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Peloponnesian War  -

One of the earliest references to gas being used in warfare dates back to the 5th century BCE and the Peloponnesian War between Athens and Sparta. During an assault on an Athenian city, Spartan forces used a lighted mixture of wood, pitch, and sulfur under the walls hoping that the noxious smoke would incapacitate their besieged foe.  

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Siege of Kirrha -

During the siege of Kirrha—a military engagement that effectively ended the First Sacred War (595–585 BCE)—forces allied with the Amphictyonic league used hellebore roots to contaminate the water supply drawn by the defenders of the town. Weakened by the poison, they quickly gave up the fight and Kirrha was vanquished. 

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Siege of Dura-Europos  -

Clouds of choking sulfur dioxide gases produced by igniting bitumen and sulfur proved very effective against Roman legionaries attempting to hold their positions during the siege of Dura-Europos in 256–57 CE. Their enemy, the Sassanians, eventually recaptured the city and deported most of the population.  

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Gas attacks at sea -

During the reign of Henry III, the English Navy decimated an invading French fleet by blinding the enemy with quicklime (calcium oxide). After positioning their vessels upwind of the French, the caustic compound was heated and its vapor allowed to drift into the opposing ships, effectively gassing their officers and crew and ending the battle. 

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Defense of Hispaniola -

The indigenous Taíno people of the Caribbean came up with a novel way of defending Hispaniola against 15th-century Spanish conquistadors. They collected gourds filled with ashes and ground hot pepper which they would throw as makeshift grenades before launching their attack. The dense, blinding smoke served as a perfect smokescreen.

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Siege of Groningen -

Several different explosive and incendiary devices were employed by German forces led by the Bishop of Münster during the 1672 Siege of Groningen. Among them were crude implements filled with smoldering deadly nightshade intended to produce toxic fumes so as to gas the city's defenders out of their positions. During the same battle, however, arsenic and sulfur-packed shells were also used by the Bishop of Münster to greater effect. The engagement ultimately led to a Dutch victory, but the chemical weaponry alerted governments across Europe to a deadly new form of warfare.  

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Strasbourg Agreement -

The signing of the Strasbourg Agreement on August 27, 1675, between France and the Holy Roman Empire effectively created the world's first international treaty banning the use of chemical weapons. It was drawn up in response to the battle at Groningen and the appearance of what was later described as "poison bullets"—the arsenic and sulfur-packed shells used during the siege. 

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Not playing fair -

The ironically named British scientist and politician Lyon Playfair (1818–1898) advocated the use of poison gas against the Russians in the Crimean War. He proposed a cacodyl cyanide artillery shell for use against enemy ships as a way to solve the stalemate during the siege of Sevastopol. The British Ordnance Department rejected the proposal as "as bad a mode of warfare as poisoning the wells of the enemy."

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Hague Conventions -

The Hague Conventions of 1899 and 1907 established a number of treaties and declarations outlining the laws of war and war crimes, among them the prohibition of the use of projectiles with the sole object to spread asphyxiating poisonous gases.

Image: Imperial War Museum, London. 

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First World War -

The French were the first to use chemical weapons during the First World War. In August 1914, they launched bromine ethyl acetate tear gas grenades against German lines in a manner more akin to subduing a riotous mob. The deployment of tear gas likely led to the accelerated use of poisonous gas. 

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First large-scale chemical attack -

In April 1915, Germany mounted the first large-scale chemical attack in warfare when it opened canisters of chlorine upwind of French, Canadian, and Algerian troops at Ypres in Belgium. The Germans exploited a loophole in the Hague Conventions of 1899 and 1907 prohibiting the firing of any projectiles "the sole object of which is the diffusion of asphyxiating or deleterious gases," by instead letting the wind carry the gas towards the enemy lines rather than launching it in artillery rounds.

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Sulfur mustard -

The most commonly used gas in the First World War was 'mustard gas,' or sulfur mustard. The French and Germans unleashed mustard gas in lethal quantities. By the Armistice, chemical shells made up 35% of French and German ammunition supplies, 25% British, and 20% American.

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Effects of mustard gas -

Named for its mustard color with an odor reminiscent of garlic or horseradish, mustard gas is an irritant and blister agent. It causes chemical burns on contact forming large blisters on exposed skin and in the lungs, often resulting in prolonged illness ending in death. 

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Blind leading the blind -

Exposure to mustard gas vapors invariably resulted in corneal ulceration. Hundreds of troops on both sides were temporarily blinded by mustard gas. Extreme exposure to sulfur mustard normally meant a permanent loss of vision. Pictured: British troops blinded by poison gas during the Battle of Estaires, 1918. 

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Death toll from gas attacks -

By the end of the war in 1918, the estimated death toll from the use of chemical weapons—mainly chlorine, phosgene, and mustard gas, used by both sides—was around 90,000. An estimated one million combatants and civilians were incapacitated by chemical agents. Numerous horses, donkeys, and mules also fell victim to gas attacks. 

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Tambov Rebellion -

The 1920–1921 Tambov Rebellion during the Russian Civil War was suppressed with poison gas after Lenin's Soviet government authorized its use against anti-Bolshevik rebels (pictured). 

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Geneva Protocol -

Signed in Geneva on June 17, 1925, and entered into force on February 8, 1928, the Geneva Protocol prohibited the use of chemical and biological weapons in international armed conflicts. 

