The fixed anti-aircraft guns such as are stationed upon eminences and buildings are of the quick firing type, the object being to hurl a steady, continuous stream of missiles upon the swiftly moving aeroplane. Some of the weapons throw a one-pound shell and are closely similar to the pom-pom which proved so effective during the South African war. Machine guns also have been extensively adopted for this duty by all the combatants, their range of approximately 2,000 yards and rapidity of fire being distinctly valuable when hostile aircraft descend to an altitude which brings them within the range of the weapon.

The greatest difficulty in connection with this phase of artillery, however, is not so much the evolution of a serviceable and efficient type of gun, as the determination of the type of projectile which is likely to be most effective. While shrapnel is employed somewhat extensively it has not proved completely satisfactory. It is difficult to set the timing fuse even after the range has been found approximately, which in itself is no easy matter when the aircraft is moving rapidly and irregularly, but reliance is placed thereon in the hope that the machine may happen to be within the cone of dispersion when the shell bursts, and that one or more of the pieces of projectile and bullets may chance to penetrate either the body of the airman or a vital part of the mechanism.

It is this uncertainty which has led to a preference for a direct missile such as the bullet discharged from a machine gun. A stream of missiles, even of rifle calibre, maintained at the rate of some 400 shots per minute is certain to be more effective, provided range and aim are correct, than shrapnel. But the ordinary rifle-bullet, unless the objective is within very close range, is not likely to cause much harm, at least not to the mechanism of the aerial vessel.

It is for this reason that greater attention is being devoted, especially by the French artillerists, to the Chevalier anti-aircraft gun, a weapon perfected by a Swiss technician resident in Great Britain. It projects a formidable missile which in fact is an armour-piercing bullet 1/2- to 3/4-inch in diameter. It is designed for use with an automatic machinegun, which the inventor has devised more or less upon the well-known French system. The bullet has a high velocity—about 2,500 feet per second—and a maximum range of 6,000 to 8,000 feet at the maximum elevation. Should such a missile strike the motor or other mechanism of the vessel it would wreak widespread havoc, and probably cause the machine to come to earth. This arm has been designed for the express purpose of disabling the aeroplane, and not for the subjugation of the airman, which is a minor consideration, inasmuch as he is condemned to a descent when his craft receives a mortal wound.

Attempts have been and still are being made to adapt an explosive projectile to this gun, but so far the measure of success achieved has not proved very promising. There are immense difficulties connected with the design of an explosive shell of this class, charged with a high explosive, especially in connection with the timing. So far as dependence upon percussive detonation is concerned there is practically no difficulty. Should such a missile strike, say, the motor of an aeroplane, or even the hull of the craft itself, the latter would be practically destroyed. But all things considered, it is concluded that more successful results are likely to be achieved by the armour-piercing bullet striking the mechanism than by an explosive projectile.

The Krupp company fully realised the difficulties pertaining to the projectile problem in attacks upon aerial craft. So far as dirigibles are concerned shrapnel is practically useless, inasmuch as even should the bag be riddled by the flying fragments, little effective damage would be wrought—the craft would be able to regain its haven. Accordingly efforts were concentrated upon the perfection of two new types of projectiles, both of which were directed more particularly against the dirigible. The one is the incendiary shell—obus fumigene—while the other is a shell, the contents of which, upon coming into contact with the gas contained within the gas-bag, set up certain chemical reactions which precipitate an explosion and fire.

The incendiary shells are charged with a certain compound which is ignited by means of a fuse during its flight. This fuse arrangement coincides very closely with that attached to ordinary shrapnel, inasmuch as the timing may be set to induce ignition at different periods, such as either at the moment it leaves the gun, before, or when it strikes the envelope of the dirigible. The shell is fitted with a "tracer," that is to say, upon becoming ignited it leaves a trail of smoke, corresponding with the trail of a rocket, so that its passage through the air may be followed with facility. This shell, however, was designed to fulfil a dual. Not only will it fire the gaseous contents out of the dirigible, but it has an explosive effect upon striking an incombustible portion of the aircraft, such as the machinery, propellers or car, when it will cause sufficient damage to throw the craft out of action.

The elaborate trials which were carried out with the obus fumigene certainly were spectacular so as they went. Two small spherical balloons, 10 feet in diameter, and attached to 1,000 feet of cable, were sent aloft. The anti-aircraft guns themselves were placed about 5,100 feet distant. Owing to the inclement weather the balloons were unable to attain a height of more than 200 feet in a direct vertical line above the ground. The guns were trained and fired, but the one balloon was not hit until the second round, while the third escaped injury until the fifth round. When struck they collapsed instantly. Though the test was not particularly conclusive, and afforded no reliable data, one point was ascertained—the trail of smoke emitted by the shell enabled its trajectory to be followed with ease. Upon the conclusion of these trials, which were the most successful recorded, quick-firing tests in the horizontal plane were carried out. The best performance in this instance was the discharge of five rounds in eight seconds. In this instance the paths of the projectiles were simple and easy to follow, the flight of the shell being observed until it fell some 18,670 feet away. But the Krupp firm have found that trials upon the testing ground with a captive balloon differ very materially from stern tests in the field of actual warfare. Practically nothing has been heard of the two projectiles during this war, as they have proved an absolute failure.

Some months ago the world was startled by the announcement that the leading German armament firm had acquired the whole of the interest in an aerial torpedo which had been evolved by the Swedish artillerist, Gustave Unge, and it was predicted that in the next war widespread havoc would be wrought therewith. Remarkable claims were advanced for this projectile, the foremost being that it would travel for a considerable distance through the air and alight upon the objective with infallible accuracy. The torpedo in question was subjected to exacting tests in Great Britain, which failed to substantiate all the claims which were advanced, and it is significant to observe that little has been heard of it during the present conflict. It is urged in certain technical quarters, however, that the aerial torpedo will prove to be the most successful projectile that can be used against aircraft. I shall deal with this question in a later chapter.

During the early days of the war anti-aircraft artillery appeared to be a much overrated arm. The successes placed to its credit were insignificant. This was due to the artillerymen being unfamiliar with the new arm, and the conditions which prevail when firing into space. Since actual practice became possible great advances in marksmanship have been recorded, and the accuracy of such fire to-day is striking. Fortunately the airman possesses the advantage. He can manoeuvre beyond the range of the hostile weapons. At the moment 10,000 feet represents the extreme altitude to which projectiles can be hurled from the arms of this character which are now in use, and they lack destructiveness at that range, for their velocity is virtually expended.

Picking up the range is still as difficult as ever. The practice followed by the Germans serves to indicate the Teuton thoroughness of method in attacking such problems even if success does not ensue. The favourite German principle of disposing anti-aircraft artillery is to divide the territory to be protected into equilateral triangles, the sides of which have a length of about six miles or less, according to the maximum effective range of the pieces at an elevation of 23 1/2 degrees.

The guns are disposed at the corners of the triangles as indicated in Figs. 13-14. Taking the one triangle as an example, the method of picking up the range may be explained as follows. The several guns at the comers of the triangle, each of which can be trained through the 360 degrees in the horizontal plane, are in telephonic touch with an observer O stationed some distance away. The airman A enters the area of the triangle. The observer takes the range and communicates with the gunner B, who fires his weapon. The shell bursts at 1 emitting a red flame and smoke. The observer notes the altitude and relative position of the explosion in regard to the aircraft, while gunner B himself observes whether the shell has burst to the right or to the left of the objective and corrects accordingly. The observer commands C to fire, and another shell is launched which emits a yellow flame and smoke. It bursts at 2 according to the observer, while gunner C also notes whether it is to the right or to the left of the target and corrects accordingly. Now gunner D receives the command to fire and the shell which explodes at 3 throws off a white flame and smoke. Gunner D likewise observes whether there is any deviation to right or left of the target and corrects in a similar manner. From the sum of the three rounds the observer corrects the altitude, completes his calculations, and communicates his instructions for correction to the three gunners, who now merely train their weapons for altitude. The objective is to induce the shells hurled from the three corners of the triangle to burst at a common point 4, which is considered to be the most critical spot for the aviator. The fire is then practically concentrated from the three weapons upon the apex of a triangular cone which is held to bring the machine within the danger zone.

This method of finding the range is carried out quickly—two or three seconds being occupied in the task. In the early days of the war the German anti-aircraft artillerymen proved sadly deficient in this work, but practice improved their fire to a marvellous degree, with the result that at the moment it is dangerous for an aviator to essay his task within an altitude of 6,000 feet, which is the range of the average anti-aircraft gun.

