On 9 April the British attacked. At Arras led by tanks and a creeping barrage, they took the German first and second lines and occupied part of their third while the Canadians swept the Germans completely off the Vimy Ridge. There was consternation at "OHL", their new defense had failed. It was Ludendorff's birthday but he refused to come to the celebratory dinner. Hindenburg “pressed the hand of my First Quartermaster-General with the words, ‘We have lived through more critical times than to-day together’” The British tried to exploit their opening with a futile cavalry charge but did not press further, because their attack was a diversion for coming French operations. In fact, their new defensive tactics had not been tested, because Sixth Army commander Ludwig von Falkenhausen had packed men in the front line and kept counterattack divisions too far back. He was replaced.