Aircraft in Warfare (1916)/Chapter 10
CHAPTER X.
(November 6th, 1914)
MISCELLANEOUS WEAPONS AND MEANS OF OFFENCE. SUPREMACY OF THE GUN.
§ 64. Other Weapons of Offence. For the fighting aeroplane there is no doubt that the gun will prove to be the most useful all-round weapon; however, several other means of offence have been suggested and to some extent have proved themselves of value. Bombs and hand-grenades, both explosive and incendiary, have been found to be of considerable service under appropriate conditions. Other means of attack have been proposed, such as rockets, air-borne torpedoes, etc.; so far, neither of these latter appears to have been successfully utilised.
The difference between a bomb and a hand-grenade is mainly a matter of size and weight, and a corresponding difference in the arrangements made for its release. Ordinarily, a hand-grenade is a small bomb of some 5 lb, or 6 lb, weight or less, containing a high explosive or inflammable charge, and is, as its name implies, thrown by hand. Requiring no particular provision for its storage or discharge, it is a weapon particularly suited to employment by scouting and other machines not primarily intended for fighting. The judicious employment of a few hand-grenades for the scattering of cavalry or the stampeding of led horses, or against troops on the march or massed in reserve, may by its effect amply justify the use of such a device. The bomb is commonly of considerably larger dimensions than the hand-grenade, and is stored or mounted in a magazine of some kind beneath the fuselage of the machine, with some mechanical device for its release, arranged either to let go a single bomb or to empty the magazine as required. It may be said that whereas the hand-grenade, in common with the machine-gun, is only suitable for injuring personnel, the legitimate objective of the bomb is materiel. Thus the depots, magazines, arsenals, oil stores, etc., of the enemy cannot be effectively destroyed by gun-fire, at least from present-day aircraft; but if attacked by a few squadrons of aeroplanes, each dropping some eight or ten 30-lb, or 40-lb, bombs, irreparable mischief might be effected in a very short space of time.
We may take it that in the future any such points will be duly protected by the fighting aeroplanes of the enemy. Consequently the bomb-dropping machine will need to be also a fighting machine itself, with a capacity for rapid fire sufficient to enable it to hold its own with the enemy. Or it will need to act in conjunction with a supporting fleet of fighting machines of sufficient strength to overpower, or at least hold, the enemy during the operation.
It is thus clear that the bomb differs from the hand grenade in not being a weapon suitable for casual employment by the reconnaissance machine. Further than this, it is a weapon which will in future warfare probably be found to possess comparatively little value, except when used in considerable numbers by machines acting in squadrons, or fleets several squadrons strong. The use of the incendiary bomb, or petrol bomb, as it is sometimes termed, is indicated where the objective is of a sufficiently inflammable character. But it is probable that in all cases in which an attack is made upon buildings of permanent character, such as in the destruction of an arms or ammunition factory, or of a dockyard, the petrol bomb will be used to complete the job by firing the wreckage remaining after high explosives have done their work.
§ 65. The Bomb: Di^culties in Connection with Aiming. The accurate directing or aiming of bombs or hand-grenades, or of any gravitationally-propelled missile, is one of great difficulty, and many suggestions for the improvement of the degree of precision attainable have been made. The problem, in a sense, is the inverse of that of firing at an aeroplane at high altitude. The period during which the projectile is at the top of its trajectory (the beginning of its fall in the case of the bomb), and in which its velocity is low, introduces considerable uncertainty as to direction; it has been proposed to minimise this difficulty by giving the bomb an initial velocity or "send off," by some form of spring or pneumatic gun. The factor affecting the aim definitely known to the pilot is the velocity of flight (relatively to the air); the factors less exactly known are the height, the direction and velocity of the wind, or, as it must be reckoned by the aeronaut, the earth drift, and the direction of the vertical. Previous observation may have given the approximate wind allowance, and the barometric reading (the aneroid) will give the altitude, which, in conjunction with a contour map, will give the pilot the figure for his height. The determination of the vertical, or "plumb," is far less simple or certain than may at first sight appear, since any pendulum device is affected by acceleration just as much as by gravity, and the reading of a damped pendulum or a spirit-level gives the apparent plumb, which may be literally anywhere.
