CHAPTER VIII
TORPEDOES AND SUBMARINE MINES
It is sad to think how much scientific skill and learning has, during the Great War, been devoted to killing people. It used to be thought that one day a great scientific invention would arise, of such deadly power that for ever afterwards war would be unthinkable; its horrors would be such that all nations would shrink from it. That prophecy, however, has not been fulfilled, nor are there any signs of it. On the contrary, each scientific achievement in the realm of warfare is quickly countered by another: so much so that with all our science in the manufacture of weapons, and our skill in using them, warfare in the twentieth century is if anything less deadly in proportion to the numbers engaged than it used to be.
There are, however, two weapons which in this war have reached a deadly efficiency which they did not seem to possess before, and to which satisfactory antidotes have not yet appeared.
These two are the submarine mine and the torpedo. The latter, particularly, had been a dismal failure previously, but as the weapon of the submarine it has now established itself. It is, however, only in connection with the submarine that it has achieved any measure of success, and, as there are strong indications that very soon the submarine itself will be robbed of its terrors, it is quite likely that the reign of the torpedo will be brief.
Although it has only just made itself felt seriously in warfare, the torpedo is a fairly old idea. In fact we can trace the general idea of it back to very ancient times. The modern weapon, however, dates from the year 1864, when an Austrian inventor approached an English engineer named Whitehead with a request to take up his idea. Mr Whitehead had at that time a works at Fiume, on the Adriatic, and it was really his genius that developed the crude idea into a practicable invention.
Thus there came into existence the Whitehead Torpedo, now used in a great many navies, and also the Schwartzkopff, which may be regarded as the German variety of the same thing.
Speaking generally, it may be described as a small automatic submarine boat. Externally, it naturally follows somewhat the lines of a fish.
Deriving its name from that curious fish which is able to give electric shocks from its snout, it likewise carries on its nose that appliance whereby it gives a shock, not electric it is true, but equally deadly, to anything which it may touch.
Since no man-made mechanism can approach the marvellous action of the fish"s fins and tail, the propulsion is achieved by a propeller like that of a steamboat, but of course on a very small scale. A single propeller, however, would tend to turn the torpedo over and over in the water, and so it has two, one behind the other, driven in opposite ways, so that the turning tendency of one is neutralised by that of the other.
The blades of the propellers are, however, set in opposite ways, so that although rotating in different directions they both push the torpedo along.
Behind the propellers, again, there are rudders for steering. One steers to right or left, as does that of an ordinary ship, while two others are so placed that they can steer upwards and downwards.
So there we have the general picture of the outside: a smooth, fish-like body with a "sting" in its nose, propellers at the rear to drive it along, and rudders to guide it.
Inside are various chambers. One contains the explosive which blows up when the nose strikes something. This "head," as it is termed, is detachable, so that it can be left off until it is really required for war. The peace-head, which is of the same size, shape and weight as the war-head, is what the torpedo carries during its earlier career. With this it can be tried and tested in safety, the war-head being subst.i.tuted when the real business of the torpedo begins.
Another chamber contains the compressed air which furnishes the motive power. This also serves to give buoyancy.
Another chamber, again, contains the engines, beautiful little things of the finest workmanship almost exactly like the finest steam-engine, but of course very small in comparison.
In the early stages the range of the torpedo was limited by the amount of compressed air which it could carry. At first sight there seems no reason why any limit should be placed upon this, but in practice there are often limitations in engineering matters which are not apparent on the surface. For example, to increase the air chamber would mean enlarging the whole torpedo, calling for more propulsive power and larger engines, and these larger engines would call for more air, thus defeating the object in view. Forcing more air in by using a higher pressure, in a similar way would necessitate a thicker chamber, to resist the higher pressure. This would add weight, calling for more buoyancy. Thus there seemed to be a practical limit beyond which it was impossible to go.
The difficulty was overcome, however, in a very cunning way. When the engines have used some of the air, and the store is somewhat exhausted, chemicals come into action which generate heat, which is imparted to the air which is left. This heat expands the air, producing in effect a larger supply of it, and enabling the torpedo to make a longer journey.
Steering in a horizontal direction--that is to say, to left or right--is done by a gyroscope. The action of a rotating wheel is discussed in the last chapter, and it is not necessary here to say more than this: a rotating wheel always tries to keep its axle pointed in the same direction. Just at the moment of starting such a wheel is set going inside the torpedo, and its arrangement is such that, should the torpedo swerve to the left, the gyroscope operates the rudder and steers it back. In the same way, if it tends to turn to the right, the ever-watchful gyroscope brings it to its true course once more. The effect of the gyroscope, therefore, acting upon the rudder, is to keep the torpedo faithfully to the direction upon which it is started.
The up and down rudders are likewise controlled quite automatically, but in a different way. Their function, clearly, is to keep the thing at a certain uniform level. Without such control a torpedo would be equally likely to jump out of the water altogether, or to go downwards vertically and bury its nose in the mud. The depth at which it is to move is determined beforehand, certain necessary adjustments are made, and the torpedo then pursues its even way, neither coming to the surface nor driving beneath its target.
