The increase of the skill of infantry in the attack, in their nicely calculated and acrobatic coördination with protecting curtains of accurate artillery fire, had been the supreme factor in the progress of tactics. As a young army we had all these lessons to learn and to apply to our own special problems. As we could not use the divisions that were at Saint-Mihiel in the initial onset in the Meuse-Argonne, we had to depend upon others from training camps and upon those which were just being relieved from the Château-Thierry area. Two of them had never been under fire; several had had only trench experience. They had not fought or trained together as an army. Many of our commanders had not been tried out. Some of the divisions were as yet without their artillery brigades; others had never served with their artillery brigades in action. By the morning of September 25th, or thirteen days after the Saint-Mihiel attack, all the infantry, the guns, the aviation, and the tanks must be in position to throw their weight, in disciplined solidarity, against a line of fortifications which had all the strength that ant-like industry could build on chosen positions. We had neither material nor time for extensive preparations. We must depend upon the shock of a sudden and terrific impact and the momentum of irresistible dash. If we took the enemy by surprise when he was holding the line weakly with few reserves, we might go far. Indeed, never was the element of surprise more essential. We were countering Ludendorff's anticipation that, if he withdrew from the salient, we should stall our forces ineffectually in the mud before Metz: countering it with the anticipation that he would never consider that a new army, though it grasped his intention, would within two weeks' time dare another offensive against the heights of the whale-back. For our dense concentrations we had only two first-class roads leading up to the twenty-mile front between the Meuse and the Forest's edge. These were ill placed for our purpose. We might form our ammunition dumps in the woods, but nothing could have been more fatal than to have built a road, for to an aviator nothing is so visible as the line of a new road. Where aviators were flying at a height of twelve thousand feet in the Battle of the Somme, they were now flying with a splendid audacity as low as a thousand feet, which enabled them to locate new building, piles of material, even well-camouflaged gun positions; and the minute changes in a photograph taken today in comparison with one of yesterday were sufficient evidence to a staff expert that some movement was in progress. An unusual amount of motor-truck traffic or even an unusual number of automobiles, not to mention the marching of an unusual number of troops along a road by day, was immediately detected.