Part 21

Comparatively few persons realize, I suppose, that fireworks almost identical with those we used to set off on the Fourth of July in the good old days before the safe-and-sane laws went into effect are utilized in aerial warfare and form a valuable and often vital asset for the aviator. Most of these aerial pyrotechnics resemble in their effects the colored lights and the Roman candles of our childhood and are used for signalling from the airplane to the ground and vice versa, or from one plane to others in the air at the same time. For this purpose every active service airplane carries one or more signalling pistols, depending upon the number of the crew. These rather formidable-appearing weapons, which look not unlike the big-barrelled affairs the pirates were wont to carry in their scarlet sashes, are similar to the Very pistols used in the trenches; their ammunition consists of cartridges very similar to shotgun shells, but larger, containing stars of various colors, like those in Roman candles, and the necessary powder charge to eject the stars. Three colors, red, green, and white, are furnished, the color of the star being indicated on the base of the cartridge, which is also serrated in such a manner that the aviator can tell the color by touch when flying at night. By different combinations of these colors an almost endless variety of signals can be conveyed. One of the strangest and most fascinating night sights on the Western Front was to see these countless stars, scarlet, yellow, emerald, shot from invisible airplanes, drifting across the purple velvet of the sky. The stars are clearly visible in the daytime and were used for many purposes, such as indicating the position of enemy troops, the presence of hostile aircraft, requests for assistance from other planes, and as a means of transmitting orders from the leader of a squadron to other machines in formation. At night the signalling pistol is of exceptional value in aiding the aviator to effect a safe landing. When approaching his home-field the pilot fires a light of a prearranged color, and if answered by a light of a proper color from the ground, he knows that the field is clear of obstructions and other machines and safe to land on. Pilots have also used their signalling pistols for firing into their gasoline-tanks and thus setting fire to their machines when forced to land in enemy territory. There are also a few cases on record of the pilot being able to hold enemy soldiers at bay with his signalling pistol long enough to prevent them from extinguishing the fire.

Night-flying is one of the most hazardous duties of the aviator, the chief danger being in the difficulty of making a safe landing. Night-landing fields are, as a rule, well illuminated by flood-lights, but near the front this was not always advisable or safe, and, owing to the difficulty of judging the distance of the machine above the ground in the darkness, accidents were by no means uncommon. In order to minimize this danger there was developed the “wing-tip flare,” which consists of a small cylinder of magnesium material in a metallic holder, one of which is fitted under each lower wing of the plane. The flares are ignited by an electric current and are controlled by push-buttons, one for each flare, in the pilot’s cockpit. In making a night-landing, when the pilot judges the plane to be but a few feet above the ground, he presses one of the buttons. The flare instantly ignites and for about fifty seconds burns with a light of approximately 20,000 candle-power, which, reflected on the ground by the under surface of the wing, enables the pilot to judge his distance and effect his landing without trouble.

The requirements of night-bombing have led to the development of a new and very interesting form of pyrotechnic known as the “airplane flare.” This flare, which weighs thirty-five pounds, is contained in a cylindrical case of sheet-iron about four feet long and five inches in diameter. The flare consists of an illuminating charge, capable of giving 32,000 candle-power for approximately ten minutes, which is attached to a silk parachute twenty feet in diameter. The cylinder is attached to the airplane by a light release mechanism similar to those used for holding bombs. On the end of the cylinder is a small pinwheel, which, revolved by the rush of air as the released cylinder hurtles downward, ignites the illuminating charge and at the same time detonates a small black-powder charge sufficient to eject the flare and its tightly rolled parachute from the case. The parachute immediately opens and the burning flare descends very slowly, illuminating a large area of territory underneath almost as brightly as though it were day. These flares were used particularly for night-bombing raids, the pilots thus being enabled to illuminate the objectives so that they could accurately drop their bombs. On several occasions, when raiding airplanes were met by heavy fire from the enemy’s antiaircraft batteries, it was found that the light from these flares was so dazzling as to make it impossible for the gunners to take accurate aim. So wide is the radius illuminated by these flares, and so intense their light, that it has been found possible by their aid to obtain aero photographs of excellent detail even on the darkest nights. I can personally vouch for the amazing brilliancy of these flares, for I saw one dropped by the Germans during one of their air-raids on Paris in the summer of 1918. It apparently landed on the Pont Alexandre III or in the Seine, yet both banks of the river, the façades of the Grand and the Petit Palais, and the Champ Elysées for several blocks in both directions were almost as bright as though illuminated by a midday sun. Standing alone in the Cours de la Reine, I had the feeling that the Kaiser’s eye was on me and that, having discovered me, he intended to drop upon me one of his steel visiting-cards. The brilliancy and unexpectedness of the glare reminded me of boyhood days in the Thousand Islands, when the captain of the _Island Wanderer_, making his nightly excursions amid the clustered, cottage-dotted isles, took keen delight in suddenly turning the beam of his powerful search-light upon some affectionate pair love-making on the shore.

