How they came to be called tanks no one seems to know clearly but that is how they will be known for all time. It has been suggested that they were so named because tank is one of the things which they certainly are not, the intention being thereby to add to the mystification of the enemy. That is by the way, however, for we are more concerned with the things than with their name.

Their precise origin is wrapped in mystery but we have it on excellent authority that they grew out of the peaceful "tractor," originally intended to drag a plough to and fro across a field in the service of the farmer. An ill.u.s.tration of one of these interesting machines will be seen in this book which will well repay a little study.

It consists of a steel frame or platform upon which is mounted a four-cylinder petrol engine with a reservoir above to carry the supply of fuel and with a radiator in front to cool the water which keeps the engine from becoming too hot. Towards the back of the vehicle is what is called by engineers a worm-gear, the function of which is to reduce the one thousand revolutions per minute of the engine to somewhere near the slow speed required of the wheels of the tractor.

This worm-gear is simply a wheel with suitable teeth on its edge in conjunction with a screw so made that its thread can engage comfortably with the teeth. This latter, because of the wriggling appearance which it presents when it is revolving is called a worm, which name it gives to the whole apparatus. Both wheel and worm are mounted in bearings which form part of a case enclosing the whole so that dirt is excluded while, the case being filled with oil, ample lubrication is a.s.sured.

The shafts of both wheel and worm emerge through holes in the case.

It will easily be seen that each single turn of the worm will propel the wheel one tooth, so that if the wheel have fifty teeth, for example, the worm will turn fifty times to the wheel's once. Thus a great reduction in speed is attainable with this device and what is equally valuable, a great increase of power also results. Thus a small engine, working at a high speed, is able by means such as this to pull very heavy loads at a slow speed.

It is evident, however, that the reduction necessary in this case cannot be attained even by a worm-gear, for there are other wheels visible which show that ordinary tooth gearing is also employed to reduce the speed even further before it is applied to driving the tractor along.

Practically all the other gear which we see in the picture, above the platform, consists of the controlling apparatus.

The object with a screw-like appearance just behind the engine is not really a screw but is a flexible coupling joining the engine to the worm-gear, its "flexibility" enabling the two to work sweetly together even though by chance they may get just a little out of line with each other.

But by far the most interesting part of the machine is that which is underneath the frame. At one end we see a pair of ordinary-looking wheels and between them the gear for swinging them to right or left for steering purposes, but even they are somewhat unusual, since they will be seen to have f.l.a.n.g.es or rims round the edge for the purpose of biting into the earth, so that they may be able to guide the machine the better in soft ground.

The back wheels, however, are quite peculiar, for there is a pair on each side and round each pair is a chain somewhat after the fashion of a huge bicycle chain. The links of this chain are made of tough steel and they are two feet wide, so that each chain forms a broad track upon which the machine moves. The links of this track-chain will be seen to be tooth-shaped so that they grip or bite deeply into the yielding ground. The teeth, moreover, are shaped like those of a saw and they are so placed as best to help the tractor forward.

Between the two chain-wheels will be noticed a row of smaller wheels and it is these which largely support the weight of the machine, the chains forming tracks upon which they run.

The wheels actually turned by the power of the engine are the chain-wheels, and their action is such as to keep on laying down and then taking up again two broad firm tracks along which, at the same time, they keep propelling the other wheels which carry the weight above. The effect, really, is just as if the machine had a pair of driving wheels two feet wide and of enormous diameter, of such diameter, in fact, that the part in contact with the ground is almost flat. Thus there is always a broad bearing surface to prevent sinking in soft earth, while the tooth-like shape of the links gives a firm hold even under very adverse conditions.

This form of construction has been used for some few years now under the name of "caterpillar" or "centipede" traction. A glance at the picture will explain those names, particularly if the chain-driven part of the vehicle be imagined to be a little longer than it is in the particular machine shown.

The idea of armouring a vehicle with bullet-proof plates is also a fairly old conception. Armoured trains were used again and again during the South African War, and armoured motor-cars became familiar to most people. In the case of cars, however, the armour could only be very light and the guns carried were limited practically to a single machine-gun and some rifles. Moreover, the operations of a car are very largely confined to such places as are blessed with good roads or smooth plains. An armoured car of the older type would have cut a poor figure amid the sh.e.l.l-holes and mine-craters of Northern France. It would have had to keep to the roads and so it was little used.

