Aircraft in Warfare (1916)/Chapter 11

by Frederick William Lanchester

CHAPTER XI.

(November 13th, 1914).

AIRCRAFT IN THE SERVICE
OF THE NAVY.

§ 69. Naval Aircraft. Special Conditions. The position of aircraft in connection with naval warfare requires to be studied almost as an independent problem, since many of the circumstances and conditions are utterly different from those which obtain on land. Apart from differences in the constructional features which, particularly in the case of the aeroplane, are considerable, the questions which arise in the matter of attack and defence are so entirely modified, at least as affecting the primary function of the arm, as to influence fundamentally the question of armament. Thus gun-fire, except as against hostile aircraft, ceases to have any appreciable value; no gun capable of being mounted in any aeroplane or dirigible at present built, or contemplated, would be of the slightest service directed against even the smallest unit of the enemy's navy. Again, when we consider the duties of reconnaisance, we are faced with totally altered conditions. In the case of the aeroplane, so long as we are confined to bases situated on or near the coast, the area which can be reconnoitred is limited to a distance of some 300 or 400 miles (possibly 500 miles) from the coast-line, this being at present an altogether outside estimate. Since we commonly have to regard our frontier as defined by the limit of the enemy's territorial waters, it is clear that any such restriction is to be considered inadmissible. In the case of the large airship, especially the rigid type, the range or radius of action is usually taken to be considerably greater, possibly some 1,000 miles as an extreme. If we admit this (crediting the dirigible with more reliability than it has yet exhibited), we are still faced with the fact that such a machine cannot operate with safety in the presence of, or within the zone patrolled by, the enemy's aeroplanes.

§ 70. Mother-ship or Floating Base. So far as the scouting aeroplane is concerned, the obvious solution to the difficulty is the provision of a floating aeroplane base, capable of accompanying, or acting in co-operation with, the fleet on the high seas, or of acting independently if required. Various schemes in this direction have been proposed; the future appears to lie between a "mother-ship" adapted to take on board the necessary complement of aeroplanes (or "seaplanes" as they are frequently termed when fitted with floats), and to fulfil the functions of storage, transport, and supply; and a more thorough-going scheme in which the floating base takes the form of a specialised vessel with a clear deck of sufficient area to permit of machines being launched or alighting without entering the water at all. In the former scheme the normal condition is that the machines are lowered into the water from which they are required to rise, and on which, in due course, they alight; in the latter the machines are not presumed to enter the water at all, any immersion is by way of being an accident, for which eventuality, however, the machines would be adapted by being furnished with floats in addition to the ordinary landing gear. To be effective a quite special design of vessel would be necessary, with a completely clear and flush upper deck. In order to obtain the requisite area it would probably be necessary to design something comparable in dimensions to one of the largest of our existing battle-cruisers, and in particular the maximum beam possible should be provided. A closer study of this problem will be given in a later chapter.

§ 71. The Armament of the Naval Aeroplane. The Employment of Bombs. Dealing for the time being entirely with the primary function of the Aeronautical Arm in the service of the Navy, we have already pointed out that the gun, whether the machine-gun or the one-pounder, is of no value whatever. Hence, if the aeroplane or the airship is to possess any power of offence at all against the ships of the enemy, it must be sought elsewhere. A great deal has been said on the subject of bomb-dropping as a means of attack on armoured ships, but it is not as well recognised as it should be how comparatively impotent a bomb, even charged with high explosive, may be when used without "tamping" against armour-plate. It is quite true that a certain amount of mischief would be wrought by a bomb of large size if successfully dropped on to the deck of a battleship or cruiser, and the effect would certainly be more disagreeable still if the recipient were a destroyer or some still smaller craft. The effect, however, would in no degree be comparable to that of a torpedo, where the inertia of the surrounding water plays an important rôle. It would, in any case, take a vast number of hits to put a first-class battleship or cruiser out of action. Further, the difficulties of aim, as pointed out in the preceding chapter, are considerable, and with the counter-aircraft armament with which warships are now being fitted, it will not, generally speaking, be possible for an aeroplane to descend to low altitude with impunity. The dropping of bombs from an airship is a matter of somewhat less difficulty; moreover, the bombs employed may themselves be of really formidable dimensions; but here the author is of opinion that an airship will not in the future be able to approach a warship of any kind by daylight without certain destruction, and it may be little or no better off by night.

