The first casualties of the chlorine gas attack in World War One were the French (mostly Algerian soldiers). They were not trained for this kind of attack. When the first Chlorine gas was released into the air, the French began to retreat in massive numbers. This left the Canadians without any French support. It also left their center open to any German attack. But the Germans were unprepared for the results of the gas attack. Their reserves of manpower were low and they failed to take advantage of the French withdrawal. Canadian and British troops quickly filled the gap in the lines to stop the Germans from attacking.