We Americans are a peace-loving people, which is the very reason why we went into the war. We had to help down the power that was disturbing the peace of the world. We do not believe in conquests—at least of the type that Germany tried to force—and yet there are certain conquests that we do indulge in once in a while.

Eleven years before Germany undertook to conquer Europe two young Americans made the greatest conquest that the world has ever seen. The Wright brothers sailed up into the heavens and gained the mastery of the air. They offered their conquest to the United States; but while we accepted their offering with enthusiasm at first, we did not know what to do with the new realm after we got it. There seemed to be no particular use in flying. It was just a bit too risky to be pleasant sport, and about all we could see in it was an exhibition for the circus or the county fair.

Not so in Europe, however. Flying meant something over there—there where the frontiers have ever bristled with big guns and strong fortifications, and where huge military forces have slept on their arms, never knowing what dreadful war the morning would bring forth. The war-lovers hailed the airplane as a new instrument with which to terrorize their neighbors; the peace-lovers saw in it another menace to their homes; it gave them a new frontier to defend. And so the military powers of Europe took up the airplane seriously and earnestly and developed it.

At first military authorities had rated the airplane chiefly as a flying scout. Some bomb-dropping experiments had been made with it, but it proved very difficult to land the bombs near the target, and, besides, machines of those days were not built to carry very heavy loads, so that it did not seem especially profitable to attack the enemy from the skies. As for actual battles up among the clouds, they were dreamed of only by the writers of fiction. But wild dreams became stern realities in the mighty struggle between the great powers of the world.

EYES IN THE SKY

As a scouting-machine the airplane did prove to be far superior to mounted patrols which used to perform scout-work. In fact, it changed completely the character of modern warfare. From his position high up in the heavens the flying scout had an unobstructed view of the country for miles and he could see just what the enemy was doing. He could see whether large forces of men were collecting for an attack. He could watch the course of supply-trains, and judge of their size. He could locate the artillery of the enemy and come back with information which in former times a scout posted in a tall tree or even in a captive balloon could not begin to acquire. Surprise attacks were impossible, with eyes in the sky. The aviator could help his own batteries by signaling to them where to send their shell, and when the firing began he would spot the shots as they landed and signal back to the battery how to correct its aim so as to drop the shell squarely on the target. The French sprang a surprise on the Germans by actually attacking the infantry from the sky. The idea of attack from overhead was so novel that armies did not realize the danger of exposing themselves behind the battle-front. Long convoys of trucks and masses of infantry moved freely over the roads behind the lines and they were taken by surprise when the French began dropping steel darts upon them. These were about the size of a pencil, with pointed end and fluted tail, so that they would travel through the air like an arrow. The darts were dropped by the hundred wherever the airmen saw a large group of the enemy, and they struck with sufficient velocity to pierce a man from head to foot. But steel darts were not used very long. The enemy took to cover and then the only way to attack him was to drop explosives which would blow up his shelter.

At the outset, air scouts were more afraid of the enemy on the ground than in the sky. The Germans had anti-aircraft guns that were fired with accuracy and accounted for many Allied planes. In those days, airplanes flew at comparatively low altitudes and they were well within the reach of the enemy's guns. But it was not long before the airplanes began to fight one another. Each side was very much annoyed by the flying scouts of its opponents and after a number of pistol duels in the sky the French began to arm their planes with machine-guns.

Two months after the war started the first airplane was sent crashing to earth after a battle in the sky. The fight took place five thousand feet above the earth, between a French and a German machine. The German pilot was killed and the plane fell behind the French lines, carrying with it a Prussian nobleman who died before he could be pulled out of the wreckage. The war had been carried into the skies. But if scouts were to fight one another, they could not pay much attention to scouting and spotting and it began to be realized that there were four distinct classes of work for the airplane to do—scouting, artillery-spotting, battling, and bombing. Each called for special training and its own type of machine. As air fighting grew more specialized these classes were further subdivided, but we need not go into such refinements.

