By the 6th of April the German thrust towards Amiens had failed, and for the moment the gate of the Somme was closed. Brought to a standstill, Ludendorff cast about for a diversion, for he could not permit the battle to decline into a stalemate, and so lose the initiative. His main purpose was the same, but he sought to achieve it by a new method. He would attack the British elsewhere on some part of the front where they were notoriously weak, and compel Foch to use up his reserves in its defence. Then, when the Allied “mass of manœuvre” had shrunk, he would strike again at the weakened door of Amiens. On Ludendorff’s plan the operation was to be a strictly subsidiary one, designed to prepare the way for the accomplishment of his main task farther south. He proposed to allot only nine divisions for the initial stroke, and to choose a battle-ground where even a weak force might obtain surprising results. That battle-ground was the area on both sides of the Lys between the La Bassée Canal and the Wytschaete Ridge. The German Staff were aware that it had already been thinned to supply ten divisions for the contest in the south, and that at the moment it was weakly held, mainly by troops exhausted in the Somme battle. Haig, as we know from his dispatch, had drawn especially upon this section, since a retreat there would not imperil the whole front so gravely as would the loss of ground between La Bassée and Arras. Nevertheless, it was a very real danger-point. The enemy had the great city of Lille to screen his assembly. Certain key-points of communications, like Béthune and Hazebrouck, lay at no great distance behind the British front. The British communications were poor, and the German were all but perfect. Any advance threatened the Channel Ports, and might be expected to cause acute nervousness in the mind of British Headquarters. Reinforcements would be demanded from Foch, and the place was far enough from the Amiens battle-ground to put a heavy strain upon the Allied power of reinforcement. Ludendorff’s aim was by a sharp, short thrust to confuse the Allied plans and absorb their reserves. If he could break through at once between La Bassée and Armentières and capture Béthune, he could swing north-westward and take Hazebrouck and the hills beyond Bailleul, and so compel a general retirement west of Dunkirk and the floods of the river Aa. But to succeed he must have a broad enough front. He must take Béthune at once and the Messines Ridge soon after, for, if the British pillars of the gate at Givenchy and Messines should stand, his advance would be squeezed into narrows where even a weak and tired force might hold it. [Sidenote: _April 8-9._]