Chemical warfare

• 1. Introduction

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  Chemical warfare carries a moral objection nearly as old as it is. In the 2nd century BC, Roman legions poisoned the water wells of besieged cities in Anatolia. Centuries before that campaign, Roman jurists had already condemned the tactic, declaring armis bella non venenis geri: war is fought with weapons, not with poisons. That contradiction, a rule stated and then broken by the very people who stated it, runs through every era this documentary covers. Why would nations sign treaty after treaty banning poison gas and then use it anyway? What made a drifting, colorless cloud so much more frightening to soldiers than an artillery shell ever was? And how do the chemicals banned today differ from the ordinary industrial compounds sitting in a factory next door? Those questions carry through the trench gas clouds of the First World War, the nerve agents Nazi Germany stockpiled but never fired, and the grenades dropped from drones over Ukraine today.

• 2. Defining The Weapon

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  Botulinum toxin, ricin and saxitoxin are not living organisms, yet the Chemical Weapons Convention treats them as chemical weapons rather than biological ones, because they are nonliving toxic products that a living organism happens to produce. Anthrax works the opposite way: an offensive attack using a living organism like that counts as biological warfare, not chemical. The convention settles most edge cases with what it calls the General Purpose Criterion. Under that rule, any toxic chemical counts as a weapon unless it serves a purpose that isn't prohibited, such as research, medicine, pharmaceuticals or protection.

  About 70 different chemicals were used or stockpiled as chemical warfare agents during the 20th century, and the convention has scheduled the entire class for elimination. Schedule 1 covers substances with almost no legitimate use outside research or protective testing, including nerve agents, ricin, lewisite and mustard gas. Any country producing more than 100 grams of a Schedule 1 chemical must report it to the Organisation for the Prohibition of Chemical Weapons, and stockpiles of these are capped at one tonne. Schedule 2 chemicals have narrower legitimate uses. Dimethyl methylphosphonate, a precursor to sarin, doubles as a flame retardant, and thiodiglycol, used to manufacture mustard gas, is also a common solvent in inks. Schedule 3 covers chemicals with real industrial value, like phosgene and chloropicrin. Phosgene is a precursor in plastics manufacturing, and chloropicrin serves as a fumigant, so the OPCW only inspects plants that produce more than 30 tons of either per year.

  Category 1 weapons are built from Schedule 1 substances, Category 2 from other scheduled substances, and Category 3 covers delivery devices and equipment with no chemical payload of their own. Herbicides, incendiaries such as napalm, and living organisms used as weapons all sit outside this entire framework, governed instead by separate rules that treat them as herbicidal, conventional or biological warfare. That legal boundary took its modern shape only once armies started using chemicals at scale, in the trenches of 1914.

• 3. Birth Of Modern Gas Warfare

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  Chlorine gas rarely killed on its own, and it was not until the 19th century that scientists and governments began seriously proposing asphyxiating or poisonous gases as tools of war. Treaty after treaty tried to ban the idea before World War I made it real anyway. Germany was the first side to use chemical warfare on the battlefield, simply opening canisters of chlorine upwind of the opposing trenches and letting the prevailing wind carry the gas across. The French answered by modifying artillery shells to carry phosgene, a method far more effective than an open canister.

  A French 26 mm cartouche suffocante rifle grenade, loaded with 35 grams of the tear-producing chemical ethyl bromoacetate, was fired from a flare carbine in autumn 1914, the very first chemical shell of the war, though it had little effect on the Germans. That same autumn, German gunners packed 10.5 cm shrapnel shells with an irritant called dianisidine chlorosulfonate and fired them at the British near Neuve Chapelle in October 1914; the attack went unnoticed by the men on the receiving end. A chemist named Hans Tappen, working in the Heavy Artillery Department of the War Ministry, then proposed the tear gases benzyl bromide and xylyl bromide to his brother, who ran the Operations Branch at German General Headquarters. Shells built to Tappen's design, nicknamed T-shells, were tested at the Wahn artillery range near Cologne on the 9th of January 1915. A shortage of them limited the first real use to an attack on Russian troops at the Battle of Bolimów on the 31st of January 1915, and cold weather kept the liquid from vaporizing properly; once again, the attack went unnoticed.

  The first attack that actually worked came at the Second Battle of Ypres, where German troops opened cylinders of chlorine and let the wind carry the gas into enemy lines. The method was simple but dangerous to run. Heavy cylinders had to be hauled to the front and stored there, exposed to enemy artillery. The whole attack also depended on the wind blowing the right way, and at the Battle of Loos, a shift in the wind blew the gas back onto the German attackers instead. A creeping cloud of gas was visible from far away, giving defenders time to prepare even as the sight of it unnerved them, so the drifting cloud did double duty as both a physical and psychological weapon.

