Chapter 34

TYPE DR-4, DE RAM CAMERA.

TYPE A-3, HAND-HELD AIRPLANE CAMERA.

TYPE L, 4 x 5 PLATE CAMERA.

MOBILE FIELD PHOTOGRAPHIC OUTFIT, USED FOR AIR SERVICE.It includes a dark room, printing lantern, and light-generating plant.

MOBILE FIELD PHOTOGRAPHIC OUTFIT, USED FOR AIR SERVICE.

It includes a dark room, printing lantern, and light-generating plant.

As the airplanes moved into higher altitudes, longer focus lenses had to be employed, special dry plates developed, and special color filters provided to overcome the haze created by humidity in the long spaces between the cameras and the ground. When the war ended, cameras were in common use taking photographs at an altitude of 4 miles with such microscopic fidelity as to show even where a single soldier had recently walked across a field.

The American Army came into the war almost innocent of any information at all on the subject of war photography. Such technical information as the allied nations had developed during the war had been most carefully guarded from us and all other neutral countries, with the result that what information we had was of a meager and conflicting sort.

Although in the early months of our participation in the war the Signal Corps, which then had charge of all phases of aerial warfare, made large purchases of motion-picture cameras, hand cameras, and view cameras, it was not until the end of 1917 that our officers were able to begin their real development of aerial photography. By this time we had received much valuable information from the foreign high commissions and samples of their earlier apparatus. Aerial photography had become one of the leading activities of the air service. Thus in April, 1917, the British service made 280,000 pictures at the front, and a great part of all flying was done to secure photographs. Moreover, the art was advancing at such a pace that practices in approved use one week at the front appeared likely to become obsolete the next, as new methods and new equipment superseded the old.

For years America had been second to none as a photographic country, and it was to be expected that this country would make notable contributions to the new science. It may indeed be wondered why, with the experimental laboratories and the skilled technicians at our command, we did not start at once to develop our own aerial designs and equipment. Our officers, however, felt that such a course would be likely to duplicate much of the work already done by the allied countries, who stood ready then to furnish to us the results of their experiences. While original research work might result in the invention here of certain equipment of superlative merit, yet we would be sure, in the course of such an undertaking, to adopt methods which had been tried and discarded by the allies and which we ourselves would have to discard when experience had proven them to be without value.

The information in our hands in December, 1917, showed that the British system of air photography differed radically from that of the French. The French cameras made a relatively large negative, 18 by 24 centimeters in dimension, on a glass plate. The magazines of the French cameras held 12 plates, and extra magazines were carried in the plane. These cameras were fitted with lenses of relatively long focus—20 inches. Three operations were necessary to make an exposure. The photographer must change the plate, set the focal plane shutter, and press the release. When the negatives were developed, fixed, washed, and dried, prints were made by contact.

The British used a smaller-sized plate, 4 by 5 inches in size. Their cameras were equipped with the only lenses available in England in the early part of the war—lenses of relatively short focus, ranging from 8 to 12 inches in this respect. Instead of making contact prints from these plates, the British made enlargements, measuring 6½ by 8½ inches. In the earlier period of our development of aerial photographic apparatus, we were in the same position as the British as regards lenses. We had no adequate supply of long-focus lenses. Consequently we followed the British designs of cameras and adopted the British system almost explicitly in the training of aerial photographers.

It had been our first thought to use films to a great extent on the front, since America was the country which had perfected the photographic film, and was therefore, presumably, best equipped in skill to adapt it to war uses. But plates had been used practically exclusively by the British, the French, and the Italians; and it appeared wisest to follow their experience at first, though all agreed that film, with its small bulk and weight, would be greatly superior for airplane use.

The Photographic Experimental Department of the Air Service, which was organized in January, 1918, had as its major problems the design and test of aerial cameras and all their parts and accessories. Equally important with this problem was that of sensitive plates, papers, color filters, and photographic chemicals. The corps of photographic and optical experts, into whose hands these matters were placed, early secured the active cooperation of the chief manufacturers of photographic apparatus and materials in this country. In the laboratories in Washington, D. C, Langley Field, Va., and Rochester, N. Y., comprehensive development work was inaugurated, leading ultimately to perfection of new designs of cameras and the development of plates and other photographic materials equal or superior to any available abroad.