AIR SCOUTS AND THEIR DANGERS

The scouting-airplane usually carried two men, one to drive the machine and the other to make observations. The observer had to carry a camera, to take photographs of what lay below, and he was usually equipped with a wireless outfit, with which he could send important information back to his own base. The camera was sometimes fitted with a stock like that of a gun, so that it could be aimed from the shoulder. Some small cameras were shaped so that they could be held in the hand like a pistol and aimed over the side of the fuselage, or body, of the airplane; but the best work was done with large cameras fitted with telescopic lenses, or "telephoto" lenses, as they are called. Some of these were built into the airplane, with the lens opening down through the bottom of the fuselage.

The scouting-airplane carried a machine-gun, not for attack, but for defense. It had to be a quick climber and a good dodger, so that it could escape from an attacking plane. Usually it did not have to go very far into the enemy country, and it was provided with a large wing-spread, so that if anything happened to the engine, it could volplane, or glide back, to its own lines. As the scouting-planes were large, they offered a big target to anti-aircraft guns, and so the work of the air scout was to swoop down upon the enemy, when, of course, the machine would be traveling at high velocity, because it would have all the speed of falling added to that which its own propeller gave it.

It was really a very difficult matter to hit a rapidly moving airplane; and even if it were hit, there were few spots in which it could be mortally wounded. Hundreds of shots could go through the wings of an airplane without impairing its flying in the least. The engine, too, could be pretty well peppered with ordinary bullets without being disabled. As for the men in the machine, they furnished small targets, and even they could be hit in many places without being put entirely out of business. And so the dangers of air scouting were not so great as might at first be supposed.

One of the most vulnerable spots in the airplane was the gasolene-tank. If that were punctured so that the fuel would run out, the airplane would have to come to the ground. Worse still, the gasolene might take fire and there was nothing the aviator dreaded more than fire. There were occasions in which he had to choose between leaping to earth and burning to death, and the former was usually preferred as a quicker and less painful death. In some of the later machines the gasolene-tank could be pitched overboard if it took fire, by the throwing of a lever, and then the aviator could glide to earth in safety.

THE SELF-HEALING GASOLENE-TANK

One of the contributions which we made to military aËronautics was a gasolene-tank that was puncture-proof. It was made of soft rubber with a thin lining of copper. There are some very soft erasers on the market through which you can pass a lead pencil and never find the hole after it has passed through, because the rubber has closed in and healed the wound. Such was the rubber used in the gasolene-tank. It could be peppered with bullets and yet would not leak a drop of gasolene, unless the bullet chanced to plow along the edge of the tank and open a long gash.

The Germans used four different kinds of cartridges in their aircraft guns. The first carried the ordinary bullet, a second type had for its bullet a shell of German silver filled with a phosphor compound. This was automatically ignited through a small opening in the base of the shell when it was fired from the gun and it left a trail of smoke by which the gunner could trace its course through the air and correct his aim. At night the bright spot of light made by the burning compound would serve the same purpose. Such a bullet, if it hit an ordinary gasolene-tank, would set fire to its contents. The bullet would plow through the tank and out at the opposite side and there, at its point of exit, is where the gasolene would be set on fire. Such incendiary bullets were repeatedly fired into or through the rubber tanks and the hole would close behind the bullet, preventing the contents from taking fire. The two other types of bullets referred to were an explosive bullet or tiny shell which would explode on striking the target and a perforating steel bullet which was intended to pierce armor or penetrate into vital parts of an airplane engine.

Machines with which artillery-spotting was done were usually manned by a pilot and an observer, so that the latter could devote his entire attention to noting the fire of the guns and signaling ranges without being hampered by having to drive the machine. These machines were usually of the pusher type, so that the observer could have an unobstructed view. They did not have to be fast machines. It was really better for them to move slowly. Had it been possible for them to stop altogether and hover over the spot that was being shelled, it would have been a distinct advantage. That would have given the observer a chance to note with better accuracy the fall of the shell. Like the scout, the spotter had to be a fast climber, so that it could get out of the range of enemy guns and run away from attacking planes.

GIANTS OF THE SKY

The largest war-planes were the bomb-dropping machines. They had to be capable of carrying heavy loads of explosives. They were usually slow machines, speed being sacrificed in carrying-capacity.

