and explain how the government spent some of the money which you paid for your Liberty Bonds. * * * * * Though in this chapter I have attempted to sketch the manifold phases of America’s preparation for obtaining supremacy in the sky, I have purposely left until the last the most important phase of all—the flying-men themselves. The personnel side of the Air Service, including the selection, training, organization, and operation of the flying forces, developed, within the year following America’s declaration of war, into one of the most remarkable educational systems in this or any other country, with a larger student body and a more diverse curriculum than any university in the world. Teaching men to fly, to send messages by wireless, to operate machine-guns in the air, to gauge the effectiveness of artillery-fire by its bursts, to read and make maps, to operate gas-engines, and to travel hundreds of miles by compass; teaching other men to read the enemy’s strategy from aerial photographs, and still others to repair instruments, ignition systems, propellers, airplane wings, and motors, required a vast network of schools and flying-fields, a huge force of instructors, many of whom themselves had to be trained, and an amazing mass of equipment and curricula. The pilot is the heart and brain of the whole flying apparatus. Parts of the airplane may break without serious result, but when the pilot breaks, even momentarily, nothing is left to direct the flight. The man and the machine come crashing to the ground. The early view that any one who “had the nerve” could fly caused hundreds of unnecessary deaths and an enormous avoidable waste of material. The lesson, for which we paid in bitter and costly experience, was that it is essential to choose flyers who are especially fitted for particular work, and then to keep them in condition to perform their duties at all times by using the same thought and care which is expended in the feeding, exercising, and conditioning of a race-horse. Nature, remember, never intended man to fly in the same sense that she did not intend him for life in a submarine. Conditions are unnatural from the time he leaves the ground until he returns. There are countless obstacles which he must overcome. He flies in an atmosphere deficient in that oxygen which is “the breath of life”; he is subjected in war to the shell-fire of antiaircraft guns and attack by enemy aircraft; he travels through space at a speed far exceeding that of the fastest express-train. In attaining altitudes and breathing rarefied air, the flyer is shaking his fist in the face of nature.