By the time my second machine arrived I had been at the front long enough to appreciate the rôle played by each of the different types of aeroplanes used in this great conflict. Camped near us was a bombarding unit. Every night when the heavens were clear these machines would go up, turning great circles over our heads until they reached the desired altitude. They would then vanish with their destructive bombs in the direction of the enemy. We could always tell when they passed over the lines, for the German search-lights would become very active, and the sky would become dotted with sparks, which in reality were exploding shrapnel. Then, in the early hours of the morning, they would return, having flown far into the enemy’s country to drop their bombs. This is tiresome and disagreeable duty, but not by any means as dangerous a one as the other branches of aviation, for bombers are practically free from interruption by enemy aeroplanes in the dark. Camped with us was the famous N-64, the crack fighting unit of the French Aviation Corps. Among its pilots were such famous aviators as Navarre, Nungesser, and Vialet, known familiarly as the "aces." Every evening just before sunset these men would take their machines up in the twilight and do "stunts" for the benefit of hundreds of admiring "poilus" gathered from neighboring camps. These were the self-same "stunts" which on many occasions had enabled them to escape from sure death at the hands of some superior enemy force. As I have said before, the fighting work, although in reality the safest, requires the most experienced and accomplished pilots. The chief duty of the Nieuports is "barrage," or sentry duty. There are always several of them flying over the lines, on the lookout for some "Boche." It is their task to swoop down like a hawk upon them and destroy or else drive them away. Of course, our own "avions de chasse" are as liable to be attacked by the enemy, and they must in consequence be continually on the "qui vive." When one of the larger reconnoissance machines is compelled to go far into the German lines on special-mission work, it is usually accompanied by a body-guard of several Nieuports. Spies, on the other hand, are carried only in the fast-flying Nieuports, which in this case are double-seated. It seems that it is comparatively easy to take a man over and leave him far in the rear of the German trenches, but going back for him is another matter. After several days the pilot returns to a prearranged place, but, as sometimes happens, his compatriot may have been caught. In this case a like fate usually awaits him at the hands of the watchful enemy.