The country occupied by a belligerent is divided up in this manner into a series of triangles. For instance, a machine entering hostile territory from the east, enters the triangle A-B-C, and consequently comes within the range of the guns posted at the comers of the triangle. Directly he crosses the line B-C and enters the adjacent triangle he passes beyond the range of gun A but comes within the range of the gun posted at D, and while within the triangular area is under fire from the guns B-C-D. He turns and crosses the line A-C, but in so doing enters another triangle A-C-E, and comes range of the gun posted at E.

The accompanying diagram represents an area of country divided up into such triangle and the position of the guns, while the circle round the latter indicate the training arc of the weapons, each of which is a complete circle, in the horizontal plane. The dotted line represents the aviator's line of flight, and it will be seen that no matter how he twists and turns he is always within the danger zone while flying over hostile territory. The moment he outdistances one gun he comes within range of another.

The safety of the aviator under these circumstances depends upon his maintaining an altitude exceeding the range of the guns below, the most powerful of which have a range of 8,000 to 10,000 feet, or on speed combined with rapid twisting and turning, or erratic undulating flight, rendering it extremely difficult for the gun-layer to follow his path with sufficient celerity to ensure accurate firing.

At altitudes ranging between 4,000 and 6,000 feet the aeroplane comes within the range of rifle and machine-gun firing. The former, however, unless discharged in volleys with the shots covering a wide area, is not particularly dangerous, inasmuch as the odds are overwhelmingly against the rifleman. He is not accustomed to following and firing upon a rapidly moving objective, the result being that ninety-nine times out of a hundred he fails to register a hit. On the other hand the advantage accruing from machine-gun fire is, that owing to the continuous stream of bullets projected, there is a greater possibility of the gun being trained upon the objective and putting it hors de combat.

But, taking all things into consideration, and notwithstanding the achievements of the artillerist, the advantages are overwhelmingly on the side of the aviator. When one reflects upon the total sum of aircraft which have been brought to earth during the present campaign, it will be realised that the number of prizes is insignificant in comparison with the quantity of ammunition expended.



CHAPTER XVI. MINING THE AIR

While the anti-aircraft gun represents the only force which has been brought to the practical stage for repelling aerial attack, and incidentally is the sole offensive weapon which has established its effectiveness, many other schemes have been devised and suggested to consummate these ends. While some of these schemes are wildly fantastic, others are feasible within certain limitations, as for instance when directed against dirigibles.

It has been argued that the atmosphere is akin to the salt seas; that an aerial vessel in its particular element is confronted with dangers identical with those prevailing among the waters of the earth. But such an analogy is fallacious: there is no more similarity between the air and the ocean than there is between an airship and a man-of-war. The waters of the earth conceal from sight innumerable obstructions, such as rocks, shoals, sandbanks, and other dangers which cannot by any means be readily detected.

But no such impediments are encountered in the ether. The craft of the air is virtually a free age in the three dimensions. It can go whither it will without let or hindrance so long as the mechanical agencies of man are able to cope with the influences of Nature. It can ascend to a height which is out of all proportion to the depth to which the submarine can descend in safety. It is a matter of current knowledge that a submarine cannot sink to a depth of more than 250 feet: an aerial vessel is able to ascend to 5,000, 8,000, or even 10,000 feet above the earth, and the higher the altitude it attains the greater is its degree of safety. The limit of ascension is governed merely by the physical capacities of those who are responsible for the aerial vessel's movement.

It is for this reason that the defensive measures which are practised in the waters of the earth are inapplicable to the atmosphere. Movement by, or in, water is governed by the depth of channels, and these may be rendered impassable or dangerous to negotiate by the planting of mines. A passing ship or submarine may circumvent these explosive obstructions, but such a successful manoeuvre is generally a matter of good luck. So far as submarines are concerned the fact must not be over looked that movements in the sea are carried out under blind conditions: the navigator is unable to see where he is going; the optic faculty is rendered nugatory. Contrast the disability of the submarine with the privileges of its consort in the air. The latter is able to profit from vision. The aerial navigator is able to see every inch of his way, at least during daylight. When darkness falls he is condemned to the same helplessness as his confrere in the waters below.

A well-known British authority upon aviation suggested that advantage should be taken of this disability, and that the air should be mined during periods of darkness and fog to secure protection against aerial invasion. At first sight the proposal appears to be absolutely grotesque, but a little reflection will suffice to demonstrate its possibilities when the area to be defended is comparatively limited. The suggestion merely proposes to profit from one defect of the dirigible. The latter, when bent upon a daring expedition, naturally prefers to make a bee-line towards its objective: fuel considerations as a matter of fact compel it to do so. Consequently it is possible, within certain limits, to anticipate the route which an invading craft will follow: the course is practically as obvious as if the vessel were condemned to a narrow lane marked out by sign-posts. Moreover, if approaching under cover of night or during thick weather, it will metaphorically "hug the ground." To attempt to complete its task at a great height is to court failure, as the range of vision is necessarily so limited.

Under these circumstances the mining of the air could be carried out upon the obvious approaches to a threatened area. The mines, comprising large charges of high-explosive and combustible material, would be attached to small captive balloons similar to the "sounding balloons" which are so much used by meteorologists in operations for sounding the upper strata of the atmosphere. These pilot balloons would be captive, their thin wires being wound upon winches planted at close intervals along the coast-line. The balloon-mines themselves would be sent to varying heights, ranging from 1,000 to 5,000 feet, and with several attached to each cable, the disposition of the mines in the air in such an irregular manner being in fact closely similar to the practice adopted in the mining of a channel for protection against submarines and hostile ships.

The suggestion is that these mines should be sent aloft at dusk or upon the approach of thick and foggy weather, and should be wound in at dawn or when the atmosphere cleared, inasmuch as in fine weather the floating aerial menace would be readily detected by the pilot of a dirigible, and would be carefully avoided. If the network were sufficiently intricate it would not be easy for an airship travelling at night or in foggy weather to steer clear of danger, for the wires holding the balloons captive would be difficult to distinguish.

The mines would depend upon detonators to complete their work, and here again they would bear a close resemblance to sea-mines. By looping the mines their deadliness could be increased. The unsuspicious airship, advancing under cover of darkness or thick weather, might foul one of the wires, and, driving forward, would tend to pull one or more mines against itself. Under the force of the impact, no matter how gentle, or slight, one or more of the detonating levers would be moved, causing the mine to explode, thus bursting the lifting bag of the vessel, and firing its gaseous contents. An alternative method, especially when a cable carried only a single mine, would be to wind in the captive balloon directly the wire was fouled by an invading aerial craft, the process being continued until the mine was brought against the vessel and thereby detonated.

Another proposed mining method differs materially in its application. In this instance it is suggested that the mines should be sent aloft, but should not be of the contact type, and should not be fired by impact detonators, but that dependence should be placed rather upon the disturbing forces of a severe concussion in the air. The mines would be floating aloft, and the advance of the airship would be detected. The elevation of the mines in the vicinity of the invading craft would be known, while the altitude of the airship in relation thereto could be calculated. Then, it is proposed that a mine within d certain radius of the approaching craft, and, of course, below it, should be fired electrically from the ground. It is maintained that if the charge were sufficiently heavy and an adequate sheet of flame were produced as a result of the ignition, an airship within a hundred yards thereof would be imperilled seriously, while the other mines would also be fired, communicating ignition from one to the other. The equilibrium of the airship is so delicate that it can be readily upset, and taking into account the facts that gas is always exuding from the bag, and that hydrogen has a tendency to spread somewhat in the manner of oil upon water, it is argued that the gas would be ignited, and would bring about the explosion of the airship.

Another method has even been advocated. It is averred in authoritative circles that when the aerial invasion in force of Great Britain is attempted, the Zeppelins will advance under the cover of clouds. Also that the craft will make for one objective—London. Doubtless advantage will be taken of clouds, inasmuch as they will extend a measure of protection to the craft, and will probably enable the invading fleet to elude the vigilance of the aeroplane scouts and patrols. Under these circumstances it is suggested that balloon-mines should be sent aloft and be concealed in the clouds. It would be impossible to detect the wires holding them captive, so that the precise location of the lurking danger would not be divined by the invader. Of course, the chances are that the invading airship would unconsciously miss the mines; on the other hand the possibilities are equally great that it would blunder into one of these traps and be blown to atoms.

An English airman has recently suggested a means of mining invading Zeppelins which differs completely from the foregoing proposals. His idea is that aeroplanes should be equipped with small mines of the contact type, charged with high explosives, and that the latter should be lowered from the aeroplane and be trawled through the atmosphere. As an illustration I will suppose that a hostile aircraft is sighted by a patrolling aeroplane. The pilot's companion in the latter immediately prepares his aerial mine, fixing the detonator, and attaching the mine to the wire. The latter is then dropped overboard, the wire being paid out from a winch until it has descended to the level of the hostile craft. The airman now manoeuvres in the air circling about the airship, dragging his mine behind him, and endeavouring to throw it across or to bring it into contact with the airship below. Naturally the latter, directly it observed the airman's object, would endeavour to elude the pursuing trawling mine, either by crowding on speed or by rising to a greater altitude. The aeroplane, however, would have the advantage both in point of speed and powers of climbing, while there is no doubt that the sight of the mine swinging in the air would exert a decisive moral effect upon those in the airship.

