Aircraft in Warfare (1916)/Chapter 3
CHAPTER III.
(September 11th, 1914).
STRATEGIC AND TACTICAL USES OF THE AERONAUTICAL ARM. AIRCAFT AS VULNERABLE TO GUN-FIRE. ARMOUR AND ALTITUDE AS MEANS OF DEFENCE.
§ 8. Strategic and Tactical Uses of the Aeronautical Arm. In the present distribution of the cavalry Arm, the distinction between the strategic and tactical uses of cavalry is clearly recognised. For purely tactical purposes it is customary to attach one or more squadrons, usually a regiment of cavalry, to each infantry division. The main cavalry force on the other hand,—known as the independent cavalry,—constitutes a separate command, taking general instructions from the headquarters staff. The independent cavalry may be engaged in operations of strategic import, as in the conduct of a reconnaissance in force, or in the execution of a wide turning or out-flanking movement, or in the countering of such a movement on the part of the enemy. Alternatively it may be employed in its tactical capacity, its full weight being thrown at some critical moment into the fighting line, it may be to attack and destroy the cavalry of the enemy, to raid and capture or put out of action his artillery, to harass him in retreat, or to convert a retreat into a rout. The divisional cavalry are, generally speaking, employed for the latter—tactical—duties only.
In a similar manner aircraft are capable of employment in duties of both strategic and tactical import, and accordingly will probably need to be divided into divisional and independent commands. Thus there is the machinery of strategic reconnaissance, whose function it is to inform the headquarters staff of the main disposition and movements of the enemy's forces, positions of his depots, magazines, etc., points of concentration and strength of his reserves, and last, but not least, his main and perhaps auxiliary lines of communication. On the tactical side there are similarly many duties to be carried out, analogous to those at present performed by cavalry; there are also duties which must be regarded as new, brought into being by the peculiar power and capacity of the aeronautical Arm; these are, in the main, such as would indicate control by the divisional command.
§ 9. The Strategic Scout and its Duties. The strategic value of the aeroplane depends mainly upon its utility for the purpose of reconnaissance; briefly it is its value as an informer, rather than as a fighter, that is of service to the headquarters staff. The duties of a machine thus acting are necessarily of an entirely different character from those of a machine employed in the minor operations of the field, whether for tactical scouting, direction of gun-fire, or otherwise. Firstly, the flight range or radius, as determined by petrol capacity, is a far more important factor in its design, since it will require to operate over a large area, and to cover long distances over the enemy's territory, where any renewal of fuel supply is impossible; secondly, its flight speed must be such as to render it reasonably secure against pursuit. Anything serious in the direction of armour or armament will be entirely out of place, since under no circum1 stances will such a machine be required to act in a combative capacity; its defence lies in its speed. It appears from all reports that the duties in question are such as to require an observer (probably a staff officer) of mature knowledge from a military standpoint, with considerable flying experience, possessing something of an intuition for reading the meaning of the incomplete and fragmentary indications which are obtainable from high altitude observation. It is evidently not impossible for a strategic scout (as we may term the machine under discussion) to descend to low altitude in pursuit of more accurate and precise information; but it is always to be remembered that any such manoeuvre is dangerous to an unarmoured machine; it may be too easily shot down or destroyed by shrapnel. In this latter event it must be regarded as having failed in its purpose. The possession of a wireless installation may be assumed, but, in the event of the machine being lost, the fact that reports had already been transmitted to headquarters would in no way mean that the machine had completely fulfilled its mission.
The work done by the strategic scout thus comprises the gleaning of information hitherto only to be obtained by espionage or by a reconnaissance in force—that is to say, by a large force of cavalry with supports of horse artillery and infantry, often involving considerable fighting and loss. It is quite improbable that aeroplane scouting will prove an entire substitute for such reconnaissance; in may be said that cavalry can feel and act where the air-scout can only see and report, but, as a prelude to cavalry reconnaissance, and as an auxiliary thereto, the services of the strategic scout should prove of the utmost utility. It will, at least, enable the cavalry force acting at a distance from its base, frequently in the rear of the enemy, to keep in constant touch with headquarters, and thus relieve the despatch rider of one of his most difficult and dangerous tasks. In service of this character it would seem probable that a flight or squadron of aeroplanes would be temporarily or Plate III.
