IN this age of scientific armament, every new invention that bears at all upon the art of warfare is carefully weighed in. the balance of military usefulness. The balloon, telegraph, telephone, automobile, motorcycle and, more recently, wireless telegraphy, have all demonstrated their ability to further the dread game of war and have, consequently, been added to the standard equipment of armies. While enthusiasts are heralding the advent of universal peace, the silent, non-sentimental sentinels of warfare are eagerly acquiring every device and invention that may give them an advantage in the next clash of arms perhaps the worlds greatest war! To the military man, warfare is a science; no sentimental theories or fancies enter into his cold calculations; no dream of the ages appeals to him unless it can add to the efficiency and destructiveness of his engines of war. Consequently, when word went round the world that man had flown, that a heavier-than-air machine had actually risen from the ground, military authorities did not let enthusiasm run away with judgment; they placed a “watch” on this new invention and the more progressive nations took steps to test it carefully with a view to its use in warfare. Within less than three years, its usefulness, even necessity, for scouting and reconnaissance work has been proven beyond a doubt, and, in consequence, the aviator has taken his place in the military establishment and aviation corps have become a part of the organization of armies. From developments in recent maneuvers, it is safe to predict that, in the next great war, the initial battle-clash will be between squadrons of scouting aeroplanes and that many a deed of devotion and daring will inspire the pen of the future historian. Much has been said and written lately about the use of the flying machine as a destructive weapon. “Bomb” dropping has been a popular feature of recent aviation meets and enthusiastic reporters have given their imaginations full rein, with the result that cities have been destroyed, forts demolished and battleships sunk. It must be observed, however, that all such tests have been made from heights of three hundred feet or less, at which range an aeroplane would not have a ghost of a show against machine guns, shrapnel, rapid-fire guns or even rifle fire. When we consider aeroplanes flying at reasonably safe heights, say between one and two miles, the problem of accurately dropping projectiles becomes a difficult one and scientific calculation must take the place of guess-work. Granting that a reasonably accurate method has been or will be developed for dropping projectiles, let us inquire what damage can be done. 1st, Against Armies.—At the beginning of a battle, usually about one-third of the troops are on the firing line in extended order, while the remaining two-thirds are massed in supports and reserves in the rear of the firing line in positions offering the best protection from the enemy's fire. These supports and reserves are massed in close order, they cannot be greatly extended, for the commanding general must have them under his thumb in order to quickly reinforce weak or threatened parts of his firing line at any time. Still farther to the rear are the wagon trains, artillery parks, lines of communication, supply -depots, etc. An aeroplane operating against armies in the field would, therefore, probably use shrapnel, an explosive shell filled with hundreds of bullets and equipped with a time-fuse in such manner that it can be exploded above bodies of troops on the march, supports, reserves, wagon trains, camps, etc. Shrapnel is considered one of the most effective projectiles used in modern warfare, and it does not require a military expert to imagine the havoc it would work on a body of troops en masse. Moreover, the moral effect of such a weapon would be tremendous. 2nd, Against Cities.—In operations against cities, aeroplanes would use incendiary bombs, small bombs filled with some material which would set fire to combustibles on contact. Dozens of such bombs could be carried and a few aeroplanes could soon start a general conflagration. Any activity on the part of the fir", department could be quickly dampened with a few shrapnel. 3rd, Against Fortifications.—Any one familiar with sea coast fortifications knows that tlie accuracy' of the big guns mounted there depends altogether upon the range-finding system. These systems are of two' kinds, horizontal and vertical Both systems depend upon more or less delicately mounted instruments, mounted in buildings screened and protected from the harbor but not from the sky. In fact, they must be above the parapet so as to get an unobstructed view toward the harbor. Consequently, it would not be necessary to pick out the separate emplacements and guns for destruction, it would only be necessary to drop a steel projectile filled with high explosive, lyddite, for instance, on or near the range-finding bases. These being out of commission, the costly guns become as useless as so much junk. Magazines, barracks and store-houses could also be destroyed. 4th, Against Battleships.—The most difficult target for an aeroplane would probably be a battleship, on account of its relatively small size and its rapid movement. Night attacks and attacks while at anchor would probably be the most usual; although, in a naval battle, aeroplanes would be able to do much to harass the enemy. A few well placed shrapnel exploded above the gunnel's would not tend to increase their accuracy, and, better, smoke bombs exploded to the windward would do much to destroy accuracy of aim. Then a high explosive would be used, and, unless protective decks are materially strengthened, would be terribly effective. Authorities to the contrary notwithstanding, the writer holds that a steel projectile filled with 200 pounds of high explosive, striking with a velocity of 500 feet per second, even though it should not penetrate the protective deck, would work terrible havoc to a battleship. Present development points to the early construction of aeroplanes that will be able to carry a load of 1,000 pounds to a height of a mile and remain there for several hours. On the other hand, those who have studied the question carefully believe that an aeroplane flying at heights' greater than one mile will be a very difficult target, indeed, for gunners on the ground. Some of the reasons for reaching this conclusion are as follows: 1st. The aeroplane is not confined to movements in a horizontal plane, but may move in any plane. Those familiar with the subject know that, in order to hit a moving battleship from a seacoast gun, it is necessary to plot ahead and lay the gun ahead of the ship, just as a shot gun is held ahead of a duck. With a swiftly moving and, probably, zig-zagging aeroplane, it will be much more difficult to plot speed and direction and lay ahead than in the case of a battleship. 2nd. The difficulty of accurate aiming in high angle fire is generally recognized. 