Attempts to render the mine harmless by discharging it prematurely with the aid of rifle and machine-gun fire would, of course, be made by the crew of the airship, but the trawling mine would prove a very difficult target to strike. If such a missile were used against an airship of the proportions of a Zeppelin the mine would inevitably be trawled across the vessel sooner or later. Once the airship had been fouled, the aviator would merely have to drive ahead, dragging the wire and its charge across the gas-bag until at last one of the contact levers of the mine was moved by being dragged against some part of the vessel, when the mine would be exploded. In such operations the aviator would run a certain risk, as he would be more or less above the airship, and to a certain degree within the zone of the ultimate explosion. But there is no doubt that he would succeed in his "fishing" exploit within a very short time.

This ingenious scheme has already been tested upon a small scale and has been found effective, the trawling bomb being drawn across its target and fired by contact within a few minutes. The experiment seems to prove that it would be simpler and more effectual to attack a hostile aircraft such as a Zeppelin in this manner than to drop free bombs at random. Moreover, we cannot doubt that the sight of a mine containing even ten or twelve pounds of high explosive dangling at the end of a wire would precipitate a retreat on the part of an airship more speedily than any other combative expedient.

The advocate of this mine-trawling method, who is a well-known aviator, anticipates no difficulty in manoeuvring a mine weighing 30 pounds at the end of 300 feet of fine wire. Success depends in a great measure on the skill of the aviator in maintaining a constant tension upon the line until it falls across its objective.

The process calls for a certain manifestation of skill in manoeuvring the aeroplane in relation to the airship, judgment of distance, and ability to operate the aeroplane speedily. The rapid ascensional capability of the airship, as compared with that of the aeroplane, is a disadvantage, but on the other hand, the superior mobility and speed of the aeroplane would tell decisively for success.

Among the many wonders which the Krupp organisation is stated to have perfected, and which it is claimed will create considerable surprise, is the aerial torpedo. Many of the Krupp claims are wildly chimerical, as events have already proved, but there is no doubt that considerable effort has been expended upon this latest missile, for which the firm is said to have paid the inventor upwards of L25,000—$125,000. Curiously enough the projectile was perfected within gunshot of the British aerodrome of Hendon and is stated to have been offered to the British Government at the time, and to have met with a chilling reception. One fact, however, is well established. The inventor went to Germany, and submitted his idea to Krupp, by whom it was tested without delay. Upon the completion of the purchase, the great armament manufacturers did not fail to publish broadcast the fact that they had acquired a mysterious new terror of the skies. That was some three years ago, and in the interval the cleverest brains of the German firm have been steadily devoting their time and energies to the improvement of the missile, the first appearance of which was recorded, in a somewhat hazy manner, in the closing days of December.

While the exact mechanism of this missile is a secret, the governing principles of its design and operation are known to a select few technicians in this country. Strange to say, the projectile was designed in the first instance in the interests of peace and humanity, but while engaged upon his experiments the inventor suddenly concluded that it would be a more profitable asset if devoted to the grim game of war. At the time the military significance of the airship and the aeroplane were becoming apparent; hence the sudden diversion of the idea into a destructive channel.

This aerial torpedo is a small missile carrying a charge of high explosive, such as trinitrotoluene, and depends for its detonation upon impact or a time fuse. It is launched into the air from a cradle in the manner of the ordinary torpedo, but the initial velocity is low. The torpedo is fitted with its own motive power, which comes automatically into action as the missile climbs into the air. This self-contained energy is so devised that the maximum power is attained before the missile has lost the velocity imparted in the first instance, the result being that it is able to continue its flight in a horizontal direction from the moment it attains the highest point in its trajectory, which is naturally varied according to requirements. But there is no secret about the means of propulsion. The body is charged with a slow-burning combustible, in the manner of the ordinary rocket, whereby it is given a rapid rotary motion.

Furthermore it is stated to be fitted with a small gyroscope in the manner of the torpedo used in the seas, for the purpose of maintaining direction during flight, but upon this point there is considerable divergence of opinion among technicians, the general idea being that the torpedo depends upon an application of the principle of the ordinary rocket rather than upon a small engine such as is fitted to the ordinary torpedo. The employment of a slow combustible ensures the maintenance of the missile in the air for a period exceeding that of the ordinary shell. It is claimed by the Germans that this projectile will keep aloft for half-an-hour or more, but this is a phantasy. Its maintenance of flight is merely a matter of minutes.

The belated appearance of this much-lauded projectile and its restricted use suggest that it is unreliable, and perhaps no more effective than the aerial torpedo which appeared in the United States during the Spanish-American War, and proved a complete failure. An effective and reliable means of combating or frustrating a dirigible attack, other than by gun-fire or resort to the drastic remedy of ramming the enemy, has yet to be devised.



CHAPTER XVII. WIRELESS IN AVIATION

In a previous chapter the various methods of signalling between the ground and the airman aloft have been described. Seeing that wireless telegraphy has made such enormous strides and has advanced to such a degree of perfection, one naturally would conclude that it constitutes an ideal system of communication under such conditions in military operations.

But this is not the case. Wireless is utilised only to a very limited extent. This is due to two causes. The one is of a technical, the other of a strategical character.

The uninitiated, bearing in mind the comparative ease with which wireless installations may be established at a relatively small expense, would not unreasonably think that no serious difficulties of a technical character could arise: at least none which would defy solution. But these difficulties exist in two or three different fields, each of which is peculiarly complex and demands individual treatment.

In the first place, there is the weight of the necessary installation. In the case of the dirigible this may be a secondary consideration, but with the aeroplane it is a matter of primary and vital importance. Again, under present conditions, the noise of the motor is apt to render the intelligent deciphering of messages while aloft a matter of extreme difficulty, especially as these are communicated in code. The engine noise might be effectively overcome by the use of a muffler such as, is used with automobiles, but then there is the further difficulty of vibration.

This problem is being attacked in an ingenious manner. It is proposed to substitute for audible signals visual interpretations, by the aid of an electric lamp, the fluctuations in which would correspond to the dots and dashes of the Morse code. Thus the airman would read his messages by sight instead of by sound.

This method, however, is quite in its infancy, and although attractive in theory and fascinating as a laboratory experiment or when conducted under experimental conditions, it has not proved reliable or effective in aeronautical operations. But at the same time it indicates a promising line of research and development.

Then there are the problems of weight and the aerial. So far as present knowledge goes, the most satisfactory form of aerial yet exploited is that known as the trailing wire. From 300 to 700 feet of wire are coiled upon a reel, and when aloft this wire is paid out so that it hangs below the aeroplane. As a matter of fact, when the machine is travelling at high speed it trails horizontally astern, but this is immaterial. One investigator, who strongly disapproves of the trailing aerial, has carried out experiments with a network of wires laid upon and attached to the surface of the aeroplane's wings. But the trailing wire is generally preferred, and certainly up to the present has proved more satisfactory.

The greatest obstacle, however, is the necessary apparatus. The average aeroplane designed for military duty is already loaded to the maximum. As a rule it carries the pilot and an observer, and invariably includes a light arm for defence against an aerial enemy, together with an adequate supply of ammunition, while unless short sharp flights are to be made, the fuel supply represents an appreciable load. Under these circumstances the item of weight is a vital consideration. It must be kept within a limit of 100 pounds, and the less the equipment weighs the more satisfactory it is likely to prove, other things being equal.

The two most successful systems yet exploited are the Dubilier and the Rouget. The former is an American invention, the latter is of French origin. Both have been tested by the British Military Aeronautical Department, and the French authorities have subjected the French system to rigorous trials. Both systems, within their limitations, have proved satisfactory.

The outstanding feature of the Dubilier system is the production of sine waves of musical frequency from continuous current, thus dispensing with the rotary converter. The operating principle is the obtaining of a series of unidirectional impulses by a condenser discharge, the pulsating currents following one another at regular intervals at a frequency of 500 impulses per second, which may be augmented up to 1,000 impulses per second. The complete weight of such an apparatus is 40 pounds; the electric generator, which is no larger than the motor used for driving the ordinary table ventilating fan, accounts for 16 pounds of this total. Under test at sea, upon the deck of a ship, a range of 250 miles has been obtained. The British Government carried out a series of experiments with this system, using a small plant weighing about 30 pounds, with which communication was maintained up to about 20 miles.