In the case of a machine "looping the loop," for example, the apparent plumb is, in fact, at one instant diametrically opposite to the true plumb, and during the whole evolution it "boxes the compass" in a vertical plane. The lateral deviations of the apparent from the true plumb, are no less serious, and, whenever a machine is turning and correctly banked, the spirit-level records the machine as being on an even keel. In other words, an error in the reading under these conditions is equal to the angle of banking, and is quite commonly as much as 30 deg, or 40 deg. It is precisely on this point—the confusion of the true with the apparent plumb—that many of the suggestions offered for the direction of bomb-dropping are found to fail; and it is quite useless for those having no knowledge of the principles involved to attempt to deal with the problem. No better way of obtaining a clear conception of the difficulty exists than a study of the pendulum accelerometer.[1][2][3]
In the case of a modern aeroplane which virtually "flies itself" it is possible to determine the true plumb with considerable exactitude under calm atmospheric conditions. Such a machine will, just like a gliding model, settle down to a definite flight velocity, known as its natural velocity, and to a known gliding angle, and will maintain a tolerably straight path; under these circumstances the apparent plumb is the true plumb. When, however, atmospheric disturbances are present, the difficulty once more makes it appearance.
In view of the above, it is doubtful whether bomb-dropping from aeroplanes will ever be found to compete with gun-fire on the score of accuracy, and it may be anticipated that the utility of this mode of offence will be confined mainly to attack on positions or objects that present a mark either of sufficient area or size to be easily hit, or of sufficient importance to justify a disproportionate expenditure of missiles. § 66. The Steel Dart. A form of gravitational projectile or missile introduced during the present war is the steel dart; this commonly consists of a piece of steel wire or rod some 5 in, or 6 in, long by 5⁄16 in, in diameter, pointed at the one end and "feathered" at the other. In size and shape the missile resembles and ordinary well-sharpened graphite pencil, the feathering being done in some cases by the milling away of the tail portion to a cruciform section; alternatively the rear two-thirds of the missile may be made of thin-gauge tube. The weight is about 1 oz. This "pencil dart" is used against the personnel of the enemy—i.e., encampments, men or cavalry on the march, etc.; the rate of fall, if dropped from a few thousand feet altitude, would be little short of the limiting velocity, say some 400 ft, or 500 ft, per second. The penetration at this velocity should be equal to several inches of spruce planking. Steel darts are either allowed to fall out of a hopper or may be simply thrown out or "sown" by hand. They appear to be quite effective when they find their mark, but their discharge and direction are subject to the same limitations as to accuracy which apply to the throwing of the hand-grenade or bomb, with much greater uncertainty as due to air resistance. Beyond this the steel dart, to be effective, must be dropped from a height—a very considerable height—and so it is not possible to make a sudden descent for the purpose of bringing off an attack, as is the case when the bomb is the weapon chosen. For these reasons the author does not believe that the dart will have a very great vogue. Once the aeroplane has been satisfactorily adapted to the carrying of a machine-gun, it is quite clear that the steel dart, weighing, as it does, as much as the ordinary Service cartridge, must be regarded as a weapon of doubtful utility.
