Not the least dangerous of the many services the airplane is performing is that of the artillery "spotter." It belongs to some particular battery whose guns are thundering away at the enemy. Hovering above No Man's Land, where its position is a trifle too exposed to be comfortable, it radiographs back to the gunners the exact locations of important objectives, then watches the firing and reports the results.

Thanks to it the big guns do not speak in vain, and almost every shot is a direct "hit."

And then there are the dreadnaughts of the sky who actually take part in an attack, flying low over the lines and attacking the enemy infantry with guns and with death-dealing bombs. They must run the gauntlet of the enemy's fire, but on the other hand they spread terror and confusion in the ranks of the soldiers ma.s.sed below, distracting their attention and leaving them open to the surprise of a sudden onslaught of Allied troops.

There are other machines which help in an attack by keeping the various parts of the long line in close communication with each other, so that all efforts are in unison. Their duties correspond in a way to those of the swift horseback rider we read of in the stories of old wars, who sped with news of great import from one commander to another. Only that the airplanes of to-day are so much more efficient than the gallant horseback rider of old, that although the line stretches across a nation, it can act as a man when the moment comes for a big "push."

Long before the war Germany had been busy turning out airplanes in large numbers in her factories, and in August, 1914, her air force was far superior in numbers to that of her great opponent France. She fondly imagined that she would be able with the greatest ease to put out her enemy's eyes, but in this she failed utterly. In spite of her military program of construction, according to which airplanes were turned out as if by clock-work, there was something wrong with her calculations. It is amusing to look back and see how German "method" had been carried to the absurd point of defeating itself. In manner truly characteristic, the Hun had standardized his airplane down to the last bolt. Every machine turned out was of exactly the same pattern, and built up of exactly the same parts--parts which could be manufactured in large quant.i.ties and put together with unusual speed. It was certainly _system_ raised to the _n_th degree. And the machines themselves were good enough--st.u.r.dy biplanes intended to be maids-of-all-work over the front lines. Yet in a little while after the fighting had begun, Germany withdrew them in more or less chagrin, and set herself to constructing others of varied patterns. They were well made and splendidly equipped, but they were not sufficiently _specialized_ for the many different kinds of work they were called on to perform.

France had a motley array of airplanes of every size, shape and make when the war broke out. They had varying systems of control, so that a pilot who flew one with ease was nothing more than a novice when he stepped into another. He did not know how its new set of levers operated, nor how the plane would behave in the air. Moreover, the parts for these French airplanes and for their engines had been specially designed by each maker, and were quite unsuitable for any other type of machine. The result was that when a machine had to be repaired at the front, it was "laid up" for a long time, while the special part it required was being ordered and made for it. When finally it arrived, very often there had been some mistake, and so there was another long period of uselessness. France had prided herself on her versatility in airship design. She now had cause to regret it as she viewed the almost helpless confusion it had caused in her air service. Her machines, moreover, were much inferior to the German in armament, speed and climbing gauges, cameras, and all the hundreds of accessories which gave the German machines their initial advantage. But experience is the best teacher, and no sooner had she seen wherein she fell short than dauntless France mustered all her resources to correcting past mistakes.

Order was brought out of confusion, and it was only a very little while before the German war lords had need to look to their laurels, for the Frenchmen were far outstripping them in the air.

There was one "accessory" which the airplane of the Hun lacked, and which all his mechanical skill and ingenuity were not able to provide: _a pilot with the dash and daring of the French!_ Even in those first dark days when the French planes were the equals of their adversaries neither in numbers nor in capabilities,--a continuous stream of gallant French pilots took to the air and proved that they could surprise and outmaneuver their slower-thinking opponents. While they held the line in their inferior craft, French manufacturers were rushing newer and better equipped machines to reenforce them.

Great Britain was far behindhand in aircraft production when the trumpet of war sounded,--in fact, her air force was considered a negligible quant.i.ty by friend and foe alike. By dint of persevering search she managed to sc.r.a.pe up a small group of planes of many makes and for the most part antiquated. She sent them--along with her "contemptible little army "--to France, and there they succeeded in holding their own during the first great German push. When the Stories of heroic fighting against hopeless odds, of British airmen flinging their lives in challenge against the foe in the great air struggle, began to reach home, the British lion repented his tardiness and a program of aircraft construction on a large scale was inst.i.tuted without delay.