_-_Plate_III.png)
R.A.F. TYPE B.E.2c. Fitted with R.A.F. (British Built) Engine.
Compare Plate XIV.
permanently attached to the independent cavalry, as in the case of the supports representing the other two Arms of the Service. Under these circumstances the command of the combined force would remain, as at present, with the cavalry leader.
(September 18th, 1914).
§ 10. The Aeroplane as an Auxiliary to Tactical Operations. The aeroplane in its employment in connection with tactical operations finds itself under conditions entirely different from those discussed in the preceding section; its duties are of a more varied character, and involve flying at lower altitudes than are compatible with security. It is likely to be almost continuously under fire, and, according to some of the experiences of the present war, it has almost as much to fear in this respect from its friends as its foes. Whereas the strategic reconnaissance machine is able to perform all its most useful work at high altitude, and avoid as far as possible the attention of, or actual contact with, the enemy, and evade pursuit by flight; the tactical machine (acting under the divisional command), whether engaged in local reconnaissance or in locating or directing gun-fire, or in other duties, must be prepared at once to tackle the enemy, and, in brief, to interfere as much as possible with the hostile aeroplane service. Under certain circumstances the instructions will undoubtedly be to make the aircraft of the enemy the first objective.
It is more than probable that it is in connection with the varied duties which in the future must fall to the Fourth Arm in its tactical usage, that differentiation of type and specialisation will eventually become the most marked. At present practically no attempt in the direction of specialisation has taken place. It is true the different machines in service vary considerably, and those responsible for the construction and specification of Service aeroplanes have already begun to talk of "reconnaissance machines" and "fighting machines;" but the distinction is one that has scarcely yet penetrated to the field of operations. When all has been said, differentiation of type must, from the Service standpoint, be looked upon as an evil, only to be justified when, and to the extent that, service conditions prove it to be necessary. So far even the broad distinction between machines for strategic reconnaissance and for tactical operations has scarcely been drawn or received recognition. The military aeroplane of to-day is something like the frontiersman's knife—made for nothing in particular, used for everything in general.
For the purpose of directing artillery fire the experience of the present war has shown the aeroplane to be effective almost beyond the most sanguine expectation. For this purpose it appears to have established its utility beyond question. Its duties in this respect may be regarded as a special branch of local reconnaissance, its function being to locate the objective and signal its whereabouts to the gun batteries to which it is attached; further to report and correct inaccuracies of fire. The exact mode or modes of signalling adopted do not so far appear to have been definitely disclosed. Some reports give the aeroplane as turning sharply when over the enemy's position; according to other accounts a smoke bomb of some kind is let fall to indicate the position to be attacked; other reports, again, mention lights as being used. It appears that lamps of sufficient power to be visible in daylight are actually being employed by the German aircraft. Possibly all these methods are in use experimentally, or different kinds of signals may be used for different purposes, to indicate initially the position, and subsequently to give corrections, either as to direction or range. Whatever the methods employed may be (and the details do not much concern us at the moment), they seem to be quite effective, and, it may be presumed, very considerably increase the fighting value of the guns. More than this, the value of aeroplane work will be relatively greater the longer the range; in fact, it may in future be found possible to employ heavy artillery of long range under conditions where, without the help of the aeroplane, it would be comparatively useless. As an illustration, there is nothing to-day to prevent a long-range battery, well served by its aeroplanes, from effectively shelling an enemy without knowing in the least the character of its objective—i.e., whether an infantry force or position, a body of cavalry, or the enemy's guns. In the present war the aeroplane appears to have been utilised by the German army, as a matter of regular routine, as an auxiliary to the artillery in the manner indicated. It has been reported again and again that the appearance of an aeroplane overhead has been the immediate prelude to the bursting of shrapnel, frequently the very first shell being so accurately placed as to indicate that the method of signalling, and, in fact, the whole performance, must have been well thought out and equally well rehearsed.
