The one-seated Nieuport, rapid, easily managed, with high ascensional speed, and capable, by its solid construction and air-piercing power, of diving from a height upon an enemy and falling upon him like a bird of prey, was then the chasing airplane _par excellence_, and remained so until the appearance of the terrible Spad, which made its _debut_ in the course of the Somme campaign, Guynemer and Corporal Sauvage piloting the first two of these machines in early September, 1916. They were armed with machine-guns, firing forward, and invariably connected with the direction of the machine's motion. The Spad is an extraordinary instrument of attack, but its defense lies only in its capacity for rapid displacement and the swiftness of its evolutions. Its rear is badly exposed: its field of visibility is very limited at the sides, and objects can be seen only above and below,--below, minus the dead angle of the motor and the cock-pit. The pilot can easily lose sight of the airplanes in his own group or that of the enemy, so that if he is alone, he is in danger of being surprised. On the other hand, one condition of his own victory is to surprise the enemy, especially if he attacks a two-seated machine whose range of fire is much broader, or if he does not hesitate to choose his victim from among a group. The Spad pilot makes use of the sun, of fog, of clouds. He flies high in order to hold the advantage of being able to pounce down upon his enemy while the enemy approaches prudently, timidly, suspecting no danger.