Discussion of the task of the pilot who must steer a photographic plane accurately over a previously selected point of interest cannot be undertaken without raising the question of who should take the picture, pilot or observer? In the English service the most general practice was for the pilot to be charged with the responsibility both of covering the objective and of exposing. If a propeller drive was used on the camera, this left to the observer only the task of changing magazines. If the camera was hand operated the plates were changed either by the observer, or else, as was frequently the case, distance operating devices were attached, so that the pilot even then did everything except change the magazines, and the observer was kept free to watch the sky for enemy aircraft. A very desirable adjunct to the camera when plates are shifted automatically or by the observer is a distance indicator, to show the pilot when the shutter is set. Electrical indicators for this purpose have been devised. [Illustration: FIG. 123.—Low view of trenches on the Yser, showing concrete structures undamaged by bombardment.] [Illustration: FIG. 124.—The Piave River. To left, destroyed bridge, to right, pontoon bridge under construction. Italian aerial photographic service.] [Illustration: FIG. 125.—Showing big gun hidden in forest. (Upper left-hand corner).] [Illustration: 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. [Illustration: 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.]