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Aviation History
1909
1909 - 0149.PDF
MARCH 13, 1909. fall and effect of the fleet's projectiles and communicate results unless the airship occupies an almost stationary position at a moderate height. Under the third heading, that of dropping bombs, we have really to deal with the airship as a new and dangerous means of actual offence. It is probable that the bombs will be few in number and large in size, and the first point of immediate interest in this connection is to know what effect the sudden release of several hundred pounds weight of bombs will have on the airship. Fortu- nately we have reliable data at hand. It was calculated by the constructor of "La Patrie" that when she suddenly escaped from her moorings she was at once relieved of a weight of 1,653 'DS-; she shot up to a height of 6,562 ft. without any injury and without the valve being touched. An airship designed for this service would be constructed with a ballonette and valve, so that gas could rapidly be let out without affecting the extended form of the aerostat. Captain Neumann estimates roughly that the unloading of I per cent, of its own weight will cause an airship to rise 262 ft. It was stated just now that the bombs used would probably be heavy and few in number ; this necessitates careful choice of target and greater accuracy in discharge. We know how intensely local the effect of high explosives is, and place no reliance on any form of bomb attack by airship which is not based on striking at a vital part, and taking care that the stroke is delivered with the same minute attention to accurate hitting as in the case of gun-fire. We do not know what effect the dropping of a heavy bomb of, say, 400 lbs. would have on a battleship ; but we do know that the uncapped cast-iron shell of 448 lbs., containing 28 lbs. of powder, which the Japanese fired from their 11-in, howitzers on 203 Metre Hill against the Russian ships at Port Arthur, were disappointing in their results ; they struck the decks at an angle of about 300 with the vertical; 4 out of 12 hits penetrated the 2-in. armoured deck of the " Peresviet," but did no great damage after penetration, and, indeed, generally speaking, none of the shells which penetrated the decks of tbe other ships seem to have played any great part in sinking them. As Engineeringsays, " the effect was less noticeable than might have been expected." A bomb dropped from an airship can, weight for weight, contain far more explosive material than a shell fired from a gun ; the former only requires a casing sufficiently strong to hold the contents, and relies for its effect entirely on the violence of the explosion ; the latter requires a case strong enough to resist the shock of discharge and the high gas pressure in the gun, and depends greaily on its penetrating power and the violent dis- ruption of its case in the form of splinters. The weight of explosive bears a very small proportion to the weight of the case. I am not aware of any experiments which would give us reliable data on this subject, but it appears to me that the time has arrived for carrying out such experiments, so that we may know for certain : — a. What is the best explosive to use for aerial bombs; b. What weight is required to render a battleship unseaworthy, to destroy a dry dock, or to wreck a battery ; c. From what height such bombs can be dropped with accuracy on their target; d. Whether the height from which they are dropped appreciably affects the violence of the explosion ; e. What effect a burst under water would have on torpedo craft and submarines and at what distance. Let us now consider what is the probable procedure of an airship under the three headings mentioned. The average height of clouds in most parts of Europe is from 3,900 ft. to 4,500 ft. in winter, and from 9,900 ft. to 13,200 ft. in summer. In cloudy or misty weather airship-, can keep very low without much danger of being seen from the ground, even when they can see sufficiently well to locate them- selves. It is exceedingly difficult for an observer on the ground to locate an airship in the dark, even with the aid of searchlights; the lower they travel the less easily will they be spotted, and on a clear night they can find their way easily over land. It may therefore be deduced that:— 1. An airship will usually carry out reconnoissances by day, and rely for safety in taking advantage of atmospheric conditions of vapour or cloud, or in her inherent power of rapidly altering her altitude. 2. Hut for discharging bombs the night will be preferred, as she can then approach within close range of her target, thus ensuring accuracy ; the proximity of the target will be limited by the effective radius of the explosion in respect of the fragile structure of the air- ship—this radius should be determined by experiment. We now come to the question of defence and counter-attack against airships. At present the only means at our immediate disposal are the high- angle batteries which exist in many of our coast fortresses, and these could readily be assisted by a suitable adaptation of the existing system of electric lights. The following table shows the capabilities of the 19-in. R.M.L. gun, on a H.A. mounting, as regards the highest altitude reached by the trajectory at 450 and 700 elevation respectively, and the horizontal distance measured to a point vertically below the highest altitude :— lO-inch R.M.L. Gun on H.A. Mounting. Ele t"on Height ot Range to Maximum Ordinate. Maximum Ordinate. 