CHAPTER V

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AVIATION EQUIPMENT AND ARMAMENT.

On one of the early days in the great war a Russian aviator, aloft in one of the primitive airplanes of that time, was engaged in locating the positions of the enemy when he chanced upon a German birdman engaged in a similar mission.

In those ancient times--for they seem ancient to us now, although less than five years have elapsed--actual fighting in the air was unknown. The aviators had no equipment for battle; indeed, it was doubtful if the thought had occurred to either side to keep down the enemy's aircraft by the use of armed force borne upon wings. In the first months of aviation in the great war the fliers of both sides recognized a sort of _noblesse oblige_ of the air, which, if it did not make for actual friendship or fraternizing between the rival air services, at least amounted to a respect for each other often evidenced by an innocuous waving of hands as hostile flying machines passed each other.

But now the wounds of war had begun to smart; and when the Russian saw the German flier going unhindered upon a work that might bring death to thousands of soldiers in the Czar's army, a sudden rage filled his heart, and he determined to bring down his adversary, even at the cost of his own life. Maneuvering his craft, presently he was flying directly beneath the German and in the same direction and was but a short distance below his enemy's plane. Then, with a pull on his control lever, the Russian shot his machine sharply upward, hoping to upset the German and to escape himself. The result was that the machines collided, and both crashed to the ground. This was probably the first aerial combat of the war.

It seems strange to us to-day that the highly complicated and standardized art of fighting with airplanes was developed entirely during the great war and, indeed, was only started after the war had been in progress for several months. Yet such was the case. At the beginning of the war there was no such thing as armament in aircraft, either of the offensive or defensive sort. It is true that a small amount of experimentation in this direction had occurred prior to the war and also in the early months of fighting, but it was not until the summer of 1915 that air fighting, as it is so well known to the entire world to-day, was begun.

In this country we had successfully fired a machine gun from an airplane in 1912, while at the beginning of the war the French had a few heavy airplanes equipped to carry machine guns. Yet in August, 1915, Maj. Eric T. Bradley, of the United States Air Service, but then a flight sublieutenant in the Royal Flying Corps, frequently flew over the lines hunting for Germans; and his offensive armament consisted of a Lee-Enfield rifle or sometimes a 12-gauge double-barreled shotgun.

The aviators in those pioneer days usually carried automatic pistols, but the danger to one side or the other from such weapons was slight, owing to the great difficulty of hitting an object moving as swiftly as an airplane travels. The earlier planes also packed a supply of trench grenades for dropping upon bodies of troops. Another pioneer offensive weapon for the airplane was the steel dart, which was dropped in quantities upon the enemy's trenches. Great numbers of these darts were manufactured in the United States for the allies, but the weapon proved to be so ineffective that it had but a brief existence.

It is said that before the pilots carried any weapons at all the first war aviators used to shoot at each other with Very pistols, which projected Roman candle balls. The start of air fighting may be said to have come when the Lewis machine guns were brought out for use in the trenches. Presently these ground guns were taken into the planes and fired from the observers' shoulders. Then for the first time war flying began to be a hazardous occupation so far as the enemy's attentions were concerned.

It was soon discovered that the machine gun was the most effective weapon of all for use on an airplane, because only with rapid firers could one hope to hunt successfully such swiftly moving prey as airplanes. It had become patent to the strategists that it was of supreme importance to keep the enemy's aircraft on the ground. Hence invention began adapting the machine gun to airplane use.

The swiftest planes of all were those of the single-seater pursuit type. It was obviously impossible for the lone pilot of one of these to drop his controls and fire a machine gun from his shoulder. This necessitated a fixed gun that could be operated while the pilot maintained complete control of his machine, and such necessity was the mother of the invention known as the synchronizing gear.

This ingenious contrivance, however, did not come at once. Most of the war planes were of the tractor type; that is, that they had the engine and propeller in front, this arrangement giving them better maneuvering and defensive powers in the air than those possessed by planes with the rear, pushing propellers. The first fixed machine gun was carried on the upper plane of the biplane so as to shoot over the arc described by the propeller. With the gun thus attached parallel to the line of flight, the pilot needed only to point the airplane itself directly at the target to have the gun trained on its objective. But such an arrangement proved to be unsatisfactory. A single belt or magazine of cartridges could, indeed, be fired from the gun, but there was no more firing on that trip, because the pilot could not reach up to the upper plane to reload the weapon.

So the fixed gun was brought down into the fuselage and made to fire through the whirling propeller. At first the aviators took their chances of hitting the propeller blades, and sometimes the blades were armored at the point of fire, being sheathed in steel of a shape calculated to cause the bullets to glance off. This system was not satisfactory. Then, since a single bullet striking an unprotected propeller blade would often shatter it to fragments, attempts were made to wrap the butts of the blades in linen fabric to prevent this splintering, and this protection actually allowed several shots to pierce the propeller without breaking it.

