Part 20 (1/2)
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 fas.h.i.+on 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 s.h.i.+rts consisting of little metal plates cunningly connected by wire links and so overlapping each other as to form a perfect s.h.i.+eld 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.