§ 72. Torpedo Attack by Air. Some experiments reported as having been made in Germany appear to indicate a direction in which aircraft may become an actual source of danger to even the most formidable battleship or cruiser. It is said that a Zeppelin has recently been fitted with means of discharging a Whitehead torpedo with complete success. We may presume that the airship is brought down close to the sea-level, and then fires the torpedo, just as is done from the deck-tube of a torpedo-boat. In view of the great range of the modern torpedo — at the present day over 2 miles — this form of attack cannot be ignored. It is evident that what is possible to the airship in this direction is also possible to the aeroplane, provided that the latter be built of sufficient carrying capacity; and whereas the airship would find it difficult to approach a battleship or cruiser within 2 miles without detection and destruction, the aeroplane would rarely find this either difficult or dangerous; the matter is mainly one of choosing the proper time and direction of attack. In the haze of the early morning, or in the dusk after sunset, an aeroplane at the distance in question is quite invisible; or again, it is frequently possible for an aeroplane to approach in broad daylight against a landscape background without being observed, especially if assisted by suitable protective colouring; much depends also upon the direction of the sun's rays. Night attack would also in many instances be possible, although the absence of light may be a greater hindrance than help to the aeronaut; added to this there is the not inconsiderable risk of being located by searchlight. The aeroplane for the duty in question will need to be somewhat larger and of greater carrying capacity than the present standard; the modern 21-in. torpedo, for example, weighs approximately 1 ton, and would require a machine of about 4 tons gross lifting power. The older model, the 18-in. weapon, weighs about 12 cwt., and would require a machine with a gross lifting-power of 2½ tons, the latter being not very much in excess of the largest machines already in service.

§ 73. Aeroplane as affected by Discharge of Torpedo. It might be thought, considering the matter superficially, that the dropping of one-quarter of the gross weight of a machine whilst in flight would be a dangerous and risky business. But closer investigation shows that this is not the case; the resulting disturbance is one which can be quite easily rectified by the pilot. In the case of the modern machine, whose flight path is stable (the dynamically-stable machine), and which is said to be—and undoubtedly is—capable of flying itself, the disturbance calculated as due to the release of the torpedo is well within the permissible limit. The only condition to be observed is that the centre of gravity of the machine shall not be thrown forward or backward by the discharge; in other words, the centre of gravity of the torpedo, as carried, must be approximately in the same vertical line as that of the machine. If this condition is complied with, the resulting disturbance, assuming the torpedo as constituting one-quarter of the gross weight, is shown by the diagram Fig. 15. The torpedo being dropped at point p₁, the path of flight p₁ p₂ becomes undulatory, the undulations dying out, as indicated in the figure, at a rate depending upon the degree of dynamic stability provided. The extent of the initial undulation is correctly represented to scale in the figure, and is the same as would be produced in a 70-mile-an-hour machine by an adverse wind gust of 10 miles per hour, a thing of everyday

Fig. 15.

Plate VIII.

"FLYING BOAT" TYPE.

Built by Messrs. White & Thompson.

Plate IX.

HYDRO-AEROPLANE H.R.E.3. R.A.F. Design for
the "Naval Wing" (Now R.N. Air Service) in 1912.

experience. The path of the torpedo is indicated by the dotted line p₁ p₂. It is even possible to diminish the disturbance still further by arranging the torpedo somewhat behind the position above assumed, so that on discharge the centre of gravity moves forward. This would in some degree compensate for the loss of weight as giving a less net change in the natural velocity. In the opinion of the author, however, it is not to be recommended, since it would result in the machine being catastrophically unstable (prior to the discharge of the torpedo), or would at least tend in that direction.