This was the state of affairs on both sides early in 1915. The French Nieuports had their fixed guns literally shooting through the propellers, the bullets perforating the blades, if they did not wreck them. As late as February, 1917, Maj. Bradley, who was by that time a flight commander in the British service, worked a Lewis gun over the Bulgarian lines with the plane propellers protected only by cloth wrappings.

All of this makeshift operation of fixed machine guns was changed by the invention of the synchronizing device. This is an appliance for controlling the fire of the fixed gun so that the bullets miss the blades of the flying propeller and pass on in the infinitesimal spaces of time when the line of fire ahead of the gun is clear of obstruction. The term "synchronizing" is not accurate, since that word implies that the gun fires after each passage of a propeller blade across the trajectory. Such is not the truth. The propeller revolves much more rapidly than the gun fires. The device is also called an "interrupter," another inexact term, since the fire of the gun is not interrupted, but only caused at the proper moments. Technicians prefer the name "gun control" for this mechanism.

Who first invented the synchronizer is a matter of dispute, but all observers agree that the Germans in the Fokker monoplanes of 1915 were the first to use it extensively. Not until some time after this did the allies generally install similar devices. Some have attributed the original invention to the famous French flier, Roland Garros.

Two types of synchronizers were developed, one known as the hydraulic type and the other as the mechanical. In operation they are somewhat similar. In each case there is a cam mounted on the engine shaft so that each impulse of the piston actuates a plunger. The plunger passes on the impulses to the rest of the mechanism. In the mechanical control the impulse is carried through a series of rods to the gun, causing the latter to fire at the proper moments. In the hydraulic control the impulse is transmitted through oil held at a pressure in a system of copper tubes. The hydraulic synchronizer is known as the Constantinisco control, commonly called the "C. C." after the military fashion of using initials. This was the device copied for American planes in the war.

In April, 1917, we knew practically nothing about the use or manufacture of aircraft guns. We had used airplanes at the Mexican border, but not one of them carried a machine gun. The Lewis gun, which is a flexible type of aircraft weapon pointed on a universal pivot by the observer in a two-place plane, was being manufactured by the Savage Arms Corporation for the British Government; but we had never made a gun of the fixed type in this country, nor did we know anything about the construction or manufacture of synchronizers.

One special requirement of the aircraft machine gun is that it must be reliable in the extreme. It is bad enough to have a gun jam on the ground, but in the air it may be fatal, for little can be done there to repair the weapon. A jam leaves the gunner to the mercy of his adversary, so in the production of aircraft armament there must be not only special care in the manufacture of the guns, but the ammunition, too, must be as perfect as human accuracy can make it. The cartridges must be either hand-picked and specially selected from the run of service ammunition, or else manufactured slowly and expressly for the purpose, with minute gauging from start to finish of the process.

Another requirement for the aircraft gun is that it must function perfectly in any position. On the ground a machine gun is fired essentially in a horizontal position, but the airman dives and leaps in his maneuvering and must be able to shoot at any instant.

Aircraft guns are subject to extreme variations of temperature, and so they must be certain to function perfectly in the zero cold of the high altitudes, regardless of the contraction of their metal parts.

Then, too, such guns must be able to fire at a much greater rate than those of the ground service. Five hundred shots per minute is regarded as sufficient for a ground gun, but aircraft guns have been brought up to a rate of fire as high as 950 to 1,000 shots per minute. The Browning aircraft gun, never used by us, but in process of development when the armistice was signed, had been speeded up to 1,300 shots per minute, with all shots synchronized to miss the blades of the propeller.

The rate of fire in the air can not be made too swift. Suppose an airplane were flying past a long, stationary target, such as a billboard, at the relatively slow speed of 100 miles an hour. Assume on this plane a flexible machine gun aimed at the billboard at right angles to the line of flight. If this is a fast machine gun, it may shoot 880 times a minute, at which rate the shots will come so fast that the explosions will merge into a continuous roar. Yet the bullets fired at such a rate from a machine moving at even such low speed will be spaced out along the billboard at intervals of 10 feet. But most of the fighting planes traveled much faster than 100 miles per hour. Thus it is entirely possible for two antagonists in the air to aim with complete accuracy at each other and both to pass unscathed through the lines of fire. The faster, therefore, the aircraft gun fired, the better the chances of bringing down the enemy plane.

The Lewis gun, invented by Col. Lewis, of the United States Army, was the weapon most generally used by the allies as the flexible gun for their airplanes, operated on a universal mount which permitted it to be pointed in any direction. The Lewis aircraft gun was the ground gun modified principally by stripping it of the cooling radiator and by the addition of a gas check to reduce the recoil. The Lewis was fed by a drum magazine, a more desirable feed for flexible guns than any belt system. The German flexible gun, the Parabellum, had the unsatisfactory belt feed.

