So how did this substance, first deployed in war, make it from the trenches to the streets?

The process began before World War I ended. While troops were still returning home, active and retired military officers began lobbying to keep their chemical-weapons inventions. Fries, who led the Chemical Warfare Service through much of the 1920s, was determined to redeploy the technology for everyday uses like controlling crowds and criminals. He enlisted fellow military veterans, now working as lawyers and businessmen, to reach out to the press and help create a commercial market for the gases.

In the November 26, 1921 issue of the trade magazine Gas Age Record, technology writer Theo M. Knappen profiled Fries, who, he wrote, “has given much study to the question of the use of gas and smokes in dealing with mobs as well as with savages, and is firmly convinced that as soon as officers of the law and colonial administrators have familiarized themselves with gas as a means of maintaining order and power there will be such a diminution of violent social disorders and savage uprising as to amount to their disappearance.”

Knappen further explained to readers:

The tear gases appear to be admirably suited to the purpose of isolating the individual from the mob spirit … he is thrown into a condition in which he can think of nothing but relieving his own distress. Under such conditions an army disintegrates and a mob ceases to be; it becomes a blind stampede to get away from the source of torture.

The psychological impacts of tear gas gave police the ability to demoralize and disperse a crowd without firing live ammunition. Tear gas was also ephemeral and could evaporate from the scene without leaving traces of blood or bruises, making it appear better for police-public relations than crowd control through physical force. By the end of the 1920s, police departments in New York, Philadelphia, Cleveland, San Francisco, and Chicago were all purchasing tear-gas supplies. Meanwhile, sales abroad included colonial territories in India, Panama, and Hawaii.

With this new demand for tear gas came new supply. Improved tear-gas cartridges replaced early explosive models that would often harm the police deploying them. Early innovators designed improved mechanisms for delivering tear gas, including pistols, grenades, candles, pens, and even billy clubs that doubled as toxic shooters. Tear gas soon became a weapon of choice for prison wardens, strike breakers, and even bankers. Tear gas-filled contraptions were fitted into vaults to stop robberies, and fastened onto the ceilings of prison mess halls to deter riots.

On July 29, 1932, in what Edgewood Arsenal, the U.S. military’s chemical research site, referred to in a memo as “a practical field test,” National Guard troops stormed the Washington, D.C. camps occupied by the “Bonus Army,” a group of veterans lobbying to receive their overdue wartime payments. During the forcible eviction that ensued, the troops fired tear gas into the encampment, engulfing it in smoke and fire. Two men were killed in the violence, and an infant child was said to have died of asphyxiation from inhaling tear gas. Though official reports of the incident claimed the baby died of natural causes, the Bonus Army only saw that denial as part of a government cover-up. The group’s ballad “No Undue Violence” mockingly testified:

“We used no undue violence”—

So, Baby Myers, be still!

Though it isn’t quite plain

To your little brain,

You were gassed with the best of will!

For the Bonus Army, tear gas became known as the “Hoover ration,” a further sign of growing economic disparity in America. But for police chiefs, business owners, and imperial consulates around the world, the eviction of the Bonus Army was a sign of the rapid damage and demoralization that tear gas could bring about.