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It has been said that the airplane is the eye of the army, and it is equally true that the camera is the eye of the airplane. Nothing more strikingly emphasizes the enormous importance attached to pictures taken from the air, showing the progress of the operations, than the fact that, during the offensive in the Argonne, the American photographic sections made _one hundred thousand aero photographs of the battle-lines in four days_.

As aerial photography was an entirely new military subject at the outbreak of the war in 1914, there were no precedents to act as guides, nor was there any special apparatus in existence. Consequently, the entire art of aerial photography was developed and brought to its present state of perfection by the Allies under the incentive of military necessity and after the war had begun. As trench warfare made aerial photography not only important but vital to the success of any proposed operations, the changes and improvements in the apparatus employed came with incredible rapidity, practices employed one week becoming obsolete the next. By April, 1917, the British Air Service alone had issued approximately 280,000 prints, and this number was equalled, if not surpassed, by the French _Section Photographique_. At the beginning of the war it was possible to fly at low altitudes and secure reasonably satisfactory pictures with such cameras, plates, and lenses as were then available. But as antiaircraft artillery was developed, the planes were forced to climb higher to keep out of their range, and owing to the necessity for longer-focus lenses, special plates, and color filters to overcome the haze existing between the camera and the earth, photography at these high altitudes became increasingly difficult.

When the United States entered the war the British, French, and Italians were using plates exclusively and we followed their lead, it not being until some months later that we turned to films. At this time the British were using 4 × 5 plates, and cameras equipped with lenses of from 8 to 12 inch focus. Instead of making contact prints from these negatives, enlargements 6½ × 8½ were made on glossy paper, it being claimed that this process gave greater control in printing. Whether the British system really had all the advantages claimed for it is open to question, but in any event we adopted it and followed it through the first nine months of the war. The great masters of photography in Rochester were by no means content to let another nation set the pace for the United States, however, and in January, 1918, a concern in that city completed a very remarkable aero camera, radically different from anything which had been seen in Europe up to that time, which was promptly adopted by the War Department. This camera, which took an 18-cm. by 24-cm. picture, had a focal length of 20 inches, held a roll of film on which 100 successive exposures could be made, and weighed only 35 pounds. Its most novel feature was the “vacuum back,” consisting of a perforated sheet which extended across the top of the chamber and over the face of which the film passed. A slight air-suction, produced by a Venturi tube placed where it would catch the rush of air past the plane, served to hold the film absolutely flat—for the slightest curvature of its surface would play havoc with the perspective of a picture taken from a height, say, of 10,000 feet. This ingenious instrument was driven by an electric motor which changed the film and automatically set the shutter, the observer having only to start the machinery going and regulate its speed according to the rate of travel of the airplane in order to obtain a series of pictures forming a continuous photograph of the territory over which the machine was passing.

Another picturesque phase of aerial photography of which the public was permitted to know next to nothing was the so-called “gun camera,” the invention of Thornton Pickard, of Altringham, England. This camera, which was designed for the purpose of training aerial gunners, imitated as closely as possible a Marlin aircraft machine-gun, and in order to make a picture it was necessary for the operator to go through the same movements as in firing a Marlin gun. The picture was made through a circular graticule synchronized with the sight on the fixed machine-gun, so if the film, upon being developed, showed that the gunner had scored a “hit” with the camera, he would have been equally successful with an actual machine-gun. The gun cameras as developed in the United States were of two kinds: one, using a regular Brownie film, took one picture each time the trigger was pulled; the other, which was virtually a motion-picture camera so constructed as to exactly replace the magazine on a Lewis gun, gave a “burst” of exposure with a rapidity equalling that of a machine-gun firing a burst of shots, and was used for training aviators in the handling of their flexibly mounted Lewis guns. The resulting film, or bromide print, consisted of a string of silhouettes of the supposed enemy plane, each with an image of the gun-sights superimposed to show where the gun was held, with reference to the target, at the instant the picture was taken.

The enormous numbers of pictures taken from the skies necessitated a corresponding development and manufacture of travelling dark rooms, seventy-five complete units of these machines being built and shipped overseas. These consisted of mobile photo laboratories, having all the equipment necessary for the rapid production of prints in the field, for when important operations are in progress it is imperative that the aero photographs reach the staff at the earliest possible moment after they are taken. The dark rooms, which were mounted on trucks, were equipped with apparatus for generating the current used in the lamps and enlargers, while trailers were fitted with sinks, tanks, enlarging cameras, and other necessary photographic apparatus. The fact should not be overlooked, moreover, that provision had to be made for training the vast and for the most part inexperienced personnel of the photographic sections in the countless new and peculiar phases of taking pictures from the skies.

