midnight
No one seemed to know what was back of it , but rather believed Siddons was to be transferred to Observation , at least during the coming battle . To this information McGee made no reply , but secretly hoped that Siddons was in fact being transferred to Observation , where his activities would be more easily accounted for due to the fact that he would be carrying an observer . Late that afternoon rain began falling , and at mess time the mess hall became the stage for exceptionally spirited banter and wild conjecture as to what would happen on the morrow . Confidential battle orders carried the information that artillery preparation would begin at midnight , continuing with great concentration until 5:30 a.m. , zero hour , when the attacking forces of nine American divisions would storm over the top in the beginning of a titanic struggle to carry the famous Hindenburg Line and sweep the Germans back through the Argonne and beyond the Meuse . Every fighting unit had been given comprehensive plans of the objectives and of the ground over which they were to advance . The air units were especially drilled in the battle plans , for Great Headquarters would look to the Observation section and to the pursuit planes for a full measure of information as to how the battle went . Major Cowan 's pursuit group was only one of the many ready to begin operations on this new front , but none could have shown more enthusiasm and eager expectancy than did this group of young men who wolfed down their evening meal and jested in a strained , light-hearted manner that betrayed the nerve tension under which they were laboring .