When the great European war broke out, it was very evident that the Entente Allies would have to exercise every resource to beat the foe which had been preparing for years to conquer the world. But who ever imagined that geologists would be called in to choose the best places for boring mines under the enemy: that meteorologists would be summoned to forecast the weather and determine the best time to launch an offensive; that psycologists would be employed to pick out the men with the best nerves to man the machine-guns and pilot the battle-planes? Certainly no one guessed that artists and the makers of stage scenery would play an important part in the conflict.

But the airplane filled the sky with eyes that at first made it impossible for an army to conceal its plans from the enemy. And then there were eyes that swam in the sea—cruel eyes that belonged to deadly submarine monsters, eyes that could see without being seen, eyes that could pop up out of the water at unexpected moments, eyes that directed deadly missiles at inoffensive merchantmen. They were cowardly eyes, too, which gave the ship no opportunity to strike back at the unseen enemy. A vessel's only safety lay in the chance that out in the broad reaches of the ocean it might pass beyond the range of those lurking eyes. It was a game of hide-and-seek in which the pursuer and not the pursued was hidden. Something had to be done to conceal the pursued as well, but in the open sea there was nothing to hide behind.

HIDING IN PLAIN SIGHT

There is such a thing as hiding in plain sight. You can look right at a tree-toad without seeing him, because his colors blend perfectly with the tree to which he is clinging. You can watch a green leaf curl up and shrivel without realizing that the curled edge is really a caterpillar, cunningly veined and colored to look just like a dying leaf; and out in the woods a speckled bird or striped animal will escape observation just because it matches the spotted light that comes through the underbrush. Nature is constantly protecting its helpless animals with colored coats that blend with the surroundings.

Long ago clumsy attempts at concealment were made when war-vessels were given a coat of dark-gray paint which was supposed to make them invisible at a distance. Actually the paint made them more conspicuous; but, then, concealment did not count for very much before the present war.

It was the eyes of the submarines that brought a hurry call for the artists, and up to them was put the problem of hiding ships in plain sight. A new name was coined for these warriors of the paint-brush: camoufleurs they were called, and their work was known as camouflage.

MATCHING THE SKY

Of course, no paint will make a ship absolutely invisible at a short distance, but a large vessel may be made to disappear completely from view at a distance of six or seven miles if it is properly painted. To be invisible, a ship must reflect as much light and the same shade of light as do its surroundings. If it is seen against the background of the sea, it must be of a bluish or a greenish tint, but a submarine lies so low in the water that any object seen at a distance is silhouetted against the sky, and so the ship must have a coat of paint that will reflect the same colors as does the sky. Now, the sky may be of almost any color of the rainbow, depending upon the position of the sun and the amount of vapor or dust in the air. Fortunately in the North Sea and the waters about the British Isles, where most of the submarine attacks took place, the weather is hazy most of the time, and the ship had to be painted of such a color that it would reflect the same light as that reflected by a hazy sky. With a background of haze and more or less haze between the ship and the periscope of the U-boat, it was not a very difficult matter to paint a ship so that it would be invisible six or seven miles away. One shade of gray was used to conceal a ship in the North Sea and an entirely different shade was used for the brighter skies of the Mediterranean.

In this way, the artists made it possible for ships to sail in safety much nearer the pursuer who was trying to find them, and by just so much they reduced his powers of destruction. But still the odds were too heavy against the merchantman. Something must be done for him when he found himself within the seven-mile danger-zone. Here again the artists came to the rescue.

Before merchant ships were armed, a submarine would not waste a torpedo on them, but would pound them into submission with shell. Even after ships were provided with guns, submarines mounted heavier guns and unless a ship was speedy enough to show a clean pair of heels, the pursuing U-boat would stand off out of range of the ship's guns and pour a deadly fire into it. But the ships, too, mounted larger guns and the submarines had to fall back upon their torpedoes.

GETTING THE RANGE FOR THE TORPEDO

In order to fire its torpedo with any certainty, the U-boat had to get within a thousand yards of its victim. A torpedo travels at from thirty to forty miles per hour. It takes time for it to reach its target and a target which is moving at, say, fifteen knots, will travel five hundred yards while a thirty-knot torpedo is making one hundred yards. And so before the U-boat commander could discharge his torpedo, he had to know how fast the ship was traveling and how far away it was from him. He could not come to the surface and make deliberate observations, but had to stay under cover, not daring even to keep his eye out of water, for fear that the long wake of foam trailing behind the periscope would give him away. All he could do, then, was to throw his periscope up for a momentary glimpse and make his calculations very quickly; then he could move to the position he figured that he should occupy and shoot up his periscope for another glimpse to check up his calculations. On the glass of this periscope, there were a number of graduations running vertically and horizontally. If he knew his victim and happened to know the height of its smoke-stacks or the length of the boat, he noted how many graduations they covered, and then by a set formula he could tell how far he was from the boat. At the same time he had to work out its rate of travel and note carefully the course it was holding before he could figure where his torpedo must be aimed.

