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Exploring the Darker Side of Everything

Chlorine Gas: The First Mass Use of a Chemical Weapon

On 22nd April 1915, French, Canadian and Algerian troops sat huddled in their squalid trenches near the town of Ypres in Belgium. With rats feasting on the dead, thick mud that could swallow a man, and a steady barrage of thunderous artillery shells landing nearby, this was already hell on an unimaginable scale.

As the artillery barrage finally ended, those in the trenches steeled themselves for the expected German attack. Men gripped their guns nervously, peering desperately out into no man’s land for any sign of the approaching enemy – an eerie silence descended on the battlefield.

Suddenly, confusion began rippling through the lines. Instead of a torrent of German soldiers heading towards them, all that could be seen was a strange, slightly green gas drifting silently across the massacred landscape. As it reached the trenches, the first coughs could be heard, which quickly turned into desperate gasping and terrified screams. The first successful mass use of chemical weapons was now underway.

A New Form of Carnage

The events of that day sparked outrage among those it had been used on, but it didn’t take long for everybody to get in on the act. Any kind of self-righteous condemnation was soon replaced by a murderous chemical weapons tic for tac that eventually cost the lives of an estimated 90,000 men during World War I. All sides eventually ended up using chlorine gas during World War I, but sadly that was just the start. 

Phosgene and then Mustard Gas quickly replaced Chlorine Gas as the murder weapon of choice as the trenches in northeast France, Belgium and on the eastern front, degenerated into an apocalyptical nightmare. 

It is telling that despite the utter devastation caused by chemical attacks, World War I proved to be the first and only war where chemical weapons were used by both sides on such a scale. Even the frazzled psychopathic mind of Adolf Hitler stopped short of chemical weapons – though it must be said that this was perhaps down to the fact that effective countermeasures against chemical warfare, such as gas masks, had drastically diminished their capabilities.       

Early Chemical Use    

While this was certainly the first major attempt to use chemical weapons on such a scale, it was not the first time chemicals or poisons had been used on the battlefield. To gauge the origins, it really depends on what you consider chemical weapons. 

Greek myths and ancient Indian epics are some of the earliest references to poisons being used in war, principally through poisoned arrowheads, but there is also reference to ‘toxic smoke’. 

In China, the use of arsenical smoke goes all the way back to 1000 BC, while there is also mention of the smoke from burning balls of toxic plants and vegetables being blown into tunnels that had been dug by besieging armies. 

In the 5th Century BC, Spartan soldiers were said to have placed a smouldering mixture of wood, pitch, and sulfur at the foot of the walls of an Athenian city they were attacking, in the hope it would incapacitate the defenders, while in the 3rd Century AD, a group known as the Sassanians used bitumen and sulfur crystals to defend their town in modern-day Syria against the invading Roman army. The result was a toxic plume of sulfur dioxide which was said to kill 19 Romans in just 2 minutes. 

The English purportedly used lime motors to hurl quicklime (the old name for calcium oxide) at a fleet of French ships sometime in the 13th Century – blinding many onboard the ships.  

As the following centuries passed, there were consistent stories of various chemicals being used in combat, but nothing concise. These attacks were usually experimental, to say the least, and it’s telling that nothing concrete really emerged as an effective form of chemical warfare.  

The Industrial Age 

Things began to change as the world barrelled headlong into the Industrial Age. The development of modern chemistry, as well as the blossoming chemical industry that accompanied it, introduced many intriguing and highly useful chemicals to the more developed nations. These included sulfuric acid, sodium carbonate, ammonium chloride and ammonium sulphate, among many others. 

At this point, there was practically no mention of using chemicals for war, instead, they were almost entirely focused on their industrial and everyday uses. 

But of course, it didn’t take long for devious minds to begin conjuring up far more destructive uses for these new chemicals that were appearing. In 1854, Lyon Playfair, British Secretary of the Science and Art Department, proposed using cacodyl cyanide artillery shells during the Crimean War, but despite his idea being accepted by some, the powers that be described his plan, as “bad a mode of warfare as poisoning the wells of the enemy” and rejected his proposal. 

During the American Civil War, we see the first mention of the topic of our video today. John Doughty, a school teacher from New York, proposed filling a 254 millimetre (10-inch) artillery shell with liquid chlorine that would then be fired at Confederate troops before dispersing deadly chlorine gas. But again, the plan was not taken up. For many, the use of such a weapon remained a barbaric act beyond even the horrors of the American Civil War.  


Considering its absolutely hellish dark side, chlorine comes with a catalogue of everyday uses. Perhaps the most well-known is its use in swimming pools to disinfect the water, while also being heavily involved in the sanitation process for sewage and industrial waste. It’s also used in the production of paper and cloth and can be found in many cleaning products, including household bleach, which is chlorine diluted with water.

Sodium chloride, the most common compound of chlorine, has been used for thousands of years, but element 17 on the periodic table wasn’t studied in any great detail until 1774 when Swedish chemist Carl Wilhelm Scheele produced chlorine by reacting manganese dioxide with hydrogen chloride. His early experiments revealed several uses for chlorine, such as its bleaching effect, but also its murderous effect on insects. 