In carefully standardizing those first airplanes there was one point which the crafty Germans overlooked: which is, that you can't make a dray horse run fast, nor a race horse draw heavy burdens. The same thing holds good with the "steeds" of the air. A plane which is designed for great speed is never as good a burden bearer as one which is built to lift heavy weights at the expense of swiftness in flight. As soon as the duties of the airplane began to be specialized, the airplane itself began to appear in certain definite types.

Now of course the duties of the airplane in wartime are numberless, but out of the early confusion _three_ types of machines were finally evolved, which, with the addition of equipment, such as a camera, machine guns, etc., are suitable for practically any sort of work over the land. They are:

1. The high speed fighting machines.

2. The reconnaissance machines.

3. The bombing machines (including the day and the night bombers).

Of all military airplanes there is none so fond of "aliases" as the high speed fighting machine. Possibly in order to baffle the uninitiated, or to surround itself with an atmosphere of uncertainty and romance, it goes by first one t.i.tle and then another. Most often we hear it called a _speed scout_, perhaps for the reason that _it does no scouting!_ At other times it masquerades proudly under the fine French t.i.tles of "Avions de Cha.s.se" or "Avions de Combat." It is referred to as a "chaser," a "pursuit machine," a "battle plane" and a "combat machine"--but whatever it is _called_, in type it is the small, fast airplane, usually a single seater, quick in climbing, agile as an acrobat, able to "go" high and far,--for its duty is to run every enemy machine out of the sky and sweep the board clean before the heavier service machines begin their tasks of the day. It should be able to reach a height of from 18,000 to 23,000 feet, or in the language of the air, it must have a high "ceiling." From alt.i.tudes so tremendous that they awe the mere earthly pedestrian it swoops down upon its unsuspecting victim, opening upon him a stream of machine gun fire. For its pilot is also a skilled gunner and a crack shot. Upon his ability to maneuver his machine swiftly and cleverly and hit his target unerringly depends his own life and the life of a costly military airplane.

The reconnaissance machines and the bombing planes may do valuable service,--and indeed they invariably do--but it is the "speed scout"

that covers itself with glory. The reason is that its career brings it nearer to the "personal combat" of the knights of old than anything in modern warfare. Driving his swift Nieuport scout as a knight would have ridden his charger, the beloved Guynemer went forth to challenge the German fighters,--and other Frenchmen and Englishmen and Americans have followed him. It is a fact beyond all question that this branch of the service has produced some of the most truly unselfish and heroic figures of the whole war. The "speed scout" pilot did not need to be a man deeply versed in military affairs--as for instance the pilot and observer of the reconnaissance machine must be,--but he did need dauntless courage, unfailing nerves of steel, dash and daring and contempt for his own safety. So wherever the "speed scout" has blazed its trail of fire across the sky, there have sprung up the names of men whose heroic deeds have made them the idols of the whole world. Usually they have been very young men--young enough for their ideals to have kept fresh and untarnished from the sordid things of life, and thus they have written their names among the immortals.

[Ill.u.s.tration: _Copyright Underwood and Underwood_

A PHOTOGRAPH OF NORTHERN FRANCE TAKEN AT A HEIGHT OF THREE THOUSAND FEET]

Less appealing to the imagination, perhaps, but no less vital to the progress of modern warfare, is the slower flying reconnaissance craft.

This machine is always a two-seater, and sometimes a three, for at the very minimum it must carry a pilot and an observer, while a gunner is a very convenient third party in case of an attack from enemy scouts. This type of machine is used for photographic work, for artillery "spotting,"

and for many general service duties over the lines. In the early days of the war it was customary for the photography airplane to be escorted on its mission by a group of fighting machines, who hovered about it and engaged in battle any airplanes of the enemy that might seek to interrupt its important work. But the last year or so have brought many improvements in airplane construction and it has been found possible to build a machine which can not only carry the heavy photographic apparatus and a couple of machine guns, but which can also travel at a good speed and climb fast enough to escape from the anti-aircraft guns.