There was always more or less uncertainty about such observations, because they had to be taken hastily, and the camoufleurs were not slow to take advantage of this weakness. They increased the enemy's confusion by painting high bow-waves which made the ship look as if it were traveling at high speed. They painted the bow to look like the stern, and the stern to look like the bow, and the stacks were painted so that they appeared to slant in the opposite direction, so that it would look as if the vessel were headed the other way. U-boats came to have a very wholesome respect for destroyers and would seldom attack a ship if one of these fast fighting-craft was about, and so destroyers were painted on the sides of ships as scarecrows to frighten off the enemy.

MAKING STRAIGHT LINES LOOK CROOKED

We say that "seeing is believing," but it is not very hard to deceive the eye. The lines in Fig.13 look absolutely parallel, and they are; but cross-hatch the spaces between them, with the hatching reversed in alternate spaces, as in Fig.14, and they no longer look straight. Take the letters on the left, Fig.15. They look all higgledy-piggledy, but they are really straight and parallel, as one can prove by laying a straight-edge against them, or by drawing a straight line through each letter, as shown at the right, Fig.16. Such illusions were used on ships. Stripes were painted on the hull that tapered slightly, from bow to stern, so that the vessel appeared to be headed off at an angle, when it was really broadside to the watcher at the other end of the periscope.

There are color illusions, too, that were tried. If you draw a red chalk-mark and a blue one on a perfectly clean blackboard, the red line will seem to stand out and the blue one to sink into the black surface of the board, because your eye has to focus differently for the two colors, and a very dazzling effect can be had with alternating squares of blue and red. Other colors give even more dazzling effects, and some of them, when viewed at a distance, will blend into the very shade of gray that will make a boat invisible at six miles. When U-boat commanders took observations on a ship painted with a "dazzle" camouflage, they saw a shimmering image which it was hard for them to measure on the fine graduations of their periscopes. Some ships were painted with heavy blotches of black and white, and the enemy making a hasty observation would be apt to focus his attention on the dark masses and overlook the white parts. So he was likely to make a mistake in estimating the height of the smoke-stack or in measuring the apparent length of a vessel.

A JOKE ON THE PHOTOGRAPHER

Early in the submarine campaign one of our boats was given a coat of camouflage, and when the vessel sailed from its pier in the North River, New York, the owners sent a photographer two or three piers down the river to photograph the ship as she went by. He took the picture, but when the negative was developed, much to his astonishment he found that the boat was not all on the plate. In the finder of his camera, he had mistaken a heavy band of black paint for the stern of the ship, quite overlooking the real stern, which was painted a grayish white. The artist had fooled the photographer and at a distance of not more than two or three hundred yards!

SEEING BEYOND THE HORIZON

The periscope of a submarine that is running awash can be raised about fifteen feet above the water, which means that the horizon as viewed from that elevation is about six miles away, and if you draw a circle with a six-mile radius on the map of the Atlantic, you will find that it is a mere speck in the ocean; but a U-boat commander could see objects that lay far beyond his horizon because he was searching for objects which towered many feet above the water. The smoke-stacks of some vessels rise a hundred feet above the water-line, and the masts reach up to much greater altitudes. Aside from this, in the early days of the war steamers burned soft coal and their funnels belched forth huge columns of smoke which was visible from twenty to thirty miles away.

When this was realized, efforts were made to cut down the superstructure of a ship as much as possible. Some vessels had their stacks cut down almost to the deck-line, and air-pumps were installed to furnish the draft necessary to keep their furnaces going. They had no masts except for slender iron pipes which could be folded down against the deck and could be erected at a moment's notice, to carry the aËrials of the wireless system. Over the ship from stem to stern was stretched, a cable, familiarly known as a "clothes-line," upon which were laid strips of canvas that completely covered the superstructure of the ship. These boats lay so low that they could not be seen at any great distance, and it was difficult for the U-boats to find them. They were slow boats; too slow to run away from a modern submarine, but because of their lowly structure, they managed to elude the German U-boats. When they were seen, the U-boat commanders were afraid of them. They were suspicious of anything that looked out of the ordinary, and preferred to let the "clothes-line ships" go.

