Concern continues to mount within the international community over whether Syrian president Bashar al-Assad will resort to using chemical weapons in the intractable war against rebels inside his troubled Middle Eastern state.
According to a piece in Wednesday’s Washington Post, Syria maintains stockpiles of nerve agents like Sarin and VX as well as mustard gas and may be preparing to introduce them in battle. As recently as last week, world leaders cautioned Damascus against using any sort weapon of mass destruction in its bid to suppress the rebels.
Following the introduction of chemical weapons during in the First World War, global opinion has largely condemned the use of gas. In fact, moral outrage over the 90,000 deaths and 1 million injuries from chlorine, phosgene and mustard gas following the conflict brought about the Geneva Protocol. The treaty, which was established in 1925, saw 38 countries renounce chemical weapons. Ninety-nine other states would follow over the subsequent decades. The Chemical Weapons Convention of 1992 achieved a near-universal rejection of poison gas. Only eight countries refused to sign the accord, including Angola, North Korea, Egypt, Israel and (you guessed it) Syria.
Should President Assad use chemical weapons on his own population, Syria will join a grim fraternity of nations that since World War One have resorted to poison gas. Here are some of the offenders. Many of them you already may know about; some you may not.
After the Great War
While Iraqi dictator Saddam Hussein released mustard gas on rebellious Kurds in 1988, the British War Office in 1920, under the direction of none other than Winston Churchill, considered a similar strategy against Kurdish and Arab insurgents in the mandate territory of Mesopotamia (present day Iraq).  “I do not understand this squeamishness about the use of gas,” said the future prime minister while advocating using non-lethal agents on rebel populations. “It is not necessary to use only the most deadly gasses. [Some] can be used which cause great inconvenience and would spread a lively terror and yet would leave no serious permanent effects on most of those affected.” While officially, the U.K. denied ever releasing any chemical weapons, some historians point to evidence contradicting that.  A year earlier the Royal Air Force did indeed drop bombs laden deadly mustard gas onto communist positions as part of the western intervention in the Russian civil war.
The Bolsheviks themselves would use poison gas in 1921 as the Red Army struggled to put down the Tambov Rebellion, a counter-revolutionary uprising among peasants a few hundred kilometers southeast of Moscow. Official newspapers at the time even celebrated its use, claiming the gas helped the regime eradicate “bandits”. 
That same year, Spain, with the cooperation of France, would touch off its six-year Rif War against Berber rebels in Morocco. During the conflict, both of the European powers would deliver mustard gas from aircraft onto enemy-held territory.
A decade later, Italy (a signatory of the 1925 Geneva Protocol) deployed mustard gas in its war in Abyssinia. The chemical, which was loaded into bombs or dispersed over wide areas as a powder, killed an estimated 150,000 Ethiopian soldiers and civilians alike.
During the same decade, Japanese forces fighting for control of China reportedly launched thousands of chemical weapon attacks throughout the region.  Tear gas as well as sneeze, nausea, and blister-inducing agents were used along with mustard gas, in some cases on the orders of the Japanese Emperor himself.  The Japanese military even set up a production facility for both chemical and biological weapons near Harbin, China. Dubbed Unit 731, the complex was home to as many as 500 scientists and thousands of support personnel. Japan reportedly developed arsenals of poison gas, as well as bubonic plague, some of which it tested on live human subjects.
The Second World War
While the major powers of Europe pledged not to launch gas attacks in any future war, it didn’t stop armies on all sides from devising, testing and stockpiling chemical weapons, just in case.
New varieties of even deadlier poisons were engineered in the lead up to World War Two. Agents that attacked the respiratory system, like diphosgene and carbonyl chloride were refined, while new gases like Tabun, Soman and Sarin that struck the central nervous system were invented. By the outbreak of war in 1939, all powers expected their enemies to use their growing stockpiles of chemical weapons.
British defence planners issued gas masks to civilian populations in anticipation of massive areal gas attacks on major cities. And Prime Minister Churchill had few qualms about deploying chemical weapons on German troops should the Nazi’s launch a cross channel invasion.
At the war’s outset, Hitler also expected the Allies to resort to gas, but despite the repeated requests from his own high command, the Fuhrer forbid his generals to initiate chemical warfare. Some have suggested that the dictator’s own personal experience as a casualty of gas attacks during the previous war instilled in the German leader a deep reluctance to order their use.  Others speculate it was a simple fear of retaliation in kind that dissuaded Hitler from using chemical weapons.  However, allied commanders expected German gas attacks, particularly as the Third Reich began to disintegrate in the war’s final months.