The first airplane camera which it was decided to put into production in America was a close copy of the British type "L," whichuse had proven to be one of the best mechanisms employed at the front. The operation of this camera was semiautomatic, the operator having nothing to do except to press the shutter-release to keep the camera at work. The operating power was derived from a small windmill or air propeller driven by the rush of air past the plane. The automatic mechanism changed the plate and set the shutter after each exposure. Because of the situation with respect to lenses these cameras were constructed to use lenses of 8-inch to 12-inch focus, and the English 4 by 5 plate. Some 750 of these cameras were constructed. They played an indispensable part in the training of nearly 3,000 aerial photographers in this country. They were also used by our bombing squadrons at the front.

At the same time it was generally agreed that we should plan to follow the French practice as soon as lenses of greater focal length could be manufactured in this country. Increase in focal length was becoming imperative, because aerial photographers were being compelled to make exposures from much greater heights than in the earlier part of the war. For the sake of those unacquainted with photography it may be stated here that lenses of short focal lengths will not record the details of objects a great distance away from the camera, the longer-focus, rarer, and more expensive lenses being required for distance work.

As a basis for the design of cameras of longer focus a sample of the 20-inch focus camera used by the French had been sent to this country by the American Expeditionary Forces. The first camera authorized of this focal length was similar in general character to this French camera. It was constructed on the unit system, each part—shutter, camera body, lens cone, and magazine—being of standardized dimensions. It was understood that these standard dimensions were to be followed in all subsequent cameras both in this country and in the countries of the allies.

The idea constantly put before all designers of aerial cameras has been that of the automatic type, in the use of which the observer or pilot will have a minimum of work. Late in 1917 the Photographic Section of the Air Service, American Expeditionary Forces, secured the rights for the manufacture of an ingenious design of automatic plate camera invented by Lieut. DeRam, of the French Army, and requested that this be put in production. In this camera the magazine, which carries 50 plates, 18 by 24 centimeters in size, rotates between each exposure, while the exposed plate is removed from the front of the pile and carried to the back. After some study here of the incomplete model, this camera was redesigned in such form as to fit it for methods of American manufacture. It was made semiautomatic in operation; that is, the work of the observer or pilot consistedmerely in releasing the shutter at will, a fresh plate always being in place. At the time of the armistice 200 of these cameras were rapidly approaching completion.

Meanwhile experiments were actively pushed in the matter of the utilization of film. Various difficulties and problems had to be solved before film could be considered practical. Considerable time was consumed in overcoming the peculiar static electrical discharges which occur on film in cold, dry regions, such as in high mountains or the upper atmosphere, and fog the sensitive surface by their light. The film camera finally decided upon was based on a fundamental design by the Folmer & Schwing organization of the Eastman Kodak Co.

This camera, known as the "K" type, carries a film on which 100 exposures, 18 by 24 centimeters in dimension, can be made at one loading. The film is held flat by an ingenious device. The film strip passes over a flat perforated sheet behind which a partial vacuum is set up by a suction, or "Venturi," tube extending outside the body of the airplane. The camera is entirely automatic, and is driven either by a wind turbine of adjustable aperture or, in war planes, by electric current from the heating and lighting circuit. The observer in the airplane needs only to start the camera and regulate its speed according to the speed with which the airplane is passing over the ground below, and the camera thereafter will, of itself, take pictures at such intervals as to map completely the terrain under observation.

In conjunction with the use of film in cameras came the question of handling the film in the dark-room; that is, the ordinary manipulations of developing, fixing, washing, and drying—a serious problem when the large dimensions of the film, its length, and difficult characteristics in handling are taken into consideration. This problem was attacked and a film developing, handling, and drying machine was produced.

Some 200 of these automatic film cameras were on order at the close of the war. Altogether over 1,100 airplane cameras of all types had been and were about to be delivered when the armistice came. These were built by the Eastman Kodak Co., Rochester; the Burke & James Co., Chicago; the G. E. M. Engineering Co., of Philadelphia; and Arthur Brock, jr., of Philadelphia.

One of the most serious problems in aerial photography is the proper mounting of the camera in the plane. Not only does the plane travel at great speed, which makes necessary exceedingly short exposures and therefore highly sensitive photographic materials, but the motor causes a continuous vibration which, communicated to the camera itself, would be fatal to obtaining sharp pictures.