It is well understood that the determination of the distance of an aeroplane of known size with approximate accuracy is a matter of perfect simplicity. Thus, if the aeroplane be flying fairly overhead, or directly towards or away from the observer, and the span be a known dimension, then by measuring the optical angle presented by the span, the distance or range is given by simple proportion. For example, holding a foot-rule square in front of one at arm's length—approximately 20 in, from the eye—the span, known to be, say, 36 ft., subtends an angle represented by, say, ½ in, on the scale; the distance is 20 × 36⁄0.5 = 1440 ft. Using such rough-and-ready "apparatus," the degree of accuracy to be expected is not great; however, the author has found it quite sufficient to determine the altitude of a machine to within 5 or 6 per cent. of the truth. If for the observer's arm and foot-rule we substitute a low-powered telescope or binocular of, say, 2 or 3 diameters magnification, with micrometer cross-wires, with which to follow up the apparent reduction in span of a receding aeroplane, until some prearranged signal is given, the range could undoubtedly be determined easily within 2 or 3 per cent. At 1 mile distance this means a degree of accuracy represented by a maximum error of about 40 yards, or sufficient to enable shrapnel to be dropped right on the mark. Parenthetically, it may be pointed out that the same method will enable the range of a hostile aeroplane to be determined, provided the type be identified, and its leading dimensions are known; it also suggests the importance of not flying exactly towards or away from, or exactly broadside to, any position of the enemy guarded by counter-aircraft artillery; flying end on to the enemy is also to be deprecated on the ground of fixity of direction.
§11. Attack by Gun-Fire. An aeroplane operating in a hostile country is liable to attack by rifle and machine-gun fire, also by shell-fire from special anti-aeroplane artillery. It has comparatively little to fear from field artillery owing to the want of handiness of the ordinary field-gun. The "laying" of a field-piece is far too clumsy a business to permit of its effective use on so small and rapidly moving a target as presented by an aeroplane in flight, though it may be effective when used against a dirigible. With regard to rifle or machine-gun (small bore) fire, calculation shows that aircraft is absolutely safe at an altitude of somewhat over 7000 ft.; it is in that region that the top of the trajectory lies for vertical shooting.
The duties of a strategic scout on long-distance work would, without doubt, permit of flying at such a high altitude, and it may be added that, although absolute immunity is not reached at less than about 7000 ft., a solitary aeroplane can only present a very unprofitable target at far lower altitudes. In fact, it may be taken that at, say, 5000 ft, or 6000 ft., the amount of small-arm ammunition required to bring down an aeroplane would be enormous. Not only has the velocity become so reduced as to render a "hit" capable of but little mischief, but the time of flight of the bullet, rising vertically to this altitude, would be about 8 or 9 seconds and the distance moved by the aeroplane 1000 ft., more or less. Therefore it would be necessary to fire into quite a different part of the heavens from that in which the aeroplane is seen, something akin to sighting into the Great Bear to hit the Pole Star. Beyond this the gyroscopic drift of a bullet fired vertically is nil, against some 30 ft, or 40 ft, under normal conditions;[1] also the error due to the earth's rotation is a matter of about 30 ft, westward, and cannot be allowed for without taking reference to the compass bearing. Taking all these things into account, it is evident that for the infantryman or gunner not specially trained, the task of bringing down an aeroplane flying at high altitude is no light one, especially when we recall the fact that for every inclination and bearing of the line of sight, the conditions differ. In designing the mounting of aeroplane-stopping artillery or machine-guns, it would be possible to render the sighting corrections for such items as gyroscopic drift and earth's rotation automatic; this could be done without difficulty, and would mean the elimination of errors whose combined value may amount to something like 60 ft, at 6000 ft, altitude—i.e., an angular magnitude represented roughly by the apparent diameter of the sun or moon.
The height to which aircraft artillery will carry is by no means subject to the same limitation as that of the small-bore machine-gun or rifle, the resistance of the air being many times greater than that due to gravity. Thus the ordinary rifle bullet, at 2,000 foot-seconds muzzle velocity, would carry to a height of over 60,000 ft. in vacuo, instead of approximately 7,000 ft, actual. If we take the case of a 1-pounder having the same velocity, its effective vertical range is well over 12,000 ft., and from that calibre upwards the range will, in practice, be more a question of the shell being properly directed than whether it will attain the height. At the best, firing from the ground at an aeroplane at high altitude, will require skilful gunnery, and when near the limit of the trajectory nothing but sheer good luck will render a hit effective. The angle of "lead" it is necessary to give to allow for the velocity of flight, as already stated, is one of the difficulties of high-altitude shooting. This angle is only constant so long as the velocity of the projectile is constant, assuming (as fairly represents the conditions) the flight speed not to vary; at extreme heights the velocity of the projectile has fallen so low that a very slight error in range-finding will be fatal to accuracy. The solution of this difficulty may be found in the employment of guns of about 3-in. bore—i.e., a 12-pounder or 15-pounder, with the concurrent advantage of a full shrapnel charge, and, in shot-gun terminology, a larger killing circle. The obvious disadvantages, however, of artillery, in place of a light automatic or machine gun, lie in its want of portability and its unhandiness, difficulties which may, in course of time, be overcome.
