Attacks to threaten Lens and Lille were to be made by the First Army in late June near Gavrelle and Oppy, along the Souchez river. The objective was to eliminate a German salient between Avion and the west end of Lens, by taking reservoir Hill (Hill 65) and Hill 70. The attacks were conducted earlier than planned to use heavy and siege artillery before it was transferred to Ypres, the Souchez operation being cut back and the attack on Hill 70 postponed. The Battle of Hill 70, south of Ypres, eventually took place from 15 to 25 August. The Canadian Corps fought four divisions of the German 6th Army in the operation. The capture of Hill 70 was a costly success in which three Canadian divisions inflicted many casualties on the German divisions opposite and pinned down troops reserved for the relief of tired divisions in Flanders. Hermann von Kuhl, chief of staff of Army Group Crown Prince Rupprecht, wrote later that it was a costly defeat and wrecked the plan for relieving fought-out (exhausted) divisions in Flanders.