Fig. 125.—Showing big gun hidden in forest. (Upper left-hand corner).
Fig. 126.—Example of spotting. Battery before and after bombardment.
If the camera is completely hand operated, as were most of those in the French and German services, there is little choice but for the observer to perform the entire operation. The exposing operation could have been delegated to the pilot, but such was not the custom with the French or with the American squadrons using French apparatus. In this method of operation the observer depends on the pilot to get the plane over the target, while the pilot depends on the observer to get the picture when the target is covered. Ample opportunity is thus offered for misunderstanding and disagreement. This can be avoided only by excellent sights properly aligned, for both pilot and observer, and by some means of communication between the two men concerned.
Fig. 127.—Photograph, made with long focus lens to determine the results of aerial bombing. The “Tirpitz” battery of long range naval guns directed on Dunkirk.
The simplest means of communication is of course direct conversation. But this is only possible in those planes, such as the DH-9, in which pilot's and observer's cockpits are immediately together, so that, by shouting, any desired information can be conveyed with fair ease. When the distance is increased to four or five feet, as in the DH 4, the loudest shouts are totally lost in the roar of the engine and the blast of the wind. Speaking tubes and telephones are now fairly good, but are none too comfortable or convenient to have strapped on one's head and face. A primitive device used to some extent in the war was merely a pair of reins attached to the pilot's arms, by which he could be directed which way to steer. There is much to be said for a simple semaphore system, where an indicator in the observer's cockpit actuates a similar dial in front of the pilot, indicating “right” or “left,” “picture obtained,” “try again,” etc. If the observer has a sight by which he can see far enough ahead to correct the pilot's error of pointing, the need for an accurate sight for the pilot is diminished.
Fig. 128.—Diagram showing relationship between focal length and area covered by plate.