The Vickers gun was the only successful weapon of the fixed type developed in the war before we became a belligerent. We were manufacturing Vickers guns in the United States prior to April, 1917; but when the Signal Corps faced the machine-gun problem, in September, 1917, it found that the Infantry branches of the Army had contracted for the entire Vickers production in this country.

Accordingly, the equipment division of the Signal Corps, in the face of marked opposition, took up the development of the Marlin gun as an aircraft gun of the fixed type. This gun, however, proved to be extraordinarily successful and was regarded by our Flying Service and by the aviators of the allies to be the equal of the Vickers in efficiency. Because of this development, when there came the need of tank guns, in June, 1918, the Aircraft Board, which had succeeded the Signal Corps as the director of aerial activities, was able to supply 7,220 Marlin machine guns within two weeks for this purpose.

The first order for Marlin guns was placed on September 25, 1917; and over 37,500 of them had been produced before December, 1918. The Marlin-Rockwell factory began producing 2,000 guns per month in January, 1918, and increased this rapidly until as many as 7,000 guns were built in one month. The Marlin gun shoots at the rate of 600 to 650 shots per minute and is fed by a belt of the disintegrating metal-link type.

As to Lewis guns, which we adopted as our flexible weapon, more than 35,000 of them were delivered to the Air Service up to December, 1918. In February, 1918, the Savage Arms Corporation built 1,500 of them, increasing their monthly deliveries until in the month of October, 1918, they turned out 5,448 of these weapons. The Lewis gun which the British had been using carried 47 cartridges in its magazine. A notable accomplishment of the manufacture of Lewis guns for our use was to increase the capacity of the magazine to hold 97 cartridges.

In our De Haviland-4 planes we installed two Marlin fixed guns, each firing at the rate of 650 shots per minute, equipping the weapons with Constantinisco controls to give the plane a maximum fire of 1,300 shots per minute through the blades of a propeller whirling at a rate as high as 1,600 revolutions per minute. Four fixed guns have also been successfully fitted to one plane and timed so that none of the bullets struck the propeller blades.

At the time the armistice was signed the rate of production of special aircraft ammunition, a classification including tracer bullets, incendiary bullets, and armor-piercing bullets, exceeded 10,000,000 rounds per month.

The original estimate for the quantity of ammunition our Flying Service should have was later greatly increased because the squadrons at the front began installing as many as four guns on a single observation plane.

Although different aviators had their own notions about the loading of ammunition belts, certain sequences in the use of the three types of special ammunition were usually observed. First usually came the tracer cartridge, which assists the gunner in directing his aim; then two or three armor-piercing cartridges, relied upon to injure the hostile engine or tap the gasoline tank; and finally one or two incendiary cartridges to ignite the enemy's gasoline as it escaped, sending him down in flames. Such a sequence would be repeated throughout the ammunition belt or magazine container.

The belts for the fixed guns carry a maximum of 500 rounds of cartridges. The belt which we furnished to our fliers at the front was made of small metallic links fastened together by the cartridges themselves. As the gun was fired and the cartridges ejected, the links fell apart and cleared the machine through special chutes. The total production of such belting in this country amounted to 59,044,755 links. Although the links are extremely simple in design, the great accuracy required in their finish made production of them a difficult manufacturing undertaking. The production and inspection of each link involved over 36 separate operations. It actually cost more to inspect belt links than to manufacture them.

We produced 12,621 British unit sights for airplane guns and sent 1,550 of them overseas. We also bought an adequate number of small electric heaters to keep the gun oil from congealing in the cold of high altitudes.

A novel undertaking for our photographic manufacturers was the production of the so-called gun cameras which are used to train airplane gunners in accuracy of fire. Target practice with a machine gun in an airplane is dangerous to the innocent bystander; and it was found to be impracticable, moreover, to tow suitable targets for actual machine-gun fire. Consequently, quite early in the war, the air services of the allies adopted the practice of substituting cameras for the machine guns on the practice planes.

One of these gun cameras, invented by Thornton Pickard, of Altringham, England, imitated in design a Marlin aircraft machine gun; and in order to make a picture with it, the gunner must go through the same movements that he would employ in firing a Marlin gun. Thus, if the gun were pointed directly on the target, the target would appear squarely in the center of the picture taken; and this showed the gunner's accuracy as well as if he had fired cartridges from the actual weapon.

These gun cameras were of two sorts. One type took a single picture each time the trigger was pulled. Those of the other sort took a number of pictures automatically at a speed approximately that of the firing of a machine gun. This latter type was much the same as a moving picture camera, the resulting film being a string of silhouettes of the target, each exposure showing whether the aim of the gunner was exact at the instant the picture was taken.

