German forces are heavily committed to the Gorlice-Tarnów offensive against Russia. On the Western Front, the ongoing offensive at Ypres is still consuming German manpower. That should mean that the Germans are weaker elsewhere in the west. Now the British and French try to take advantage of this weakness by launching simultaneous offensives. British forces are to attack the German defenders of the Aubers Ridge, near Neuve Chapelle. Further south, the French will attack in the Artois region, hoping to take the Vimy Ridge and reduce a German held salient.
The British attack is a disaster. The British are short on artillery shells and have only enough for an ineffective 40 minute barrage. When the British infantry attack they find that German defences are far stronger than expected and their way is barred by vast fields of barbed wire. The attackers (troops from Britain and Ireland and also India) are cut to pieces by German machine guns. By the time the attack is called off they have suffered some 11,000 casualties.
The French do somewhat better in their sector. They have been able to batter the Germans with a 1,200 gun artillery bombardment lasting for six days. Thanks to this bombardment and careful planning, the French attackers break the German line and in places advance for up to 5 kilometres. However, the gains are costly and the cohesion of French forces breaks as they advance. The heavy losses make it nigh impossible that these early successes will be effectively exploited.
The Allies’ plan of attack (Webmatters: First World War, Carte de Route)