Ludendorff, on his side, knew that he must hold the hinge of the door. He might yield toward the west, if necessary, but must not yield in front of Mézières and Sedan. The neck of the bottle must not be closed. The measure of our initial success, whatever the intrepidity of our attack, must depend largely upon how far we were able to take the Germans by surprise, and the depth of our advance must depend upon our ability to bring up our artillery and ammunition and food for our men. To the rear of the line from the Meuse to the Argonne Forest there are literally only two roads of approach. If we attempted to build more, they would immediately be visible to the aeroplane observers of the enemy. We could not build more when our engineers and our laborers were occupied at Saint Mihiel. If we arranged elaborate dumps of ammunition, these would inevitably be seen by the enemy or their presence would be communicated in some way as past experience had proved. To move long columns of troops and transport by day was equally an advertisement of our plan for an enormous attack which was the thing that we wished to conceal when the success of the attack was to depend upon secret mobilization and a swift blow. If we were to repair the old roads across the broad area of the shell-crushed no-man's-land and through the trench systems after our attack, this also required the assembling of a great deal of material in view of the enemy. No part of a modern army's arrangements is more difficult than the handling of the necessarily dense vehicular traffic behind the immediate front, even if ample supplies are brought to the railheads. The numbers of motor trucks and ambulances required were incredible. Our Service of Supply, which had been concentrating all its energies and material toward Saint Mihiel, now had to prepare for another equally great offensive. New railheads, new railways, new hospitals, new headquarters, and new routes of transport had to be established. With the certainty that the Saint Mihiel sector, if it became violent, would consume large quantities of ammunition we had to provide for the immense consumption of ammunition which would undoubtedly be required in the Meuse-Argonne. The continued fighting throughout the summer, with additional and unexpected requirements for the new offensive campaign, had made increasingly heavy drafts upon transport and animals. It was no use to say that more horses were coming from Spain and from America; they were needed now. All the tanks and aeroplanes and the light and heavy artillery which were in the making at home or on the docks at New York would be of no service unless they were in the battle. The lack of sufficient railway lines and shortage of rolling stock required accordingly more travel on the limited roads approaching the area of concentration east and west of Verdun.