  French engineers solved the wind problem by putting phosgene into a non-explosive artillery shell instead of a cylinder. Because the shells traveled independent of wind, any target within artillery range became vulnerable. Clear, nearly odorless phosgene shells also landed with a soft plop rather than an explosion. Soldiers often mistook them for duds, and only realized the danger once the gas had already begun to work. The British solved the opposite problem, getting enough gas onto a target at once, with the Livens Projector, a large-bore mortar dug into the ground that fired a 14 kilogram gas cylinder up to 1,500 meters. Historians estimate 500,000-1.3 million casualties from chemical agents during the war, of which 2-4 percent died. At least 1,300 civilians were also injured by the weapons, and at least 4,000 more were hurt producing them.

  Italian forces used gas sporadically during the Second Italo-Ethiopian War in the years between the wars, and in 1930 Japan turned to chloroacetophenone to put down a rebellion in Formosa.

• 4. Restraint And Atrocity

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  Nazi Germany poured research into nerve agents throughout World War II and then never used a single one, not even in the final defense of the country. Adolf Hitler's own experience with poison gas during World War I, combined with fear that the Allies would retaliate in kind, is one suggested reason. Military historian Ian V. Hogg offers another: German scientists could not find any antidote for their own nerve agents, and hesitated to unleash a weapon they had no defense against. Germany also assumed that a British ban on publishing organophosphate research meant the Allies had discovered nerve agents too. In fact, the Allies remained unaware of the German G-series agents until they captured an ammunition dump in April 1945; the publication ban had actually aimed to stop Axis nations from tracking Allied advances in insecticides and herbicides meant to boost food production. The Allies nonetheless drew up comprehensive plans for both defensive and retaliatory chemical use and stockpiled large quantities of their own agents, just in case.

  The Imperial Japanese Army kept fighting a chemical war of its own, using such weapons in China and Burma through 1943 against both Kuomintang and Communist People's Liberation Army troops. Unit 731 ran experiments with chemical warfare agents on prisoners of war in 1940 and 1943. After President Roosevelt threatened retaliation in kind in 1942, Japan was forced to limit its use of these weapons in the Pacific theatre. By 1944, Japan had gradually shifted production toward conventional high-explosive and incendiary shells, though it kept a stockpile of chemical munitions in reserve for retaliation.

  Against civilians, above all against Jews, Nazi Germany used poison gas extensively, deploying vast quantities of Zyklon B and carbon monoxide to murder roughly three million people. It remains the deadliest use of poison gas in recorded history. The world would not wait long to test the battlefield restraint that had spared Europe, in wars fought far from the trenches of the first war or the islands of the Pacific.

• 5. Cold War And Postwar Battlefields

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  Egyptian forces used small amounts of chemical agents during the North Yemen civil war between 1963 and 1967, causing hundreds of casualties. A far larger use of chemicals followed in Vietnam, where the United States dropped over 90,000 tons of chemical agents, mostly Rainbow Herbicides along with tear gas, in what counts as one of the largest chemical attacks on record. In the Iran-Iraq War, roughly 100,000 Iranian troops became casualties of Iraqi chemical weapons. Iraq also turned mustard gas and nerve agents on its own Kurdish population, killing more than 5,000 people and injuring many more in the 1988 Halabja chemical attack.

  Cuba's intervention in Angola brought a smaller, quieter use of organophosphates. On the 22nd of September 1991, during the battle of Šibenik, Federal Yugoslav authorities accused Croatian forces of using non-lethal chemical agents to storm a naval base in the city's harbour. Terrorist groups picked up the same tools soon after. In Japan during the 1990s, that included the 1994 Matsumoto incident and the 1995 Tokyo subway sarin attack, proof that chemical weapons no longer required a state or a battlefield at all. Not every chemical campaign in this history has targeted soldiers or civilians directly; some took aim at the land itself.

• 6. Twenty-First Century Fronts

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  Syria's Ba'athist government turned to sarin, chlorine and mustard gas in numerous deadly attacks on civilian populations during its civil war. Russia has taken a different, quieter approach in its invasion of Ukraine, reportedly deploying CS gas through K-51 grenades dropped from unmanned drones. On the 13th of December 2024, the Ukrainian military said more than 4,800 chemical weapons incidents had been recorded against its forces since the war began, hospitalizing over 2,000 soldiers and killing three. Ukrainian officials said the gas use was often masked by heavy artillery, rocket and bomb attacks meant to force soldiers from their positions, and that cold weather reduced how well the K-51 grenades worked. A 2024 US aid package to Ukraine included nuclear, chemical and radiological protective equipment in response.