In September, 1917, the Eastman Kodak Co. began the development of a camera gun of the "burst" or automatic moving-picture type. After our authorities had seen the model, the Navy ordered a number of them, while the Air Service placed increasing orders for these instruments until 1,057 had been produced and delivered to the Government by November, 1918. This camera was not used in the fixed airplane guns, but was designed to train the operators of the flexible Lewis gun. The camera exactly replaced the ammunition magazine on a Lewis gun.

Of the single-shot gun cameras 150 were delivered during the hostilities. This design was obtained from Canada and duplicated here.

The use of the so-called Bromotype paper in gun cameras was one of the interesting phases of this development. As everyone acquainted with photography knows, a picture is made ordinarily by exposing a sensitized plate or film, developing the latter to make a negative, then exposing sensitive print paper to the light that comes through the negative, thus reversing the lights and shadows and creating a positive in the exact semblance of the subject photographed. A concern in Cleveland, Ohio, the Positype Co., produced Bromotype paper which could be exposed directly in the camera, coming out of the developing process as a positive without the intervention of a film or plate negative.

Bromotype paper is much more highly sensitized than ordinary print paper, so that it may be adequately exposed in an instantaneous, high-speed snapshot. The exposure is then developed in the ordinary way in the dark room, the familiar negative image appearing on the surface in the ruby light of the lantern. At this point the special developing process enters. The paper negative, without being fixed, is immersed in a bath of chemicals that dissolves away the sensitized surface that has been oxidized by the light from the camera lens--that is, the image--leaving on the paper only the unoxidized, or unexposed, parts of the sensitization. The paper now presents an unbroken white surface. It is then redeveloped by a special solution, and the picture in its true values of light and shade thus comes into existence. The entire development and finishing of this paper requires only 2½ to 3 minutes.

Under this system, of course, only one finished print of each exposure can be made; but the airplane gunners needed only one print to show their aim. Positype paper was thus admirably adapted for use in the airplane gun cameras; and because of its cheapness and the simplicity and rapidity of its use, it was rapidly supplanting film at the training camps in this country when the armistice was signed.

AIRPLANE BOMBS.

The American production of bombs to be dropped from airplanes was not started so soon as production in some of the other branches of ordnance development, due to numerous difficulties encountered in working up the design of this new matériel. Although aerial bombing was steadily increasing in effectiveness and magnitude when hostilities ended, yet this kind of fighting was a development that came relatively late in the war; and the lack of perfected standards at the time this country became a belligerent helped to impede our program.

Some of the bombs first designed and put into production were later rejected by our forces in France, as they had become obsolete before being shipped overseas. We managed to manufacture a great quantity of unloaded bombs by the time the armistice was signed, enough, in fact, to provide for the Army's needs during another year of warfare. These had to be loaded with explosives before they were ready for use. We lacked adequate facilities for loading bombs with explosives, although these facilities were being provided rapidly when the war ended. The result was that the thousands of completed American bombs remained unloaded, while practically all the bombs used by our fliers in France were of foreign manufacture.

Military science had had some small experience with aerial bombing prior to the great war. Italian aviators had dropped bombs of an ineffective sort during Italy's war in Africa. When Mexico was having a civil war in 1914 American air-sailors of fortune on one side or the other dropped bombs on troops from their planes.

In the great war the first nation to attempt bombing on any systematic scale was Germany, who sent her Zeppelins over London and Paris early in the conflict and released bombs upon the heads of the helpless civilians. Yet this early and impressive effort was, in its difficulties, out of all proportion to the actual damage done to the city of London, largely due to the fact that Germany had not yet produced effective aerial bombs. The frightful scenes and noises of a bomb raid probably did more to reduce the morale in these early days than the destruction caused by the exploding missiles.

It is an exceedingly difficult trick to drop a bomb from any considerable altitude and hit what you are aiming at. The speed of the airplane, its height above the ground, the shape of the bomb itself, and the currents of air acting on the falling missile influence its line of flight. The aviator approaching an enemy target drops the bomb long before his airplane is directly above the object aimed at.

The line of the bomb's flight is a parabolic curve. The speed at which the airplane travels at first propels the bomb forward, almost as if it had been shot from a stationary gun. As the downward velocity of the bomb increases very rapidly, it soon becomes so great in proportion to velocity forward that the course of the missile bends sharply downward until, as it nears the ground, it is falling nearly in a vertical line. Hence, it becomes evident that accurate bomb dropping is an art attained only by much practice on the part of the aviator.

The latest bombing machines were equipped with sights which enabled the birdman to drop these deadly objects with greater accuracy than had been possible earlier in the war. While some of the expert European bombers scorned the new inventions in sights and preferred to continue the use of makeshift sights which they themselves had invented and installed on their planes, the average accuracy of bomb dropping was considerably greater after bomb sights came into general use.

