Hand-held cameras for naval work have practically the same design as those for land work. In view of the smaller number of pictures taken on naval trips, and the consequent absence of any need for great speed in changing plates, the ordinary two-plate dark slide has been found satisfactory in the English service. But these are much less convenient than the bag magazines used in the U. S. Naval hand camera (Fig. 31). The sights on the naval hand camera are preferably of the rectangular, field indicating type, especially useful in photographing extended objects such as convoys. As the flying boat travels comparatively slow, it is easy for the observer to stand up to take pictures, and the sight is conveniently placed on top. But if held out over the side for verticals the sight must be on the bottom. Rectangular sights in both positions are provided in the English camera (Fig. 186). Naval cameras should be immune from moisture, which means doing away with all wooden slides or grooves. A praiseworthy practice is to carry the camera in a waterproof bag. [Illustration: FIG. 181.—Airplane photography as an aid to salvaging. Position of wrecked merchantman twelve fathoms down revealed by photograph from the air. Photograph by British Air Service.] [Illustration: FIG. 182.—A sea plane.] [Illustration: FIG. 183.—A flying boat.] [Illustration: FIG. 184.—A dirigible or “blimp”—possibly the photographic aircraft of the future.] [Illustration: FIG. 185.—English “Type 18” hand camera on bracket for exposing through side window of flying boat. British official photograph.] [Illustration: FIG. 186.—Camera mounted in bracket from forward cockpit of flying boat. British official photograph.]