Despite the number of Allied offensives and German counterattacks, no significant advances were made on the western front in 1915. The relentless artillery barrages, entrenchments and barred wire meant that both sides ended up deadlocked. The Germans launched one major offensive at Ypres, April 1915, where they introduced chlorine gas as part of a ‘mass casualties’ strategy. After the French retreated at Ypres, the Germans aimed at keeping the Allies at bay for the rest of the year, while making steady gains on the eastern front. A series of Allied offensives seeking to capture the Noyon Salient, running from Neuve Chapelle to Verdun, were parried with heavy casualties as the Germans introduced the new Fokker aircraft, which drove the Allied reconnaissance aircraft from the skies. By the end of 1915, the French and British were ready to launch new more sophisticated fighter aircraft, restoring their air superiority.