But the idea of an armoured vehicle was good and a good idea is never entirely lost. Sooner or later some genius puts it to good use. Thus the idea of an armoured vehicle came to be a.s.sociated with the idea represented in the centipede tractor and the result was the tank.

Why not armour a large centipede, said someone? Make it very big and strong. It will trample down the barb-wire entanglements as if they were gra.s.s. If made long enough and rightly balanced it will pa.s.s over the trenches like a moving bridge. Nothing but a direct hit from a heavy gun will do it much harm. For, observe, the mechanism can be entirely covered up, all the vital parts can be well protected, and the chain tracks can be so strong as to be almost undamageable.

[Ill.u.s.tration: _By permission of_ _Messrs. Foster and Co._

THE PARENT OF THE TANK.

Here we see an innocent agricultural tractor with caterpillar hind wheels. It is out of such a machine that the idea of the formidable tank was evolved.]

Thus we get a glimpse of the growth of this simple peaceful agricultural machine into one of the most striking mechanical achievements of the Great War.

Another thing which seems to have grown more or less of itself is the bomb or grenade. Before the time of modern accurate fire-arms hand-grenades were quite a recognized weapon. The "Grenadier" Guards owe their t.i.tle to this fact and carry the design of a bursting grenade upon their uniforms. Yet until a few years ago everyone thought that such things were done with for ever: that with modern rifles soldiers would seldom get near enough together to use grenades and that if they did the bayonet would be the weapon to be used.

When, however, the Germans were driven back at the battle of the Marne and found themselves compelled to entrench in order to avoid further disaster, it soon became evident that neither rifle nor bayonet nor both together entirely filled the needs of the infantryman.

Since the Allies were not powerful enough to drive the Germans from their trenches forthwith, they, too, had to entrench. Gradually the trenches drew nearer and nearer together and at the same time skill in entrenching increased. Thus a time soon arrived when both rifle and bayonet were largely useless for purposes of offence. Then the hand-grenade came into its own again, for the men could throw it from the depths of their own trench high into the air in the hope that it would fall into the trenches of the enemy. The call for these quickly produced the supply. There is little need to describe them here, for who among us has not intimate friends who used them again and again? This much may be said, however. They were little hollow b.a.l.l.s of cast iron, sometimes chequered so that when they burst they flew into many fragments. Inside was a charge of explosive with a suitable fuse or firing mechanism. Some were fixed to the end of a stick for convenience in throwing, while others were simply handled like a cricket-ball.

They serve to show us, however, how an old idea may under fresh conditions be revived into what is practically a new invention.

Another example of the same sort is the revival of chain mail. Who, but a few years ago, would have thought it possible that modern soldiers would go to battle sheathed in shirts consisting of little metal plates cunningly connected by wire links and so overlapping each other as to form a perfect shield for all the more vital parts of the body? To what extent these were worn I do not know, for the British soldier is a very shy fellow in some ways and there are few who would not be a trifle ashamed to let their comrades see them thus garbed. They would feel that it was a confession of fear, and however afraid an Englishman may be he will never admit it. He is really a pious fraud, for the more he is really afraid inwardly the more courageously will he act just to hide his fear.

Since, however, the bullet-proof helmet is worn officially nowadays there seems no reason whatever why the bullet-proof waistcoat should not be adopted officially too. It is very light and very flexible and it is claimed that it is quite effectual in stopping rifle and machine-gun bullets.

Thus we see in what different ways inventions grow. Some are warlike from first to last, like the gun and the torpedo, but we find a vast range of peaceful things growing into implements of warfare, as the farmer's tractor has been developed into the tank, while not less interesting are the old ideas revived and adapted to modern needs, exemplified by the hand-grenade and the chain armour.

CHAPTER XXIV

AEROPLANES

Of all the great inventions perhaps the most striking because of the suddenness with which they have come upon us are those relating to the navigation of the air. Until a few years ago "to fly" was taken to typify the impossible. Now we see men flying every day and there is scarcely anyone who has not had a friend or relative in the Flying Corps.

Recent experience, too, has shown that this one invention has revolutionized warfare in several important departments, particularly in the use of very heavy long-range artillery. Huge guns, hidden in a hollow or behind a hill, have been set to throw sh.e.l.ls on to an unseen target, while a man in an aeroplane above watches the result and signals back by wireless. Thus by the aid of aircraft the power of artillery has been immensely increased.

Again, aircraft have superseded cavalry for reconnaissance purposes, that is to say, for finding out the enemy's strength and preparedness.

