (Tear gas can in fact be lethal, especially to children.) The CWS even started holding public tests for police departments in which hundreds of officers were asked to try to catch men armed with gas grenades. An article in the New York Times from 1921 described the scene at a demonstration in Philadelphia: “Police Supt. Mills took a battalion of his huskiest men into a roped-off enclosure with instructions to capture six men who were armed with 150 tear gas bombs. Three times they charged, but each time were driven back, weeping violently as they came within range of the charged vapor.”

The U.S. War Department, however, was moving to disband the CWS and initially placed a federal ban on the use and distribution of tear gas in domestic settings shortly after the war in 1919. Because the CWS was the only producer of tear gas at the time, this essentially prevented police departments from getting their hands on it. Yet, this ban only applied to the federal entities; local police could still use it and private industries were still allowed to sell it. In the 1920s, former CWS officers began establishing companies to manufacture tear gas. The CWS, which was still allowed to distribute the agent for research purposes, sent small samples to these companies to help with development. By 1923, more than 600 cities possessed tear gas. Prison wardens, strike breakers, and banks also purchased their own stocks. Use on civilians became widespread.

In the ensuing decades, tear gas would play a central role in quashing protests related to overdue wartime payments from World War I in the 1930s, the Vietnam War in the 1960s, the World Trade Organization in the 1990s, and Occupy Wall Street in the 2010s. Though several international treaties have prohibited use of tear gas in war, governments around the world still regularly use it on their own people.