3rd. Refraction, or the bending of light rays from a rarer to a denser medium, will complicate matters. 4th. Projectiles fired at a very high angle, especially at aeroplanes hovering over an army in the field, will return to the vicinity from which fired, whether the target is hit or not. 5th. An aeroplane in close quarters would probably drop smoke bombs to obscure the eneIly's vision, on the principle of the cuttlefish. However opinions may differ, the rapid development of the aeroplane for military and i:.iv;i[ purposes, especially in Europe, behooves us to consider it most seriously in the problems of seacoast and canal fortification that now confront us. We like to boast of our splendid isolation, of the steel throated monsters that guard the entrances to our harbors. Suppose, for instance, that, ten years hence, every battleship is equipped with flying machines; also, that an enemy's fleet appears fifty miles off New YorK. Would it be necessary to pass our forts in order to destroy the metropolis? Hardly; a fleet of aeroplanes would be despatched; within an hour they would be over the city; obeying wireless orders from their commander, they would maneuver over the thickly built section and soon it would be a mass of flames. Fantastic? Possibly so; but, in view of the recent extensive and successful use of the aeroplane in European maneuvers and, also, of the fact that other nations are spending many millions of dollars for aeronautical purposes, it might not be unwise for our Congress to depart from its usual policy of economy by appropriating a million dollars to enable the army and navy to fully test this new arm. Nations, as well as individuals, are sometimes penny wise and pound foolish. A careful study of the problem of dropping projectiles reveals a certain relationship to the problems presented in mortar fire. In mortar fire, the theoretical trajectory of the projectile la a parabola, as shown in Fig. 1. Neglecting atmospheric resistance, the ascending and descending halves of the parabola: are equal and symmetrical. The apex of the trajectory is a point at which the vertical component of the muzzle velocity has been used up in overcoming gravity and only the horizontal component remains. From this point the projectile falls with an acceleration due to gravity and, theoretically, would strike a target on a level with the muzzle of the gun with the same velocity it had when it left the gun. It is evident that, if an aeroplane should be moving on a level with the apex of the trajectory considered and in the vertical plane containing the trajectory, with a velocity equal to the horizontal component of the muzzle velocity, and should, at the apex, drop a projectile of the same weight, size and shape as that of the mortar, the projectile thus dropped would take the identically same path and strike with the same velocity as the mortar projectile. In other words, the problem is similar to that of mortar fire and only one-half of the trajectory has to be taken into account. Briefly considered, the mathematical aspects of the problem are as follows: If an aeroplane, moving horizontally in vacuo, with a velocity of, say, 20 meters per second, should release a projectile at a point, A, Fig. 2, the projectile would take a parabolical path whose form and equation would be determined entirely by the height of the aeroplane and its speed with respect to the surface of the earth. The general equation of such a parabola is readily calculated and is, x2 = -y; in which x is the horizontal dis- g tance in front of the' target at which the projectile must be released; y is the height above the ground; v is the velocity of the aeroplane with respect to the ground; g is the constant of gravitation for the particular place. Knowing all the factors in the second member of this equation, the value of x is readily found. This gives a right angle triangle, AOT, Fig. 2, in which, knowing x and y, the angle, a, :3,t which a line of sight (telescope) in the vertical plane containing the target must be set in order to strike the target, T, can be readily computed. Each velocity of the aeroplane and each height will, when substituted in the above equation, give a different triangle and, con sequently, a different value for the angle, a. Substituting for every possible height and every possible speed will give a series of values for this angle which may be easily tabulated. This discussion has considered the projectile in vacuo. It is apparent that the resistance of the atmosphere will depress the trajectory, as shown by the dotted lines in Fig. 2. Consequently the table above referred to would have to be corrected for atmospheric resistance and additional correction-tables constructed for winds and hygrometric conditions. Such correction tables would be relatively simpler than similar tables used in artillery and naval practice. Apex A patented device, of which the writer is the inventor, takes scientific consideration of all the factors that enter into this problem. This device consists of a series of concentric rings universally mounted (that is, mounted on gimbals at right angles to each other). The center of gravity being considerably below the center of support, the inner ring assumes a horizontal position when symmetrically loaded. A telescope, with graduated arc and vernier, is mounted on the inner ring at right angles to the plane of the ring. The line of sight of this telescope therefore describes a vertical plane when revolved, enabling the operator to lay off the angle, a, for the particular height and speed used. Consulting Fig. 2, it is evident that, when the line of sight intersects the target, T, the projectile should be released. In order to solve the equation above given, it is Fig.2 necessary to know v, the velocity of the aeroplane with respect to the /ground. There is no instrument for measuring this velocity; it can, however, be readily determined by using the device above described. Consulting Fig. 3, it may be seen that, when the angle a is 45 degrees, the distance y equals distance x. Therefore, in order to determine the speed over the ground, set the telescope at 45 degrees from the vertical and fly horizontally. Knowing the height from the barometer, note when some conspicuous object, as a tree, crosses the field and start a stop-watch. Then revolve the telescope to a vertical position and continue the flight to B, at which point the tree will again cross the field. At this point, stop the watch. Line of Flight Fig. J The speed over the ground will equal the height divided by the elapsed time. These speeds may be tabulated by taking all possible heights divided by all possible elapsed times. It is apparent, also, that the whole operation will take scarcely more than a minute unless the height is very great.
This article was originally published with the title "Dropping Bombs from Flying Machines" in Scientific American 105, 18, 388-389 (October 1911)