45° ... 7,300 feet ... 4,600 yards 7O° ... 12,600 „ ... 2,870 „ From this table it is clear that existing H.A. batteries would be unable to interfere with the airships engaged by day in reconnaissance or observation to any appreciable extent, since, in order to attain a height of only 7,30a ft., it is necessary that the battery should not be more than 4,600 yds. from a point vertically below the target. This obviously limits the sphere of action of H.A. batteries to such an extent that airships can defy them with impunity, and this, apart from the fact that their rate of fire and the excessively long time of flight, renders it hopeless to attack an airship on the move. But the case of an airship dropping bombs is on a different footing. Here it is essential that the airship should take up a position vertically above the target, and remain there sufficiently long to discharge her bomb with accuracy. Once she is over the target, there may be little delay in releasing the bomb; but it will undoubtedly take an appreciable time to manoeuvre into position, and while she is hovering, so to speak, she will offer a target to a H.A. battery. It seems unlikely that an airship could discharge bombs from a greater height than 5,000 ft., owing, not merely to the difficulty of ensuring a hit, but also to the fact that the attainment of a high altitude cannot be achieved without the sacrifice of ballast, which in this case means bombs. At a rough approximation, in such a case as we are considering, 250 lbs. weight would have to be sacrificed for every 1,000 ft. of altitude. We shall be quite justified, therefore, in considering that any area within 5,400 yards of a H.A. battery is protected by it, in respect to the attack of a bomb airship, since at this distance the vertical field of fire attains a height of 5,000 ft. The difficulty of spotting the airship at night will be very great ; she has everything to gain by a night attack, inasmuch as she is not only more difficult to see, but she is more difficult to spot at a low altitude than at a high altitude. The lower the altitude, the greater weight or bombs she can carry, and the greater the accuracy with which she can discharge them. Everything, therefore, points to night attack. It is clear that the field of operations of the airship must be illuminated, otherwise she would have nothing to fear in the way of attack. The idea of trying to pick up an airship with search- lights may be dismissed at once ; the only practical plan seems to be to illuminate all fields of operation which may be used for the attack of vital areas by means of suitably arranged dispersed beams pointing skywards. It is most unlikely that any of our coast-defence guns would be able to attack a reconnoitring airship, as she would naturally run inland out of range, and then turn and approach the harbour from the land side. It is possible that some of the movable armament might keep her on the movt, but it can scarcely be expected that anything more than this could be effected, and there would obviously be limitations to the employment of the movable armament fur such a purpose, inasmuch as although their fire is unlikely to cause much uneasiness to the airship, it is certain to cause a considerable amount of bodily discomfort to persons on terra firma who may be hit by splinters and bullets. Thus far we have dealt only with existing means of defence, and it appears that thoug-i they are obviously inadequate, yet they are not without value. The introduction of armament for special em- ployment against airships seems to be an immediate want. The Germans have tackled the question for land operations, and it is time that we did the same for harbour defence. The most suitable gun would appear to be a light Q.F. gun on a special mounting with an all-round traverse and a possible elevation of 7°°> a shell weighing 3 lbs., containing an easily detonated explosive, and having a high muzzle velocity , the fuze must be a specially sensitive one in order to cause explosion on penetration of the gas envelope. The effect aimed at would be the explosion of the gas in the envelope, thus ensuring the complete destruction of the airship. This will be a far more effective method of attack than that suggested for H.A. batteries, inasmuch as the latter would be dependent on damage done by shrapnel bullets to the personnel or to the motor, the penetration of the envelope by bullets being incapable of producing a sufficiently appreciable effect on the buoyancy to render the airship unserviceable as an aerostat. Counter'Attack. But artillery alone will scarcely be able to deny to an enemy's air- ships such access to the upper air of our harbours and dockyards as may be necessary for reconnoitring and observation ; this role can only be satisfactorily fulfilled by harbour airships, or, perhaps better still, by aeroplanes, and the artillery defence must in this respect be regarded as auxiliary only.
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