THE BRITISH MYSTERY SHIPS

The Germans had some very unhealthy experiences with the "Q-boats" or "mystery ships" of the British. These were vessels rigged up much like ordinary tramp steamers, but they were loaded with wood, so that they would not sink, and their hatches were arranged to fall open at the touch of a button, exposing powerful guns. They also were equipped with torpedo-tubes, so that they could give the U-boat a dose of its own medicine. These ships would travel along the lanes frequented by submarines, and invite attack. They would limp along as if they had been injured by a storm or a U-boat attack, and looked like easy prey. When a submarine did attack them, they would send out frantic calls for help, and they had so-called "panic" parties which took to the boats. Meantime, a picked crew remained aboard, carefully concealed from view, and the captain kept his eye upon the enemy through a periscope disguised as a small ventilator, waiting for the U-boat to come within range of certain destruction. Sometimes the panic party would lure the submarine into a favorable position by rowing under the stern as if to hide around the other side of the ship. At the proper moment, up would go the white ensign—the British man-of-war flag—the batteries would be unmasked, and a hail of shell would break loose over the Hun. Many a German submarine was accounted for by such traps.

Submarines themselves used all sorts of camouflage. They were frequently equipped with sails which they would raise to disguise themselves as peaceful sloops, and in this way they were able to steal up on a victim without discovery. Sometimes they would seize a ship and hide behind it in order to get near their prey.

CAMOUFLAGE ON LAND

But the call for the wielders of the paintbrush came not only from the sea. Their services were needed fully as much on land, and the making of land camouflage was far more interesting because it was more varied and more successful. Besides, it called for more than mere paint; all sorts of tricks with canvas, grass, and branches were used. Of course, the soldiers were garbed in dust-colored clothing and shiny armor was discarded. The helmets they wore were covered with a material that cast no gleam of light. In every respect, they tried to make themselves of the same shade as their surroundings. Like the Indians, they painted their faces. This was done when they made their raids at night. They painted their faces black so that they would not show the faintest reflection of light.

A PAPER HORSE

The most interesting camouflage work was done for the benefit of snipers or for observers at listening-posts close to the enemy trenches. It was very important to spy on the enemy and discover his plans, and so men were sent out as near his lines as possible, to listen to the conversation and to note any signs of unusual activity which would be likely to precede a raid. These men were supplied with telephone wires which they dragged over No Man's Land, and by which they could communicate their discoveries to headquarters. Some very ingenious listening-posts were established. In one case a papier-mÂchÉ duplicate of a dead horse was made, which was an exact facsimile of an animal that had been shot and lay between the two lines. One night, the carcass of the horse was removed and the papier-mÂchÉ replica took its place. In the latter a man was stationed with telephone connection back to his own lines. Here he had an excellent chance to watch the enemy. On another occasion a standing tree, whose branches had been shot away, was carefully photographed and an exact copy of it made, but with a chamber inside in which an observer could be concealed. One night while the noise of the workmen was drowned by heavy cannonading, this tree was removed and its facsimile was set up instead, and it remained for many a day before the enemy discovered that it was a fake tree-trunk. It provided a tall observation post from which an observer could direct the fire of his own artillery.

FOOLING THE WATCHERS IN THE SKY

In the early stages of the war, it seemed impossible to hide anything from the Germans. They had eyes everywhere and were able to anticipate everything the Allies did. But the spies that infested the sky were the worst handicap. Even when the Allies gained control of the air, the control was more or less nominal because every now and then an enemy observer would slip over or under the patrolling aËroplanes and make photographs of the Allies' lines. The photographs were carefully compared with others previously taken, that the slightest change in detail might be discovered. Airplane observers not only would be ready to drop bombs on any suspicious object or upon masses of troops moving along the roads, but would telephone back to their artillery to direct its fire upon these targets. Of course, the enemy knew where the roads were located and a careful watch was kept of them.

The French did not try to hide the roads, but they concealed the traffic on the roads by hanging rows of curtains over them. As these curtains hung vertically and were spaced apart, one would suppose that they would furnish little concealment, but they prevented an observer in an aËroplane from looking down the length of a road. All the road he could see was that which lay directly under his machine, because there he could look between the curtains; if he looked obliquely at the road, the curtains would appear to overlap one another and would conceal operations going on under them.