The Germans paid a great deal of attention to big bomb-dropping machines, particularly after their Zeppelins proved a failure. Their huge Gothas were built to make night raids on undefended cities. The Italians and the British retaliated with machines that were even larger. At first the French were inclined to let giant planes alone. They did not care to conduct long-distance bombing-raids on German cities because their own important cities were so near the battle-front that the Germans could have done those places more harm than the French could have inflicted. Later they built some giant machines, although not so large as those of the Italians and the British.

The large triplane Capronis built by the Italians held a crew of three men. They were armed with three guns and carried 2750 pounds of explosives. That made a useful load of 4000 pounds. The machine was driven by three engines with a total of 900 horse-power.

The big British plane was the Handley-Page, which had a wing-spread of 125 feet and could carry a useful load of three tons. These enormous machines conducted their raids at night because they were comparatively slow and could not defend themselves against speedy battle-planes. The big Italian machines used "search-light" bombs to help them locate important points on the ground beneath. These were brilliant magnesium torches suspended from parachutes so that they would fall slowly and give a broad illumination, while the airplane itself was shielded from the light by the parachute.

But these giants were not the only bombing-machines. There were smaller machines that operated over the enemy's battle-line and dropped bombs on any suspicious object behind the enemy lines. These machines had to be convoyed by fast battle-planes which fought off hostile airmen.

HOW FAST IS A HUNDRED AND FIFTY MILES PER HOUR?

In naval warfare the battle-ship is the biggest and heaviest ship of the fleet, but in the air the battle-planes are the lightest and the smallest of the lot. They are one-man machines, as a rule, little fellows, but enormously speedy. Speed is such an important factor in aËrial warfare that there was a continuous struggle between the opposing forces to produce the faster machine. Airplanes were constantly growing speedier, until a speed of 150 miles per hour was not an uncommon rate of travel. It is hard to imagine such a speed as that, but we may gain some idea if we consider a falling object. The observation platform of the Woolworth Building, in New York, is about 750 feet above the ground. If you should drop an object from this platform you would start it on a journey that would grow increasingly speedy, particularly as it neared the ground. By the time it had dropped from the sixtieth story to the fifty-ninth it would have attained a speed of nearly 20 miles per hour. (We are not making any allowances for the resistance of the air and what it would do to check the speed.) As it passed the fiftieth story it would be traveling as fast as an express-train, or 60 miles per hour. It would finally reach the ground with a speed equal to that of a fast battle-plane—150 miles per hour.

The battle-plane was usually fitted with a single machine-gun that was fixed to the airplane, so that it was brought to bear on the target by aiming the entire machine. In this the plane was something like a submarine, which must point its bow at its intended victim in order to aim its torpedo. The operator of the battle-plane simply drove his machine at the enemy and touched a button on his steering-lever to start his machine-gun going.

SHOOTING THROUGH THE PROPELLER

Now, the fleetest machines and the most easily manoeuvered are those of the tractor type, that is, the ones which have the propeller in front; but having the propeller in front is a handicap for a single-seater machine, for the gun has to be fired through the propeller and the bullets are sure to hit the propeller-blades. Nevertheless the French did fire right through the propeller, regardless of whether or not the blades were hit; but at the point where they came in line with the fire of the gun they were armored with steel, so that there was no danger of their being cut by the bullets. It was calculated that not more than one bullet in eighteen would strike the propeller-blade and be deflected from its course, which was a very trifling loss; nevertheless, it was a loss, and on this account a mechanism was devised which would time the operations of the machine-gun so that the shots would come only when the propeller-blades were clear of the line of fire.

A cam placed on the propeller-shaft worked the trigger of the machine-gun. This did not slow up the fire of the machine-gun. Quite the contrary. We are apt to think of the fire of the machine-guns as very rapid, but they usually fire only about five hundred rounds per minute, while an airplane propeller will make something like twelve hundred revolutions per minute. And so the mechanism was arranged to pull the trigger only once for every two revolutions of the propeller.

FIGHTING AMONG THE CLOUDS

There was no service of the war that began to compare with that of the sky fighter. He had to climb to enormous heights. Air battles took place at elevations of twenty thousand feet. The higher the battle-plane could climb, the better, because the man above had a tremendous advantage. Clouds were both a haven and a menace to him. At any moment an enemy plane might burst out of the clouds upon him. He had to be ready to go through all the thrilling tricks of a circus performer so as to dodge the other fellow and get a commanding position. If he were getting the worst of it, he might feign death and let his machine go tumbling and fluttering down for a thousand feet or so, only to recover his equilibrium suddenly and dart away when the enemy was thrown off his guard. He might escape into some friendly cloud, but he dared not hide in it very long, lest he get lost.

