Gas represented one of the most horrific developments in military technology produced by World War One. These 10 facts tell part of the story of this terrible innovation.
 1. Gas was first used at Bolimów by Germany
Gas first saw use in January 1915 at the battle of Bolimów. The Germans launched 18,000 shells of xylyl bromide in preparation to attack. The attack never took place though as unfavourable winds blew the gas back toward the Germans. Casualties were minimal, however, as the cold weather prevented the xylyl bromide fluid from evaporating fully.
Listen Now2. Gas was climate dependent
In the wrong climate gases would disperse quickly, which reduced their chances of inflicting significant casualties on the enemy. Favorable conditions in contrast could sustain a gas’ effect long after the initial attack; mustard gas could remain effective in an area over several days. Ideal conditions for gas were an absence of strong wind or sun, either of which caused the gas to dissipate quickly; high humidity was also desirable.
British infantry advance through gas at Loos 1915.
3. Gas was not officially lethal
The effects of gas were horrific and their consequences could take years to recover from, if you recovered at all. Gas attacks were, however, often not focused on killing.
Gases were divided into lethal and irritant categories and irritants were by far the more common including infamous chemical weapons like mustard gas (dichlorethylsulphide) and blue cross (Diphenylcyonoarsine). The fatality rate of gas casualties was 3% but the effects were so debilitating even in non-fatal cases that it remained one of the war’s most feared weapons.
Phosgene was one of the more common of the lethal gases. This photo shows the aftermath of a phosgene attack.
4. Gases were categorised by their effects
The Gases used in World War One came in 4 main categories: Respiratory Irritants; Lachrymators (tear gases); Sternutators (causing sneezing) and Vesicants (causing blistering). Often different kinds were used together to inflict the maximum possible damage.
A Canadian soldier receiving treatment for mustard gas burns.
5. Germany, France and Britain used the most gas in WWI
The most gas was produced by Germany, totaling 68,000 tons. The British and French were the closest after that with 25,000 and 37,000 tons respectively. No other nation came close to this volume of gas production.
Listen Now6. Key to German advances at the 3rd Battle of the Aisne
In May and June of 1918 German forces advanced from the Aisne River toward Paris. They initially made swift progress aided by extensive artillery use. During the initial offensive 80% of long range bombardment shells, 70% shells in the barrage on the front line and 40% of shells in the creeping barrage were gas shells.
Gas casualties awaiting treatment.
7. Gas was not the only chemical weapon of WWI
Although not as significant as gas, incendiary shells were deployed in World War One. These were launched mainly from mortars and comprised either of white phosphorous or thermit.
Gas being emitted from cylinders at Flanders.
8. Gas was actually launched as a liquid
The Gas used in shells during WWI was stored in liquid form rather than as a gas. It only became a gas when the fluid dispersed from the shell and evaporated. This is why the effectiveness of gas attacks was so weather dependent.
Sometimes gas was released in vapour form from canisters on the ground but this increased the chances of the gas blowing back at the army using it therefore making the liquid based shells the more popular system for deployment.
Australians wearing gas masks at Ypres in 1917 .
9. Gas was used to undermine enemy morale
As it was heavier than air gas could find its way into any trench or dugout in a way that other forms of attack could not. Consequently it impacted on morale by causing anxiety and panic, especially early in the war when no one had experienced chemical warfare before.
Gassed by John Singer Sargent (1919).
10. Gas usage was almost unique to World War One
The gas warfare of World War One was so horrific that it has rarely been used since. In the interwar period the French and Spanish used it in Morocco and the Bolsheviks used it against rebels.
After the 1925  Geneva Protocol prohibited chemical weapons their use further diminished. Fascist Italy and Imperial Japan also used gas in the 1930s, however, against Ethiopia and China respectively. A more recent use was by Iraq in the Iran-Iraq War 1980-88.
A soldier in a gas mask during the Iran-Iraq war.