In the French system the Reuget transmitter is employed. The apparatus, including the dynamo, which is extremely small, weighs in all 70 pounds. A small alternator of 200 watts and 100 volts is coupled direct to the aeroplane motor, a new clutch coupler being employed for this purpose. By means of a small transformer the voltage is raised to 30,000 volts, at which the condenser is charged. In this instance the musical spark method is employed.

The whole of the high tension wiring is placed within a small space so as not to endanger the pilot, while the transformer is hermetically sealed in a box with paraffin. The aerial comprises a trailing wire 100 feet in length, which, however, can be wound in upon its reel within 15 seconds. This reeled antenna, moreover, is fitted with a safety device whereby the wire can be cut adrift in the event of an accident befalling the aeroplane and necessitating an abrupt descent. With this apparatus the French authorities have been able to maintain communication over a distance of 30 miles.

In maintaining ethereal communication with aeroplanes, however, a portable or mobile station upon the ground is requisite, and this station must be within the radius of the aerial transmitter, if messages are to be received from aloft with any degree of accuracy and reliability. Thus it will be recognised that the land station is as important as the aeroplane equipment, and demands similar consideration.

A wide variety of systems have been employed to meet these conditions. There is the travelling automobile station, in which the installation is mounted upon a motor-car. In this instance the whole equipment is carried upon a single vehicle, while the antenna is stowed upon the roof and can be raised or lowered within a few seconds. If motor traction is unavailable, then animal haulage may be employed, but in this instance the installation is divided between two vehicles, one carrying the transmitting and receiving apparatus and the generating plant, the other the fuel supplies and the aerial, together with spare parts.

The motive power is supplied by a small air cooled petrol or gasoline motor developing eight horse-power, and coupled direct to a 2-kilo watt alternator. At one end of the shaft of the latter the disk discharger is mounted, its function being to break up the train of waves into groups of waves, so as to impart a musical sound to the note produced in the receiver. A flexible cable transmits the electric current from the generator to the wagon containing the instruments. The aerial is built up of masts carried in sections.

The Germans employ a mobile apparatus which is very similar, but in this instance the mast is telescopic. When closed it occupies but little space. By turning the winch handle the mast is extended, and can be carried to any height up to a maximum of about 100 feet. The capacity of these mobile stations varies within wide limits, the range of the largest and most powerful installations being about 200 miles. The disadvantage of these systems, however, is that they are condemned to territories where the ground at the utmost is gently undulating, and where there are roads on which four-wheeled vehicles can travel.

For operation in hilly districts, where only trails are to be found, the Marconi Company, has perfected what may be described as "pack" and "knapsack" installations respectively. In the first named the whole of the installation is mounted upon the backs of four horses. The first carries the generator set, the second the transmitting instruments, the third the receiving equipment, and the fourth the detachable mast and stays.

The generator is carried upon the horse's saddle, and is fitted with a pair of legs on each side. On one side of the saddle is mounted a small highspeed explosion motor, while on the opposite side, in axial alignment with the motor, is a small dynamo. When it is desired to erect the installation the saddle carrying this set is removed from the horse's back and placed upon the ground, the legs acting as the support. A length of shaft is then slipped into sockets at the inner ends of the motor and dynamo shafts respectively, thus coupling them directly, while the current is transmitted through a short length of flexible cable to the instruments. The mast itself is made in lengths of about four feet, which are slipped together in the manner of the sections of a fishing rod, and erected, being supported by means of wire guys. In this manner an antenna from 40 to 50 feet in height may be obtained.

The feature of this set is its compactness, the equal division of the sections of the installation, and the celerity with which the station may be set up and dismantled in extremely mountainous country such as the Vosges, where it is even difficult for a pack-horse to climb to commanding or suitable positions, there is still another set which has been perfected by the Marconi Company. This is the "knapsack" set, in which the whole of the installation, necessarily light, small, and compact, is divided among four men, and carried in the manner of knapsacks upon their backs. Although necessarily of limited radius, such an installation is adequate for communication within the restricted range of air-craft.

Greater difficulties have to be overcome in the mounting of a wireless installation upon a dirigible. When the Zeppelin was finally accepted by the German Government, the military authorities emphasised the great part which wireless telegraphy was destined to play in connection with such craft. But have these anticipations been fulfilled? By no means, as a little reflection will suffice to prove.

In the first place, a wireless outfit is about the most dangerous piece of equipment which could be carried by such a craft as the Zeppelin unless it is exceptionally well protected. As is well known the rigidity of this type of airship is dependent upon a large and complicated network of aluminium, which constitutes the frame. Such a huge mass of metal constitutes an excellent collector of electricity from the atmosphere; it becomes charged to the maximum with electricity.

In this manner a formidable contributory source of danger to the airship is formed. In fact, this was the reason why "Z-IV" vanished suddenly in smoke and flame upon falling foul of the branches of trees during its descent. At the time the Zeppelin was a highly charged electrical machine or battery as it were, insulated by the surrounding air. Directly the airship touched the trees a short circuit was established, and the resultant spark sufficed to fire the gas, which is continuously exuding from the gas bags.

After this accident minute calculations were made and it was ascertained that a potential difference of no less than 100,00 volts existed between the framework of the dirigible and the trees. This tension sufficed to produce a spark 4 inches in length. It is not surprising that the establishment of the electric equilibrium by contact with the trees, which produced such a spark should fire the hydrogen inflation charge. In fact the heat generated was so intense that the aluminium metallic framework was fused. The measurements which were made proved that the gas was consumed within 15 seconds and the envelope destroyed within 20 seconds.

As a result of this disaster endeavours were made to persuade Count Zeppelin to abandon the use of aluminium for the framework of his balloon but they were fruitless, a result no doubt due to the fact that the inventor of the airship of this name has but a superficial knowledge of the various sciences which bear upon aeronautics, and fully illustrates the truth of the old adage that "a little learning is a dangerous thing." Count Zeppelin continues to work upon his original lines, but the danger of his system of construction was not lost upon another German investigator, Professor Schiitte, who forthwith embarked upon the construction of another rigid system, similar to that of Zeppelin, at Lanz. In this vessel aluminium was completely abandoned in favour of a framework of ash and poplar.

The fact that the aluminium constituted a dangerous collector of electricity rendered the installation of wireless upon the Zeppelin not only perilous but difficult. Very serious disturbances of an electrical nature were set up, with the result that wireless communication between the travelling dirigible and the ground below was rendered extremely uncertain. In fact, it has never yet been possible to communicate over distances exceeding about 150 miles. Apart from this defect, the danger of operating the wireless is obvious, and it is generally believed in technical circles that the majority of the Zeppelin disasters from fire have been directly attributable to this, especially those disasters which have occurred when the vessel has suddenly exploded before coming into contact with terrestrial obstructions.

In the later vessels of this type the wireless installation is housed in a well insulated compartment. This insulation has been carried, to an extreme degree, which indicates that at last the authorities have recognised the serious menace that wireless offers to the safety of the craft, with the result that every protective device to avoid disaster from this cause has been freely adopted.

The fact that it is not possible to maintain communication over a distance exceeding some 20 miles is a severe handicap to the progressive development of wireless telegraphy in this field. It is a totally inadequate radius when the operations of the present war are borne in mind. A round journey of 200, or even more miles is considered a mere jaunt; it is the long distance flight which counts, and which contributes to the value of an airman's observations. The general impression is that the fighting line or zone comprises merely two or three successive stretches of trenches and other defences, representing a belt five miles or so in width, but this is a fallacy. The fighting zone is at least 20 miles in width; that is to say, the occupied territory in which vital movements take place represents a distance of 20 miles from the foremost line of trenches to the extreme rear, and then comes the secondary zone, which may be a further 10 miles or more in depth. Consequently the airman must fly at least 30 miles in a bee-line to cover the transverse belt of the enemy's field of operations. Upon the German and Russian sides this zone is of far greater depth, ranging up to 50 miles or so in width. In these circumstances the difficulties of ethereal communication 'twixt air and earth may be realised under the present limitations of radius from which it is possible to transmit.

But there are reasons still more cogent to explain why wireless telegraphy has not been used upon a more extensive scale during the present campaign. Wireless communication is not secretive. In other words, its messages may be picked up by friend and foe alike with equal facility. True, the messages are sent in code, which may be unintelligible to the enemy. In this event the opponent endeavours to render the communications undecipherable to one and all by what is known as "jambing." That is to say, he sends out an aimless string of signals for the purpose of confusing senders and receivers, and this is continued without cessation and at a rapid rate. The result is that messages become blurred and undecipherable.