The experimenters of the Air Service carried out a long, extensive, and most interesting investigation at Langley Field to make clear the whole question of preventing the vibration of the airplane camera.The scientists worked out a method of making the camera itself record the vibrations communicated to it by the plane when the box was not held by a proper vibration-neutralizing suspension.

The plan adopted was to send up a camera thus mounted on an airplane, focus it on a light on the ground below, open the shutter, and take a time exposure from the swiftly-flying plane. The result, of course, was a streak, or trail, written on the plate by the point of light below, the jagged or wavy character of this trail indicating the vibrations of the camera and determining the proper principles of a suitable mounting.

The first thought was to do this work at night, as the British had done, when the light below would pierce the darkness distinctly. But night flying is hazardous, and a better plan was called for. Nor would the proposal to use an extremely strong light in broad daylight do, because, while the light would indeed be photographed continuously across the plate, so also would the surrounding ground, and the general result would be a fogging or blurring of the outlines of the streak.

Finally the problem was solved by conducting the aerial experimental work over woodland in the late afternoon. A strong, reddish light was placed in the woods so as to be visible from above. The surrounding green foliage supplied a frame of sufficient contrast to the light to make its impression distinct on the plate. To emphasize the contrast, the camera lens was covered with a reddish colored ray filter, and this brought out sharply the outline of the streak.

These tests resulted in the design and production of new and unique camera mountings which successfully stopped all vibrations of the camera.

A problem on which it was necessary to have the closest cooperation of the plane designers was that of installing the large 20-inch focus cameras in the airplane. There is little room at best in a plane, and the demands for armament, wireless, and bombing space all had to receive attention. In the American service a distinct advance was made in the design of a special plane intended primarily for photographic reconnaissance. Several of these planes, which were the most completely equipped for photographic purposes of any designed during the war, were built and would have been put into quantity production in the late fall of 1918.

Parallel with this development of apparatus went studies of the sensitive materials and methods of photography from the air. Because of the swift motion of the plane extremely short exposures are imperative. Consequently, the most advanced technique of instantaneous photography had to be applied. The cooperation of various plate manufacturers was obtained, who brought out especially for the Government several new plates which showed ontest to be superior to any which had appeared in the war on either side.

As an airplane rises higher and higher in the sky, the moisture of the intervening atmosphere between the machine and the ground creates a haze which makes aerial photography above a certain height unsatisfactory and even impossible with the naked lenses as used on the ground. The problem of finding the best means for piercing aerial haze occupied the attention of a corps of experts working both in the laboratory and in the field. The solution lay in the use of special color filters of general yellow hue which obscured the bluish light characteristic of haze. Filters of new materials specially adapted to airplane use were made available as a result of this study.

Field equipment of quite new and special design for performing photographic operations had to be designed and built. Among the most interesting of these developments was the photographic truck or mobile photographic laboratory. This consisted of a specially designed truck and trailer containing all the equipment necessary for the rapid production of prints in the field. The truck body was equipped with a dynamo for furnishing the electrical current required for lights and drying fans, while each unit was provided with an acetylene generator for emergency use, if the electrical apparatus should break down. The mobile dark room carried on the trailer of each unit was equipped with tanks, enlarging camera, printing boxes, and other necessary apparatus. In all, some 75 of these field laboratories were constructed.

While the development of apparatus and new materials was from a popular standpoint in many ways the most interesting phase of the work of the photographic scientists, nevertheless it should be remembered that the great problem in this, as in all other fields of American endeavor, was to produce the supplies in tremendous quantities. In October, 1918, we shipped overseas 1,500,000 sheets of photographic printing paper, 300,000 dry plates and 20,000 rolls of film. We also sent 20 tons of photographic chemicals. These were merely the principal items in the consignment. Besides paper, plates and chemicals, the field force required developing tents, trays, printing machines, stereoscopes, and travelling dark rooms, to name only some of the principal items. Much of the material already on the market was not suitable for the purpose, a fact requiring the production of specially manufactured supplies.

It is interesting to consider that without fireworks, and particularly some of the familiar forms of them used to celebrate the Fourth of July, war flying would have lost much of its efficiency. Night flying would have been well-nigh impossible, while day flying would have had to invent substitutes for fireworks had the latter not been available.

MARLIN MACHINE GUN WITH FIXED MOUNTING, ON A JN-4 FUSELAGE.