It is a peculiar sensation that comes over an aviator when he is flying through a thick mass of clouds. He is cut off from the rest of the world. He can hear nothing but the terrific roar of his own motor and the hurricane rush of the wind against his ears. He can see nothing but the bluish fog of the clouds. He begins to lose all sense of direction. His compass appears to swing violently to and fro, when really it is his machine that is zig-zagging under his unsteady guidance. The more he tries to steady it, the worse becomes the swing of the compass. As he turns he banks his machine automatically, just as a bicyclist does when rounding a corner. He does this unconsciously, and he may get to spinning round and round, with his machine standing on its side. In some cases aviators actually emerged from the clouds with their machines upside down. To be sure, this was not an alarming position for an experienced aviator; at the same time, it was not altogether a safe one. A machine was sometimes broken by its operator's effort to right it suddenly. And so while the clouds made handy shelters, they were not always safe harbors.

To the battle-plane fell the task of clearing the air of the enemy. If the enemy's battle-planes were disposed of, his bombing-planes, his spotters, and his scouts could not operate, and he would be blind. And so each side tried to beat out the other with speedier, more powerful, and more numerous battle-planes. Fast double-seaters were built with guns mounted so that they could turn in any direction.

THE FLYING TANK

The Germans actually built an armored battle-plane known as the flying tank. It was a two-seater intended mainly for attacking infantry and was provided with two machine-guns that pointed down through the floor of the fuselage. A third gun mounted on a revolving wooden ring could be used to fight off hostile planes. The bottom and sides of the fuselage or body of the airplane from the gunner's cockpit forward were sheathed with plates of steel armor. The machine was a rather cumbersome craft and did not prove very successful. A flying tank was brought down within the American lines just before the signing of the armistice.

AMERICA'S HELP

Our own contribution to the war in the air was considerable, but we had hardly started before the armistice brought the fighting to an end. Before we entered the war we did not give the airplane any very serious consideration. To be sure, we built a large number of airplanes for the British, but they were not good enough to be sent to the front; they were used merely as practice planes in the British training-schools. We knew that we were hopelessly outclassed, but we did not care very much. Then we stepped into the conflict.

"What can we do to help?" we asked our allies, and their answer gave us a shock.

"Airplanes!" they cried. "Build us airplanes—thousands of them—so that we can drive the enemy out of the air and blind his armies!"

It took us a while to recover from our surprise, and then we realized why we had been asked to build airplanes. The reputation of the United States as a manufacturer of machinery had spread throughout the world. We Americans love to take hold of a machine and turn it out in big quantities. Our allies were sure that we could turn out first-class airplanes, and many of them, if we tried.

Congress made an appropriation of six hundred and forty million dollars for aËronautics, and then things began to hum.

A BIRTHDAY PRESENT TO THE NATION

The heart of an airplane is its engine. We know a great deal about gasolene-engines, especially automobile engines; but an airplane engine is a very different thing. It must be tremendously powerful, and at the same time extremely light. Every ounce of unnecessary weight must be shaved off. It must be built with the precision of a watch; its vital parts must be true to a ten-thousandth part of an inch. It takes a very powerful horse to develop one horse-power for a considerable length of time. It would take a hundred horses to supply the power for even a small airplane, and they would weigh a hundred and twenty thousand pounds. An airplane motor of the same power would weigh less than three hundred pounds, which is a quarter of the weight of a single horse. It was this powerful, yet most delicate, machine that we were called upon to turn out by the thousand. There was no time to waste; a motor must be designed that could be built in the American way, without any tinkering or fussy hand-work.

Two of our best engineers met in a hotel in Washington on June 3, 1917, and worked for five days without once leaving their rooms. They had before them all the airplane knowledge of our allies. American engine-builders offered up their trade secrets. Everything was done to make this motor worthy of America's reputation. There was a race to have the motor finished by the Fourth of July. Sure enough, on Independence Day the finished motor was there in Washington—the "Liberty motor," a birthday present to the nation.

