In August 1914 the French used tear gas grenades containing ethylbromoacetate. Designed for use in civil riots by the police their effects were not even noticed by the Germans.
In October 1914 it was the turn of the Germans who shelled the British at Neuve Chapelle with an irritant. If anybody noticed it certainly never made the official dispatches.
In January 1915 the German chemist, Dr Karl von Tappen of the Kaiser Wilhelm Institute in Berlin suggested adding xylyl bromide (a tear gas) to their artillery shells.
On the 31st January, 18,000 of these White Cross shells were fired at the Russians during the battle of Bolimov. However the Germans had overlooked a primary element - the temperature. The gas froze in the winter air and failed to have any effect.
In March the shells (beefed up with bromoacetone) were fired against the French troops at Nieuwpoort - the left hand end of 800 kilometres of trenches.
Despite the milder temperatures and the dispersal of the gas, once again the experiment went unnoticed - but Dr Tappen went into the history books as the man who had dared to start gas warfare on a large scale.
With the failure of the shells however von Tappen lost interest and it would fall to his Director to carry large scale gas warfare onto the battlefield.
Fritz Haber was one of Germany's most brilliant scientists and from the very outset promoted the idea of using a weapon that Germany already possessed in enormous quantity - chlorine gas.Short biography of Fritz Haber
As a by-product of her chemical industry it was already available in quantity. All the plants had to do was bottle it or stick it in shells.
As shells were already in short supply by 1915 the decision was made to package the gas in steel cylinders and deploy it on the wind against the enemy.
Haber searched for a war winning weapon and envisaged hundreds of tons of the gas being directed towards the Allied lines whilst German soldiers advanced behind it wearing simple gas masks.
Chlorine is a gas that reacts with the fluids in bodily tissue to form hydrochloric acid. Even in small doses it is highly debilitating once inhaled and exposure to large doses would prove fatal.
The problem for the Germans was that the prevailing winds tended to come from the west - towards their lines rather than away from them.
After close observations however it was calculated that the Ypres Salient looked a promising choice. Initially from the eastern side against the British and then, when the promised wind turned towards the south-west, from the northern side against the French.
Haber was so obsessed with his pet project that he went to the front to ensure that the preparations were carried out correctly.
The first large scale gas attack is therefore dated as the 22nd April 1915 when 160 tons of chlorine in nearly 6,000 cylinders were released by the 35th and 36th Pioneer Regiments into the breeze near Langemark.
The 2nd Battle of Ypres had begun.2nd Ypres 1915
The results were a mixed bag. A huge breach was made in the French line with a thousand of them dying and a further two thousand incapacitated. The French reports speak of losses of 60% amongst their front line units.
The German soldiers though had not come away totally unscathed and the German High Command had flinched from the idea of truly going for the throat - which is what Haber wanted: a deadly, one time only, war winning blow.
By the time that the Germans launched a second gas attack against the Canadian front line on the 24th April local initiatives had already come up with makeshift facemasks.
A third attack on the 5th May against Hill 60 on the eastern part of the salient delivered some ground but in reality the initiative had been lost.