TWO LEWIS MACHINE GUNS WITH MOVABLE MOUNTING, IN THE OBSERVER'S COCKPIT OF A DE HAVILAND-4.

AIRPLANE FLARE.

HOLT WING-TIP FLARE HOLDER.

The squadron fields near the front were kept as dark as possible at night for obvious reasons. The first inkling that a squadron commander might have of the approach of one of his aviators at night would be the sudden appearance high in the air of a green or red or white Roman-candle ball. This would be the signal inquiring if the landing field were clear. A pyrotechnic star of a predetermined color, shot from the ground, would answer the homing birdman; and, if the signal were in the affirmative, he would descend through the sheer blackness, unable to see clearly, yet confident that he would make his landing safely.

As the plane neared the ground suddenly under one of the wings a flare of dazzling power would commence to burn, for a few seconds flooding the field with light. In that brief space of time the plane would have made its landing, and soon field and quarters would again be obscured under the protecting blanket of darkness.

Every service airplane at the front was equipped with one or more signaling pistols. In appearance these weapons were more murderous than the "gat" carried by a desperado of the movies, but, like the prize bulldog with the undershot jaw, they were more deadly in looks than in deeds. Their formidable-appearing cartridges were larger than the shells used in shotguns, resembling the latter almost identically in appearance; but every one of these shells contained only a Roman-candle ball and a sufficient charge of powder to eject the star a good distance into the air. The sound of the discharge was a mere whisper of the shattering roar that might be expected from such a redoubtable piece of ordnance. These aviation pistols were similar to the Very signal pistols used in the trenches.

The stars shot were three colors, red, green and white, and the color of a cartridge's star was painted on the end of the shell. This base was also ridged with a different pattern for each color, so that the aviator at night could feel with his fingers and tell the color of the cartridge without seeing it.

Codes of numerous messages were worked out in different combinations of these three colors. The stars were quite visible in broad daylight, too, and were used for many signaling purposes. They indicated the position of enemy troops or the presence of hostile aircraft, they called for help from other airplanes, and they signaled squadron orders when the machines were flying in formation.

But the signal pistol had a more sinister use. If the pilot were driven down in enemy territory, it became his duty to destroy his machine. In some cases the signal pistol was used effectively to set airplanes on fire under such conditions. The pilot had only to open his gasoline tank and fire a Roman candle ball into the escaping fluid. In other cases when the aviator landed amid enemy troopshe was able to hold them at bay with his signal pistol until his plane was burned beyond the possibility of salvage.

While we manufactured Very pistols in this country, all of those actually used by our fliers in France were purchased abroad.

Night-flying is one of the most hazardous duties of the aviator, the chief danger being in landing. The fields well back of the front were usually brightly illuminated by flood lights at night, but those nearer the enemy were left in darkness, as a rule, to protect them from the attacks of hostile aircraft. The aviator at night can usually see the ground faintly, but he is unable to make an accurate judgment of the distance of his machine above the ground. This danger was greatly alleviated when the wing-tip flares were invented. The wing-tip flare consisted of a small cylinder of magnesium material in a metallic holder, one flare being fitted under each lower wing of the plane. Each flare was controlled by a push button in the pilot's cockpit. Pressure on the button sent an electric spark into the magnesium and touched it off.

When the descending pilot at night judged that he was near the ground he pushed one of the buttons. Immediately the flare ignited and burned for about 50 seconds with the brilliant light of 20,000 candle power. Being hidden by the wing, this light did not dazzle the eyes of the aviator, but the reflection from the under surface of the wing lighted up the field for an adequate distance in all directions.

Another important use of pyrotechnics occurred in those enterprises known as night-bombing raids. Since both sides kept their vulnerable ammunition dumps and their important buildings completely unlighted at night, even though the night raider knew he was in the general vicinity of his objective, hits from bombs dropped from aloft were almost accidental. To enable the night bomber to see his target the interesting piece of pyrotechnics known as the airplane flare was invented. This was a great charge of magnesium light held in a cylindrical sheet-iron case nearly four feet long and half a foot in diameter, the exact dimensions being 46 inches by 5 inches. The flare weighed 32 pounds. Within the cylinder was not only the magnesium stick but also a silk parachute 20 feet in diameter. The entire cartridge was attached to the airplane by a release mechanism similar to those holding the drop-bombs.