But there is another danger attending the use of wireless upon the battlefield. The fact that the stations are of limited range is well known to the opposing forces, and they are equally well aware of the fact that aerial craft cannot communicate over long distances. For instance, A sends his airmen aloft and conversation begins between the clouds and the ground. Presently the receivers of B begin to record faint signals. They fluctuate in intensity, but within a few seconds B gathers that an aeroplane is aloft and communicating with its base. By the aid of the field telephone B gets into touch with his whole string of wireless stations and orders a keen look-out and a listening ear to ascertain whether they have heard the same signals. Some report that the signals are quite distinct and growing louder, while others declare that the signals are growing fainter and intermittent. In this manner B is able to deduce in which direction the aeroplane is flying. Thus if those to the east report that signals are growing stronger, while the stations on the west state that they are diminishing, it is obvious that the aeroplane is flying west to east, and vice versa when the west hears more plainly at the expense of the east. If, however, both should report that signals are growing stronger, then it is obvious that the aircraft is advancing directly towards them.

It was this ability to deduce direction from the sound of the signals which led to the location of the Zeppelin which came down at Luneville some months previous to the war, and which threatened to develop into a diplomatic incident of serious importance. The French wireless stations running south-east to north-west were vigilant, and the outer station on the north-west side picked up the Zeppelin's conversation. It maintained a discreet silence, but communicated by telephone to its colleagues behind.

Presently No. 2 station came within range, followed by Nos. 3, 4, 5, 6, and so on in turn. Thus the track of the Zeppelin was dogged silently through the air by its wireless conversation as easily and as positively as if its flight had been followed by the naked eye. The Zeppelin travellers were quite ignorant of this action upon the part of the French and were surprised when they were rounded-up to learn that they had been tracked so ruthlessly. Every message which the wireless of the Zeppelin had transmitted had been received and filed by the French.

Under these circumstances it is doubtful whether wireless telegraphy between aircraft and the forces beneath will be adopted extensively during the present campaign. Of course, should some radical improvement be perfected, whereby communication may be rendered absolutely secretive, while no intimation is conveyed to the enemy that ethereal conversation is in progress, then the whole situation will be changed, and there may be remarkable developments.



CHAPTER XVIII. AIRCRAFT AND NAVAL OPERATIONS

When once the flying machine had indicated its possibilities in connection with land operations it was only natural that endeavours should be made to adapt it to the more rigorous requirements of the naval service. But the conditions are so vastly dissimilar that only a meagre measure of success has been recorded. Bomb-throwing from aloft upon the decks of battleships appeals vividly to the popular imagination, and the widespread destruction which may be caused by dropping such an agent down the funnel of a vessel into the boiler-room is a favourite theme among writers of fiction and artists. But hitting such an objective while it is tearing at high speed through the water, from a height of several thousand feet is a vastly different task from throwing sticks and balls at an Aunt Sally on terra firma: the target is so small and elusive.

Practically it is impossible to employ the flying machine, whether it be a dirigible or an aeroplane, in this field. Many factors militate against such an application. In the first place there is a very wide difference between dry land and a stretch of water as an area over which to manoeuvre. So far as the land is concerned descent is practicable at any time and almost anywhere. But an attempt to descend upon the open sea even when the latter is as calm as the proverbial mill-pond is fraught with considerable danger. The air-currents immediately above the water differ radically from those prevailing above the surface of the land. Solar radiation also plays a very vital part. In fact the dirigible dare not venture to make such a landing even if it be provided with floats. The chances are a thousand to one that the cars will become water-logged, rendering re-ascent a matter of extreme difficulty, if not absolutely impossible. On the other hand, the aeroplane when equipped with floats, is able to alight upon the water, and to rest thereon for a time. It may even take in a new supply of fuel if the elements be propitious, and may be able to re-ascend, but the occasions are rare when such operations can be carried out successfully.

In operations over water the airman is confronted with one serious danger—the risk of losing his bearings and his way. For instance, many attempts have been made to cross the North Sea by aeroplane, but only one has proved successful so far. The intrepid aviator did succeed in passing from the shore of Britain to the coast of Scandinavia. Many people suppose that because an airman is equipped with a compass he must be able to find his way, but this is a fallacy. The aviator is in the same plight as a mariner who is compelled from circumstances to rely upon his compass alone, and who is debarred by inclement weather from deciding his precise position by taking the sun. A ship ploughing the waters has to contend against the action of cross currents, the speed of which varies considerably, as well as adverse winds. Unless absolute correction for these influences can be made the ship will wander considerably from its course. The airman is placed in a worse position. He has no means of determining the direction and velocity of the currents prevailing in the atmosphere, and his compass cannot give him any help in this connection, because it merely indicates direction.

Unless the airman has some means of determining his position, such as landmarks, he fails to realise the fact that he is drifting, or, even if he becomes aware of this fact, it is by no means a simple straightforward matter for him to make adequate allowance for the factor. Side-drift is the aviator's greatest enemy. It cannot be determined with any degree of accuracy. If the compass were an infallible guide the airman would be able to complete a given journey in dense fog just as easily as in clear weather. It is the action of the cross currents and the unconscious drift which render movement in the air during fog as impracticable with safety as manoeuvring through the water under similar conditions. More than one bold and skilful aviator has essayed the crossing of the English Channel and, being overtaken by fog, has failed to make the opposite coast. His compass has given him the proper direction, but the side-drift has proved his undoing, with the result that he has missed his objective.

The fickle character of the winds over the water, especially over such expanses as the North Sea, constitutes another and seriously adverse factor. Storms, squalls, gales, and, in winter, blizzards, spring up with magical suddenness, and are so severe that no aircraft could hope to live in them. But such visitations are more to be dreaded by the lighter-than-air than by the heavier-than-air machines. The former offers a considerable area of resistance to the tempest and is caught up by the whirlwind before the pilot fully grasps the significant chance of the natural phenomenon. Once a dirigible is swept out of the hands of its pilot its doom is sealed.

On the other hand, the speed attainable by the aeroplane constitutes its safety. It can run before the wind, and meantime can climb steadily and rapidly to a higher altitude, until at last it enters a contrary wind or even a tolerably quiescent atmosphere. Even if it encounters the tempest head on there is no immediate danger if the aviator keep cool. This fact has been established times out of number and the airman has been sufficiently skilful and quick-witted to succeed in frustrating the destructive tactics of his natural enemy.

Only a short while ago in France, British airmen who went aloft in a gale found the latter too strong for them. Although the machine was driven full speed ahead it was forced backwards at the rate of 10 miles per hour because the independent speed of the aeroplane was less than the velocity of the wind. But a dirigible has never succeeded in weathering a gale; its bulk, area, and weight, combined with its relatively slow movement, are against it, with the result that it is hurled to destruction. All things considered, the dirigible is regarded as an impracticable acquisition to a fleet, except in the eyes of the Germans, who have been induced to place implicit reliance upon their monsters. The gullible Teuton public confidently believes that their Dreadnoughts of the air will complete the destruction of the British fleet, but responsible persons know full well that they will not play such a part, but must be reserved for scouting. Hitherto, in naval operations, mosquito water-craft, such as torpedo-boats, have been employed in this service. But these swift vessels suffer from one serious disability. The range of vision is necessarily limited, and a slight mist hanging over the water blinds them; the enemy may even pass within half-a-mile of them and escape detection.

The Zeppelin from its position 1,000 feet or more above the water, in clear weather, has a tremendous range of vision; the horizon is about 40 miles distant, as compared with approximately 8 miles in the case of the torpedo-boat. Of course an object, such as a battleship, may be detected at a far greater range. Consequently the German naval programme is to send the Zeppelin a certain distance ahead of the battleship squadron. The dirigible from its coign of vantage would be able to sight a hostile squadron if it were within visual range and would communicate the fact to the commander of the fleet below. The latter would decide his course according to information received; thus he would be enabled to elude his enemy, or, if the tidings received from the aerial scout should be favourable, to dispose his vessels in the most favourable array for attack.

The German code of naval tactics does not foreshadow the use of dirigible aircraft as vessels of attack. Scouting is the primary and indeed the only useful duty of the dirigible, although it is quite possible that the aerial craft might participate in a subsequent naval engagement, as, indeed, has been the case. Its participation, however, would be governed entirely by climatic conditions. The fact that the dirigible is a weak unit of attack in naval operations is fully appreciated by all the belligerents.

The picture of a sky "black with Zeppelins" may appeal to the popular imagination, and may induce the uninitiated to cherish the belief that such an array would strike terror into the hearts of the foe, but the naval authorities are well aware that no material advantage would accrue from such a force. In the first place they would constitute an ideal target for the enemy's vessels. They would be compelled to draw within range in order to render their own attack effective, and promiscuous shooting from below would probably achieve the desired end. One or more of the hostile aircraft would be hit within a short while. Such disasters would undoubtedly throw the aerial fleet into confusion, and possibly might interfere with the tactical developments of its own friends upon the water below.