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Interwar years -

Despite the Geneva protocol being ratified by 65 states, chemical agents were still occasionally used to subdue populations and suppress rebellions. Combined Spanish and French forces, for example, dropped mustard gas bombs against Berber rebels and civilians during the Rif War in Spanish Morocco. Similarly, the Italians bombed the Libyans in the late 1920s using mustard gas; later, during the 1930s, Italy again deployed mustard gas against Ethiopian forces during the Second Italo-Abyssinian War.  

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Second World War -

During the late 1930s, the Imperial Japanese Army frequently used chemical weapons against Communist Chinese troops and guerillas during the Second Sino-Japanese War. Pictured: Japanese special naval landing forces wearing gas masks and rubber gloves during a chemical attack in the Battle of Shanghai, 1937. 

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Second Sino-Japanese War -

In fact, it was only in the Sino-Japanese theater that Japan's chemical warfare policy permitted the use of chemical weapons. Japan largely prohibited their use in the Pacific against the Allies, whom they feared could respond in kind with overwhelming force. Pictured: Chinese military personnel take air raid protection measures in Manchukuo after the outbreak of the war.  

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Zyklon B -

While no chemical weapons were used on European battlefields, poisonous gas was used elsewhere during the Second World War to absolutely dreadful ends.

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The Holocaust -

To facilitate the Final Solution during the Holocaust, Nazi Germany gassed over a million Jews, Slavs, and others using carbon monoxide and hydrogen cyanide, including Zyklon B. A cyanide-based pesticide, Zyklon B was developed by private chemicals firm IG-Farben, whose chief engineer, Max Faust, is seen with SS chief Heinrich Himmler on a visit to Auschwitz. After the war, several IG Farben directors stood trial at Nuremburg accused of war crimes and crimes against humanity.  

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The SS John Harvey cover-up -

On December 2, 1943, German aircraft attacked the Italian port of Bari killing over 1,000 people, and sinking 28 ships, including the US Liberty ship SS John Harvey. What wasn't known at the time is that the vessel was carrying a secret cargo of mustard gas destined for the Mediterranean theater and intended for use in retaliation by the Allies if German forces initiated chemical warfare. An explosion sent liquid sulfur mustard spilling into the water creating a deadly vapor that swept over the city wounding nearly 700 civilians and sailors alike. By the end of the month, 83 of the hospitalized military victims had died. The number of civilian casualties was never ascertained. A cover-up ensued. Allied High Command suppressed news of the presence of mustard gas, in case the Germans believed that the Allies were preparing to use chemical weapons. The whole episode remained obscure until 1967 when the book Disaster at Bari was published. Pictured is the SS John Harvey and other Allied ships ablaze after the attack. 

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Post-Second World War -

While the threat of thermonuclear conflict made all the headlines during the Cold War, behind the scenes both the Soviet and Western governments put enormous resources into developing chemical and biological weapons. At Porton Down in England, secret research led to the development of the highly toxic VX nerve agent in 1952. By 1961, the United States was producing large amounts of VX and performing its own nerve agent research. 

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Yemen Civil War -

The 1960s saw sporadic use of chemical weapons in various conflict zones around the world. They were allegedly deployed against Yemini tribesmen during the North Yemen Civil War in the 1960s, with a noted attack on the villages of Gahar and Gadafa in Wadi Hirran taking place on May 10, 1967. The Red Cross believes the gas used was probably a derivative of either phosgene, mustard gas, lewisite, chloride, or cyanogen bromide. 

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Rhodesian Bush War -

Rhodesia's protracted struggle against a growing African nationalist insurgency in the late 1970s led to allegations that Rhodesian security forces were using chemical and biological weapons against its determined guerilla foe. 

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Iran–Iraq War -

During the Iran–Iraq War (1980– 1988) chemical weapons employed by Saddam Hussein killed and injured numerous Iranians and Iraqi Kurds. In fact, mustard and nerve gas caused over one million casualties, according to the Non-Proliferation Review. Pictured: members of the Iranian Basiji (mobilized volunteer forces) march in gas masks and chemical warfare suits. 

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Halabja chemical attack -

The largest chemical weapons attack directed at a civilian-populated area in history occurred on March 16, 1988 when Iraqi dictator Saddam Hussein ordered the bombing of the Kurdish city of Halabja in Iraqi Kurdistan using mustard gas and nerve agents. Anywhere between 3,200 and 5,000 people died in the unprovoked strike, which further injured 10,000.  

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Japan sarin attacks -

The sarin gas attacks perpetrated by members of the Aum Shinrikyo doomsday cult in Japan—one in Matsumoto in the center of the country and another on the Tokyo subway—killed a total of 20 people and injured thousands. The incidents refocused world attention on the potential use of chemical weapons by terrorists.  

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Chemical Weapons Convention -

Signed in 1993 and ratified in 1997, the Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction (otherwise known as the Chemical Weapons Convention or CWC) became the first multilateral treaty to ban an entire category of weapons of mass destruction (WMD). 

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Ghouta chemical attack -

On August 21, 2013, the Syrian opposition-held Damascus suburb of Ghouta was struck by rockets containing the nerve agent sarin. Many hundreds died following the attack, including dozens of children. The episode was the deadliest use of chemical weapons since the Iran–Iraq War. 

Sources (Elsevier) (Science Direct) (University of Kansas) (United Nations) (Reuters) (Springer) (Wollheim Memorial) (Harvard University) (The Patriot) (History) (BBC) 

See also: History's most notorious poisonings

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