By the 19th Century, chlorine was being used for disinfection, both on a small scale and much larger, most notably the Paris cholera outbreak of 1832, when chlorine gas was dissolved in lime-water to disinfect large parts of the French capital. It was also used to clean and deodorize hospitals, sewers, prisons, stables and even used during the embalming of dead bodies. 

In 1908, Jersey City in New Jersey installed the first continuous application of chlorination to drinking water in the United States and it quickly became a key component of water purification across the country. But over the following decade, its use would swing from the sanitary to the murderous. 

Early Days of World War I   

While the events of the 22nd April 1915, as the Second Battle of Ypres got underway, may represent the first time a mass chemical attack caused significant casualties, it was not the first use of gas during World War I. 

Now, before we dive into the full horror of chemical warfare during the Great War, let’s start with the Hague Convention of 1899 in which all major nations gathered to agree on a set of rules relating to laws of war and war crimes in the body of secular international law. One of these points, ratified by every nation present with the exception of the United States, was a ‘Declaration concerning the Prohibition of the Use of Projectiles with the Sole Object to Spread Asphyxiating Poisonous Gases’

In short, this meant that it was now an international crime to use asphyxiating poisonous gases on the battlefield. And I suppose it must have made sense at the time. The true horror of what chlorine gas could do was slowly emerging and just 15 years before the nightmare in Europe began, there still appeared a level of decency regarding war that would soon evaporate.

It’s also worth clarifying the wording of the document because it left a slight loophole that would later be exploited in the early days of World War I. Asphyxiation means that the body isn’t getting the required amount of oxygen it needs, which can lead to a loss of consciousness, brain injury, or ultimately death. 

However, this did leave open the possibility of using tear gas, which has a relatively short period of effectiveness and is rarely fully disabling or deadly – therefore it was not classed under the Hague declaration of 1899 – which brings us nicely back to World War I.    

The French used 26 mm (1 inch) grenades filled with ethyl bromoacetate to create tear gas in August 1914, but the gas produced was so small, it wasn’t even detected by the German soldiers it was supposed to demobilize. 

On 31st January 1915, German artillery fired 18,000 shells containing liquid xylyl bromide tear gas on Russian soldiers stationed on the Rawka River, west of Warsaw during the Battle of Bolimov. Fortunately for the Russians, the chemical froze instead of vaporising and this revolutionary form of attack came to nothing.  

Chlorine Gas 

If there was a grey area relating to the use of tear gas under the rules of the Hague Convention of 1899, the use of chlorine gas was an entirely different matter. 

Numerous German chemical companies, including BASF, Hoechst and Bayer, had been making chlorine as a by-product of their dye manufacturing for several years. As World War I began, and as the true nature of this new potential form of warfare presented itself, Germany, and other countries involved in the war, began testing a wide range of weaponry that might give them the edge on the battlefield. 

The German gas warfare program was headed by Fritz Haber who was working out of the Kaiser Wilhelm Institute for Chemistry in Berlin. In partnership with some of the major German chemical companies at the time, Haber began exploring ways of discharging chlorine gas against enemy trenches.     

Chlorine is a diatomic gas meaning it contains two atoms that are chemically bonded and it is around two and half times denser than air. It comes with a pale green colour, a stale metallic taste, and an odour that has been described as a ‘mix of pineapple and pepper’ – though to our modern noses we would probably say it smells of bleach. 

After its release, it almost immediately begins to irritate the eyes, nose, lungs, and throat of those exposed – but things can quickly become a whole lot worse. Chlorine can react with water in the lungs to form hydrochloric acid, which destroys the tissue and quickly leads to either long-term lung damage or death. With lower concentrations, if the gas doesn’t reach the lungs, it can still cause coughing, vomiting, and eye irritation – in short, you don’t want to be anywhere in the vicinity of a shell landing with chlorine gas inside. 

As the Germans began finalising their plans to use chlorine on the battlefield, special troop units, Pioneer Regiments 35 and 36, were created to handle this new form of warfare, under the command of Otto Peterson, with Haber and Friedrich Kerschbaum as advisors. And these units weren’t simply comprised of your everyday soldiers, in fact, they were filled with some of the best chemists and physicists around, including future Nobel laureates James Franck, Gustav Hertz, and Otto Hahn.

22nd April 1915

As the gas began to reach the first soldiers on 22nd April 1915, chaos quickly ensued. Nothing like it had ever been seen and within seconds the air was filled with desperate screams as the gas began to seep into the lungs of those on the frontlines.

A total of 150 tons of chlorine gas deployed in 5,730 cylinders had been fired from the German lines across a front measuring roughly 6.4 km (4 miles), the result was hellish bedlam as some soldiers simply collapsed into the trenches, never to stand up again, while thousands turned and ran, abandoning their line, desperate to escape the mysterious deadly gas pouring through the area. It’s thought that around 1,100 men died in the world’s first mass chemical attack. 