These sights were adjusted to height, air speed, and strength of wind. When these adjustments had been made, the two sighting points were in such position that, if the bomb were dropped when the target was in line with them, an accurate hit would be registered.

We adopted a British sight, tested and found satisfactory by the Royal Flying Corps, and known as the High Altitude Wimperis, and in the United States as the Bomb Sight Mark I-A. On November 11, 1918, American factories, working on contracts placed by the Ordnance Department, had produced 8,500 of them. The job of turning out this intricate mechanism was turned over to Frederick Pearce & Co., of New York City, in January, 1918. Later in the year additional contracts were given to the Edison Phonograph Works and to the Gorham Manufacturing Co. These contracts called for 15,000 sights. By December 12, 1918, these concerns had completed a total of 12,700 of them.

[Illustration: A 250-POUND DEMOLITION BOMB CARRYING 125 POUNDS OF EXPLOSIVE AND HAVING HEAVY CAST-STEEL NOSE AND PRESSED SHEET STEEL REAR BODY.]

[Illustration: A 25-POUND FRAGMENTATION BOMB CARRYING 3 POUNDS OF EXPLOSIVES, DESIGNED FOR USE AGAINST TROOPS.]

[Illustration: A 40-POUND INCENDIARY BOMB OF THE INTENSIVE TYPE, WITH STEEL NOSE AND FUSIBLE ZINC REAR CASING.]

[Illustration: AIRPLANE FLARE.]

[Illustration: MARK I, HIGH CAPACITY DROP BOMB. A 105-POUND DEMOLITION BOMB, CARRYING 55 POUNDS OF EXPLOSIVE.]

[Illustration: MARK II, HIGH CAPACITY DROP BOMB, NOW OBSOLETE, HAVING BEEN FOUND TOO SMALL FOR DEMOLITION PURPOSES.]

[Illustration: MARK II--A FRAGMENTATION DROP BOMB.

A 20-pound fragmentation bomb, made from a converted 3-inch artillery shell, carries 1½ pounds of explosives to be used against troops. Projection at nose causes burst to take place above ground.]

[Illustration: DROP BOMB, MARK III.]

Airplane bombs are shaped so as to offer the least possible resistance to the air. They have fins on their tails to steady them lest they tumble over and over. On the smaller types of bombing planes, such as the De Haviland-4, the bombs were usually carried underneath the lower wings or under the fuselage, hanging horizontally by hooks or fastened by bands around the bodies of the bombs, according to their type. The bombs were dropped by a quick-release mechanism operated by a small lever within the fuselage. The production of these release mechanisms, of which several types were made, was one of the troublesome jobs in connection with the airplane bombing.

All bombs are carried on the planes either suspended under the wings or fuselage of the plane or in a compartment in the fuselage. The manner of carrying and the design of the release mechanism is determined by the type of plane used. Since the weight-carrying capacity of the planes is limited, release mechanisms must be designed with a view to lightness as well as safety. These mechanisms are so designed that the observer can release any desired number of bombs either as a salvo or in a "trail fire," and the order of releasing must be so arranged that the balance of the plane will be disturbed as little as possible; that is, if bombs are carried under the wings they should be released alternately from each wing. All bombs are fitted with a safety mechanism which enables the observer to drop them either "armed" or "safe," i. e., so that they will explode or not as desired. An occasion might develop where the aviator would have to get rid of his bombs over his own lines. These various points are all taken care of in the design of the release mechanism and are controlled by the observer with an operating-control handle placed in the observer's cockpit.

All of the bombs used by our fliers and by the fliers of the other nations at war were of three distinctive types--demolition bombs, fragmentation bombs, and incendiary bombs.

Our Ordnance Department built demolition bombs in five different weights: 50 pounds, 100 pounds, 250 pounds, 500 pounds, and, finally, the enormous bomb weighing 1,000 pounds--half a ton. The most frequently used demolition bombs, however, were those of the 100-pound and 250-pound sizes. The demolition bombs were for use against ammunition dumps, railways, roads, buildings, and all sorts of heavy structures where a high-explosive charge is desired. These bombs had a shell of light steel which was filled with trinitrotoluol--T. N. T., as it is more commonly known--or some other explosive of great destructive power. The charge was set off by a detonator held apart from the dangerous contents of the bomb by a pin. As the bomb was released by the mechanism the pin was automatically drawn out, and the detonator slid down into position so as to explode the bomb the instant it struck its object.

The first contract let for drop bombs of any type was given to the Marlin-Rockwell Corporation of Philadelphia in June, 1917. This contract was for the construction of 5,000 heavy drop bombs of the design known as the Barlow, and also for 250 sets of release mechanisms for this bomb. We were able to go ahead with the production of this bomb at this early date since it was the only one of which we had completed designs and working drawings when we entered the war. In November, 1917, this order was increased to 13,000, and in April, 1918, to 28,000.