When over his objective at night the pilot or observer touched a button and the entire cartridge, iron case and all, dropped from the plane. A pin wheel on the lower end of the case was instantly spun by the rush of air, and the resulting power not only ignited the magnesium but at the same time detonated a charge of black powder sufficient in force to eject from the case the flare and its tightly rolled parachute. The parachute immediately opened; and the burning flare descended slowly, flooding a large area of the ground below with a light of 320,000 candlepower, this light burning for about 10 minutes.

Such a light not only enabled the bomber to drop his destructive missiles accurately, but it was found by experience that it dazzled the eyes of antiaircraft gunners below and made their aim inaccurate. The light of this flare was so strong that it was possible for the airplane above to obtain photographs of good detail on the darkest of nights.

We were just starting to produce these flares when the war ended. In fact the actual production of pyrotechnic supplies in this country was small, the American Expeditionary Forces depending almost exclusively for these supplies upon French and British sources.

When the commander of an airplane squadron sends an aviator into the high altitudes, he sends him into climate that much of the year is colder and more severe than any known on earth, even at the North Pole. Not only is the temperature of the air likely to be many degrees below zero at the heights which war planes attained, but the flier must face this bitter cold in the gale of wind that is never blowing less than 100 miles per hour.

Consequently when we trained a corps of aviators to fly at altitudes of 18,000 to 20,000 feet above the western front, it was necessary for us to design and manufacture for them the warmest clothing ever made. They were dressed more warmly than any Polar exploration party that ever set forth, more warmly in fact than any other class of men in the world. For we not only gave them the protection of all the fine wool, leather, and fur that they could wear without hindering their movements, but in addition we literally wrapped them in flexible electric heaters.

The first purchases of aviators' flying clothes were made by the coordinated action of the Council of National Defense and the Quartermaster's Department. It was soon apparent that the design of such clothing was a special matter which the aviation authorities themselves should control, and purchases thereafter were all made by the Bureau of Aircraft Production. There were no standard styles at the time, so it became necessary for us to develop our own equipment. This development resulted in an output for the flier that became standard.

In moderate weather the flier wore upon his head a woolen hood, or helmet, extending well down over the forehead to the eyes, and around the neck to the shoulders. In cold weather, or for high-flight work, this headgear was augmented by a silk helmet of double thickness, having between its layers an electrically heated pad connected by copper wire to the electric generator on the plane's engine. Outside of this was worn a soft leather helmet lined with fur, extending down over the back of the head, covering the ears and cheeks, and fastening under the chin. Then the face was entirely coveredwith a leather face mask lined with wool and having an opening for the eyes, over which were worn a pair of goggles. When the pilot was also required to operate the radio system, in place of the fur-lined helmet he wore the radio helmet. This was of leather and resembled the other in appearance, but it contained the receiver of the wireless telephone, enabling the flier to hear what was spoken to him in an ordinary tone of voice several miles away.

In addition to this equipment the aviator who went up to the great heights wore the oxygen mask. This was of rubber, and, besides supplying oxygen, it contained a transmitter, allowing him to speak as well as to hear by wireless.

Over the body was worn a one-piece flying suit extending from the feet to the throat, belted and buttoned tight at the ankles and wrists. The outer material of this suit was waterproof, and when it was buttoned on there were no gaps through which the air might penetrate. This suit was lined throughout with fur.

It was a considerable problem to find a fur of extreme warmth with a pelt strong enough to withstand rough usage and still not be too great in bulk, and purchasable at a price not too extravagant. After the furs of many beasts had been examined and tested, it was determined that the hide and fur of a Chinese Nuchwang dog met these requirements better than any other. We were making so many of these suits that we required all of the dogskins we could get, not only in this country, but in China. Merely the final purchase of these pelts before the armistice was signed was for nearly 500,000 of them, and that many dogs in an interior Chinese province gave up their lives that the American aviation warfare might succeed.

With its waterproof outer surface and its furry lining, it might seem that such a garment would be warm enough for any work. But the aircraft authorities of the United States were not content until they had installed between the fur and the outer covering thin, flexible, electric-heat units connected by silk-covered wire with the dynamo on the engine. Similar heating pads were placed in the gloves and moccasins of the fliers.

