Now it is quite certain on the events which have since taken place that the German Headquarters Staff clearly recognised these possibilities. Not only is that shown by the heavy losses they incurred in the wedging battles, which lasted from the middle of November to early part of February, but in the adoption of tactics, designed, as their relative strength in numbers fell, to economise their force. In short, not being able to change the features of the situation, they made a virtue of necessity by trying as far as they could to convert their front into an impregnable barrier of defence, and concurrently doing their utmost to increase the Allies' losses. Evidently both these means were calculated to delay the accomplishment of the Allied scheme. If at the same time there could be set on foot in the Allied countries the legend, not that the Germans had failed in their great invasion project, as they had, but that they were successfully withstanding an attempt of the Allied forces to push them back, then public opinion in the Allied countries might grow tired of the struggle, and at the finish withdraw from it, leaving Belgium in German hands. The Government of Germany well knew that in England more especially, where the misconception of military operations was profound, operations would be estimated on the, for the immediate purposes of this campaign, entirely false basis of a movement of the front from place to place. The object of the Allied commanders, and the conditions of a successful Allied advance would, in all probability, be alike misunderstood. Experience has shown that these calculations were only too well founded. The nearer the Allied scheme approached to accomplishment, the more energetic became the efforts to propagate the notion that it was a failure. The German plan of defence, which may be dealt with first, had then, apart from political calculations, two main features. The first was the fortification along their front of advantageous points in such a manner that they could be permanently held. The second was an elaboration of the tactics of trench warfare. From Ypres southwards to the spur of Notre Dame de Lorette near Arras the German front followed approximately the "inland coastline" already spoken of, and the only break in it geographically of any consequence was the valley of the Lys, the flat stretch lying between the hills south of Ypres and the spur at Aubers south-west of Lille.