The 6th French army, which by a vigorous forward thrust had driven the enemy out of Rheims, was to push up through the transverse gap to Berry-au-Bac, and assault the hostile positions on the hillsides along the east side of the gap. Along these hills the Germans had settled themselves in force. Here, too, there were many chalk quarries and caves, which the Germans were using as shelters and stores. At first sight it might well seem that the frontal attack undertaken by the British was not strictly a necessary operation. Clearly, the feasible way of driving the Germans out of their fastness was to turn the flanks of the position on the west through Lassigny and Noyon, and on the east through Berry-au-Bac. The main operation was, of course, that of turning the position from the west, for the right of the German position remained its vulnerable point. It was essential, however, to the success of that operation that General von Kluck should not be able to meet it in force until, at all events, the Allied troops had taken a firm grip. Now, if the British army had assumed a merely watching attitude on the south side of the Aisne, and had in consequence been able to extend their line from the south of Craonne down the river to, say, Attichy, some ten miles below Soissons, that, while leaving nearly the whole strength of the 6th French army free to undertake the turning movement, would at the same time have left General von Kluck also free to throw his main strength against it. A vigorous and pressing attack along his front was consequently essential, in order to keep his main force employed. Not only was the attack essential, but it had to be launched against him without delay, and before he could recover from the effects of his retreat. Including the troops recalled from Amiens, Generals von Kluck and von Bülow had under their command, nominally at any rate, ten army corps. If, deducting losses and war wastages, we put their strength in effectives at not more than the equivalent of six corps--it could have been very little more--yet six corps was, _in the positions they held_, a force fully able to cope with the nine corps making up the three Allied armies pitted then against them. Bearing in mind, indeed, the natural defensive advantages of the ridges on which the Germans had established themselves, and their facility for moving troops either for the purposes of defence or of counter-attack, their strongholds could have been held by three corps, leaving the remainder to be used on the flank for active operations.