Shells also have to be carefully avoided, for, though destined for some far-away target below you, they sometimes in their flight destroy aeroplanes unintentionally. As I have already explained, we devoted much time to this subject at Châteauroux, learning the trajectories of the different calibers. Still, at the front, the theory is not so easily put into practice. It seems almost impossible to keep track of all the artillery massed by your own side, especially in such a sector as Verdun, where the guns often were placed so close together that their wheels almost touched. On more than one occasion when flying quietly through the air my machine has given a sudden lurch, and I have heard the dull "tung" of a passing shell. There is none of the whistling we are accustomed to on the earth; merely the dulled sound caused by the sudden displacement of the air. My own machine finally arrived, after delays that seemed interminable, and my two mechanics immediately set to work installing the various instruments, and painting it. These two men were personally responsible to me for the condition of the motor and planes, but, as pilot, I was the master of the machine, which was reserved for my own use. In fact, each aeroplane has painted on its body and rudder the name and distinguishing marks of its pilot and escadrille. After a few short flights I became aware of the fact that my biplane, in spite of all my efforts to correct it, showed a strong tendency to lean to the right. At times I could hardly make a turn to the left. This was a serious matter at the front, as an enemy might at any moment appear on my "weak" side and I would be placed in a serious position. I therefore mentioned the matter to my captain. To my surprise, he immediately ordered a new machine for me and gave directions that the one I was using should be sent back to the factory. The defect in this particular case was one mechanics could not remedy, and it seems that it was nothing out of the ordinary to send a machine back to the shops. At the front a pilot must have a perfect machine to work with or none at all. The life of a good aeroplane seldom is more than fifty hours of actual flying. During this time the organization of the escadrille was perfected. The pilots were divided into two "watches," one-half being on duty while the other was "standing by" ready for service in case of emergency. All the pilots except myself were "disponibles." I was exempt because I had no machine, and was therefore for the time being my own master, even when it came to rising in the morning. When the others on duty were awakened, at early dawn, I would be awakened with the rest. My turn had not yet come, however, and I could just turn over and sleep to my heart’s content.