Shovels and picks were again brought into use. Some of the men made an observation of the bank alongside of the guns, while others began to dig into the hills. Others brought up short sections of young trees, which were planted upright side by side and placed across the top to form a sort of roof or ceiling. The earth, as it was taken out, was pitched up on top of the roof thus formed. The holes were dug into the banks from six to eight feet deep, and usually six feet wide. Each of the shelters thus made room for four men. Really, each was intended for eight men, but as half of the men would be on duty, while the other half would be at rest, it will be seen that much space was economized. The mess shelters were somewhat larger or rather, longer, but not any deeper, and heavy posts were set at intervals, to hold the roof and the earth. As these places were on the rear side of the steep bank they were protected from shot or shell, however vigorous might be the bombardment, but, of course, the guns were subject to be hit by well-aimed shots. The boys took keen delight in digging their shelter and in carpeting the floor with the stray leaves, which were found all about the gun emplacements after the protecting boughs had been put overhead. True, the easy chairs were not the most comfortable, as they had to improvise the furniture from the odd sticks and branches which were obtainable. But this didn't matter. They were going to have a taste of the work with a 75-millimeter battery. "That Nieuporte machine is making observations now," said Alfred, "and the puff indicates that they have located two of the batteries." "Well done," said the captain. "Glad you can read the signals so well. Take your station at No. 2; and you, Ralph, go to No. 4. Report to the lieutenant there, and give him the benefit of your observation." It was a proud moment for the boys. They saluted and stationed themselves as ordered. There had not been one moment of silence during the entire morning. The guns were constantly booming, and sometimes there would be a rattle, as though salvos of machine guns were brought into action. Anti-airship guns were always flashing, and high in the air white and gray puff balls would announce the explosion of shells, trying to feel out the positions of the airships. "That was a German shrapnel," said Ralph, "and the one this side a French high explosive." "How do you know?" asked one of the men. "By the color of the smoke," replied Ralph. "There, did you see the two that came together, one with very white smoke on the right; the other with a sort of gray, off to the left? That last one was from a French gun." "What's the matter with that Farman machine?" said one of the gunners. "He acts queerly." "The wing must be shot off, or he wouldn't spiral in that way," replied Ralph. "He's coming down, but he has the machine in control, I think," remarked one of the men. [Illustration: _Method of Signaling from Airplanes_]