But though the mass was thus made up again, there is a wide difference between a great army consisting wholly of first line troops and an army, even of equal numbers, formed of troops of varying values. The driving head was no longer solid. In the battle on the Somme when the British occupied positions from Ham to Peronne, and the French army delivered a flank attack on the Germans along the line from St. Quentin to Guise, the invaders were again checked. From St. Quentin to Peronne the course of the Somme, a deep and dangerous river, describes an irregular half-circle, sweeping first to the west, and then round to the north. General von Kluck had here to face the far from easy tactical problem of fighting on the inner line of that half-circle. He addressed himself to it with vigour. One part of his plan was a wide outflanking movement through Amiens; another was to throw a heavy force against St. Quentin; a third was to force the passage of the Somme both east and west of Ham. These operations were undertaken, of course, in conjunction with the army of General von Bülow. Part of the troops of von Bülow, the 10th, and the Reserve Corps of the Prussian Guard were heavily defeated by the French at Guise. But while it was the object of the French and British to make the German operations as costly as possible, it formed, for reasons which will presently appear, no part of their strategy to follow up local advantages. Why it formed no part of their strategy will become evident if at this point a glance is cast over the fortunes of the other German armies. The army of General von Bülow had been engaged against the French in the battle at Charleroi and along the Sambre, and again in the battle at St. Quentin and Guise, and admittedly had in both encounters lost heavily. The army of General von Hausen had been compelled to fight its way across the Meuse in the face of fierce opposition. At Charleville, the centre of this great combat, its losses, too, were severe. Again, at Rethel, on the line of the Aisne, there was a furious six days' battle. The army of Duke Albert of Wurtemberg had twice been driven back over the Meuse into Belgian Luxemburg. The army of the Crown Prince of Germany, notwithstanding its initial success at Château Malins, had been defeated at Spincourt. The army of the Crown Prince of Bavaria had been defeated with heavy loss at Luneville. Divisions of the German army operating in Alsace had been worsted, first at Altkirch, and again at Mulhausen. Taking these events together, the fact stands out that the first aim in the strategy of General Joffre was, as far as possible, to defeat the German armies in detail, and thus to hinder and delay their co-operation. He was enabled to carry out that object because the French mobilisation had been completed without disturbance.