The shells hurled from the Zeppelins would probably inflict but little damage upon the warships beneath. Let it be conceded that they weigh about 500 pounds, which is two-thirds of the weight of the projectile hurled from the Krupp 128-centimetre howitzer. Such a missile would have but little destructive effect if dropped from a height of 1,000 feet. To achieve a result commensurate with that of the 28-centimetre howitzer the airship would have to launch the missile from a height of about 7,000 feet. To take aim from such an altitude is impossible, especially at a rapidly moving target such as a battle-cruiser.

The fact must not be forgotten that Count Zeppelin himself has expressed the opinion, the result of careful and prolonged experiments, that his craft is practically useless at a height exceeding 5,000 feet. Another point must not be overlooked. In a spirited naval engagement the combatants would speedily be obliterated from the view of those aloft by the thick pall of smoke—the combination of gun-fire and emission from the furnaces and a blind attack would be just as likely to damage friend as foe.

Even if the aircraft ventured to descend as low as 5,000 feet it would be faced with another adverse influence. The discharge of the heavy battleship guns would bring about such an agitation of the air above as to imperil the delicate equilibrium of an airship. Nor must one overlook the circumstance that in such an engagement the Zeppelins would become the prey of hostile aeroplanes. The latter, being swifter and nimbler, would harry the cumbersome and slow-moving dirigible in the manner of a dog baiting a bear to such a degree that the dirigible would be compelled to sheer off to secure its own safety. Desperate bravery and grim determination may be magnificent physical attributes, ut they would have to be superhuman to face the stinging recurrent attacks of mosquito-aeroplanes.

The limitations of the Zeppelin, and in fact of all dirigible aircraft, were emphasised upon the occasion of the British aerial raid upon Cuxhaven. Two Zeppelins bravely put out to overwhelm the cruisers and torpedo boats which accompanied and supported the British sea-planes, but when confronted with well-placed firing from the guns of the vessels below they quickly decided that discretion was the better part of valour and drew off. In naval operations the aeroplane is a far more formidable foe, although here again there are many limitations. The first and most serious is the severely limited radius of action. The aeroplane motor is a hungry engine, while the fuel capacity of the tank is restricted. The German military authorities speedily realised the significance of this factor and its bearing upon useful operations, and forth with carried out elaborate endurance tests. In numerable flights were made with the express purpose of determining how long a machine could remain in the air upon a single fuel supply.

The results of these flights were collated and the achievements of each machine in this direction carefully analysed, a mean average drawn up, and then pigeon-holed. The results were kept secret, only the more sensational records being published to the world. As the policy of standardisation in the construction of aeroplanes was adopted the radius of action of each type became established. It is true that variations of this factor even among vessels exactly similar in every respect are inevitable, but it was possible to establish a reliable mean average for general guidance.

The archives of the Berlin military department are crowded with facts and figures relating to this particular essential, so that the radius of action, that is the mileage upon a single fuel charge, of any class and type of machine may be ascertained in a moment. The consequence is that the military authorities are able to decide the type of aeroplane which is best suited to a certain projected task. According to the dossier in the pigeon-hole, wherein the results of the type are filed, the aeroplane will be able to go so far, and upon arriving at that point will be able to accomplish so much work, and then be able to return home. Consequently it is dispatched upon the especial duty without any feeling of uncertainty.

Unfortunately, these experimental processes were too methodical to prove reliable. The endurance data were prepared from tests carried out in the aerodrome and from cross-country trials accomplished under ideal or fair-weather conditions. The result is that calculations have been often upset somewhat rudely by weather conditions of a totally unexpected character, which bring home vividly the striking difference between theory and practice.

The British and French aviation authorities have not adopted such methodical standardisation or rule of thumb inferences, but rather have fostered individual enterprise and initiative. This stimulation of research has been responsible for the creation of a type of aeroplane specially adapted to naval service, and generically known as the water plane, the outstanding point of difference from the aeroplane being the substitution of canoes or floats for the wheeled chassis peculiar to the land machine. The flier is sturdily built, while the floats are sufficiently substantial to support the craft upon the water in calm weather. Perhaps it was the insular situation of the British nation which was responsible for this trend of development, because so far as Britain is concerned the sea-going aeroplane is in dispensable. But the salient fact remains that to-day the waterplane service of Great Britain is the most efficient in the world, the craft being speedy, designed and built to meet the rough weather conditions which are experienced around these islands, and ideal vessels for patrol and raiding duties.

So far as the British practice is concerned the waterplane is designed to operate in conjunction with, and not apart from, the Navy. It has been made the eyes of the Navy in the strictest interpretation of the term. In any such combination the great difficulty is the establishment of what may be termed a mobile base, inasmuch as the waterplane must move with the fleet. This end has been achieved by the evolution of a means of carrying a waterplane upon, and launching it from, a battleship, if necessary.

For this purpose a docking cradle or way has been provided aft where the aeroplane may be housed until the moment arrives for its employment. Several vessels have been devoted to this nursing duty and are known as parent ships to the waterplane service. All that is requisite when the time arrives for the use of the seaplane is to lift it bodily by derrick or crane from its cradle and to lower it upon the water. It will be remembered that the American naval authorities made an experiment with a scheme for directly launching the warplane from the deck of a battleship in the orthodox, as well as offering it a spot upon which to alight upon returning from a flight, while Wing-Commander Samson, R.N., D.S.O., the famous British airman, repeated the experiment by flying from a similar launching way installed upon H.M.S. Hibernia. But this practice has many shortcomings. So far as the British and French navies are concerned, the former process is preferred. Again, when the waterplane returns from a flight it is admitted that it is simpler, quicker, and safer for it to settle upon the water near the parent ship and to be lifted on board.

As a sea-scout the waterplane is overwhelmingly superior to the dirigible as events have conclusively proved. Its greater mobility and speed stand it in excellent stead because it is able to cover a larger area within a shorter space of time than its huge and unwieldy contemporary. Furthermore, it is a difficult target to hit and accordingly is not so likely to be brought down by hostile fire. There is another point in its favour. The experience of the war has proved that the numerically inferior enemy prefers to carry out his naval operations under the cover of the mist and haze which settle upon the water, and yet are of sufficient depth to conceal his identity and composition. Such mists as a rule comprise a relatively thin bank of low-lying vapour, which while enveloping the surface of the water in an impenetrable pall, yet permits the mast-heads of the vessels to stand out clearly, although they cannot be detected from the water-level or even from the control and fighting tops of a warship. A scouting waterplane, however, is able to observe them and note their movement, and accordingly can collect useful information concerning the apparent composition of the hidden force, the course it is following, its travelling speed, and so forth, which it can convey immediately to its friends.

The aeroplane has established its value in another manner. Coal-burning vessels when moving at any pronounced speed invariably throw off large quantities of smoke, which may be detected easily from above, even when the vessels themselves are completely hidden in the mist. It was this circumstance which revealed the presence of the British squadron in the affair of the Bight of Heligoland.

The German airman on patrol duty from the adjacent base on the island of Heligoland detected the presence of this smoke, above the low-lying bank of fog, although there were no other visible signs of any vessels. Fully cognisant of the fact that the German Fleet was at anchor in a safe place he naturally divined that the smoke proceeded from a hostile squadron, evidently bent upon a raid. He returned to his headquarters, conveyed the intelligence he had collected to his superior officers, upon receipt of which a German cruiser squadron was sent out and engaged the British vessels to its own discomfiture. But for the airman's vigilance and smartness there is no doubt that the British squadron would have accomplished a great coup.

This incident, however, served to reveal that the aerial scout is prone to suffer from over-keenness and to collect only a partial amount of information. Upon this occasion the German watchman detected the presence of the British torpedo-boat and light cruiser force. Had he continued his investigations and made a wider sweep he would have discovered the proximity of the British battle-cruiser squadron which routed the German force, the latter having acted on incomplete information.

While the low-lying sea-fog is the navigator's worst enemy, it is the airman's greatest friend and protection. It not only preserves him against visual discovery from below, but is an excellent insulator of sound, so that his whereabouts is not betrayed by the noise of his motor. It is of in calculable value in another way. When a fog prevails the sea is generally as smooth as the pro verbial mirror, enabling the waterplanes to be brought up under cover to a suitable point from which they may be dispatched. Upon their release by climbing to a height of a few hundred feet the airmen are able to reach a clear atmosphere, where by means of the compass it is possible to advance in approximately the desired direction, safe from discovery from below owing to the fog. If they are "spotted" they can dive into its friendly depths, complete their work, and make for the parent ship.