For this purpose there is first of all a "hydrostatic valve." This little appliance, which is open to the action of the water, responds to changes in pressure. The pressure at any point under water is exactly proportional to the depth. At ten feet, for example, it is precisely ten times what it is at one foot. So the hydrostatic valve is adjusted to set the rudders straight when the water-pressure upon it is a certain amount. If, then, it dives downwards the pressure increases and the valve operates the rudders so as to bring it upwards, while if it rise too high the decrease of pressure causes it to be guided downwards.
This action, however, is too sudden and violent, so that with it alone the torpedo would proceed by leaps and bounds. After being low it would come up too suddenly, overshoot the mark, only to be steered downwards again equally suddenly.
The valve, therefore, is combined with a pendulum, whose action tends to restrain these too sudden changes, with the result that under the influence of the two things combined the torpedo keeps fairly well to an even course, only varying upwards or downwards to an extent which is negligible.
Finally, there is an interesting little feature about the firing mechanism which merits a description. The actual firing is caused by the driving in of a little pin which projects at the nose of the torpedo.
Suppose that, in the process of pointing the torpedo and launching it upon its course, that pin were to be knocked accidentally, an awful disaster would result. It must be provided against, therefore, and the method adopted is beautiful in its certainty and simplicity.
Normally, the firing-pin is fixed by a screw so securely that no accidental firing is possible. There is, however, a little propeller-like object a.s.sociated with it, which is driven round by the water as the torpedo is pushed through it, and this unscrews, and thereby releases the pin. The little "fan" has to rotate a certain number of times before the pin is released, and it is quite impossible for this number to be accomplished before the torpedo has proceeded to a safe distance from the ship which fires it. On board the ship, therefore, and so long as it is near the ship, it is quite safe, but by the time it reaches its target it is ready to explode.
As far as is known, the foregoing description gives a true general description of the torpedoes now in use. Those of different powers may vary in detail, but, broadly, they are as just described.
There are others, however. The Brennan, for instance, was once adopted and largely used by the British for harbour defence. This was controlled from the sh.o.r.e by wires. It was driven, so to speak, with wire reins, and thus guided it could fairly hunt down its prey, turning to right and to left as required.
Of greater scientific interest, perhaps, still, is the "Armor1" wireless controlled torpedo. This is the invention of two gentlemen, Messrs Armstrong and Orling, whose first syllables combine to form the t.i.tle of the torpedo.
Of this, two very interesting features may be mentioned. Firstly, the wireless control. In the chapter on Wireless Telegraphy there is described the coherer, a simple little apparatus which we might describe as a door which is opened by the "waves" which travel through the ether from the sending apparatus. Whenever the key of the sending apparatus is depressed these waves travel forth, and when they fall upon the coherer it "opens." Normally, the coherer is shut, but when acted upon by the incoming waves it opens and lets through current from a battery, which current can be caused to perform any duty which we may wish. Thus, ignoring the intermediate steps, we get this: whenever the sending key is depressed current flows through the coherer and performs whatever duty is set before it.
And now picture to yourself a tooth wheel with four teeth. A catch normally holds one of the teeth, but when the catch is lifted for a moment it lets that tooth slip and the next one is caught. At every lifting of the catch the wheel turns a quarter of a turn. Then imagine that that catch is operated by an electro-magnet energised by the current which pa.s.ses through the coherer. We see, then, that every time the sending key is depressed the wheel turns a quarter turn.
Attached to the wheel is a little crank which turns with it, and the pin of this crank fits in a slot in the end of a bar like the tiller of a boat. Suppose that, to commence with, the tiller is straight, so as to steer the boat straight. Depress the key, the wheel turns a quarter turn and the tiller is set so as to steer to one side, say the left. Another pressure upon the key and a second quarter turn brings the tiller straight again. Yet another pressure, another quarter turn, and the tiller is steering to the right. Thus by simply pressing the key the correct number of times the torpedo can be made to travel in any desired direction.
The second ingenious feature of this weapon is the means by which it is made visible to the man who is controlling it from the sh.o.r.e or ship.
Probably the reason why these torpedoes are not used more is that the man who guides them is of necessity himself visible. He has to be posted somewhere where he can follow its course, or he has no idea how to steer it. Consequently, he would be an object for attack by the enemy. Such a torpedo would be useless in a submarine, for the submarine would need to come to the surface in order that the observer might get a sufficiently good view to be able to steer the torpedo, and we all know that when upon the surface a submarine is a very vulnerable craft.
But that is by the way. The point is how to make the torpedo very clearly visible while it is still under water. A short mast might be used, but that would be liable to be shot away. The inventor had a happy inspiration when he made it blow up a jet of water, like a whale does.
