Chapter XVIII: The Torpedo

In parts of South America there lives a little fish, which, if you touch its nose, gives you a severe electric shock. The natives call it the "torpedo." When an artificial fish came to be invented, capable of giving a very nasty shock to anyone touching its snout, that name was bestowed upon it too.

Even more than the submarine, the torpedo resembles a fish with its graceful outlines and its fins and tail, the chief difference being that the tail of the torpedo carries a couple of little rotating propellers. Looked at another way we may say that the torpedo is an automatic submarine. As a matter of fact, we all know it best as the weapon of the submarine.

It was originally invented by an Austrian who took it to a Mr. Whitehead, an Englishman who then had an engineering works at Fiume. This gentleman took up the idea and developed it into the Whitehead torpedo, which is to-day used by half the navies in the world, the rest using something very similar. It is curious to note that the German variety is called the Schwartzkopf, the meaning of which is "blackhead."

The smooth, steel, fish-like body consists of two separate parts, which can be detached from each other. The front part called the "head" is made in two kinds, the war-head and the peace-head. The former contains a large quantity of explosive and the mechanism for firing it on coming into contact with any hard body. It is only used in actual warfare. The peace-head is precisely the same shape and weight as the other but is quite harmless, so that when it is fitted to the torpedo the latter can be handled with perfect safety, a valuable feature during the frequent exercises through which our sailors go in their efforts to attain perfection in the use and handling of these valuable weapons.

So much for the head. The body of the torpedo contains a beautiful little engine precisely similar to a steam-engine but on a small scale, which is driven by compressed air, a store of which is carried in a compartment provided for the purpose.

Then there is an automatic steering apparatus controlled by a gyroscope, the purpose of which is to keep the torpedo steered in precisely that direction in which it is started. If any outside force, such as current or tide, deflects it from its path the gyroscope, acting through a rudder at the tail, brings it back again.

Like the submarine, moreover, it has rudders which can steer it upwards or downwards and these again are controlled automatically so that having been set to travel at a certain depth the torpedo can be launched into the water with the practical certainty that it will descend to that depth and then maintain it.

This remarkable result is attained by the use of two devices acting in combination, namely, a hydrostatic valve and a pendulum. Either of these alone would set the thing going by leaps and bounds, at one time above the required depth and at another equally below it, and so on alternately. The hydrostatic valve consists of a flexible diaphragm, one side of which is in contact with the water outside, so that since the pressure increases with increasing depth, it is bent inwards more or less as the depth varies. This deflection is made to control the horizontal rudders. Suppose that things are adjusted for the rudders to steer the torpedo horizontally when at a depth of ten feet: if it descends to twelve feet the increased deflection of the diaphragm will so change the rudders that they will tend to steer slightly upwards: if, on the other hand, it rises to eight feet the contrary will happen, with the result that it will descend. As has been said already, this alone would result in a continually undulating course, so the pendulum is introduced to check the too decided changes in direction and so produce a practically straight course.

There is an interesting feature, too, about the propeller. It is "twin" but not, as in ships, two screws side by side. Instead, they are both set upon one shaft or rather upon two concentric shafts, like the two hands of a clock. The hour-hand of a clock is on one shaft, a solid one, which itself turns inside the shaft of the minute hand, which is hollow. The propellers of the torpedo are likewise, one on a tubular shaft and the other on a solid shaft inside it. These two shafts turn in opposite directions, but since the two propellers are made opposite "hands" they both equally push the torpedo along. The reason for this arrangement is that without it the action of a single propeller would tend to turn the torpedo over and over. Instead of the torpedo turning the propeller the propeller would to some extent turn the torpedo.

The range of the torpedo depends, clearly, upon the quantity of compressed air which it is able to carry and that is limited by certain practical considerations. One of these is the space required to store it, and a very ingenious method has been invented whereby the limited supply is eked out so that in effect its quantity is increased. As the air is used up the pressure in the air-chamber naturally falls and when that has gone on to a certain extent chemicals come into action which generate heat, whereby the remaining air is raised in temperature. This, of course, increases the volume of air and the result is just the same as if a greater quantity were carried to commence with.