§ 67. The Rocket and the Air-Borne Torpedo. A suggestion which has been made over and over again is that of the employment of the rocket in some shape or form; the objective is usually presumed to be a dirigible or airship, and the rocket is to be fired from a rockettube or gun of some kind from an attacking aeroplane. There are two replies to this suggestion: firstly, no weapon can be contemplated as forming part of an aeroplane armament which is confined in its purpose to the attacking of the airship. The airship is already being regarded as a prospective {[lang|fr|bonne bouche}} for the aeroplane squadron fortunate enough to encounter it in the open, and, as the recent exploit at Dusseldorf has shown, it is not in a much happier condition when at home. It is already recognised that the airship may not expose itself to the attentions of hostile aeroplanes, and when the latter are able to attack by one-pounder shell fire, in addition to bombs (explosive and incendiary), the airship, already little more than a name in active hostilities, will cease to have any, even verbal, interest. Apart from the above, the supposed effectiveness of the rocket, or of other spitfire projectile, is based to a great extent upon a misconception. The modern airship is not so easily set on fire as is commonly supposed; in the rigid type, as exemplified in the Zeppelin, it is reported that the space between the gas-bags and the outer envelope is charged with a non-flammable gas, and it may be penetrated by any ordinary rocket through and through without the smallest chance of ignition.[4]
The aerial torpedo (proposed by the author in 1897) at first sight appears promising. Such a torpedo would consist of a gliding model of high velocity adapted to be launched from a gun or pneumatic projector of some kind, and carrying a charge of explosive and an impact fuse actuated by the striking of the aerofoil member on some part of the enemy's craft. Again, we are confronted with the fact that any such weapon would be of little service apart from attack on an airship, and so may be looked upon as useless lumber.
§ 68. The Supremacy of the Gun. The real fact at the bottom of the whole question is the vital importance of high velocity in any projectile directed against a rapidly moving target, and its doubly vital importance when the craft from which it is projected is also in rapid motion. This is universally recognised wherever the gun is to be found, and it is nowhere more important than in the attack on aircraft by aircraft, and in particular aeroplane on aeroplane. Any lapse of time whilst the projectile is in its flight introduces a corresponding uncertainty owing to the relative difference of motion between gun and mark. Thus a projectile travelling at 200 ft, or 300 ft, per second, such as a rocket or aerial torpedo, would require to be directed at a point so far removed from the aircraft it is intended to hit, that, in the case of an aeroplane, the chances of success would be remote in the extreme.
In brief, nothing but gun-fire gives the necessary rapidity to ensure a reasonable degree of accuracy and useful percentage of hits, and it is probable that for some time to come the demand will be for higher and higher velocity in order that the effective range may be increased. This, however, is looking into the future; at present, the problem of mounting a gun in a satisfactory manner, and getting the highest possible rate of discharge—i.e., rounds per minute—are the more immediate concern of the aeroplane constructor. The relation of the ordinary flight velocity to the mean velocity of the projectile is round about 12 to 1, and this gives the angle of lead necessary to aim in front of the objective from a fixed mounting. When firing from another aeroplane moving in the opposite direction, the angle of lead will be six to one more or less, a considerably greater allowance than is known in any other branch of gunnery. With the highest muzzle velocity and slow-moving aircraft the angle of lead under these conditions is about 1 in 15. The angle of lead given by a pigeon-shot when the bird is flying fast across the line-of-sight is about 1 in 20, and even here the demand, under the stress of competition, is for higher and higher velocity. This may be taken as a sure indication of what may be expected in the eventual future of aeronautical gunnery.
- ↑ Philosophical Magazine. August, 1905; also Proceedings of the Institution of Automobile Engineers, vol. iv., page 124.
- ↑ See: XXXII. The pendulum accelerometer, an instrument for the direct measurement and recording of acceleration (1905) The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, Volume 10, Issue 56, pp. 260-268 [1] (Wikisource contributor note)
- ↑ See: Tractive Effort and Acceleration of Automobile Vehicles on Land, Air and Water (1909) Proceedings of the Institution of Automobile Engineers, vol. iv., pp. 123–166 [2] (Wikisource contributor note)
- ↑ This feature was actually proposed some years ago to the authorities in this country, and was understood to be a matter of secrecy. However, according to Navy and Army Illustrated (September 12, 1914), it now appears to be an established feature of some of the later German Zeppelins.