Only a few years ago a General who needed information as to his foe would send forward a screen of cavalrymen who would cautiously creep forward until, judging by what they could see and by what sort of a reception they got, they were able to form some idea of the foe's arrangements. Nowadays, however, the airmen sail over his head and take photographs of him and his positions. A careful commander to-day not only screens his men and his guns from view along the land but he also tries his best to make them invisible from above. And, speaking of inventions, the soldiers have shown a degree of ingenuity in making themselves and their guns invisible which almost merits a volume to itself.

The airman, therefore, goes up and sails over the enemy. He may be simply observing for some particular unit of artillery, or he may be sent to find out things generally--nothing in particular, but anything which seems likely to be of use. He looks out intently and carefully, moreover he not only looks with his own eyes: as has just been mentioned, he takes photographs, which can be developed on his return and studied minutely at leisure. He may, or may not, according to circ.u.mstances, send back reports of an urgent nature by wireless telegraphy.

In some cases these duties are all carried out by one man, but in others there are two: one the pilot who looks after the working of the machine, and the other the observer whose whole attention can thus be devoted to scrutinizing the enemy.

Of course, when aeroplanes go on scouting expeditions like this they are apt to be attacked by the enemy both by anti-aircraft guns and also by other aeroplanes. The former can only be met by high speed and the steering of a somewhat erratic course so as to confuse the gunners and prevent them from taking good aim.

The other aeroplanes, however, must be met by actual fighting. The only way to defeat them is to go for them and attack them, a machine-gun being the most usual weapon.

Besides those who go up for definite scouting operations or to "spot,"

as it is termed, for the artillery, there are other machines whose sole duty is fighting. These go up for the purpose of driving off those machines of the enemy which may come prying, or to keep the ground, so to speak, for the scouting machines and enable them to do their work unmolested.

Then there are, of course, still others whose function is to carry out bombing expeditions.

All these different duties call for different types of machine, but I do not propose to go into the differences here since changes are so rapid in this particular field that only the general principles remain unchanged for any length of time. What has just been hinted, however, as to the different kinds of work which the aeroplane is called upon to do will enable the reader to see why different kinds of machines are needed.

So far we have only spoken of aeroplanes. There is a kind of machine sometimes called a hydroplane but which we are gradually getting to call a sea-plane. The latter term is much to be preferred, since the former is also in use to denote a special kind of high-speed boat.

Now a sea-plane only differs from an aeroplane in that it has floats instead of wheels. The aeroplane has wheels to enable it to alight upon and arise from the ground: the sea-plane has floats by which it can alight upon the water and arise from the water also.

In some instances this float idea is made so p.r.o.nounced a feature of the machine that it becomes a flying boat.

Sea-planes are therefore really only aeroplanes specially adapted for a certain purpose. They are really just as much aeroplanes as those machines which go by that name. It is somewhat unfortunate, therefore, that a separate term is used to describe them. But there it is: names grow in a very curious way, not always in a logical way, and a name having once stuck to a thing in the mind of the public it is very difficult to make any alteration.

Aeroplanes, then, may be said to include a subdivision known as sea-planes, and for the rest of this chapter what is said of aeroplanes will apply to sea-planes also.

Without doubt, these are the fastest vehicles in existence. Many of them can exceed a speed of a hundred miles an hour. Consequently, the pilot lives while he is aloft in the equivalent of a furious gale, and it would seem as if that must produce such a degree of cold as to be almost unendurable. Moreover, it appears that this cold is almost as bad in summer as in winter, for the temperature high up in the air is much the same all the year round. The consequent m.u.f.fling up with thick clothes and gloves, while it mitigates the cold, must add greatly to the pilot's difficulties in managing his machine. The protection for his eyes and ears which is made necessary by the same conditions must likewise add to his difficulties or at any rate to his discomfort. On the other hand, the effect of gliding at a very high speed over a perfectly smooth track, for that is in effect what it is, is very exhilarating, which to some extent compensates for the other drawbacks.

Moreover, the handling of such a machine in the air, particularly if a fight is included in the programme, appeals strongly to the sporting instincts of young men, so much so that during the War, in spite of the dangers and hardships, and the continual loss of life, there was never a dearth of men anxious to become pilots.

Owing to these considerations, too, it follows that the best aviators are to be found in those lands where the people are most devoted to sports. Hence, as we have it on excellent authority, the young men of Great Britain and the United States, with their love of adventure and their strong sporting instincts, make better men in the air than the Germans.