Instead of the rather helpless, clumsy, slow-flying reconnaissance machines of the early part of the war, we now have powerful "aerial dreadnaughts," which no longer need to run away, but can stay and fight it out when they are interrupted in the course of their air duties.

Military photography is one of the most fascinating of the side issues of the war. Before the day of the airplane it was the scout or spy who worked his way secretly into the enemy's lines and at great personal risk,--and often after many thrilling adventures, if the story books are to be believed--brought back to his commanding officer news of the disposition of troops, etc., in the opposing camp. To-day the spy's job has been taken away from him. No longer is it necessary for him to creep under cover of night past the guard posts of the enemy. A big, comfortable and efficient airplane flies over the ground by broad daylight and collects the necessary information a great deal better than the spy ever could have secured it.

[Ill.u.s.tration: _Copyright Underwood and Underwood_

AN AIRPLANE VIEW OF THE CITY OF RHEIMS, SHOWING THE CATHEDRAL]

A reconnaissance camera has very little in common with a kodak. The observer does not tilt it over the edge of the machine, focus it on some interesting object and "snap" his picture. As a matter of fact it works more after the manner of a gun. It is fixed in the bottom of the airplane, facing downward. The observer has been instructed before leaving the ground that a certain area or trench is to be photographed.

Straight to the beginning of that trench line the pilot heads his machine. The observer compares the country over which he is flying with the chart or map which he carries. Just as a gunner sights a target, he locates the beginning of the trench line to be photographed through a bull's eye, and immediately pushes the b.u.t.ton which sets the camera working. From that point the camera operates automatically, taking a series of overlapping pictures of the country it looks down upon. With calm determination the pilot holds his machine to the course laid out, in spite of any opposition that may arise in his path, for the slightest deviation from that fixed line of flight will mean a gap in the reconnaissance report which the pictures represent. But once he has covered the required area, he turns and flees. In less time than it takes to tell that magazine of films is being developed in a dark room.

From there the printed pictures are rushed to an expert interpreter who reads the secret meanings of the things he sees--this or that dark blotch or peculiar looking speck suggests to his trained mind a machine gun nest, a railroad center, an observation post, a barbed wire entanglement, a camouflaged battery, an ammunition dump, or what-not.

Pasted together so that they give a continuous view of the foe's territory, the printed pictures are hurried to headquarters, where in a few brief moments their message has been turned into a command to the troops. By the word that those pictures bring the battle is directed, and the blow is aimed straight at the enemy's vital spots.

Occasionally instead of a series of photographs of a trench line or limited area, a continuous set of pictures of a broad s.p.a.ce of country is desired. Then instead of a single machine as described above, a squadron of reconnaissance machines set forth, flying in V formation, with the leader of the squadron flying in front at the point of the V.

The moment he reaches the area to be photographed, he notifies the machines behind him by firing a smoke rocket with a signal pistol. At that signal the V broadens instantly, so that it becomes almost a straight line, the commander keeping only slightly ahead so that he may lead the way. On and on that broad V formation of airplanes sweeps, every camera registering, and all keeping close enough together to produce slightly overlapping photographs. Each machine will bring home a long line of pictures of the country over which it pa.s.sed, and those lines, pieced together, will make a large military map of the entire region. That is if everything goes smoothly, which in war time it seldom does. More likely that plucky V will be pounced upon by a herd of fast fighting machines whose duty it is to see that none ever return with their information to headquarters. There will follow a terrific contest; the observer in the reconnaissance machine becomes a gunner, and fires away at his pursuers, while the never-failing camera keeps steadily on with its job of recording. As nearly as possible the V formation is held, for much depends upon it, but suddenly a great gap appears in the line. "Done for" with a direct hit, one brave machine goes crashing earthward. That will mean a gap in the "map" that is in the making.

Still the V presses on relentlessly. One of the planes begins to lag behind. There is something wrong with its engine. It does its best to keep up with its fellows, but soon it is left behind, and the enemy craft dive after it. Battered and torn, its numbers depleted sadly, several of its crew wounded, its wings perhaps riddled with bullets, the photographing squadron turns its face toward home, and, flying now as high as possible to keep out of sight, puts on all speed for the safe side of No Man's Land. Military photography _sounds_ easy and comfortable. It _demands_ the type of courage which can make a man stick to a given line of flight, even when certain death lies straight ahead.

