They were sent to defend against several German Divisions who faced them from the northwest. The Canadians had arrived in Flanders a few months earlier and had not expected to see much action. They were in for an unpleasant awakening.

On that fateful day of 22 April 1915, gas warfare was unleashed for the first time on unsuspecting Dominion troops holding the front lines, and the necessity of protecting troops from gas warfare began.

The first masks the troops used that day were no better than soaked rags tied around their mouths to protect them against the chlorine gas that drifted into their trenches. Within a few months, production began on a primitive gas mask and millions of them were sent to the front.

Early versions were just hoods with small eyepieces that soldiers pulled over their heads. As the war progressed and the use of even deadlier gas by both sides became commonplace, the gas mask became more sophisticated, until eventually and perhaps regrettably, next to his Lee Enfield rifle, the gas mask became the soldiers best friend.

Between the 14 and 17 April 1915, the First Canadian Division was ordered to relieve a French Division at Ypres, an ancient Belgian city in Flanders. To the left of the 2nd and 3rd Canadian Brigades, was the 45th French Algerian Division, while on their right, was the 28th British Division.

The Canadians were first ordered to reinforce the 4500 yards of trenches which the French had vacated. They did not have time, as the Germans began to launch a massive attack to test the use of gas as an offensive weapon.

At about 5:00 p.m., with winds blowing directly into the positions of the French and Algerians, the Germans began what is believed to be the largest gas attack that had ever been attempted. The terrible gas threw the Algerians and a French territorial unit into unrestrained panic as the Germans unleashed 160 tons of chlorine gas from 5700 canisters.

The soldiers in the Canadian lines could see the yellow and greenish coloured gas cloud move directly through the French positions settling in their trenches. Many of the French choked to death almost immediately as chlorine gas causes the lungs to begin to disintegrate upon contact.

Other French and Algerian soldiers, in abject terror, left their trenches and attempted to run from the unrelenting cloud of horror. The survivors fled in panic, gasping for breath, choking on the gas and literally vomiting up their lungs, their faces purple. The more exertion they spent, the more gas they inhaled and their terror only magnified. Death was the only relief, because medical officers had no idea how to treat those affected and protective gas masks were unknown to the Allies.

The initial gas attack had not hit the Canadian line directly, but the Division’s left flank was now fully exposed by the breach left by the French. German infantry now began to pour into the positions left behind by the panicked French soldiers.

Reacting quickly, Generals Currie and Turner, commanding the 2nd and 3rd Canadian Brigades respectively, moved men into the gap left by the dead and retreating French in an attempt to hold the original positions. Amazingly, the Canadian soldiers found surviving French colonial infantry resisting the enemy.

The Germans wearing crude gas masks, took advantage of the initial effectiveness of their new and terrifying weapon. They now turned a second chlorine gas attack against Canadian positions. On 24 April a second greenish, yellow cloud rolled directly against a 700 meter front held by the 8th Battalion of Currie’s 2nd Brigade and the 15th Battalion of Turner’s 3rd Brigade.

Lieutenant Colonel George Nasmith, a Canadian trained as a chemist, identified the chlorine gas and recommended the first emergency measures taken to help save lives. Canadian soldiers were instructed to urinate on their cotton ammunition bandoliers, handkerchiefs, or puttees and hold these urine soaked items over their noses. This action saved many lives, but the effect of the gas was devastating on the two affected battalions directly hit by the gas.

Vomiting, gasping and barely able to see or breathe, the men of the 15th Battalion directly in the path of the gas were still able to fight, but were forced to retreat to the base of Gravenstafel Ridge where the German attack was stopped, but with the terrible loss of 647 Canadian casualties.

Somehow, artillery fire and rifle and machine gun fire from flanking companies unaffected by the gas, as well as the resolve of those men affected, but still able to fight, slowed the German advance. The tenacity of the Canadians had stopped the Germans from overrunning Ypres. In five days of fighting, the Canadian casualties numbered more than 6,000, with 1,250 taken prisoner, but the Germans had failed to take advantage of their new and terrible chemical weapon.

Cluny Macpherson, a Canadian doctor from St. John's, Newfoundland, quickly came up with the idea of a gas mask made of fabric and metal. Using a helmet taken from a captured German prisoner, he added a canvas hood with eyepieces and a breathing tube.

The helmet was treated with chemicals that would absorb the chlorine used in the gas attacks. He had invented the world's first gas mask. After a few improvements, Cluny Macpherson's helmet became the first gas mask to be used by the British army.

The Allied High Command immediately adopted the idea and developed bulky, makeshift gas masks that were claustrophobic and which restricted vision, but were helpful in saving the lives of soldiers.

This Canadian's invention was the most important protective device of the First World War, protecting countless soldiers from blindness, disfigurement or injury to their throats and lungs. Gas masks are worn by millions of soldiers around the world today.

The Germans continued their use of chemical weapons, including the use of mustard gas, which would seriously affect soldiers even wearing gas masks. Mustard gas was first used in artillery shells in mid 1917 and caused severe and painful blistering of the skin which would effectively remove soldiers from combat.

The First World War saw the first use of chemical weapons and today nations such as Iraq under Saddam Hussein, used even more terrible and deadly weapons of death. We can only hope that they will never be used again.