One of the biggest challenges during WWI was the inability to move very quickly and once the French launched the first gas attack against advancing German soldiers, it gained popularity.

The reasons included debilitating or killings enemy troops, causing them to abandon their trenches or posts and making it easier for advancing troops to get through.

The French attack did not use a lethal gas, but it was effective.

The Germans used chlorine gas at the Second Battle of Ypres and it was thought to be a harmless smokescreen. As soon as the gas arrived at the French front line, it did major damage and caused the troops to flee.

Britain formed Gas Attack companies after this battle, and sent them to the front lines to release compressed coloring gas against the Germans. That wasn't a wise choice, because a wind shift caused the gas to cloud over the British and it cost 2000 injured soldiers and around 100 deaths.

In addition to chlorine gas, mustard gas and phosgene were used frequently. The Germans, French and British were the most frequent users of poison gas attacks and although they didn't kill a high number of soldiers, they were effective at incapacitating many soldiers and causing severe injuries.