Inventions of the Great War

by A. Russell Bond

Now the ordinary range-finder, used in the army and in the navy, is an arrangement for spreading the eyes apart to a considerable distance. Of course the eyes are not actually spread, but their vision is. The range-finder is really a double telescope. The barrel is not pointed at an object, but it is held at right angles to it. You look into the instrument at the middle of the barrel and out of it at the two ends. A system of mirrors or prisms makes this possible. The range-finder may be a yard or more in length, which is equivalent to spreading your eyes a yard or more apart. Now, the prisms or object-glasses at the ends of the tube are adjustable, so that they will turn in until they focus directly on the target whose range you wish to find, and the angle through which these glasses are turned gives a measure of the distance of the target. The whole thing is calculated out so that the distance in feet, yards, or meters, or whatever the measure may be, is registered on a scale in the range-finder. Ordinarily only one eye is used to look through the range-finder, because the system of mirrors is set to divide the sight of that one eye and make it serve the purposes of two. That leaves the other eye free to read the scale, which comes automatically into view as the range-finder is adjusted for the different ranges.

On the battle-ships enormous range-finders are used. Some of them are twenty feet long. With the eyes spread as far apart as that and with a microscope to read the scale, you can imagine how accurately the range can be found, even when the target is miles away. But on land such big range-finders cannot conveniently be used; they are too bulky. When it is necessary to get the range of a very distant object, two observers are used who are stationed several hundred yards apart. These observers have telescopes which they bear upon the object, and the angle through which they have to turn the telescope is reported by telephone to the battery, where, by a rapid calculation, it is possible to estimate the exact position of the target. Then the gun is moved up or down, to the right or to the left, according to the calculation. The observers have to creep as near to the enemy as possible and they must be up high enough to command a good view of the target. Sometimes they are placed on top of telegraph poles or hidden up a tall tree, or in a church steeple.

GETTING THE OBSERVER OFF THE GROUND

This was the method of getting the range in previous wars and it was used to a considerable extent in the war we have just been through. But the great European conflict brought out wonderful improvements in all branches of fighting; and range-finding was absolutely revolutionized, because shelling was done at greater ranges than ever before, but chiefly because the war was carried up into the sky.

A bird's-eye observation is much more accurate than any that can be obtained from the ground. Even before this war, some observations were taken by sending a man up in a kite, particularly a kite towed from a ship, and even as far back as the Civil War captive balloons were used to raise an observer to a good height above the ground. They were the ordinary round balloons, but the observation balloon of to-day is a very different-looking object. It is a sausage-shaped gas-bag that is held on a slant to the wind like a kite, so that the wind helps to hold it up. To keep it head-on to the wind, there is a big air-bag that curls around the lower end of the sausage. This acts like a rudder, and steadies the balloon. Some balloons have a tail consisting of a series of cone-shaped cups strung on a cable. A kite balloon will ride steadily in a wind that would dash a common round balloon in all directions. Observers in these kite balloons are provided with telephone instruments by which they can communicate instantly with the battery whose fire they are directing. But a kite balloon is a helpless object; it cannot fight the enemy. The hydrogen gas that holds it up will burn furiously if set on fire. In the war an enemy airplane had merely to drop a bomb upon it or fire an incendiary bullet into it, and the balloon would go up in smoke. Nothing could save it, once it took fire, and all the observers could do was to jump for their lives as soon as they saw the enemy close by. They always had parachutes strapped to them, so they could leap without an instant's delay in case of sudden danger. At the very first approach of an enemy airplane, the kite balloon had to be hauled down or it would surely be destroyed, and so kite balloons were not very dependable observation stations for the side which did not control the air.

As stated in the preceding chapter, just before the fighting came to an end, our army was preparing to use balloons that were not afraid of flaming bullets, because they were to be filled with a gas that would not burn.

MAKING MAPS WITH A CAMERA

Because airplanes filled the sky with eyes, everything that the army did near the front had to be carefully hidden from the winged scouts. Batteries were concealed in the woods, or under canopies where the woods were shot to pieces, or they were placed in dugouts so that they could not be located. Such targets could seldom be found with a kite balloon. It was the task of airplane observers to search out these hidden batteries. The eye alone was not depended upon to find them. Large cameras were used with telescopic lenses which would bring the surface of the earth near while the airplane flew at a safe height. These were often motion-picture cameras which would automatically make an exposure every second, or every few seconds.

(C) Underwood & Underwood