Despite both side’s non-first use policy, there were a handful of instances in which chemical weapons were unleashed. None led to all out chemical war.
In the opening week of the conflict, Polish troops near Jaslo deployed mustard gas against German engineers who were trying to secure a vital railway bridge. Twelve of the German soldiers were exposed to the agent; two were killed.  According to the University of Virginia’s Jeffrey Legro, Germany refused to reciprocate in kind. Berlin’s response was similar following conclusive proof of isolated Soviet gas artillery attacks and areal chemical raids against Wehrmacht troops in the summer of 1941.
The largest gas incident of the war occurred two years later in Italy. In December 1943, a massive cloud of mustard gas was accidentally released from the American transport vessel John Harvey when a convoy of 30 Allied supply ships moored at Bari on the Adriatic came under attack by 105 Luftwaffe Ju-88 bombers. The John Harvey was carrying a top secret payload of 540 tons of mustard gas artillery shells in its hold that were waiting to be used in retaliation in the event of a German gas attack on British and American landings in Italy. The massive surprise air strike, which has been called a “little Pearl Harbor” caused the deadly gas release that incapacitated more than 600 Allied personnel, killing
more than 100. A substantial amount of the chemical was also released into the water injuring merchant sailors and crewmembers from U.S. Navy ships sent in to rescue survivors of the raid. An unknown number of Italian civilians were also exposed, but some estimate that as many as 1,000 perished. The entire incident was suppressed not only form the general public, but from Allied troops in Italy. Commanders were frantic that the Germans not have any pretext to retaliate using gas. Not even the medics and doctors who were tending those exposed to the gas were informed about the true nature of the burns and injuries they encountered. When the Allies were forced to acknowledge details of the accidental release, they stressed that the weapons were in theatre to be used only in retaliation.
A similar occurrence took place at Anzio earlier that year when a German artillery shell struck an American munitions dump releasing a cloud of poison gas that drifted over Wehrmacht positions. Fearful that the enemy might retaliate, the ranking American officer quickly dispatched an emissary under a flag of truce to the opposing commander to explain that the release was unintentional. The Germans accepted the explanation at face value. [Source: Jeffrey Legro “Military Culture and Inadvertent Escalation in World War Two” in International Security, Spring 1994.]
Post War Period
Chemical weapons would be used in anger only sporadically during the post war period, largely by smaller powers in the developing world.
Case in point, royalist forces in the North Yemen Civil War from 1962 to 1970 suffered repeated gas attacks in the final years of the war. In one of the more well known incidents, Egyptian and Soviet backed republican forces reportedly used a gas of unknown composition against forces under the personal command of Prince Hassan bin Yayha at the town of Kitaf in late 1966. At least 240 were exposed to the suspected agents, 140 died. A second attack was directed at units commanded by another member of the royal family, Prince Mohamed bin Mohsin on May 2, 1967. Seventy-five were killed in the incident, which involved a mixed assortment of agents that likely included phosgene, mustard gas, lewisite, and cyanogen bromide.  In June, republican forces launched a widespread chemical attack on a range of royalist targets killing more than 1500 in total. London and Washington condemned what it considered Egyptian involvement in the attacks. Cairo denied all involvement.
Lesser-known incidents of chemical attacks were recorded (or in some cases merely suspected) in the 1980s. The Vietnamese might have used phosgene gas against Khmer Rouge insurgents in 1984 and 1985 as the latter sought refuge along the border with Thailand.  Argentine forces unleashed non-lethal tear gas to break up the handful of British troops defending the governor’s residence on the Falkland Islands. More recently, Sri Lankan government forces reportedly released phosgene against Tamil rebels in 2009. 
The eight-year war between Iran and Iraq saw more poison gas used than any other time since the First World War. In fact, upwards of 100,000 Iranian soldiers suffered from exposure to poison gas during the bloody conflict – an estimated 5 percent of all battlefield casualties have been attributed to chemical weapons.  Nerve gas alone killed 20,000 Iranians. Mustard gas, produced domestically in Iraq with assistance from Britain, France, the U.S., West Germany and Holland was another weapon in Saddam Hussein’s chemical arsenal.  The Iraqis resorted to gas early in the war as a means of tipping the balance of power away from the numerically superior Iranians. Later, when American and coalition forces attacked Iraq in 1991 and 2003, Allied commanders expected to encounter poison gas. They never did.
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