The explosion is brought about by the pressing in of a pin which normally projects from the nose or point of the torpedo, and it would be very easy to knock this accidentally, causing a premature explosion, were not precautions taken to prevent it. These take the form of a little fan which is turned by the water as the torpedo proceeds through it. The firing-pin is locked by means of a screw so that it cannot be operated until it has been released by the withdrawal of the screw and that can only be done by the fan. Thus, while on the submarine or whatever ship carries it, the torpedo cannot be fired: it only becomes capable of explosion after it has passed through the water for a certain distance, far enough, that is, for the fan to have undone the screw. Thus the maximum of safety is combined with the maximum of sensitiveness when the object aimed at is struck.

There are other forms of torpedo which although little used are by no means lacking in interest. There is the Brennan, for example, at one time much favoured in the British Navy. Its propellers were operated from the shore, by the pulling of two very flexible steel wires. The effect was much as if the thing were driven by reins, as a horse is driven. On shore was a powerful engine with two large drums on which the wires could be wound and by which they could be drawn in at a very high speed. By pulling one more than the other the torpedo could be steered and it is said that such a torpedo could be made to follow a ship through complicated evolutions and fairly hunt it down, finally overtaking and striking it.

The purpose of such weapons was clearly to defend a port or roadstead against enemy craft which might try to rush in. It needed to be controlled by someone perched upon an eminence of some sort from which he could watch its course and guide it as might be necessary.

Compare this with the ease with which the Whitehead torpedo is just slipped into the water and then left to itself. A submarine has in its bows either one or two tubes just large enough to hold the torpedo easily. At the front is a flap door which is kept closed while the torpedo is slipped into its place. Then the similar door at the rear of the tube is closed after which the front one can be opened. Water of course flows in and surrounds the torpedo when this takes place and a little push from some compressed air sends it floating out. As it emerges from the tube the engines are set going automatically and likewise the gyroscope which steers it, after which it continues to proceed in a straight line, soon seeking and maintaining the desired depth.

Other vessels besides submarines have submerged torpedo-tubes like these, but others again have tubes of a different kind. These are fixed on the deck and have the advantage that they can be pointed in any direction almost like a gun, whereas the others are either fixed rigidly in the vessel or are only slightly movable. In the case of these other tubes the torpedo is shot over the side of the ship, off which it leaps into the water somewhat like a man diving.

One other kind of steerable torpedo may be mentioned because of its ingenuity, although so far as is known it is not in actual use. It is called the Armorl, a compound of the names of its inventors, Messrs. Armstrong and Orling. It is controlled by wireless telegraphy in a very simple but effective manner. The rudder which steers it is connected to a small crank in such a way that as the crank revolves it turns the "helm" first to one side and then to the other. Suppose that, to commence with, the rudder is straight: a quarter of a revolution of the crank sets it to one side, say, the right: another quarter sets it straight again: a third quarter sets it to the left: and so on. The crank is turned by a wound-up spring, the effect of which is, however, normally held in check by a catch. When a wireless impulse comes along the catch is lifted for a moment, the crank slips round a quarter of a turn and the rudder is moved accordingly. Every impulse changes the position of the rudder and by sending suitable series of impulses it can be set as desired and changed at any moment.

A difficulty with all these guided torpedoes is that they must carry some indication whereby their place at any moment will be made visible to the man in control. A little mast and flag would do, for example, but it would be a fair mark for the enemy's guns and being shot away would leave the torpedo uncontrollable. The same objection seems to apply to the wireless antenna which this last type must carry with which to receive their guiding impulses, but that can be made light and almost invisible. It is when the thing is clearly visible that the danger arises, and, of course, to serve its purpose it must be visible. The way in which this difficulty was overcome by Messrs. Armstrong and Orling is a beautiful example of ingenuity. They cause a jet of water to be blown upwards by compressed air, something like the spouting of a whale, so familiar in books of natural history. That forms a mast which is clearly visible, yet the enemy may blaze away at it to their heart's content without damaging it in the least.