Part 21

When the United States entered the war the Vickers was the only type of fixed gun in use on either English or French planes and was used on all the planes which General Pershing bought in France. When the Equipment Division of the Signal Corps faced the machine-gun situation in September, 1917, it was alarmed to find that the entire production of Vickers in the United States had already been contracted for to supply the imperative requirements of the infantry. There was another gun on the market at this time, however—the Marlin—and toward its development for aircraft use the officers of the Signal Corps bent all their energies. Though the Marlin was adopted in the face of violent opposition, it resulted in providing sufficient fixed guns to arm the American planes, the wisdom of the action being proved by the fact that up to the time of the Armistice no other fixed guns were ready for delivery. The Marlin has been adapted to all American-built planes which carry fixed or synchronized guns, over 37,000 having been produced up to December, 1918. This gun shoots .30-calibre ammunition at the rate of 600 to 650 shots a minute and is fed from a belt of the disintegrating metal-link type. In December, 1917, the first order was placed for Lewis aircraft guns, over 39,000 of them being delivered to the American Air Service within the following twelvemonth. A notable improvement in the aircraft model of the Lewis gun was an increase in the depth of the magazine pan, so that each magazine holds 97 cartridges instead of 47 as previously. The Browning aircraft machine-gun was just coming into production when the war ended. This weapon embodies the best features of every known machine-gun and would probably have replaced all other types in use. It is a belt-fed gun of the recoil type—both the Marlin and Lewis are gas-operated—is as near fool-proof as a machine-gun can be made, and has the amazing rate of fire of 950 shots a minute. Of it the inventor is said to have remarked: “If it had four more parts it could play a tune; if it had seven more parts it could talk.”

The ammunition for fixed aircraft guns, such as the Marlin and Browning, is carried in belts containing a maximum of 500 rounds. In the earlier days of the war these belts were of woven web, but it was found that taking care of them, when empty, in the limited space of the fuselage, was always a source of annoyance and not infrequently a source of danger to the aviator. To remedy this a belt was designed and furnished to the American Expeditionary Forces which consisted of small metallic links held together by the cartridges themselves. As the gun fires, the links drop apart, chutes being provided so that they fall clear of the airplane. Another minor though interesting feature of aircraft armament is the small electric heater which is now provided for the purpose of keeping the gun warm and thus preventing the oil from congealing in high altitudes.

Efforts to make the bursts of fire from aircraft guns of maximum effectiveness have led to the development of three distinct types of ammunition—tracer, armor-piercing, and incendiary. The tracer type of ammunition was developed to assist the gunner in correcting his aim, and is equally useful by night or day, as the course of the bullet can be traced by a trail of white smoke in the daytime and by a bright spark at night. Armor-piercing ammunition has a projectile consisting of a hard steel core with a soft nickel casing. The object of this ammunition, as its name implies, is to pierce any of the metallic parts of an enemy plane, particularly the gasoline-tanks or the engine, the soft nickel casing acting as a lubricant and preventing the steel core from glancing off. Incendiary ammunition is loaded with yellow phosphorus. When the cartridge is fired the rifling in the barrel of the machine-gun opens a small hole in the case of the projectile, thus permitting the phosphorus to come in contact with the air, whereupon it immediately ignites and sets fire to any inflammable part of a plane which it may hit. It is customary to load the belts or pans of aircraft machine-guns with these three types of special ammunition in a certain sequence, depending upon the notions of the pilot himself. A sequence commonly used was, first, the tracer cartridge, which assisted the gunner in correcting his aim; next, two or three armor-piercing cartridges, in the hope that they would pierce the enemy’s gasoline-tank or damage his engine; and then one or two incendiary cartridges, which if the gasoline-tank was pierced would ignite the leaking gasoline and set fire to the machine. This sequence was continued throughout the loading of the belt or pan.

Another branch of sky warfare which was being rapidly developed was aerial bombing. Though bombs of a sort were used by Italian aviators against the Arabs during the Libyan campaign, and by American soldiers of fortune serving with the Villista forces in northern Mexico, these attempts were so amateurish and ineffective as to merit no serious consideration. It may be said that the first bombs dropped from an aircraft in the history of warfare were those loosed from the German Zeppelin which raided Antwerp in August, 1914. I speak with a certain personal knowledge of my subject, for the first bomb dropped on the night in question exploded less than a hundred yards from the window in which I was sitting, demolishing a house and killing three persons.

Many people seem to be under the impression that bomb-dropping is about as simple as dropping a brick out of an upper-story window onto the head of a man beneath. This is not so. As a matter of fact, it is extremely difficult to drop a bomb from an airplane so that it will hit a desired target, for, owing to the speed at which the plane travels, the bomb when released does not drop to the ground vertically, but falls in a parabolic curve, something like that described by a man who jumps from a street-car when it is in motion. For this reason the bomb must be released some moments before the airplane is directly over the target, the ability of an aviator to determine the exact moment to pull his release mechanism being acquired only through long experience. Bomb-sights have recently been perfected, however, which have largely eliminated this element of chance. These sights have numerical scales mathematically calculated, so that when adjusted for height, air-speed as shown by the air-speed indicator, and calculated speed of the wind with or against the airplane, two sighting points are moved into such a position that if the bomb is dropped when the desired target comes in line with them, it will reach its objective—provided, of course, the aviator has made his calculations and set his sights correctly. All this sounds rather complicated, I know, and it _is_ complicated, but if the pilot uses the sight correctly his chances of hitting his target are enormously increased. All bombing planes are fitted with quick-release mechanisms, which hold the bombs firmly in a vertical or horizontal position, according to the type and size carried. On the smaller bombing planes, such as the De Havilland 4, the release mechanisms are placed underneath the fuselage or the lower wings, but on the large types, such as the Handley-Page, the bombs are carried inside the fuselage. By a quick jerk of a lever the pilot releases his bomb precisely as a hangman, by jerking a lever, drops the trap on which the condemned man stands. And the consequences are usually much the same in both cases.

There were three distinct types of bombs—demolition, fragmentation, and incendiary—in use by the American Air Service when the war ended. American demolition bombs are made in 50, 100, 250, 500, and 1,000 pound weights, the 100 and 250 pound sizes being used chiefly. These bombs consist of a light steel casing filled with TNT or other high explosive and a detonator separated from the explosive by a safety-pin. When the bomb is released from the airplane the safety-pin is automatically pulled out, permitting the detonator to slide down into such a position that the bomb will explode the instant it strikes the ground. These demolition bombs are primarily designed for use against buildings, fortifications, and other heavy structures where a high-explosive charge is desired. Had the war continued long enough to have permitted of our aviators letting loose a few 1,000-pound bombs on some of the trans-Rhine strongholds, the Germans would have learned what the San Francisco earthquake was like. Fragmentation bombs are considerably smaller, the size most frequently used weighing twenty pounds. They have a thicker case than the demolition bombs and are constructed so as to explode a few inches above the ground. These bombs are for use against troops in trenches or in the open and depend upon the scattering of the fragments for their effect. Incendiary bombs weigh about fifty pounds and contain charges of oil emulsion, thermite, and metallic sodium, which burn for several minutes with the intense heat of a plumber’s blow-lamp. They are used against ammunition-depots, storehouses, and other structures of inflammable construction, the purpose of the metallic sodium being to discourage the efforts of any one who attempts to put out the fire, as it explodes violently when water is poured on it.

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.