On their hands, besides the electrically heated gloves, the fliers wore gauntlets of muskrat fur, these extending well up the arms and being of special design which allowed the fingers of each glove to remain in a fur-lined pocket or to be withdrawn from the pocket without removing the gloves from the hand. Over the electrically heated moccasins were worn leather moccasins extending well up the calf of the leg and lined with heavy sheep wool. These were fastened with straps and buckles. Thus clad, our aviators were acknowledged generally to be the most warmly and efficiently equipped of any at the front.

Besides these special garments for warmth, the fliers required many other items of clothing, such as sweaters, leather coats, fur-lined coats, helmets, and many styles of goggles.

The total cost of air clothing, provided or in course of manufacture on November 11, 1918, was over $5,000,000. Some of the major items in round numbers were 50,000 fur-lined flying suits (at $36.25), 100,000 leather helmets, an equal number of leather coats, costing anywhere from $10 to $30 each, and over 80,000 goggles at $3.50 apiece.

Even to-day the veteran of the air squadron scoffs at the newfangled outfits of oxygen masks and tanks carried in an experimental way on some of the high-flying planes at the western front when hostilities ceased. Nevertheless, had the war continued a few months longer, it is probably true that the oxygen apparatus would have been included in the indispensable equipment of every airplane in the front areas. Such a development, had it occurred, would have been due largely to the efforts of the American Aircraft Service.

Many aviators who have gone into high altitudes, fought there, and lived to tell about it, doubt the necessity of oxygen-supplying apparatus, since they themselves returned safely without it. Nevertheless the experiments conducted by the Bureau of Aircraft Production demonstrated conclusively that the flyer artificially supplied with oxygen in the high altitudes is much more efficient than one who is without it. These experiments were conducted in a room which duplicated the conditions at high altitudes. At 19,000 feet the pressure of the atmosphere is one-half the atmospheric pressure at sea level. The lack of pressure in itself causes no appreciable physical or mental reaction; but the reduced pressure at 19,000 feet means that in a given amount of air there is only one-half the oxygen that there is in a similar amount at sea level. The lack of oxygen is serious.

Experienced aviators were placed in an air-tight chamber under the observation of Government scientists. The air in this chamber was then exhausted until it corresponded to the atmosphere at the 19,000 feet level. The subjects were then set at small mechanical tests, such as the pushing of certain buttons when different colored lights were turned on, these tasks requiring a degree of mental concentration. In this and similar tests it was discovered that not only do the subjects lose accuracy in the attenuated air, but their movements become conspicuously slower. In the parlance of the pilot they become "dopey." More than one returning aviator has confessed to this feeling when at a high altitude.

When the British analyzed their air casualties during the first year of the war they found that 2 of each 100 fliers in the casualty list were killed or hurt by the enemy, 8 of them owed their misfortune to defects in the planes, while the other 90 came to the hospital or the grave because of themselves, their carelessness or recklessness, their physical failings, and all other things which may be summed up in the human equation. A thorough study on the part of the British disclosed the fact that practically all of the flying personnel was suffering from what became known as oxygen fatigue, caused by flying so many hours each day in altitudes where there was not enough oxygen to feed the body properly.

Before the war broke out the aviation record was 26,246 feet above sea level. In January, 1919, this record had been lifted nearly a mile, the high point being an altitude of 30,500 feet. Early in the war pilots at the 7,000 feet level could laugh at antiaircraft fire, and few machines ever went above 10,000 feet. Thus with the first equipment the "ceiling"—that is, the average high level to which every day flying goes—was about 12,000 feet.

When the war closed, a pilot was not safe under the 15,000 feet level, due to the development of antiaircraft guns, and the safest machine had become that which could fly highest. The aviators were demanding a working ceiling of 18,000 feet, and were obtaining it, too, from the latest type of planes. It was evident that the reduced oxygen at this ceiling was responsible for casualties among the fliers, and we could expect the ceiling to be pushed even higher as antiaircraft guns became more powerful. The need of oxygen equipment was plainly indicated. Even at 18,000 feet the aviator relying upon the normal oxygen supply at that altitude, while he may feel perfectly fit, is actually slow to judge distances, to aim his guns, to fire them, and to maneuver his plane.

