[2] Falkenhayn wanted to use the gas to cover the transfer of Imperial German Army units to the Eastern Front to assist its ally Austria-Hungary with the Gorlice–Tarnów offensive against the Russian Empire.

On 22 April 1915 at about 5:00 p.m., the 4th Army released 171 t (168 long tons) of chlorine gas on a 6.5-kilometre (4.0 mi) front between the hamlets of Langemark[b] and Gravenstafel[c] This sector of the Allied line was held by the 87th Territorial Division (comprising older reservists from 10th Military District, headquartered in Rennes), alongside the 45th Infantry Division (France) (comprising troops from the (North African) 19th Military District).

[7] Troops fled in all directions, ...haggard, their overcoats thrown off or opened wide, their scarves pulled off, running like madmen, directionless, shouting for water, spitting blood, some even rolling on the ground making desperate efforts to breathe.A 6 km (4 mi) gap in the French front was left undefended.

Casualties were especially heavy for the 13th Battalion (Royal Highlanders of Canada) of the Canadian Expeditionary Force (CEF), which was enveloped on three sides and had over-extended its left flank after the Algerians of the 45th Division broke.

[10] In an action at Kitcheners' Wood, the 10th Battalion of the 2nd Canadian Brigade was ordered to counter-attack in the gap created by the gas attack.

The after-effects seem to be a bad swelling of the eyes, but the sight is not damaged.Dusk was falling when from the German trenches in front of the French line rose that strange green cloud of death.

Hundreds of them fell and died; others lay helpless, froth upon their agonized lips and their racked bodies powerfully sick, with tearing nausea at short intervals.

The whole air was tainted with the acrid smell of chlorine that caught at the back of men's throats and filled their mouths with its metallic taste.

[13] Within days the British were advised by John Scott Haldane to counter the effects of the gas by urinating into a cloth and breathing through it.

Some of the first fighting in the village involved the stand of Lance Corporal Frederick Fisher of the 13th Battalion CEF's machine-gun detachment; Fisher went out twice with a handful of men and a Colt machine gun, preventing advancing German troops from passing through St. Julien into the rear of the Canadian front line.

[18] The next day the York and Durham brigades of the Northumbrian Division counter-attacked, failing to secure their objectives but establishing a new line closer to the village.

[20] Despite hundreds of casualties, the 2nd Battalion Royal Dublin Fusiliers participated without respite in the battles at Frezenberg and Bellewaarde.

When the gas reached the front Allied trenches, soldiers began to complain of chest pains and a burning sensation in the throat.

[citation needed] Captain Francis Scrimger of the 2nd Canadian Field Ambulance may have passed the order to use urine to counteract the gas, on the advice of Lieutenant-Colonel George Gallie Nasmith.

Other soldiers preferred to use a handkerchief, sock or flannel body-belt, dampened with a sodium bicarbonate solution and tied across the mouth and nose, until the gas passed.

Private W. Hay of the Royal Scots arrived in Ypres just after the chlorine-gas attack on 22 April 1915:[23] We knew there was something was wrong.

When we got to Ypres we found a lot of Canadians lying there dead from gas the day before, poor devils, and it was quite a horrible sight for us young men.

Having discovered that they could advance, they arrived in large numbers in the area on which the gas had spread itself some minutes before, and took possession of the arms of the dead men.

The Germans moved field artillery forward, placing three army corps opposite the 27th and 28th Divisions on the Frezenberg ridge (50°52′05″N 2°57′00″E / 50.868°N 2.950°E / 50.868; 2.950).

[24] The German attack began on 8 May with a bombardment of the 83rd Brigade in trenches on the forward slope of the ridge, but the first and second infantry assaults were repelled by the survivors.

The Germans were prevented from advancing further by the counter-attacks of the Princess Patricia's Canadian Light Infantry (PPCLI) and a night move by the 10th Brigade.

[26] We had only just time to get our respirators on before the gas was over us.German forces managed to advance and occupy the British line to north and left of the Battalion.

fire remained accurate and constant, whenever a target presented itself, until dusk.By the end of the battle, British forces had withdrawn to a new line 3 miles closer to Ypres, thereby resulting in a compression of its surrounding salient.

After all the examples our gallant Allies have shown of dogged and tenacious courage in the many trying situations in which they have been placed throughout the course of this campaign it is quite superfluous for me to dwell on this aspect of the incident, and I would only express my firm conviction that, if any troops in the world had been able to hold their trenches in the face of such a treacherous and altogether unexpected onslaught, the French Division would have stood firm.The Canadian Division mounted an effective defence but had 5,975 casualties by its withdrawal on 3 May.

The division was unprepared for the warfare prevailing on the Western Front, where linear tactics were ineffective against attackers armed with magazine rifles and machine guns.

[38] Lance Sergeant Elmer Cotton described the effects of chlorine gas, It produces a flooding of the lungs—it is an equivalent death to drowning only on dry land.

The colour of the skin from white turns a greenish black and yellow, the tongue protrudes and the eyes assume a glassy stare.

During the Second Battle of Ypres, Lieutenant colonel John McCrae, Medical Officer of the 1st Brigade CFA, wrote "In Flanders Fields" in the voice of those who perished in the war.