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Aerial Photography from Balloons and Kites.—Photography from the air had been developed and used to a limited extent before the Great War, but with very few exceptions the work was done from kites, from balloons, and from dirigibles. Aerial photographs of European cities had figured to a small extent in the illustration of guidebooks, and some aerial photographic maps of cities had been made, notably by the Italian dirigible balloon service. Kites had been employed with success to carry cameras for photographing such objects as active volcanoes, whose phenomena could be observed with unique advantage from the air, and whose location was usually far from balloon or dirigible facilities.

As a result of this pre-war work we had achieved some knowledge of real scientific value as to photographic conditions from the air. Notable among these discoveries was the existence of a veil of haze over the landscape when seen from high altitudes, and the consequent need for sensitive emulsions of considerable contrast, and for color-sensitive plates to be used with color filters.

The development of aerial photography would probably however have advanced but little had it depended merely on the balloon or the kite. As camera carriers their limitations are serious. The kite and the captive balloon cannot navigate from place to place in such a way as to permit the rapid or continuous photography of extended areas. The kite suffers because the camera it supports must be manipulated either from the ground or else by some elaborate mechanism, both for pointing and for handling the exposing and plate changing devices. The free balloon is at the mercy of the winds both as to its direction and its speed of travel. The dirigible balloon, as it now exists after its development during the war, is, it is true, not subject to the shortcomings just mentioned. Indeed, in many ways it is perhaps superior to the airplane for photographic purposes, since it affords more space for camera and accessories, and is freer from vibration. It is capable also of much slower motion, and can travel with less danger over forests and inaccessible areas where engine failure would force a plane down to probable disaster. But the smaller types as at present built are not designed to fly so high as the airplane, and the dirigibles, both large and small, are far more expensive in space and maintenance than the plane. For this one reason especially they are not likely to be the most used camera carriers of the aerial photographer of the future. Inasmuch as the photographic problems of the plane are more difficult than those of the dirigible and at the same time broader, the subject matter of this book applies with equal force to photographic procedure for dirigibles.

Development of Airplane Photography in the Great War.—The airplane has totally changed the nature of warfare. It has almost eliminated the element of surprise, by rendering impossible that secrecy which formerly protected the accumulation of stores, or the gathering of forces for the attack, a flanking movement or a “strategic retreat.” To the side having command of the air the plans and activities of the enemy are an open book. It is true that more is heard of combats between planes than of the routine task of collecting information, and the public mind is more apt to be impressed by the fighting and bombing aspects of aerial warfare. Nevertheless, the fact remains that the chief use of the airplane in war is reconnaissance. The airplane is “the eye of the army.”

In the early days of the war, observation was visual. It was the task of the observer in the plane to sketch the outlines of trenches, to count the vehicles in a transport train, to estimate the numbers of marching men, to record the guns in an artillery emplacement and to form an idea of their size. But the capacity of the eye for including and studying all the objects in a large area, particularly when moving at high speed, was soon found to be quite too small to properly utilize the time and opportunities available in the air. Moreover, the constant watching of the sky for the “Hun in the sun” distracted the observer time and time again from attention to the earth below. Very early in the war, therefore, men's minds turned to photography. The all-seeing and recording eye of the camera took the place of the observer in every kind of work except artillery fire control and similar problems which require immediate communication between plane and earth.

The volume of work done by the photographic sections of the military air service steadily increased until toward the end of the war it became truly enormous. The aerial negatives made per month in the British service alone mounted into the scores of thousands, and the prints distributed in the same period numbered in the neighborhood of a million. The task of interpreting aerial photographs became a highly specialized study. An entirely new activity—that of making photographic mosaic maps and of maintaining them correct from day to day—usurped first place among topographic problems. By the close of the war scarcely a single military operation was undertaken without the preliminary of aerial photographic information. Photography was depended on to discover the objectives for artillery and bombing, and to record the results of the subsequent “shoots” and bomb explosions. The exact configurations of front, second, third line and communicating trenches, the machine gun and mortar positions, the “pill boxes,” the organized shell holes, the listening posts, and the barbed wire, were all revealed, studied and attacked entirely on the evidence of the airplane camera. Toward the end of the war important troop movements were possible only under the cover of darkness, while the development of high intensity flashlights threatened to expose even these to pitiless publicity.

Limitations to Airplane Photography Set by War Conditions.—The ability of the pilot to take the modern high-powered plane over any chosen point at any desired altitude in almost any condition of wind or weather gives to the plane an essential advantage over the photographic kites and balloons of pre-war days. There are, however, certain disadvantages in the use of the plane which must be overcome in the design of the photographic apparatus and in the method of its use. Some few of these disadvantages are inherent in the plane itself; for instance, the necessity for high speed in order to remain in the air, and the vibration due to the constantly running engine. Others are peculiar to war conditions, and their elimination in planes for peace-time photography will give great opportunities for the development of aerial photography as a science.

Chief among the war-time limitations is that of economy of space and weight. A war plane must carry a certain equipment of guns, radio-telegraphic apparatus and other instruments, all of which must be readily accessible. Many planes have duplicate controls in the rear cockpit to enable the observer to bring the plane to earth in case of accident to the pilot. Armament and controls demand space which must be subtracted from quarters already cramped, so that in most designs of planes the photographic outfit must be accommodated in locations and spaces wretchedly inadequate for it. Economy in weight is pushed to the last extreme, for every ounce saved means increased ceiling and radius of action, a greater bombing load, more ammunition, or fuel for a longer flight. Hence comes the constant pressure to limit the weight of photographic and other apparatus, even though the tasks required of the camera constantly call for larger rather than smaller equipment.

To another military necessity is due in great measure the forced development of aerial photographic apparatus in the direction of automatic operation. The practice of entrusting the actual taking of the pictures to observers with no photographic knowledge, whose function was merely to “press the button” at the proper time, necessitated cameras as simple in operation as possible. The multiplicity of tasks assigned to the observer, and in particular the ever vital one of watching for enemy aircraft, made the development of largely or wholly automatic cameras the war-time ideal of all aerial photographic services. Whether the freeing of the observer from other tasks will relegate the necessarily complex and expensive automatic camera to strictly military use remains to be seen.