This jet is quite easy to see, yet no shot can destroy it. Compressed air blows up this tell-tale jet which the observer can see, and by its means he can guide the torpedo at will.
A submarine mine may be regarded as a stationary torpedo. It consists of a metal case filled with a powerful charge of explosive which floats harmlessly in the water until some unfortunate vessel strikes against it, when it blows up with sufficient force to make a hole in the stoutest ship.
There are two cla.s.ses of mine: one which is laid in peace time, to protect harbours and channels; and the other, which is laid during actual warfare.
The former are anch.o.r.ed in a more or less permanent way. The services of divers are used to place them in position. In some cases they float well down in the water, out of the way of pa.s.sing ships, but come up nearer the surface when needed. This result is achieved by having an anchor chain of such a length that when fully extended the mine floats a little way under the surface, just high enough to be struck by a pa.s.sing ship, together with what is called an "explosive link." The link is used to loop together two parts of the chain, and so, in effect, to reduce its length. Wires pa.s.s from the link to the sh.o.r.e, and when an electric current is sent along these wires the link bursts asunder, liberates the chain, and the mine floats up to the full length of its chain.
Another plan is to let the mines float high up always, but to fire them, not by the touch of the ship but by electricity from the sh.o.r.e. In this way a safe channel is kept for friendly vessels, while an enemy can be destroyed.
Necessarily, those mines which are hurriedly laid in war time are very different from these. To be of much use, a mine must be concealed below the surface. If it floats upon the water it will be visible, and can be avoided, or, at all events, easily picked up. It is practically impossible to set a floating object at a certain depth in the water, except by anchoring it to another, heavier, object, which will lie at the bottom. Therefore mines have to be anch.o.r.ed in some way.
But the sea varies in depth, so that the length of the anchor chain must be varied, or else some of the mines will be on the surface, thereby advertising the presence of the mine-field, while others will be below the depth of even the biggest ship. In warfare, however, mines need to be laid quickly. There is no time to sound for the depth and then to adjust the length of cable accordingly. Hence the mine must be so made as to set itself correctly at a pre-determined depth.
Possibly some readers may think that such things might be made to float, of themselves, at the right depth. It is a fact, however, that a thing either floats upon the surface of water or falls to the bottom. Water is practically incompressible, so that the water at the bottom of the sea is no heavier than that near the surface. The conditions which prevail in air and allow a balloon to float at any desired height do not apply.
The only thing, in this case, is to have an anchor chain or rope of the right length.
So let us picture a mine-laying ship steaming along, probably in the dead of night, surrept.i.tiously laying mines in the hope that the enemy will run into them on the morrow.
Along the deck of the ship are small railway lines, and on these lines stand what appear to be trains of small trucks, each truck having small wheels to run on, and each bearing a large round metal ball. As the ship travels along, the crew, handling these deadly things quite freely, as if they were innocent of any danger, propel them along to the stern, and at regular intervals push one overboard. That is all.
The freedom with which the men handle them is not folly, for they are then quite harmless. Nor need they trouble about the length of rope, for that adjusts itself. Just tumble the things overboard, and in due time they anchor themselves at the right depth and set themselves in the right condition for blowing up any ship which may get amongst them.
The truck-like object upon wheels is not the mine itself: it is the sinker which lies at the bottom of the sea. The round ball which it bears is the mine, and the two are connected together by a wire rope. To commence with, this rope is coiled upon a drum in the sinker, which drum is either held tightly or is free to revolve according to the position of a catch. That catch is held open, so that the drum is free, by a weight at the end of a short rope. Let us a.s.sume that that rope is ten feet long.
Then, when the whole thing is tumbled into the water, the weight sinks first ten feet below the sinker, which, being more bulky in proportion to its weight, follows downwards more slowly. While sinking, the weight is pulling upon its rope and holding open that catch, so that the drum pays out its rope and the mine lies serenely upon the surface. As soon as the weight touches bottom, however, the pull on the short rope ceases, the catch grips the drum, no more rope is paid out, and the sinker, in settling down its last ten feet, has to drag the mine down too. Thus, quite automatically, by what is really a beautifully simple arrangement, the mine becomes automatically anch.o.r.ed at a depth below the surface equal to the length of the short rope. By making that rope the desired length, the depth of the mine under the water can be fixed.
There are various methods of firing these mines, all of which work perforce by the concussion of the ship itself. In some cases the sudden tilting over causes an electric contact to be made, and permits a battery in the mine to cause the explosion. Another way is to furnish the mine with projecting horns of soft metal, inside which are gla.s.s vessels containing chemicals. The ship, striking a horn, bends it, breaks the gla.s.s, and liberates the chemicals which cause the explosion.
In the type of mine largely used by the British Navy there is a projecting arm pivoted on the top of the mine and projecting from it horizontally. The mine itself rolls along the side of the pa.s.sing ship, but the arm simply trails or sc.r.a.pes along. Thus the mine turns in relation to the arm, and a trigger is thereby released, which fires the mine.