The Barlow bomb, however, was destined never to cut any figure in our fighting in France. The production was slow, due to the necessity of constant experimentation to simplify a firing mechanism which was regarded as too complicated by the experts of the War Department. Finally, in June, 1918, when 9,000 of these bombs and 250 sets of release mechanisms had been produced, a cablegram came from the American Expeditionary Forces canceling the entire contract.

Meanwhile, the final type of demolition bomb, known variously as the Mark I, II, III, IV, V, or VI, depending upon its size, had been developed here. In December, 1917, a contract for 70,000 of the size known as Mark II, weighing 25 pounds, was given to the Marlin-Rockwell Corporation. But in June the American Expeditionary Forces informed us that this bomb would not be of value to the Air Service abroad because of its small explosive charge, and the contract was cut down to 40,000 bombs, which number the Army could use in training its aviators. By the end of November, 1918, bomb bodies of the Mark II size to the number of 36,840 had been completed.

By the end of March, 1918, we had developed here a series of demolition bombs that promised to meet every need of our Air Service abroad in projectiles of their class. We let contracts for the manufacture of 300,000 of the 50-pound Mark III size, these contracts being reduced later to a total of 220,000. The manufacturers were the A. O. Smith Corporation, an automobile parts concern of Milwaukee, Wis.; the Edward G. Budd Manufacturing Co. of Philadelphia; and Hale & Kilburn of Philadelphia. Six months later the A. O. Smith Corporation had reached a production of 1,200 of these bombs a day, and completed their contract in October. Both the other concerns also completed their contracts in the autumn of 1918.

[Illustration: TWO OF THE LARGEST DEMOLITION DROP BOMBS.

The larger of these two bombs weighs 1,000 pounds and carries 570 pounds of explosive. The smaller weighs 550 pounds and carries 280 pounds of explosive. They are both made with a heavy cast-steel nose and pressed metal rear body.]

[Illustration: MARK II BOMB RELEASE MECHANISM FOR HANDLEY-PAGE MACHINE, SHOWING MARK I AND MARK IV BOMBS IN PLACE.]

[Illustration: MARK IX-A RELEASE MECHANISM AS ATTACHED TO MARK II RELEASE FOR HANDLEY-PAGE PLANE.]

The A. O. Smith Corporation had tooled up their factory so as to become one of our largest producers of airplane bombs. In addition to the contract already mentioned, during 1918 this concern received orders for approximately 300,000 demolition bombs of the 100-pound (Mark I) size. By November 11, 1918, they had turned out 153,000 of these and had developed a capacity for building 7,000 drop bombs daily. Another large manufacturer of drop bombs was McCord & Co., of Chicago, a concern which in 1918 received orders for nearly 100,000 bombs of the 250-pound, 550-pound, and 1000-pound sizes. By the day the armistice was signed this concern had produced 39,400 completed bombs. These bombs were the heaviest and largest ones intended for use by our service abroad.

The fragmentation bombs differ from the demolition bombs in that they have thick metal walls and consequently smaller charges of explosive. They throw showers of fragments like those of high-explosive artillery shell. The demolition bombs contain, on the other hand, the maximum possible amount of explosive and produce destruction by the force of explosion. Fragmentation bombs always have instantaneous firing mechanisms, while demolition bombs are usually provided with delayed fuses, allowing them to penetrate the target before explosion.

The fragmentation bombs produced by the Ordnance Bureau were smaller than the demolition type, the size most commonly used weighing 24 pounds. These bombs had thick cases and were constructed so that they would explode a few inches above the ground. As the bombs reach a velocity downward of over 500 feet per second, the mechanism had to operate to an accuracy of less than one-thousandth of a second. They were designed for use against bodies of troops.

The fragmentation bombs were a late development in this class of work. The timing device to explode the bomb at the proper distance from the ground was undertaken by three concerns. The contracts for approximately 600,000 of these devices were let in July, 1918. The John Thomson Press Co. of New York City completed its contract for 100,000 mechanisms by the end of October, 1918. The National Tool & Manufacturing Co. of St. Louis completed its contract for 100,000 shortly after the armistice was signed. The Yale & Towne Manufacturing Co., Stamford, Conn., which had contracted to build approximately 400,000 of these devices, had turned out 150,000 by the end of November, 1918. Other concerns which manufactured various parts for the fragmentation bombs were the American Seating Co. of Grand Rapids, Mich., makers of school desks and seats, and the Dail Steel Products Co. of Lansing, Mich.

