The disadvantage of the 28th's sector from the start was that there was no screen of foliage to cover a deployment before a charge. On the night of the 26th the battalion which had been held up by the Perrières Hill was marched round, to carry out the plan of "scalloping," for an attack on the Chêne Tondu, which was an escarpment projecting out of the Forest into the valley of the Aire north of Montblainville, like a wood-covered promontory into a strait. It commanded the whole river valley and the Forest edge on its front. Its slopes were irregular, with every irregularity seeming to favor the defender, who at every point looked down-hill upon the attacker. Behind it was another escarpment, even stronger, the Taille l'Abbé. Between the two the enemy had ample wooded space for moving his reserves and artillery free from observation. Should the Chêne Tondu be lost, the enemy had only to withdraw with punishing rearguard fire to this second bastion. On the reverse slope of the Taille l'Abbé were hospitals, comfortable officers' quarters, and dugouts, while the artillery in position there could shoot over the Chêne Tondu with plunging fire upon its approaches. Along the heights of the Forest edge and other heights to the rear, other guns, as many as the Germans could spare for the sector, might find perfect camouflage and security. There were also the heights of the east bank of the Aire to consider. With the river winding past their feet they interlocked across the valley. Thus advancing down the valley meant advancing against heights in front as well as on the flanks. Stretching back to the whale-back itself beyond the heights of the east bank were other heights, even more commanding, whose reverse slopes offered the same kind of inviting cover for long-range artillery as the reverse slopes on the west bank. If a height on one bank were not taken at the same time as the corresponding height on the other, this meant murderous exposure for the men in the attack that succeeded. Therefore, thrifty and fruitful success required a uniformity of movement by the three divisions of the First Corps in conquering the heights of both banks of the Aire and of the Forest's edge. For the 28th the taking of the Chêne Tondu was the keystone of the advance. Until it had this height, the 28th could not support the movement of the 77th in the Forest or of the 35th on the east bank of the Aire. The Germans had concentrated their immediate reserves on the Chêne Tondu, and their guns on its supporting heights.