It would be impossible, with one machine making one flight, to obtain anything like a comprehensive report as to an enemy’s doings—at least not in reasonable time. This is why, when a large area has to be covered, the Commander of aeroplanes will order out a regular squadron of machines. After a conversation with his immediate superior, the officer who is in charge of the airmen and observers will discuss with them the area which each machine shall cover. Again maps will be consulted, and aerial routes will be laid down. It will be the aim of the officer instructing the airmen to spread out his scouts so as to present a complete report, when the reconnaissance is effected. When the whole of the ground to be reconnoitred has thus been marked out upon the maps, each observer—who will be equipped with his own personal map of the fighting area—will be instructed as to the course he shall steer. He will duly note this, and return to his machine. Whereupon, the pilots will soar into the air from their camp, and speed away upon their missions. The pilot of the aeroplane will be concerned with nothing save the control of his machine. He will not need to trouble himself about the route taken, or about what is seen below. This work will fall upon the observer, who will be placed in the machine with an uninterrupted view of the country below him, and who will instruct the pilot as to the course he shall steer, and the elevation he shall maintain. The observer, indeed, will be in charge of the aeroplane. Upon him will rest the responsibility of the success of the expedition, from the point of view of the information to be obtained. But the work of the pilot will be important, also. Upon his skill, in manipulating the machine, will depend the carrying out of the flight, and the safe return of the aeroplane to Headquarters. Thus the fleet of air-scouts will start upon their errand of observation. Each machine will mount steadily, until an altitude, under ordinary conditions, of between 3000 and 4000 feet has been reached. Then, at this height, they will sweep out over the enemy’s lines. The altitude mentioned is generally regarded as a good height for reconnoitring work because it permits the observer a fairly-detailed view of the ground below, and places him, also, at what is considered a safe elevation, so far as artillery fire is concerned. The important question of the vulnerability of aircraft, in regard to artillery fire, will be dealt with fully in a later section.