on the night of 22 april 1915, the germans launched the first poison gas attack of the war on the western front. the object of their attack was the ypres salient, and they concentrated their initial attack on two french divisions, the 45th (algerian) and 79th (territorial). attacking in the evening of the 21st, the two french divisions found themselves ill-prepared to cope with the chlorine gas and promptly broke, leaving a gap in the line four miles wide.