The Battle of Le Transloy took place between 1st October and 11th November 1916 and was at first successful. The Allied advance was eventually halted by what?

In February 1916, the Germans began their attack on Verdun and the French troops intended for the Somme Offensive were sent to defend the town. Consequently, the British forces, intended for a supporting role, became the core of the attack.  What was to follow was one of the bloodiest engagements of World War 1.