  Amnesty International's September 2016 report, titled Scorched Earth, Poisoned Air, documented at least 30 suspected chemical weapons attacks by the Sudanese Armed Forces in the Jebel Marra region of Darfur between January and September 2016, killing an estimated 200 to 250 people, many of them children. After armed conflict broke out between the Sudanese Armed Forces and the Rapid Support Forces in April 2023, further allegations of industrial chemicals used as weapons followed. In May 2025, the US State Department determined that the Sudanese Armed Forces had used chemical weapons during 2024, triggering sanctions against its leadership, including General Abdel Fattah al-Burhan.

• 7. Poisoning The Land

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  Agent Orange was never designed to kill people directly; herbicidal warfare targets crops and the cover that plants provide, not human bodies. The British sprayed it during the Malayan Emergency, and the United States sprayed far more of it during the Vietnam War, but some batches carried dioxins as manufacturing impurities. Those dioxins, not the herbicide itself, cause long-term cancer and genetic damage that leads to serious birth defects.

  Vietnam's government says the spraying defoliated about 24 percent of the forests of Southern Vietnam and exposed up to four million people to Agent Orange. It further estimates that as many as three million people developed illness as a result, while the Red Cross of Vietnam puts the number left disabled or with related health problems at up to one million. The United States government has called these figures unreliable. Washington also fought North Vietnamese forces and their allies across the border in Laos and Cambodia, dropping an estimated 475,500 US gallons of Agent Orange on Laos and 40,900 US gallons on Cambodia. Because both countries were officially neutral, the US tried to keep its military involvement there secret, and it has since said Agent Orange was not widely used in either country. As a result, the US has not offered assistance to affected Cambodians or Laotians, and it limits benefits for American veterans and CIA personnel who served there.

  The United States used napalm extensively during the Korean War and the Vietnam War, but because its destructive force comes from fire rather than direct chemical action, the law treats it as conventional warfare, not chemical warfare. A different, smaller-scale attack on agriculture came earlier still: during the Mau Mau Uprising in 1952, the poisonous latex of the African milk bush was used to kill cattle. That improvised killing of livestock sits at one extreme of this weapon's history; the other extreme is the decades-long, multi-nation effort now underway to destroy industrial-scale stockpiles for good.

• 8. Toward Elimination

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  In 1997, incoming Halliburton chief executive and future US Vice President Dick Cheney tried to stop the Senate from ratifying a treaty banning chemical weapons at all. In a letter dated the 8th of April 1997 to Senator Jesse Helms, chairman of the Senate Foreign Relations Committee, Cheney argued it would be a mistake for America to join. Nations likely to comply with the Chemical Weapons Convention, he wrote, were not likely to threaten the United States militarily anyway, while the governments worth worrying about were likely to cheat even as signatories. The Senate ratified the treaty that same month regardless, by a 74-26 vote on the 24th of April, and the United States deposited its instrument of ratification at the United Nations on the 25th of April 1997, just days before the convention entered into force.

  That convention had been years in the making, growing out of a UN Conference on Disarmament in Geneva in 1980 and concluding on the 3rd of September 1992. The United States became one of 87 original state parties, and President Bill Clinton sent the treaty to the Senate for ratification on the 23rd of November 1993, where Helms held it up for years. Upon ratification, the US declared a stockpile of 29,918 tons of chemical weapons and committed to destroying all of it. In the years that followed, Albania, Libya, Russia, the United States and India together declared over 71,000 metric tons of chemical weapon stockpiles and destroyed a third of them, though the 2012 deadline the US and Russia had agreed to came and went with both countries still working.

  India declared a stockpile of 1,044 tons of sulfur mustard in June 1997, and by 2006 had destroyed more than 75 percent of it. On the 14th of May 2009, India told the United Nations it had destroyed its entire chemical weapons stockpile, the only one of six declared possessor states to meet its original deadline. Russia declared the largest arsenal of any nation, 39,967 tons in 1997, and only announced full destruction in September 2017, having leaned on funding from Canada to help finish a destruction facility at Kizner. Iraq joined the convention only in 2009, becoming its 186th State Party, and its later 2011 accession made it the sole State Party exempted from the treaty's destruction timeline. Japan, for its part, is still destroying chemical weapons it abandoned on Chinese soil during the Second Sino-Japanese War, using mobile destruction facilities in Nanjing since September 2010.

  The United States took the longest of the major powers, closing its ninth and final storage site, the Blue Grass Army Depot in Kentucky, only after starting elimination there in 2019. By May 2021 it had destroyed all of its Category 2 and Category 3 weapons and 96.52 percent of its Category 1 stockpile. In July 2023, the Organisation for the Prohibition of Chemical Weapons confirmed that the last American chemical munition, and the last chemical weapon declared by any state party to the Chemical Weapons Convention anywhere in the world, had been verified as destroyed. The declared stockpiles are gone, but the chemistry did not stop moving during the decades it took to destroy them. The 1990s had already produced an entirely new class of nerve agents, the Novichok series, developed while most of the treaty's framework was still being built.