In considering the development of military aeronautics it must be borne in mind that the maximum altitudes attained by airplanes increased enormously during the war. In 1914 the record for altitude was 26,246 feet, or slightly less than five miles. By January, 1919, the record had been raised to 30,500 feet, an increase of more than four-fifths of a mile. In 1915 the Western Front pilots worked at 7,000 feet without fear of attack from the ground, and few machines flew at heights of more than 10,000 feet. In fact, the “ceiling” with the early equipment was about 12,000 feet. In the closing months of the war, however, as a result of the development of the antiaircraft artillery, it became necessary for aviators to climb to 15,000 feet over the enemy lines, and tactics of the air made that machine safest which could fly highest.

Now it may not have occurred to you that the higher you ascend the greater becomes the decrease in atmospheric pressure. At 19,000 feet the pressure of the atmosphere is one-half the pressure at sea-level. That means that a given amount of air in the lungs of an aviator flying at that height gives only half the oxygen that it would were he on the ground. It is, then, the lack of oxygen, and not, as many suppose, the low pressure itself, which makes men weak and slow of action at high altitudes. Though these facts have been determined by medical research, it is a curious phase of the flyer’s psychology that most aviators laugh at the idea. Yet any one who has crossed the Rockies or ascended one of the Alpine peaks by funicular has noticed that as the altitude increases the breathing becomes quicker and deeper, the heart beats faster and faster. But though the pilot may, as he asserts, continue to feel perfectly fit and well, he is not as efficient as when near the ground. His reactions become slower, he is less prompt to judge distances, to aim his guns, to fire, to manœuvre his plane—and this despite the fact that he is usually quite unconscious of any impairment of his faculties. He will feel dizzy but perfectly happy—autointoxication, I believe the doctors call it—whereas, as a matter of fact, he has lost his judgment; and if he attempts to stay at these altitudes he will gradually pass into a condition of partial and sometimes total unconsciousness, lose control of his machine, and come crashing to the earth.

The imperative necessity of maintaining flyers at the highest possible efficiency was brought home to the aviation authorities through studying the reports of English air-casualties during the first year of the war. The records divided these as follows: 2 per cent were due to the enemy, 8 per cent were due to the plane, and 90 per cent were due to the men, which clearly indicated that something was radically wrong with the personnel and that prompt action was necessary. A thorough study of the situation disclosed the fact that practically all of the flying personnel was suffering from what is known to scientists as oxygen fatigue, caused by flying for many hours a day at high altitudes where there was not enough oxygen to feed the body. As a result of this discovery, Lieutenant-Colonel Dreyer, of the Royal Army Medical Corps, designed an oxygen apparatus for use by the British air forces, the manufacture of which was immediately begun in Paris. So pressing was the need for these apparatus that an automobile was kept waiting at the plant where they were being manufactured to rush each one to the front as soon as it was finished.

An original model of this apparatus was brought to the United States shortly after we entered the war, but as it was made entirely by hand, it had to be redesigned to meet our manufacturing conditions. The perfected oxygen equipment, as used in the American Air Service, consists of a small tank, or tanks, according to the amount of oxygen carried, a pressure device, a face-mask covering the mouth and nose, and a tube connecting the mask with the oxygen reservoir. The American mask has combined with it the interphone whereby the pilot and observer can converse with each other while in the air and, in certain cases, the receiver of the radio telephone. In May, 1918, six complete apparatus were sent overseas by special messenger to be tried out under battle conditions, and when the war ended 5,000 had been manufactured and accepted. All American military planes flying at an altitude of over 10,000 feet are now fitted for the installation of oxygen equipment. This includes day-bombing, pursuit, and chase planes, and a percentage of night-bombing and observation machines. So much importance was attached by the military authorities to supplying our flying-men with oxygen that a special oxygen division was organized and sent to France for the purpose of installing the apparatus in the planes. Yet, as I have previously remarked, the flyers themselves persist in regarding the apparatus, probably because of the discomfort involved in wearing it, with amused scepticism.

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Of all the inventions which have sprung from the war, none is more amazing, to my way of thinking, than the radio telephone. Think of standing on the ground and holding a conversation in a normal tone of voice with an aviator so high in the sky that you cannot see his airplane with the naked eye. Think of it! Before we entered the war, any one save a handful of enthusiastic scientists would have ridiculed such a suggestion, yet to-day, at any one of a score of flying-fields, you can sit at an office desk and converse with aviators in the clouds as easily as though you were sitting opposite them at a dinner-table.

[Illustration: RADIO TELEPHONE APPARATUS IN OPERATION ON AN AIRPLANE.

The pilot and observer are able to talk to each other through the same instrument by means of which they communicate with the ground.

_Photograph by Signal Corps, U. S. A._]

[Illustration: PRESIDENT WILSON TALKING WITH AN AVIATOR IN THE CLOUDS BY MEANS OF THE RADIO TELEPHONE.

_Photograph by Signal Corps, U. S. A._]

[Illustration: A RANGE-FINDER FOR ASCERTAINING THE ALTITUDE AND SPEED OF AIRPLANES.

One of the most remarkable inventions of the war. This instrument not only ascertains the altitude and position of an airplane but by means of an electric connection automatically sets the sights on the antiaircraft gun.]