"Flying airplanes for war purposes is something different to ordinary flying. The principal practice is to learn the methods of attack and defense. But that is not all. The airplane is the eye of the army; the observer must know how to observe. He must be able not only to see, but to put his knowledge into such form that it can be handed in in the form of a report. While he may get the information he must learn that the information is not for his own gratification, but for the use of the men in the field," said Tom. "Do all the machines carry a pilot and an observer?" asked Ralph. "Not by any means," answered Tom. "The first duty of a pilot is to learn how to control his machine when approaching an enemy, and how to attack or to avoid him. For that purpose he has a machine gun which he uses in flying." "I had no idea that there was so much to do in the business," said Alfred. "That is only part of the practice," continued Tom. "The most interesting part of the work is to practice flying in squadron formation, to observe the signals of the commanding officer and to execute movements. For this purpose two squadrons oppose each other, and sally forth, the object being to judge the objects of an attacking force and to devise means to repel the enemy." The boys sat on their improvised bunks until a late hour that night. They discussed the airplanes; the men they had met; their work in rescuing the fallen aviators, and the things they had learned in this, to them, the most eventful day. "I wonder what father would say if he knew we were going to join the aviation corps?" said Alfred. "Well, I wonder what he will say when he hears what we were doing in Belgium," replied Alfred. "He must have gotten our letters by this time," said Ralph. "Then why doesn't he answer our telegram?" asked Alfred. "Why, we forgot to go back to the city and inquire for it," said Ralph. "That's so; but we've been too busy for that; we must do that the first thing in the morning," said Alfred. CHAPTER III THE WOUNDED AVIATORS They were out early the next morning, and started for the tramway a mile distant. They passed Tom's hangar, and stopped for a moment to take a look at his machine. As they were leaving they heard his voice: "Going to leave us?" he inquired. "No; but we must go to the city to get our mail, and we are expecting a telegram," shouted Ralph. "Get back by eleven o'clock if you can," was the answer. "We'll be here, sure," said Alfred. "He must mean that we can have a try in the machine at that time, I suppose," remarked Ralph. "I imagine that's why he wants us back then," answered Alfred. They covered the mile in record time. The idea of going up in a machine was a stimulus, and they talked about it all the way, and wondered what it would feel like to sail above the earth in a war-machine.