Sometimes a machine carries both bombs and a camera, and, as it drops its missiles, keeps a continuous record of its "hits" to carry home. And that brings us to the bombing machine, last but not least of the trio of military airplanes.

The bomber that works by day and near to its own lines, is similar to the reconnaissance machine, except that it does not usually carry a radio apparatus or a camera. Instead, the greater part of its cargo consists of bombs, dread instruments of destruction which will fall on the railroad junctions, troop trains, staff headquarters or ammunition dumps of the enemy. The day bomber is never used for long distance work, and so it does not need to be of tremendous size, as the machine which must carry fuel for an all night run as well as a large quant.i.ty of bombs to drop on a far away important objective.

The night bomber is the giant of the sky. The greatest genius of the cleverest designers has been expended upon its construction. More and more its tremendous importance is being recognized. Its activities precede every great offensive movement, for it flies over the enemy's country, leaving a trail of terrible destruction in its wake, and "preparing the soil" for the infantry advance. Deep in the territory of the foe it searches out the great supply centers and railway terminals and there it unloads its cargo of bombs.

If the Allies had possessed a sufficient number of these huge bombing planes they could have carried on an aerial warfare against Germany which would have defeated her without nearly so great a sacrifice of the lives of the infantry. The work is dangerous, but a single bombing plane could have wreaked more vengeance upon the Hun than perhaps a whole regiment of the bravest fighters. Consequently its use would have meant economy of human lives.

These fearful shadows that walk by night require pilots of the utmost skill to navigate the sea of darkness, as well as bomb droppers and gunners whose training has been perfect. The largest of them are equipped with either two or three powerful engines, each working a separate propeller. Such a machine can carry as much as five tons of explosives, with fuel for a twelve hours' flight.

The night bomber is very often a huge triplane, for the extra wing surface gives greater lifting power. At the same time the triplane has greater stability and has a fair chance of reaching home even when one of its planes has been badly damaged. It is the same with a machine which has two or more engines: even when one of these has been put out of order by the shots of the enemy the airplane can still reach home.

The night bombers must travel long distances, carry great cargos, bomb their objectives and make their escape, and so in the construction of their machines as much stability, lifting power and speed as possible has been the aim.

Usually it is some important munition base or factory center that is supplying the German troops, which the airmen set out to bomb. They travel in squadrons not only for safety, but because in this way an almost unlimited number of bombs can be carried and dropped simultaneously. Often a second squadron follows the first at a short distance. By the light of the terrible fires that the first set of explosives dropped are bound to start, this second squadron can drop its bombs with greater precision directly on important buildings that must be destroyed.

Moving slowly under their great load of explosives, and flying low, these two squadrons of destroyers start for some point in the heart of the German Empire. Like ghosts they "feel their way" mile after mile.

They are not anxious to invite detection, for under the great weight of their "messages" to Germany, they would not be able to maneuver quickly or to climb to safety.

Once those tons of explosives have been released and the noise of their dreadful havoc has aroused the anti-aircraft gunners of the enemy, those bombing planes will find the earth an uninviting sort of region and they will be glad to spring into the protecting silence and darkness of the upper air. And this they can do easily, for, rid of their load, they possess unusual climbing powers. The second squadron of bombers, flying over the same territory may expect a warm reception, and they will need to do their work quickly and beat a hasty retreat.

Such are the mysterious doings of the night. When the early dawn appears, gray and heavy eyed, it will find the bombing planes tucked away drowsily in their hangars, scarcely knowing themselves whether the journey up the Rhine was a reality or merely a terrifying dream.

And with the dawn their daylight sisters will take up the work near home. Word has just come that enemy reinforcements are moving up to the front along certain roads. "Fine," sings out a young lieutenant, appearing unexpectedly on the field from a small, carefully camouflaged office. "We will make them dance for us this morning!" He talks quickly and determinedly with a group of pilots, giving instructions, charging all to keep the formation. Machines are gone over to make sure that everything is in perfect condition. Then the first bombing plane, bearing the flight leader, "taxis" across the field, appearing to stagger under its great burden. Suddenly it takes to the air, and like a large graceful bird, its clumsiness all gone, it soars up into the blue.