Some idea of the quantity of fragmentation bombs in our program may be gained from the fact that the contract for the Cordeau-Bickford fuse used in the fragmentation bomb, let to the Ensign-Bickford Co. of Simsbury, Conn., called for the manufacture of 550,000 linear feet of fuse, or more than 100 miles of it. The contracts for fuse were placed in August and September, 1918, and the Ensign-Bickford Co. finished up the job on November 7, four days before the armistice was signed.

The Government discovered that 3-inch shell rejected for various reasons could be re-machined and used to make these airplane fragmentation bombs. The various arsenals had a large supply of them in storage. In August and September, 1918, contracts were let to large numbers of concerns to convert over 500,000 of these shell into fragmentation bombs, and by November 30, nearly 21,000 of the new bombs had been delivered.

These bombs, made from the 3-inch shell, as far as the machining of the bodies is concerned were turned out in various quantities by the following firms:

Vermont Farm Machinery Co., Bellows Falls, Vt. Richmond Forgings Corporation, Richmond, Va. Bethlehem Steel Co., Bethlehem, Pa. Consolidated Car Heating Co., Albany, N. Y. S. A. Woods Machine Co., South Boston, Mass. Westfield Manufacturing Co., Westfield, Mass. Wheeling Mold & Foundry Co., Wheeling, W. Va. A. P. Smith Manufacturing Co., East Orange, N. J. Watervliet Arsenal, Watervliet, N. Y. Keystone Machine Co., York, Pa. McKiernan Terry Drill Co., Dover, N. J.

The nose-firing mechanism for these bombs was produced by the Yale & Towne Manufacturing Co., Stamford, Conn.; the National Tool & Manufacturing Co., St. Louis, Mo.; and the John Thomson Press Co., New York City; while the rear cap stabilizer assemblies were produced by the Dail Steel Products Co., Lansing, Mich., and the American Seating Co., Grand Rapids, Mich.

The last item on the bomb program to come into production was the fragmentation bomb Mark II-B, which was an exact copy of the British Cooper bomb, the most effective bomb of this type in use by the allied nations. Contracts for this bomb were not let until August 17, 1918, to the Lycoming Foundry & Machine Co., of Williamsport, Pa., and the Paige-Detroit Motor Car Co., of Detroit, Mich. The former company by December 1 was producing these bombs at the rate of 500 per day and the latter was just coming into quantity production the first week in December.

[Illustration: TWO VIEWS, MARK V RELEASE TRAP (RIGHT HAND) WITH UNIVERSAL NOSE AND TAIL BEAM, MOUNTED ON T-RAILS UNDER RIGHT WING OF DH-4 PLANE.

Upper--Front view, showing operating tube connected to alternating cam in fuselage. Two Mark III demolition drop bombs (150 pounds) held by supporting straps; one bomb released, showing free supporting strap. Lower--Rear view, showing method of retaining stabilizer by tail clip with three Mark III demolition drop bombs.]

[Illustration: TWO VIEWS OF MARK X RELEASE TRAP ON PLANES.

Shows Mark X release trap (Cooper) mounted upon T-rails under wing of DH-4 plane. Bowden control wire and casing connected to fuselage. Two Mark II-B fragmentation bombs suspended--one arming vane retained, the other free.]

When the United States entered the war no satisfactory incendiary bombs had yet been produced by any country, and consequently a long period had to be given over to experimentation before quantity production could be attained. We produced two types of incendiary bombs, the first being of the scatter type, designed for use against light structures, grain fields, and the like, and the second of the intensive type, for use against large structures. Later on in our program we abandoned the manufacture of the scatter type incendiary bombs on cable instructions from abroad, as it was found that the wet climate made a bomb of this type of little value. The American intensive bomb, while it had not yet come up to our ideal and was in process of evolution during its manufacture, nevertheless was regarded by our officers as more effective than any other bomb of its type in existence, since it produced a larger and hotter flame.

Our intensive incendiary bombs weighed about 40 pounds each and contained charges of oil emulsion, thermit, and metallic sodium, a combination of chemicals that burns with intense heat. These bombs were used against ammunition depots or any structures of an inflammable nature. The sodium in the charge was designed to have a discouraging effect upon anyone who attempted to put out the fire of the burning charge, since metallic sodium explodes with great violence if water is poured upon it.

Of the scatter bombs we built 45,000 before abandoning the manufacture, an action taken in September, 1918. When hostilities ceased we had out contracts for 122,886 of the intensive bombs and about 86,000 of them had been delivered ready for loading.