The first oxygen apparatus was designed for the British Air Service and was made at the plant of de Lestang in Paris. The demand for the apparatus was so great that an automobile was constantly kept waiting at the factory that as soon as each set was finished it could be rushed straight to the front. The first British squadron which used oxygen equipment reported that its men gave six times the service of any other British squadron.

Our Air Service adopted the Dreyer oxygen apparatus, which was the original device produced by the British. We found it to be a hand-made appliance, but under our direction we adapted it to American methods of manufacture. The British apparatus was built to supply oxygen to one man only. We changed it to take care of two men. The model received was too heavy; we reduced the weight. Finally we added improvements to make it more efficient and reliable and redesigned it to meet American factory methods.

GUNNER IN COCKPIT EQUIPPED WITH OXYGEN HELMET AND TELEPHONE RECEIVER, OPERATING MOVABLE MACHINE GUN.

AVIATOR'S OXYGEN HELMET EQUIPPED WITH TELEPHONE RECEIVER.

OXYGEN APPARATUS FOR BREATHING AT HIGH ALTITUDES.

Such an equipment has to be entirely automatic in its operation and as reliable as human ingenuity can make it. The Dreyer device embodies several instruments all of which must work perfectly under widely varying conditions. In use its tanks will contain oxygen under pressure ranging from 100 pounds to 2,250 pounds per square inch, yet the mechanism must deliver the oxygen to the aviator at a constant rate regardless of its tank pressure. Then the whole apparatus is subjected to temperatures that may be as high as 80° above zero or as low as 30° below. It must function evenly in the atmospheric pressure at any altitude up to 30,000 feet, delivering more oxygen as the atmosphere thins. Such was the problem of manufacture. Yet, taking up the work in January, 1918, we turned out six complete equipments by May 3, 1918, sending them overseas by special messenger for actual test on the front. Twenty-eight days later we shipped 200 sets. By the end of the war we had built 5,000 complete oxygen equipments. Of this number 3,600 had been sent to ports of embarkation awaiting shipment, and over 2,300 of these had been shipped overseas. In October we had reached a production rate of 1,000 sets per month.

Some of the difficulties of this production may be read in the description of the complicated character of the apparatus. The equipment consists of a small tank or tanks, the pressure apparatus, the tube leading from the reservoir, and finally the face mask covering the mouth and nose. The mask has combined with it either the interphone, a mechanism which cuts off the roar of the engine from the ears of the passengers and allows the pilot and observer to talk freely with each other, or in certain cases the receiver of the radio telephone or telegraph.

The flow-regulating apparatus consists of five parts. In front of the pilot is a high-pressure gauge to indicate the supply of oxygen in the tank. In the tank there is a high-pressure valve with an upper chamber which compensates for the temperature. There is also a shut-off valve, hand operated, which can be set to provide a flow of oxygen to one man, to two men, or to none at all. Then there is a regulating valve operated by an aneroid barometer which adjusts the oxygen flow to the altitude, the flow increasing as the machine goes higher. Finally in the pilot's view there is a flow indicator consisting of a small fan wheel which tells the aviator that the oxygen is actually flowing.

The mask presented a difficult problem, as it must be big enough to contain the radio receivers and still enable the aviator to see and work. Yet the mask must keep its adjustment in a gale of wind at least 100 miles per hour in velocity.

The actual use of the equipment on the front was just starting when the armistice was signed. We sent across to France a specialdivision of experts to take charge of the installation of these equipments on the planes. At the close of hostilities we required all military planes flying above an altitude of 10,000 feet to be equipped with oxygen apparatus. This class included day bombing, pursuit, and chassé planes, and a certain number of night bombing planes, and Army and corps observation planes.

TWO VIEWS OF BOMB SIGHTS USED ON AIRPLANES.Upper picture shows bomb sight on De Haviland 4. Lower picture shows high-altitude bomb sight. Set from readings of instruments showing altitude and air speed. It indicates to the bomber the precise instant for release of the bomb in order to reach the target.

TWO VIEWS OF BOMB SIGHTS USED ON AIRPLANES.

Upper picture shows bomb sight on De Haviland 4. Lower picture shows high-altitude bomb sight. Set from readings of instruments showing altitude and air speed. It indicates to the bomber the precise instant for release of the bomb in order to reach the target.

AVIATORS EQUIPPED WITH TELEPHONE TRANSMITTERS AND HEAD SETS TO COMMUNICATE WITH EACH OTHER.

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