In one case, the Germans completely covered a sunken road with canvas painted to represent a road surface. Under this canvas canopy, troops were moved to an important strategic point without the slightest indication of such a movement.

HIDING BIG GUNS

Nature's tricks of camouflage were freely used in the hiding of the implements of war on land. Our big guns were concealed by being painted with leopard spots and tiger stripes, the color and nature of the camouflage depending upon the station they were to occupy. In many cases, they were covered with branches of trees or with rope netting overspread with leaves. So careful was the observation of the air scouts that even the grass scorched by the fire of the gun had to be covered with green canvas to prevent betrayal of the position of the gun.

ROADS THAT LED NOWHERE

In the making of an emplacement for a gun it was of the utmost importance that no fresh upturned earth be disclosed to the aËrial observers. Even foot-paths leading to it had to be concealed. Plans were carefully made to cover up all traces of the work before the work was begun. Where it was impossible to conceal the paths, they were purposely made to lead well beyond the point where the emplacement was building, and, still further to deceive the enemy, a show of work was sometimes undertaken at the end of the path. Wherever the sod had to be upturned, it was covered over with green canvas. The earth that was removed had to be concealed somewhere and the best place of concealment was found to be some old shell-hole which would hold a great deal of earth without any evidence that would be apparent to an observer in an aËroplane. If no shell-hole were handy, the excavated material had to be hauled for miles before a safe dumping-ground could be found. As far as possible everything was sunk below the earth level. Big pits were dug in which the mortars were placed, or if a shell-hole were empty, this was used instead.

SHADOWLESS BUILDINGS

Any projection above the ground was apt to cast a shadow which would show up on the observer's photographs. This was a difficulty that was experienced in building the hangars for airplanes. The roofs of these sheds were painted green so as to match the sod around them, but as they projected above their surroundings, they cast shadows which made them clearly evident to the enemy. This was overcome by the building of shadowless hangars; that is, hangars with roofs that extended all the way to the ground at such an angle that they would cause no shadow except when the sun was low. In some cases, aËroplanes were housed in underground hangars, the approach to which was concealed by a canvas covering. As for the machines themselves, they scorned the use of camouflage. Paint was little protection to them. Some attempt was made to use transparent wings of cellon, a material similar to celluloid, but this did not prove a success.

THE PHOTOGRAPHIC EYE

Although camoufleurs made perfect imitations of natural objects and surroundings, they were greatly concerned to find that the flying observers could see through their disguises. To the naked eye the landscape would not show the slightest trace of any suspicions object, but by the use of a color-screen to cut out certain rays of light, a big difference would be shown between the real colors of nature and the artist's copies of them. For instance, if a roof painted to look like green grass were viewed through a red color-screen, it would look brown; while the real grass, which apparently was of exactly the same shade as the roof, would look red. It had not been realized by the artists who had never studied the composition of light, that there is a great deal of red in the green light reflected by grass, and that if they were to duplicate this shade of green, they must put a certain amount of red paint in their imitation grass roofs. Air scouts did not depend upon their eyes alone, but used cameras so that they could study their photographs at their leisure and by fitting the cameras with different color-screens, they could analyze the camouflage and undo the patient work of the artist.

A CALL FOR THE PHYSICIST

To meet this situation, another man was summoned to help—the physicist, who looks upon color merely as waves of ether; who can pick a ray of light to pieces just as a chemist can analyze a lump of sugar. Under his expert guidance, colors of nature were imitated so that they would defy detection. Aside from this, the physicist helped to solve the tricks of the enemy's camoufleurs.

But the physicist had barely rolled up his sleeves and got into the fray when the armistice was signed which put an end to the shams as well as to the realities of the great war. While the work of camouflage was not completed, we owe an inestimable debt to the men who knew how to fake scenery and to their learned associates who count the wave lengths of light, and although their trade was a trade of deception and shams, there was no sham about the service they rendered.

MAKING SHIPS VISIBLE

While in war safety lies in invisibility, in peace the reverse is true. Now that the war is over, it may seem that the work of the camoufleurs can find no useful application; but it was impossible to learn how to make objects invisible without also learning how to make them conspicuously visible. As a consequence, we know now how to paint a ship so that it will show up more clearly in foggy weather, thereby reducing the danger of collision. We know, too, how to paint light-ships, buoys, etc., so that they will be much more conspicuous and better guides to mariners, and how to color railroad signals and road signs so that they will be more easily seen by locomotive engineers and automobile drivers.