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quickly or remain in action so long as the flash-ranging sections whose equipment was lighter and could be more quickly set up than that of the sound-rangers.

Sound-ranging was a product of the recent war.

Whether

it will prove useful in future wars is an open question but its usefulness to the Allies in the recent war was beyond question for, due to it, they possessed a marked advantage over their enemy in being able to locate and silence hostile batteries under conditions where all other means failed.

VI

WAR-TIME PHOTOGRAPHY

HERBERT E. IVES

EFORE the great war, photography had figured but little as a military aid. It was used principally for making records; pictures of men and equipment, camps and battlefields, as in the famous Brady photographs of our Civil War. In quite recent wars some actual views of battles while in progress have been produced, with men and artillery in action. These were made possible by the practical development of instantaneous photography, and were due to the enterprize of the newspaper photographer catering to a public accustomed to get its news as much through photographs as through headlines. But the use of photography as an essential to the preparation as well as to the carrying out of military tactics is a development of the last war, as peculiar to it as is the development of the airplane. It is in fact in the airplane that the photographic camera has developed from a mere recorder of minor aspects of battles already lost or won, into the chief guide to their fighting and a really important military weapon. Any account of wartime photography must therefore be devoted largely to this newest form, photography from the air.

But we must not infer, because airplane photography has completely outdistanced all other kinds in military application, that the services of the less novel forms of photography have been small. On the contrary, the use of photography for securing records, for instruction, and in apparatus for the most diverse purposes for instance in the sound-ranging of big guns has been on a scale that would have warranted remark

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merely from the standpoint of the magnitude of the service rendered. By way of record of American participation in the war we have photographs showing every structure erected in France, beginning with the docks of debarkation, and leading on up to gun emplacements at the front. All the details of modern warfare are preserved for future information and instruction; how trenches are built, how barbed wire is wound and supported, how telephone lines are strung, how gas attacks .are launched and met, how guns are camouflaged. Thanks to photography there can henceforth be no excuse for ignorance of the full meaning of waging war.

The most novel feature of this record work is probably the use of the moving picture, which has practically come into being since the Spanish War and the Boer War. Through its use vivid records of all military operations are available in our war colleges for instruction and study. Preparation, training, and even "going over the top" are all faithfully delineated. Just as in the industries moving pictures are furnishing the most valuable records of construction methods and operations, so it has been in the war. Take, for instance, that real epic in cinematography, the story of the 14-inch naval guns; the construction of their railway mountings in Philadelphia, their transportation across the ocean, their assembly at a French port, their cautious creeping over French railway bridges, their detours around the too short French tunnels, until finally we see them in action against the Metz-Meziers railway. It may well be questioned whether the only adequate history of the war will not after all be the photographic one.

Other war-time uses of moving pictures must not be overlooked. Instruction in the use of machine guns, trench mortars, even in the handling of an airplane, has been made more vivid and more interesting, and so more easily grasped by the student when given through clever moving pictures. And their help in keeping up the morale of the men by supplying healthful amusement must by no means be forgotten, with a Y. M. C. A. budget for moving pictures of nearly two and a half millions.

Of the many applications of photography to military instruction one of the most striking and novel is the "camera gun." devised to train aviators in machine gun marksmanship. As at first worked out this consisted merely of a camera mounted on the machine gun support and capable of one exposure at a time. As finally improved and produced by an American manufacturer, this consists of a camera attachment to the Lewis gun which copies in every respect the behavior of the gun itself. Not only may single exposures be made but even "bursts," if the trigger is held back. On the pictures is impressed a target, to show how nearly the aim was correct, while in the latest form a clock dial is incorporated, so that when two aviators return from practice, they have a complete record not only of the number of hits, but also of who made the first "kill."

The chief photographic novelty of the war, aerial photography, owes its existence and rapid development both to the extensive use of the airplane, and at the same time to the very limitations of the plane. The chief function of the airplane is reconnaissance, the gathering of information on enemy military dispositions and movements; and it is this new all-embracing point of view which the air gives that has enabled the airplane to well-nigh revolutionise warfare. But it was early found that the human eye was quite unequal to the opportunities presented by the plane. More could be seen in a single glance downward than could possibly be remembered. Then later, as the flying was driven higher, the magnification given by the unaided eye was insufficient; the use of camouflage made necessary minute study of the view; and last but not least, the attention of the observer had to be given more and more to the military duty of defending the plane against "the Hun in the sun." All of these problems were met in a truly ideal manner by the use of photography. A single exposure with a long-focus camera produces a record faithfully depicting in an instant every detail of a large area in a form eminently suitable for study and general dissemination. From being a happy

experiment, aerial photography grew to be one of the main activities of the air forces. The war had not been in progress a year before the aerial photograph was the indispensable guide to all military operations. Enemy lines were completely photographed each day or even oftener. Negatives to the number of scores of thousands were made every month by the Allied armies, and from these, toward the end, half a million prints (in round numbers) were distributed each week to intelligence officers, to artillery headquarters, even to infantry company commanders to guide them in their local operations. So searching indeed did aerial photography become that as the war drew to a close all troop movements had to be made at night or under cover of bad weather. Elaborate attempts to camouflage batteries and fixed structures against the eye of the camera were met by the development of a corps of experts in a new art, the interpretation of aerial photographs.

The technical problems to be solved in the development of photography from the air were numerous.1 Practically every resource of scientific photography had to be pressed into service and carried to further development by intensive research before aerial photographs with the necessary quality were procurable. As might be surmised, the foremost problems to be met were those introduced by the altitude, the speed, and the vibration of the new camera platform. The great altitudes reached by army reconnaissance flying- 18,000 to 20,000 feet - brought demands for lenses of very long focus and for combinations of sensitive plate and color filter to pierce the layer of haze almost always present on the earth's surface. The speed of the battle plane, sometimes as high as 150 miles an hour, when considered with respect to the earth, demanded lenses of large aperture and shutters capable of giving extremely short exposures in order to prevent blurring due to the motion of the image. The vibration from the engine necessitated not only

1 For a comprehensive account of the technical aspects of aërial photography see "Airplane Photography," by the present writer, published by J. B. Lippincott & Co.

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