Because of the heavy losses sustained at Ypres Salient, 15,000 British and Indian troops arrived to provide the much-needed support. Unfortunately, the yellow flags that the 15,000 advancing troops raised to protect themselves from British artillery, also gave away their positions to the German gunners. Because they were easy targets, the centerlines began to break, and the Germans released more gas, making any further advancement from the Allied forces impossible. The French troops who were ordered to assist the British flank, shot their commanding officers for fear of also being exposed to the gas. The Germans were able to hold off many attacks with the help of gas, but any of their attempts of advancement were difficult when they tried combining gas deployment with an infantry charge. Winds were generally so unpredictable that advancing troops found themselves moving into their own poisonous cloud. Eventually the Allied forces received simple respirators reducing immediate danger from the gas. "The horrible part of it is the slow lingering death of those who are gassed," General Charteris wrote in his diary" (Gilbert 145). Hundreds of troops that were exposed to the chlorine gas lay out in the open trying to breath as much fresh air as possible, but because of the water in their lungs, they slowly drowned to death. The symptoms of Chlorine gas were easily preventable with the use of a gas mask. Because of this there was a need for a deep penetrating poison. Frederick Guthrie, a German scientist, combined ethylene with dichloride .
and noticed the blistering effects on his skin. With further experimentation on mice, he realized the toxicity of the chemical and its potential use as a weapon in war.
Mustard gas had many devastating effects, but damage to the eyes was the most common. The first symptoms generally occurred two hours after initial exposure to the poisonous gas.