Probably the most important service of all is performed by machines under heading (1). If a successful offensive can be maintained over the enemy's lines he is unable to intelligently direct his artillery fire, and can obtain no information regarding reinforcements, or troop concentrations for an impending attack. With fighting aeroplanes clearing the way for our own observation machines and artillery spotters, the enemy is not only blinded, but is blocked in any attempt to attack or concentrate his forces. The fact that the French aerial offensive at Verdun was so efficiently and well maintained accounts for the failure of the heavy German artillery. Driven far back over their own lines, the German aviators were seldom able to observe the placing of the shells, and as a result their gunners were practically trusting to luck in reaching their target. An immediate and accurate bombardment always followed one of the very infrequent German air raids over the French lines. Whenever the French, partially abandoned their aerial offensive in favor of a defensive campaign, they soon lost their mastery of the air. As long as enemy machines can be kept back of their own lines, new trench systems can be constructed, transportation lines can be extended and ammunition dumps arranged, undertakings that would be highly precarious with enemy observation machines continually passing overhead.
Fig. 1. Italian "Pomilio" Two Seater Biplane. Courtesy "Flying."
To maintain an effective offensive places a tremendous strain on both the men and the machines, for though the aeroplanes do not penetrate far beyond the lines they usually meet with superior numbers, and in addition are continually in range of the anti-aircraft guns. In an attack over hostile country a slight mishap may cause the loss of a 'plane, for usually the distance from its base is so great as to prevent a gliding return. Over its own lines an engine failure is usually only a temporary inconvenience. Fighting aeroplanes, for the offensive, are small high powered machines generally of the single seater type, and are capable of high horizontal and climbing speeds. The armament consists of a machine gun of the Lewis type, and occasionally a few light bombs may be included in the equipment. As they do not carry out operations far to the rear of the enemy's lines they are provided with fuel for only two or three hours, and this reduced fuel load is necessary for the high speeds that must necessarily be attained. The area is limited to permit of quick maneuvers in attack and escape, and at the same time to reduce the head resistance and weight. The horizontal speed may run up to 150 miles per hour, with a climbing velocity that may exceed 1,000 feet per minute. Such machines are variously known as "Speed Scouts," "Chasers," or "Pursuit Type" (French "DeChasse"). At the beginning of the war the chasers were largely of the monoplane type, but at present the biplane is in almost exclusive use.
Fig. 2. Machine Gun Mounting on Morane Monoplane. Gun Fires Directly Through the Propeller Disc. The Deflecting Plate Attached to the Root of the Propeller Blade Protects the Propeller When in Line of Fire. Ammunition in This Gun Is Furnished in Straight Strips or "Clips."
The aeroplane employed for surveys of the enemy country and battle front (2) are of an entirely different type and are much larger and slower. These "Reconnaissance" machines are generally of the two-seater type, the personnel consisting of an observer and the pilot, although in some cases a third man is carried as an assistant to the observer, or to handle a machine gun against an attack. Since their speed is comparatively low, they are generally provided with an escort of chasers, especially when employed on distant missions, this escort repelling attacks while the observations are being made.
Fig. 2-a. Machine Gun Mounting on S. P. A. D. Biplane. Gun Is Rigidly Attached to Fuselage Top in Front of Pilot.
For accurate observation and mapping, the speed of an observation machine must be necessarily low, and as they are additionally burdened with a wireless set, an observer, a large fuel reserve, and other impedimenta, they have a comparatively great area and are therefore lacking in the maneuvering qualities of the chaser. The span will average about 40 feet, and the weight carried per horsepower is greatly in excess of that of the chaser. From a number of examples, the reconnaissance type will average from 16 to 18 pounds per horsepower, while the loading of the scout is from 8 to 12. This means that the former has comparatively little reserve power for rapid climbing. The present reconnaissance type is always armed, and must not be confused with the early machine by that name, which, in fact, was merely an enlarged training machine and had neither offensive nor defensive powers. The Observer acts as gunner, and is located at a point where he has the greatest possible range of vision, and where the angle of fire is as little obstructed as possible.