Rapidly the other big birds follow suit, and at a signal they are off, the flight commander heading the group, and the others following in close formation, like a huge flock of wild geese.

On and on they fly, until beneath them appears the winding ribbon of road that is their objective. It is crowded with marching troops, gun wagons, supplies. As they swoop close to the earth they catch a swift glimpse of white faces turned up at them with terror. Then panic falls upon the marching column and, helter-skelter, every man tries to break away to a point of safety. In another moment guns are turned upon the bombers, but they dodge the flying sh.e.l.ls and let go their heavy explosives, which crash to earth with dreadful uproar. Where a few moments before the Huns were following their way undisturbed there is now a road in which great furrows are plowed; huge holes gape open and a hopeless ma.s.s of debris covers the earth. The columns of the enemy will be blocked for many hours while the ma.s.s is being cleared away.

Satisfied with the results of their exploit the bombing squadron turns swiftly toward home.

How simple a matter it seems at first glance to release a bomb and hit a given point below. Actually it requires the very highest skill. To begin with, the airplane is moving at tremendous speed, and the bombardier (as the man who drops the bombs is called) has to know exactly how the forward motion of the airplane will affect the direction that the bomb takes on its course toward the earth. Moreover the bomb has a speed at starting equal to the speed of the airplane, and this beginning speed is increased by the action of gravity drawing it down. It may be aided in its journey by the wind or r.e.t.a.r.ded, according to the wind's direction, and this too must be taken into account, if the target is to be hit.

Bomb dropping can only be carried out successfully with the aid of the most delicate and complicated range-finding mechanism, with which every bombing plane is equipped. The Germans have led the way in inventions for this purpose, and their Goertz range finder is perhaps the best in the world.

The bombs themselves are generally carried in vertical position, one-above another, in the body of the airplane, and by an automatic arrangement, as one is released, another slips into place, ready to be dropped.

Now that we have made the acquaintance of the three types of machines that are used over the trenches--the "speed scout" or small fighting machine; the larger armed reconnaissance plane; and largest of all, the bomber--let us go back and give just a hasty glance at the main points of their construction.

First we must recall the "A B C facts" we learned about wing construction. A wing gains lifting power from two sources: the upward pressure of the air current underneath it, and the force of the vacuum above it which is created by the arch of the wing. If a wing is only slightly arched it can move _forward_ through the air more swiftly, but it will not have the _lifting power_ of the high arched wing. This is the reason that an airplane which must be a weight carrier cannot be as fast in flight as the "speed scout," which has only its pilot and a machine gun to carry.

The "speed scout" is always a small machine, usually a single-seater, with a gun in front that fires over or through the propeller. In the early part of the Great War it was most often a monoplane, but the smaller biplane took its place, because, with practically the same speed, it combines greater stability.

The planes of the speed scout are very flat as compared with those of the reconnaissance craft. This airplane must carry machine guns, photography apparatus, radio, and a pilot, an observer, and often a gunner. Its wings must therefore be arched to give it lifting power, but at the same time it becomes a much slower flying machine than its smaller sister.

Lifting power of a wing can of course be increased _up to a certain point_ by increasing the wing area, so that a greater air pressure is created below. Beyond that certain point the machine would become unwieldy and would lose its balancing properties. Yet this idea has been put into practise in building the latest types of aerial dreadnaughts used for reconnaissance. These airplanes have gained their lifting power partly by increasing the wing spread and partly by arching the wing.

Thus a wing has been secured which offers the minimum resistance to forward motion through the air, together with the maximum weight carrying ability. Biplanes of this type are by far the most popular of those designed for general service, for they combine speed, climbing ability, and lifting power,--thanks to their strong armament they can defend themselves or run away quickly as the situation demands.

But there is one other method which has not yet been mentioned of increasing the lifting power of an airplane. It is simply to add a third wing. When we have made the wings of the biplane as large as we dare, and have curved them to make them weight-bearers, if the resulting machine is still not strong enough to carry as many tons of explosives as we desire, there is only one thing left to do and that is to add a third wing. Thus the triplane made its appearance in answer to the call for planes which could carry vast cargoes of explosives and fuel for journeys of many hours over the enemy's country. The huge night bombing machine of the present time is almost always of the triplane type.