If the Germans had hoped that the chlorine gas would sow enough chaos that a gap in the front would appear, they were entirely correct. Across the front, men were fleeing the gas and away from the German line. But quite inexplicably, the Germans weren’t entirely prepared. Whether it was from shock at the devastating effect the gas was having, a fear of what it might do to them, or simply poor battlefield management, only small numbers of Germans made it to the enemy trenches but were quickly thrown back by a counter-attack. Like so much of World War I, a savage loss of loss had yielded absolutely no gain on the battlefield. 

Further Use    

In many ways, what occurred on 22nd April 1915 had simply been a test of this new weapons capability, and while no tangible military gain had been achieved, its deadly effect had been astonishingly clear. 

The public announcement of the attack was met with international outrage but the Germans barely skipped a beat. Chlorine gas was used a further three times in the coming weeks on the Western Front and for the first time in the East, against the Russians, on 6th August 1915 – an event that has come to be known by the quite phenomenal name – Attack of the Dead Men. 

As German chlorine cylinders began landing in and around the Osowiec Fortress in what is northeast Poland today, the deadly gas quickly began to decimate the Russian units defending the structure. Just to make sure, the Germans then poured conventional ordnance on the fortress – a total of 1,700 Russians died either from the gas or bullets and shells. 

As the barrage ended, German soldiers stood and began making their way forward, expecting little to no resistance – but how wrong they were. Suddenly Russian soldiers began rising defiantly from defensive positions, many coughing horribly, foaming at the mouth, with blood and even parts of their own lungs being forced out. In what must be one of the most astonishing acts in World War I, and perhaps in any war, around 100 Russians, many on the verge of death, staggered forward to meet thousands of approaching Germans. 

Even to the most battle-hardened troops, what came lurching towards the German soldiers was too much. Upon seeing the horrifying state of the Russians and their quite relentless drive even under the most appalling conditions, most simply turned and fled, with some describing what they had seen as zombie-like – hence the name – Attack of the Dead Men. This tiny detachment of Russians somehow managed to push back a reported 7000 German soldiers. 

But it certainly wasn’t just the Germans who used chemical weapons. They may have lit the spark, but pretty soon, every major nation embroiled in the conflict was using them. While chlorine gas was soon replaced by more effective methods of killing, it still accounted for the largest amount of chemical weapons used in World War I, with 93,800 tons produced throughout the conflict.   

The first British use of chlorine gas, during the Battle of Loos on 25th September 1915, was nothing short of disastrous as a change in wind direction blew the poison back over British soldiers.   

The Next Generation  

Despite its horrific effect, the use of chlorine in World War I was fairly limited. It could be easily seen and smelt, which made surprise attacks impossible. The gas was also water-soluble, meaning that anybody with a water-soaked rag could place it over their mouths and noses and they would probably be OK. There were even stories of urine-drenched rags being used effectively, which is an unpleasant thought, and yet infinitely better than the alternative. Once gas masks became part and parcel of every soldier’s kit, their effectiveness became even less. 

But while the physical numbers of those killed by Chlorine gas were quite small, the physiological effect was enormous. Many soldiers throughout the war claimed they had been gassed when no gas attack had taken place. The smoke on the battlefield, along with the psychological trauma, could quite easily play tricks with the mind. 

However, soldiers soon learnt how to effectively counter chlorine attacks. As strange as it sounds, the very worst thing you could do was to run away as any form of movement inflamed the lungs and would quickly lead to death. It was better to stay put and preferably to stand above the trenches because the gas would sink to the bottom. Easier said than done with a wall of guns looking to pick off those crazy enough to stick their head above the parapet.      

But as I mentioned earlier, chlorine gas was quickly replaced by more deadly chemical weapons during the war, namely phosgene, and mustard gas, both of which killed far more people than chlorine ever did. It’s thought that 190,000 tons of chemical gases were used during World War I, affecting 1.3 million people directly, leading to 90,000 deaths. And this wasn’t just soldiers. Roughly 100,000–260,000 casualties were civilians, people unlucky enough to be downwind of these horrific weapons when they were released. 

Chlorine gas was rarely used after World War I until quite recently when it was used by insurgents in Iraq in 2007 and by the Syrian government during the still ongoing Syrian Civil War between 2016 and 2018. 

In terms of destructive weapons, chlorine gas is fairly low-grade which is why it’s barely been used since the trenches of World War I, but it lit the fuse on a series of steps that has gradually developed deadlier and harder to trace chemical weapons. 

Today, we worry about Novichok, Sarin, VX and Cyclosarin – weapons infinitely worse than what was seen on the battlefield on 22nd April 1915, but nonetheless, certainly the continuation of humanity’s horrifying desire to kill as many, as quickly and as silently as possible. Today there are chemical weapons that could effectively destroy vast swaths of populations in an instant, but it all began in the muddy nightmare that was The Second Battle of Ypres during the First World War, with a wall of green smoke floating silently towards the unsuspecting soldiers.  

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