All things considered, it would appear probable that attack on aeroplanes at high altitude from the ground will be found impracticable, or at least uncommercial. Not only have we to reckon with the various considerations above discussed, but also with the fact that, in our climate at least, not more than one day in four is sufficiently clear to render high-altitude shooting possible, and though it is true that an aeroplane, to make observation, cannot remain above or in the clouds, it presents but a poor mark under bad weather conditions.
An aeroplane operating at high altitude will probably need to be hunted and driven off or destroyed by armed machines of its own kind.
§ 12. Defence from Gun-Fire. It is manifestly not possible for an aeroplane to perform all the duties required of it, in connection with tactical operations at high altitude,[2] and whenever it descends below 5,000 ft., or thereabouts, it is liable to attack from beneath; in fact, at such moderate altitudes it must be considered as being under fire—mainly from machine-gun and rifle—the whole time it is over or within range of the enemy's lines. Protection from the rifle bullet may be obtained in either of two ways; the most vital portions of the machine, including the motor, the pilot, and gunner, can only be effectively protected by armour-plate; the remainder of the machine, including the wing members, the tail members, and portions of the fusilage not protected by armour, also the controls, struts, and the propellor, can be so constructed as to be transparent to rifle fire—that is to say, all these parts should be so designed that bullets will pass through without doing more than local injury and without serious effect on the strength or flying power of the machine as a whole; in certain cases components will require to be duplicated in order to realise this intention. It is important to understand clearly that any intermediate course is fatal. Either the bullet must be definitely resisted and stopped, or it must be let through with the least possible resistance; it is for the designer to decide in respect of each component which policy he will adopt. The thickness of the armour required will depend very much upon the minimum altitude at which, in the presence of the enemy, it is desired to fly; also upon the particular type of rifle and ammunition brought to bear. There is a great deal of difference in penetrative power, for example, between the round-nosed and pointed bullets used in an otherwise identical cartridge.
If it were not for the consideration of the weight of armour, there is no doubt that an altitude of about 1000 ft, would be found very well suited to most of the ordinary tactical duties of the aeroplane. At such an altitude, however, the thickness of steel plate necessary becomes too serious an item for the present-day machine, even allowing for the very excellent and highly efiicient bullet-proof treated steel which is now available; at the altitude in question the minimum thickness that will stop a 0.303 Mark VI, round-nose bullet is 3 mm. (⅛ in.), but if attacked by the modern pointed-nose Mauser, nothing short of 5 mm, or 6 mm, is of avail. If we compromise somewhat in the matter of altitude and prescribe 2000 ft, as the minimum height for which protection is to be given, the figures become 2 mm. (about 14 S.W. gauge) for the 0.303 round-nosed bullet, and for the pointed Mauser 3 mm, or slightly over; at present it is not expected that it will pay to armour a machine for the Plate IV.
_-_Plate_IV.png)
SKELETON OF TYPE B.E.2. Showing position of Tank, Seats, Engine and Body structure.
Illustrates the extent of the vulnerable target presented by an Aeroplane.
duties ill question more heavily; thus we may take 2000 ft, as representing the lower altitude limit of ordinary military flying. Anything less than this will be referred to in the present series of articles as low-altitude flying. On this question of armour it cannot be too strongly insisted that anything less than the thickness necessary definitely to stop the projectile is worse than useless; a "mushroomed" bullet, possibly accompanied by a few detached fragments of steel, is infinitely more disagreeable and dangerous than a bullet which has not been upset.
An aeroplane armoured in all its vitals with 3 mm, steel, and otherwise designed on the lines indicated, flying at not less than 2000 ft, altitude, will be extremely difficult to bring down; so much so, that unless its exposed structural members be literally riddled and shattered by rifle and machine-gun, or unless a gun of larger calibre be brought to bear, it will be virtually impossible to effect its capture by gun-fire alone.