Of course that did not mean that we were ready at once to turn out Liberty motors by the thousand. The engine had to undergo many tests and a large number of alterations before it was perfectly satisfactory and then special machinery had to be constructed before it could be manufactured in quantity. It was Thanksgiving Day before the first manufactured Liberty was turned out and even after that change upon change was made in this little detail and that. It was not until a year after we went to war that the engine began to be turned out in quantity.

There was nothing startlingly new about the engine. It was a composite of a number of other engines, but it was designed to be turned out in enormous quantities, and it was remarkably efficient. It weighed only 825 pounds and it developed over 420 horse-power. Some machines went up as high as 485 horse-power. An airplane engine weighing less than 2 pounds per horse-power is wonderfully efficient. Of course the Liberty was too heavy for a light battle-plane (a heavy machine, no matter how powerful, cannot make sharp turns), but it was excellent for other types of airplanes and large orders for Liberty engines were made by our allies. Of course we made other engines as well, and the planes to carry them. We built large Caproni and Handley-Page machines, and we were developing some remarkably swift and powerful planes of our own when the Germans thought it about time to stop fighting.

FLYING BOATS

So far we have said nothing about the seaplanes which were used in large numbers to watch for submarines. These were big flying boats in which speed was not a very important matter. One of the really big machines we developed, but which was not finished until after the war, was a giant with a 110-foot span and a body or hull 50 feet long. During the war seaplanes carried wireless telephone apparatus with which they could call to destroyers and submarine-chasers when they spotted a submarine. They also carried bombs which they could drop on U-boats, and even heavy guns with which they could fire shell.

A still later development are the giant planes of the N.C. type with a wing-spread of 126 feet and driven by four Liberty motors. They carry a useful load of four and a half tons.

Early in the war, large guns were mounted on airplanes, but the shock of the recoil proved too much for the airplane to stand. However, an American inventor produced a gun which had no recoil. This he accomplished by using a double-end gun, which was fired from the middle. The bullet or shell was shot out at the forward end of the gun and a dummy charge of sand was shot out at the rear end. The sand spread out and did no damage at a short distance from the gun, but care had to be taken not to come too close. These non-recoil guns were made in different sizes, to fire 1½-inch to 3-inch shell.

THE AUTOMATIC SEAPLANE

Another interesting development was the target airplane used for the training of aËrial gunners. This was a small seaplane with a span of only 18½ feet, driven by a 12-horse-power motor, the whole machine weighing but 175 pounds. This was sent up without a pilot and it would fly at the rate of forty to fifty miles per hour until its supply of gasolene gave out, when it would drop down into the sea. It afforded a real target for gunners in practice machines.

Early in the war an American inventor proposed that seaplanes be provided with torpedoes which they could launch at an enemy ship. The seaplane would swoop down out of the sky to within a short distance of the ship, drop its projectile, and fly off again, and the torpedo would continue on its course until it blew up the vessel. It was urged that a fleet of such seaplanes protected by a convoy of fast battle-planes could invade the enemy harbors and destroys its powerful fleet. It seemed like a rather wild idea, but the British actually built such torpedo-planes and tested them. However, the German fleet surrendered before it was necessary to blow it up in such fashion.

AIRPLANES AFTER THE WAR

With the war ended, all the Allied powers have large numbers of airplanes on their hands and also large numbers of trained aviators. Undoubtedly airplanes will continue to fill the skies in Europe and we shall see more and more of them in this country. Even during the war they were used for other purposes than fighting. There were ambulances on wings—machines with the top of the fuselage removable so that a patient on a stretcher could be placed inside. A French machine was furnished with a complete hospital equipment for emergency treatment and even for performing an operation in case of necessity. The flying hospital could carry the patient back to the field or base hospital after treatment.

Mail-carrying airplanes are already an old story. In Europe the big bombing-machines are being used for passenger service between cities. There is an air line between Paris and London. The airplanes carry from a dozen to as many as fifty passengers on a single trip. In some cities here, as well as abroad, the police are being trained to fly, so that they can police the heavens when the public takes to wings. Evidently the flying-era is here.