Low-lying sea-fogs are favourable to aerial raids provided the scout is able to catch sight of the upper parts of landmarks to enable him to be sure of the correctness of his line of flight-in cases where the distance is very short compass direction is sufficiently reliable-because the bank of vapour not only constitutes a perfect screen, but serves as a blanket to the motor exhaust, if not completely, at least sufficiently to mislead those below. Fogs, as every mariner will testify, play strange tricks with the transmission of sound. Hence, although those on the vessels below might detect a slight hum, it might possibly be so faint as to convey the impression that the aviator was miles away, when, as a matter of fact, he was directly overhead. This confusion arising from sound aberration is a useful protection in itself, as it tends to lure a naval force lying in or moving through the fog into a false sense of security.

The development of the submarine revealed the incontrovertible fact that this arm would play a prominent part in future operations upon the water: a presage which has been adequately fulfilled during the present conflict. The instinct of self-preservation at once provoked a discussion of the most effective ways and means of disguising its whereabouts when it travels submerged. To this end the German naval authorities conducted a series of elaborate and interesting experiments off the island of Heligoland. As is well known, when one is directly above a stretch of shallow water, the bottom of the latter can be seen quite distinctly. Consequently, it was decided to employ aerial craft as detectives. Both the aeroplane and the dirigible took part in these experiments, being flown at varying heights, while the submarine was maneouvred at different depths immediately below. The sum of these investigations proved conclusively that a submarine may be detected from aloft when moving at a depth of from 30 to 40 feet. The outline of the submerged craft is certainly somewhat blurred, but nevertheless it is sufficiently distinct to enable its identity to be determined really against the background or bottom of the sea. To combat this detection from an aerial position it will be necessary inter alia to evolve a more harmonious or protective colour-scheme for the submarine. Their investigations were responsible for the inauguration of the elaborate German aerial patrol of harbours, the base for such aerial operations being established upon the island of Heligoland.

So far the stern test of war as applied to the science of aeronautics has emphasised the fact that as a naval unit the dirigible is a complete failure. Whether experience will bring about a modification of these views time alone will show, but it is certain that existing principles of design will have to undergo a radical revision to achieve any notable results. The aeroplane alone has proved successful in this domain, and it is upon this type of aerial craft that dependence will have to be placed.



CHAPTER XIX. THE NAVIES of THE AIR

Less than three years ago the momentous and spectacular race among the Powers of Europe for the supremacy of the air began. At first the struggle was confined to two rivals—France and Germany—but as time progressed and the importance of aerial fleets was recognised, other nations, notably Great Britain, entered the field.

Germany obtained an advantage. Experiment and research were taken up at a point which had been reached by French effort; further experiments and researches were carried out in German circles with secret and feverish haste, with the result that within a short time a pronounced degree of efficiency according to German ideals had been attained. The degree of perfection achieved was not regarded with mere academic interest; it marked the parting of the ways: the point where scientific endeavour commanded practical appreciation by turning the success of the laboratory and aerodrome into the channel of commercial manufacture. In other words, systematic and wholesale production was undertaken upon an extensive scale. The component parts were standardised and arrangements were completed with various establishments possessed of the most suitable machinery to perfect a programme for turning out aeronautical requirements in a steady, continuous stream from the moment the crisis developed.

The wisdom of completing these arrangements in anticipation is now apparent. Upon the outbreak of hostilities many German establishments devoted to the production of articles required in the infinite ramifications of commerce found themselves deprived of their markets, but there was no risk that their large plants would be brought to a standstill: the Government ordered the manufacture of aeroplane parts and motors upon an extensive scale. In this manner not only were the industrial establishments kept going, but their production of aeronautical requirements relieved those organisations devoted to the manufacture of armaments, so that the whole resources and facilities of these could be concentrated upon the supply of munitions of war.

In France the air-fleet, although extensive upon the outbreak of war, was somewhat heterogeneous. Experiment was still being pursued: no type had met with definite official recognition, the result being that no arrangements had been completed for the production of one or more standard types upon an elaborate scale comparable with that maintained by Germany. In fact some six months after the outbreak of war there was an appreciable lack of precision on this point in French military. Many of the types which had established their success were forbidden by military decree as mentioned in a previous chapter, while manufacturing arrangements were still somewhat chaotic.

Great Britain was still more backward in the new movement. But this state of affairs was in a measure due to the division of the Fourth Arm among the two services. A well-organised Government manufactory for the production of aeroplanes and other aircraft necessities had been established, while the private manufacturers had completed preparations for wholesale production. But it was not until the Admiralty accepted responsibility for the aerial service that work was essayed in grim earnest.

The allocation of the aerial responsibilities of Great Britain to the Admiralty was a wise move. Experience has revealed the advantages accruing from the perfection of homogeneous squadrons upon the water, that is to say groups of ships which are virtually sister-craft of identical speed, armament, and so on, thus enabling the whole to act together as a complete effective unit. As this plan had proved so successful upon the water, the Admiralty decided to apply it to the fleet designed for service in the air above.

At the time this plan of campaign was definitely settled Great Britain as an aerial power was a long way behind her most formidable rival, but strenuous efforts were made to reduce the handicap, and within a short while the greater part of this leeway had been made up. Upon the outbreak of war Great Britain undoubtedly was inferior to Germany in point of numbers of aircraft, but the latter Power was completely outclassed in efficiency, and from the point of view of PERSONNEL. The British had developed the waterplane as an essential auxiliary to naval operations, and here was in advance of her rival, who had practically neglected this line of experiment and evolution, resting secure in the assurance of her advisers that the huge dirigibles would be adequate for all exigencies on the water.

Indeed, when war was declared, all the Powers were found more or less wanting so far as their aerial fleets were concerned. If Germany's huge aerial navy had been in readiness for instant service when she invaded Belgium, she would have overcome that little country's resistance in a far shorter time and with much less waste of life. It was the Belgians who first brought home to the belligerents the prominent part that aircraft were destined to play in war, and the military possibilities of the aeroplane. True, the Belgians had a very small aerial navy, but it was put to work without delay and accomplished magnificent results, ascertaining the German positions and dispositions with unerring accuracy and incredible ease, and thus enabling the commander of the Belgian Army to dispose his relatively tiny force to the best advantage, and to offer the most effective resistance.

Great Britain's aerial navy, while likewise some what small, was also ready for instant service. The British Expeditionary force was supported by a very efficient aerial fleet, the majority of the vessels forming which flew across the Channel at high speed to the British headquarters in France so as to be available directly military preparations were begun, and the value of this support proved to be inestimable, since it speedily demoralised the numerically superior enemy.

France, like Germany, was somewhat dilatory, but this was attributable rather to the time occupied in the mobilisation of the Fourth Arm than to lack of energy. There were a round 1,500 aeroplanes ostensibly ready for service, in addition to some 26 dirigibles. But the fleet was somewhat scattered, while many of the craft were not immediately available, being in the shops or in dock for repairs and overhaul. During the period of mobilisation the so-called standing military force was augmented by about 500 machines which were acquired from private owners. The aeroplane factories were also, overhauled and re-organised so as to be in a position to remedy the inevitable wastage, but these organisation efforts were somewhat handicapped by the shortage of labour arising from the call to arms. France, moreover, imperilled her aerial strength by forbidding the use of 558 machines which were ready for service.

Germany's aerial fleet was of similar proportions to that of her Gallic neighbour, but curiously enough, and in strange contrast, there appeared to be a lack of readiness in this ramification of the Teuton war machine. The military establishment possessed about 1,000 machines—active and reserve—of which it is estimated 700 were available for instant service. During the period of mobilisation a further 450 machines were added to the fleet, drawn for the most part from private owners. So far as the dirigibles were concerned 14 Zeppelins were ready for duty, while others were under construction or undergoing overhaul and repair. A few other types were also in commission or acquired during mobilisation, bringing the dirigible force to 40 machines all told.

But the greatest surprise was probably offered by Russia. Very little was known concerning Russian activities in this particular field, although it was stated that large orders for machines had been placed with various foreign manufactories. Certain factories also had been established within the Empire, although the character of their work and its results and achievements were concealed from prying eyes. In Russia, however, an appreciable number of private aeroplanes were in operation, and these, of course, were placed at the disposal of the authorities the moment the crisis developed.

The British and French aeroplane manufacturers had been busy upon Russian orders for many months previous to the outbreak of hostilities, while heavy shipments of component parts had been made, the assembling and completion of the machines being carried out in the country. It is generally believed that upon the outbreak of war Russia had a fleet of 800 aeroplanes in hand, of which total 150 were contributed from private sources. Even the dirigible had not been overlooked, there being nearly 20 of these craft attached to the Russian Army, although for the most part they are small vessels.

In comparison with the foregoing large aerial navies, that of Great Britain appeared to be puny. At the moment Great Britain possesses about 500 machines, of which about 200 are waterplanes. In addition, according to the Secretary of the Admiralty, 15 dirigibles should be in service. Private enterprise is supported by the Government, which maintains a factory for the manufacture of these craft.