One of the large manufacturers of incendiary bombs was the Conron-McNeal Co., of Kokomo, Ind., manufacturers of skates. The company had to equip its plant with new machinery especially for handling this novel manufacturing enterprise. In all, they produced 50,000 bombs and were turning them out at the rate of 400 per day when the armistice was signed. This concern was the pioneer in the manufacture, the subsequent contractors profiting by the experience of the Conron-McNeal Co., and consequently being able to obtain quantity production more quickly than the Kokomo plant had been able to reach it. The Globe Machine & Stamping Co., of Cleveland, Ohio, built 30,000 bombs and 36,400 firing mechanisms before hostilities closed, and eventually reached a production rate of 500 bombs and 1,000 firing mechanisms per day. Parrish & Bingham, also of Cleveland, produced 13,000, and were turning them out at the rate of 400 daily when the production was stopped. The C. R. Wilson Body Co., of Detroit, built 42,562 of the intensive bombs and reached a daily production of 500. The New Home Sewing Machine Co., of Orange, Mass., manufactured 20,000 firing mechanisms for the scatter-type bombs.

One of the interesting phases of the bomb manufacturing program grew out of the necessity for target practice for our aviators. For this work we built dummy bombs of terra cotta, costing about a dollar apiece. Instead of loading these bombs with explosive, we placed in each a small charge of phosphorus and a loaded paper shotgun shell, so that the bomb would eject a puff of smoke when it hit its object. The aviators could see the smoke puffs and thereby determine the accuracy of their aim.

The Gathmann Ammunition Co. of Texas, Md., was the first contractor for dummy bombs, building 10,000, which were delivered in the spring of 1918. In the spring and summer of 1918, the Atlantic Terra Cotta Co., the New Jersey Terra Cotta Co., both of Perth Amboy, N. J., and the Federal Terra Cotta Co. of Woodbridge, N. J., each built 25,000 of these bombs. In September additional contracts for 50,000 dummy bombs were given to each of these three concerns, while another contract for 25,000 went to the Northwestern Terra Cotta Co. of Chicago. By the end of November these concerns had delivered nearly 34,000 of the 175,000 bombs contracted for, and were turning them out at the rate of 1,300 per day.

The Essex Specialty Co. manufactured 10,000 phosphorus rolls for dummy bombs, and the Remington Arms-U. M. C. Co. supplied 10,000 shotgun shells for the first bombs produced. Later the Remington Arms Co. produced 100,000 shotgun shells for dummy bombs.

AIRPLANE PHOTOGRAPHIC SUPPLIES.

In four days of the final drive of the Yankee troops in the Argonne district the American photographic sections of the Air Service made and delivered 100,000 prints from negatives freshly taken from the air above the battle lines. This circumstance is indicative of the progress made by military intelligence from the days when a commander secured information of the enemy's positions only by sending out patrols, or from spies. The coming of the airplane destroyed practically all possibility for the concealment by day of moving bodies of men or of military works. Mere observation by the unaided eye of the airmen, however, soon proved inadequate to utilize properly the vantage point of the plane. The insufficient and often crude and inaccurate drawings brought in by the airplane observer were early succeeded by the almost daily photographing of the entire enemy terrain by cameras, which recorded each minute feature far more accurately than the human eye could possibly do. The airplane, to quote the common saying, had become the eye of the Army, but the camera was the eye of the airplane.

This development in military information-getting from start to finish was entirely the product and an evolution of the great war. When the war broke out in 1914 there were no precedents for the military photographer to go by, nor had any specialized apparatus ever been designed by either side for this purpose. As a result the first crude makeshifts were rapidly succeeded by more and more highly developed equipment.

At the outset of the war, before antiaircraft guns were brought to efficiency, it was possible for the observation planes of the British, the French, and the Germans to fly at low altitudes and take satisfactory pictures with such photographic appliances as were then in common use. But as the "Archies" forced the planes to go higher in the air, special equipment had to be designed for longer distance work under the adverse conditions of vibration and speed, such as exist on airplanes. It is a tribute to the photographic technicians of the world that they were able to produce at all times equipment to meet these increasing demands.

[Illustration: TYPE DR-4, DE RAM CAMERA.]

[Illustration: TYPE A-3, HAND-HELD AIRPLANE CAMERA.]

[Illustration: TYPE L, 4 x 5 PLATE CAMERA.]

[Illustration: 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," which use 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 consisted merely 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 on test 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.

THE FIREWORKS OF FLYING.

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.

[Illustration: MARLIN MACHINE GUN WITH FIXED MOUNTING, ON A JN-4 FUSELAGE.]

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

[Illustration: AIRPLANE FLARE.]

[Illustration: 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 troops he 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.

KEEPING OUR FLIERS WARM.

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 covered with 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.

PROTECTION IN HIGH ALTITUDE FLYING.

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.

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

[Illustration: AVIATOR'S OXYGEN HELMET EQUIPPED WITH TELEPHONE RECEIVER.]

[Illustration: 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 special division 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.

[Illustration: 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.]

[Illustration: AVIATORS EQUIPPED WITH TELEPHONE TRANSMITTERS AND HEAD SETS TO COMMUNICATE WITH EACH OTHER.]

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