By the time the first line is driven back the defending army knows where the enemy has chosen to strike and is ready for him on the second line or "line of resistance." Here the battle is on in all its fury. If here again the enemy advances, there is still a third line of "battle positions." This is practically the last entrenched position that the defenders have. If they are driven back from this into the open country beyond, it becomes a serious thing for the retreating army, as many of their big guns will have been lost, and their forces are apt to be more or less disorganized, while the enemy is flushed with the victory he has so far gained. The cannonade kept on with increasing fury all through the early morning. "Heinie must have plenty of ammunition," remarked Frank. "He's spending it freely." "It beats anything we've been up against since we came to the front," observed Billy. "It seems to be coming nearer and nearer all the time," said Bart. "I guess this is going to be our busy day." There was intense activity all through the lines. Orderlies galloped from place to place with orders. Big motor cars rumbled up, loaded with troops who were hastily placed in position. The big guns of the Allied forces had opened up and were sending back shell for shell over the enemy lines. For over two hours the artillery kept up the Titanic duel. The fog was lifting, though still heavy in some of the low-lying sections. The Thirty-seventh was resting easily on its arms, ready for whatever might happen. "We may not see so much fighting after all," remarked Billy, after a while. "The fellows in front seem to be holding pretty well. Perhaps they'll throw the Huns back right from the start." "Don't kid yourself," replied Frank grimly. "That first line is almost sure to go. It's expected to. It's only a forlorn hope anyway. We'll get our stomachs full of fighting before the day is over." Even while he spoke there were signs of confusion up in front. Groups of men came in sight evidently retreating. Machine gun crews, bringing their weapons with them, were hurriedly setting them up in new positions. There would be a few discharges and then they would be forced to retreat still further. They were fighting splendidly, and putting up a dogged resistance, yielding ground only foot by foot, but to the experienced eyes of the boys there was no mistaking the signs. The enemy had broken through the first line positions. "Well, it's nothing more than we knew would happen," remarked Frank, as his frame tingled with the excitement of the coming fight which he knew would soon be upon him. "That's so," agreed Bart. "But what gets me is that the line was broken so quickly. I thought it would be afternoon at least before the Huns got as far as this." The lines opened up to let the newcomers through so that they could go to the rear and re-form.