During the two years preceding the outbreak of war the various Powers grew remarkably reticent concerning the composition and enlargement of their respective aerial fleets. No official figures were published. But at the same time it is a well-known fact that during the year 1913 France augmented her flying force by no fewer than 544 aeroplanes. Germany was no less energetic, the military acquisition in this branch, and during the self-same year, approaching 700 machines according to the semi-official reports published in that country.

The arrangements concluded for the manufacture of additional craft during the war are equally remarkable. The principal factory in Germany, (now devoting its energies to the production of these craft, although in happier days its normal complement of 4,000 men were responsible for the production of another commercial article) possesses facilities for turning out 30 complete aeroplanes per week, according to the statement of its managing director. But it is averred that this statement is purposely misleading, inasmuch as during the first fortnight of the campaign it was producing over 50 aeroplanes per week. It must be remembered that Germany is responsible for the supply of the majority of such craft for the Austrian armies, that country purchasing these vessels in large numbers, because in the early days of the conflict it was notoriously weak in this arm. Since the declaration of war strenuous efforts have been made to remedy this state of affairs, particularly upon the unexpected revelation of Russia's aerial strength.

It is computed that upon the outbreak of war the various Powers were in the position to show an aggregate of 4,980 aircraft of all descriptions, both for active service and reserve. This is a colossal fleet, but it serves to convey in a graphic manner the importance attached to the adrial vessel by the respective belligerents. So far as Germany is concerned she is sorely in need of additional machines. Her fleet of the air has lost its formidable character, owing to the fact that it has to be divided between two frontiers, while she has been further weakened by the enormous lengths of the two battle-fronts.

Russia has been able to concentrate her aerial force, which has proved of incalculable value to the Grand Duke Nicholas, who has expressed his appreciation of the services rendered by his fliers. The French likewise have been favoured by Fortune in this respect. Their aerial navy is likewise concentrated upon a single frontier, although a pronounced proportion has been reserved for service upon the Mediterranean sea-board for co-operation with the fleet. France suffers, however, to a certain degree from the length of her battle-line, which is over 200 miles in length. The French aerial fleet has been particularly active in the Vosges and the Argonne, where the difficult, mountainous, and densely wooded country has rendered other systems of observation of the enemy's movements a matter of extreme difficulty. The Germans have laboured under a similar handicap in this territory, and have likewise been compelled to centre a considerable proportion of their aerial fleet upon this corner of the extended battlefield.

It is in this region that the greatest wastage has been manifest. I have been informed by one correspondent who is fighting in this sternly contested area, that at one time a daily loss of ten German machines was a fair average, while highwater mark was reached, so far as his own observations and ability to glean information were concerned by the loss of 19 machines during a single day. The French wastage, while not so heavy upon the average, has been considerable at times.

The term wastage is somewhat misleading, if not erroneous. It does not necessarily imply the total loss of a machine, such as its descent upon hostile territory, but includes damage to machines, no matter how slight, landing within their own lines. In the difficult country of the Vosges many aeroplanes have come to earth somewhat heavily, and have suffered such damage as to render them inoperative, compelling their removal from the effective list until they have undergone complete overhaul or reconstruction. Upon occasions this wastage has been so pronounced that the French aviators, including some of the foremost fliers serving with the forces, have been without a machine and have been compelled to wait their turn.

I am informed that one day four machines, returning from a reconnaissance in force, crashed successively to the ground, and each had to be hauled away to the repair sheds, necessitating withdrawal from service for several days. Unfortunately the French, owing to their decision to rule out certain machines as unsuited to military service, have not yet perfected their organisation for making good this wastage, although latterly it has been appreciably reduced by greater care among the aviators in handling their vessels.

The fast vessels of the French aerial fleet have proved exceptionally valuable. With these craft speeds of 95 and 100 miles or more per hour have been attained under favourable conditions, and pace has proved distinctly advantageous, inasmuch as it gives the French aviators a superiority of about 40 per cent over the average German machine. It was the activity and daring of the French fliers upon these high speed machines which induced the German airmen to change their tactics. Individual effort and isolated raiding operations were abandoned in favour of what might be described as combined or squadron attack. Six or eight machines advancing together towards the French lines somewhat nonplussed these fleet French mosquito craft, and to a certain degree nullified their superiority in pace. Speed was discounted, for the simple reason that the enemy when so massed evinced a disposition to fight and to follow harassing tactics when one of the slowest French machines ventured into the air.

It is interesting to observe that aerial operations, now that they are being conducted upon what may be termed methodical lines as distinct from corsair movements, are following the broad fundamental principles of naval tactics. Homogeneous squadrons, that is, squadrons composed of vessels of similar type and armament, put out and follow roughly the "single line ahead" formation. Upon sighting the enemy there is the manoeuvring for position advantage which must accrue to the speedier protagonist. One then, witnesses what might almost be described as an application of the process of capping the line or "crossing the 'T.'" This tends to throw the slower squadron into confusion by bending it back upon itself, meanwhile exposing it to a demoralizing fire.

The analogy is not precisely correct but sufficiently so to indicate that aerial battles will be fought much upon the same lines, as engagements between vessels upon the water. If the manoeuvres accomplish nothing beyond breaking up and scattering the foe, the result is satisfactory in as much as in this event it is possible to exert a driving tendency and to force him back upon the lines of the superior force, when the scattered vessels may be brought within the zone of spirited fire from the ground.

Attacks in force are more likely to prove successful than individual raiding tactics, as recent events upon the battlefield of Europe have demonstrated more or less convincingly. An attack in force is likely to cause the defenders upon the ground beneath to lose their heads and to fire wildly and at random, with the result that the airmen may achieve their object with but little damage to themselves. This method of attacking in force was essayed for the first time by the British aerial fleet, which perhaps is not surprising, seeing that the machines are manned and the operations supervised by officers who have excelled in naval training, and who are skilled in such movements.

No doubt this practice, combined with the daring of the British aviators, contributed very materially to the utter demoralisation of the German aerial forces, and was responsible for that hesitancy to attack a position in the vicinity of the British craft which became so manifest in the course of a few weeks after the outbreak of hostilities.

One of the foremost military experts of the United States, who passed some time in the fighting zone, expressed his opinion that the British aerial force is the most efficient among the belligerents when considered as a unit, the French flier being described by the same authority as most effective when acting individually, owing to personal intrepidity. As a scout the French aviator is probably unequalled, because he is quick to perceive and to collect the data required, and when provided with a fast machine is remarkably nimble and venturesome in the air. The British aviators, however, work as a whole, and in the particular phases where such tactics are profitable have established incontestable superiority. At first the German aerial force appeared to possess no settled system of operation. Individual effort was pronounced, but it lacked method. The Germans have, however, profited from the lessons taught by their antagonists, and now are emulating their tactics, but owing to their imperfect training and knowledge the results they achieve appear to be negligible.

The dirigible still remains an unknown quantity in these activities, although strange to relate, in the early days of the war, the work accomplished by the British craft, despite their comparatively low speed and small dimensions, excelled in value that achieved by the warplanes. This was particularly noticeable in matters pertaining to reconnaissance, more especially at night, when the British vessels often remained for hours together in the air, manoeuvring over the hostile lines, and gathering invaluable information as to the disposition and movements of the opposing forces.

But it is probably in connection with naval operations that the British aerial fleet excels. The waterplanes have established their supremacy over the naval dirigible in a striking manner. British endeavour fostered the waterplane movement and has carried it to a high degree of perfection. The waterplane is not primarily designed to perform long flights, although such may be carried out if the exigencies demand. The practice of deputing certain vessels to art as "parent ships" to a covey of waterplanes has proved as successful in practice, as in theory. Again, the arrangements for conveying these machines by such means to a rendezvous, and there putting them into the water to complete a certain duty, have been triumphantly vindicated. At the time this idea was embraced it met with a certain degree of hostile criticism: it was argued that the association of the two fighting, machines would tend towards confusion, and impair the efficiency of both.

Practice has refuted this theory. The British aerial raids upon Cuxhaven and other places would have been impossible, and probably valueless as an effective move, but for the fact that it was possible to release the machines from a certain point upon the open sea, within easy reach of the cooperating naval squadron. True, the latter was exposed to hostile attack from submarines, but as results proved this was easy to repel. The aircraft were enabled to return to their base, as represented by the rendezvous, to be picked up, and to communicate the intelligence gained from their flight to the authorities in a shorter period of time than would have been possible under any other circumstances, while the risk to the airmen was proportionately reduced.

The fact that the belligerents have built up such huge aerial navies conclusively proves that the military value of the Fourth Arm has been fully appreciated. From the results so far achieved there is every indication that activity in this direction will be increased rather than diminished.

THE END