§ 74. Aeroplane and Submarine. It is well known that the submarine, although when submerged invisible to an observer or "look-out" on the deck of a warship or other vessel, is clearly visible, and may be readily located by an aeronaut from a sufficient altitude. The conditions are similar to those frequently noticed when fish in a river are seen clearly from a bridge, but are invisible from the river-bank. The torpedo-boat or destroyer when operating against the submarine is at a considerable disadvantage, inasmuch as when the latter is submerged the only visible sign of its presence is its periscope—a pole of a few inches in diameter, projecting some few feet out of the water. Ordinarily it is the point where the periscope "rips" the surface that forms the most conspicuous visible indication. Thus we may anticipate that, in the future, operations directed against the submarines of an enemy will involve the employment of aircraft, at least as a means of reconnaissance. It is an important fact that in this particular service the enemy (the submarine) has no power of offence; hence it is possible that the dirigible may prove itself as well suited to the work as the aeroplane. It is true that the modern submarine is being fitted with guns of light calibre, but these are only available after the vessel has come to

Fig. 16.

the surface. We may presume that in any operations of the description contemplated, one or more destroyers or light cruisers will accompany the aircraft scout, and the conning-tower of the submarine will be blown away within a few seconds of its appearance.

§ 75. Attack on Submarine by Aeroplane. Destruction by Bomb. It is not in any sense certain or likely that the operations of aircraft in relation to the submarine will be confined to observation. In the opinion of the author, aircraft, whether aeroplane or dirigible, will prove to be the submarine's most dangerous enemy, the submarine being attacked by bombs charged with high explosive while submerged. Owing to the absence of any danger of counter-attack the aeroplane may fly as low as deemed desirable to obtain the necessary accuracy of aim, and much of the difficulty commonly associated with bomb-dropping will accordingly vanish. Such an attack is depicted (somewhat diagrammatically) in Fig.  16, in which, for the purpose of illustration, the machine is shown as flying at a quite low altitude of about 60 ft., and when at the point A to drop a bomb, which, having the velocity of the machine in flight, describes the trajectory A B whilst the machine is travelling to the point C; the motion of the submarine in the intervening time is indicated by the dotted outline. It is not to be anticipated that in practice it will be found necessary to come down to as low an altitude as that shown in order to ensure the degree of accuracy required.

The type of bomb appropriate to the duty in question, although not greatly different from that required in connection with land service, will need a certain amount of consideration. In view of the fact that the size of the hole blown in the skin of the submarine is not important, the charge of explosive may be quite moderate; probably 10 lb, or 15 lb, of wet guncotton will be ample. A bomb of torpedo-like form, about 6 in, in diameter, and fitted with a sheet-metal cruciform tail, as shown diagrammatically in Fig. 17, would probably be found suitable; it would be furnished with a positive impact or contact fuse at its nose. The usual way of dropping a bomb of this type is broadside on, pointing in the direction of flight; the axis then remains tangent to the trajectory throughout the fall, the tail acting in the manner of the feathering of an arrow.

A bomb of the type described in the preceding paragraph will travel through water under the influence of gravity at a no inconsiderable velocity. Taking its weight to be (immersed) about half a hundredweight, its limiting velocity in water will be about 50 ft. per second,

Fig. 17.

which is ample to ensure the certain action of the contact fuse. Thus it will be impossible for a submarine to escape by deep immersion, presuming it to remain sufficiently visible to permit of attack.

§ 76. Submarine Activity as Affected by Aircraft. In brief, the aeroplane, and to some degree other aircraft, suitably armed, may be expected to prove an effective check on the unbridled activity of the submarine. With a properly-equipped naval aeroplane service, supported by a few fast, light cruisers, such as the type known as the "destroyer leader," the enemy's submarines will be unable to roam at large or to make unexpected attacks on our cruiser patrols. They will need to operate under the protection of a supporting force, and will only leave that protection at the risk of almost certain destruction. Or they will require to confine their activities to raiding by night—a form of activity in which their radius of action is essentially limited, and, save under exceptional circumstances, of doubtful promise. It must not be assumed, however, that the service necessary for the effective patrolling of the seas by aeroplane will prove at all a simple or easy matter. The provision of the needed bases, coastal and floating, alone will be a formidable matter, and as the radius of action of the submarine is increased, and the field of operations is thereby widened, the work will become more and more arduous. Again, the enemy's aircraft will always have to be reckoned with.

Thus, although the air service may be looked to to provide an effective limit to the power of the submarine, we can never expect or anticipate that the value or utility of the latter will be by any means nullified.

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