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We have seen how the miniature automatic submarine which we call a torpedo can make its way along under water to an enemy ship. We wish to see now how the torpedo explodes on reaching the enemy.
Picturing the torpedo as a great fish, we think of the head being filled with explosives. At the very nose is a projecting pin which, if driven forcibly inwards, will explode the contents of the head. Therefore as soon as the torpedo strikes the enemy ship a violent explosion occurs, causing a great hole to be torn in the hull of the ship, so that she sinks very quickly.
The torpedo contains a very powerful or what we call a very high explosive, so great care must be taken that it is not exploded accidentally when handling the torpedo. In the illustration facing page 160 you see some sailors cleaning a torpedo, but you may be very sure that it has no explosive head. While practising torpedo-firing, the explosive head is replaced by a dummy head filled with wood to bring it up to the weight of the real head. Even in warfare, when a torpedo has to be fired at an enemy ship, the explosive head is not attached until required.
It would be disastrous if the torpedo were to be accidentally exploded while getting it into the tube, so a safety-pin is kept in until the torpedo is being pushed into the tube. This makes it quite impossible for the torpedo to be exploded by an accidental blow. But there must be no possible chance left of the torpedo exploding during the act of sending it off from the tube, and this is arranged by a clever invention.
I have seen children in a country village running about with little paper windmills on the ends of sticks, probably having got them from some travelling rag merchant in exchange for some rags. As the children run through the air these little windmills spin round and round, just as propellers do. Perhaps some of you have seen little brass propellers used as an ornament or mascot at the front of a motor-car. As the motor-car travels through the air this little propeller spins round. There is an arrangement something like this on the nose of a torpedo.
It is needless to say that the little propeller or water-wheel arrangement on the front of a torpedo is not for ornament. As the torpedo is forced through the water this little water-wheel spins round. When the torpedo sets out on its journey, this little water-wheel is in a position which prevents the piston-pin being driven in to cause the explosion. As the torpedo flies through the water, the little water-wheel gradually works its way along a spindle, and by the time the torpedo has travelled about fifty yards, the piston is free of the water-wheel and may now be driven inwards.
Even this ingenious precaution is not considered sufficient. The resistance of the water is great, so there must be no possibility of the piston being driven in by the pressure of the water. To secure this the piston is still held by a little copper pin, and only a powerful blow will break this pin, and release the piston or plunger which is to provide the explosion. When the torpedo travelling about 30 or 40 miles per hour strikes the ship, this little copper pin is broken, allowing the plunger to fire the explosives.
If you should read the history of torpedoes you will find it stated that during the American Civil War at least 25 of the Federal ships were blown up by torpedoes. This statement is misleading to us nowadays, when we have come to think of a torpedo as a small automatic ship, propelled under water. The torpedoes used in the American Civil War were not like that; they were mostly floating mines, which would explode when a ship struck them. We still use such mines. One of the vessels in the American Civil War was destroyed by a moving torpedo, but in this case the torpedo was carried on a spar at the bow of a boat, which was mostly submerged in the water, so that it could creep up to a warship in the dark. Late one evening the Commander of a United States warship thought he saw a plank in the water coming towards his ship, and then a great explosion took place beneath his ship. This early attempt at a submarine was a boat not entirely under the water, and the whole boat really acted as a torpedo, which meant that when the explosion occurred down went the crew of the attacking boat along with the enemy ship.
The next idea was to send out torpedoes attached to cables, by means of which they were driven along and guided also. It was such a torpedo that was the ancestor of our modern torpedo. About fifty years ago, an officer in the Austrian Navy invented a small automatic ship which could carry an explosive. It travelled on the surface of the water, being driven along by means of a small engine, and it was guided by ropes attached to it. This little ship exploded when it struck the enemy ship. The Austrian Government did not think much of the invention, but the inventor thought it might be made into a practical war machine, and he applied to an English engineer, who happened to be in charge of some engineering works in Hungary. The name of this English engineer was Whitehead, and his name has become famous in connection with torpedoes. Many boys have heard of the Whitehead torpedo. It was through the failure of this Austrian naval officer that Whitehead came to think about torpedoes. He got a trusted mechanic and his own son (then a boy) to work with him in secret. It took them two years of hard work to turn out the first Whitehead torpedo. It was rather erratic in its behaviour, but the British Government saw that there were great possibilities in a weapon of this kind, so they bought the patent rights of the invention, and they encouraged Whitehead to go on improving this little automatic ship. One improvement followed another, until there appeared the torpedo as described in the previous chapter.
You can easily guess that a torpedo must cost a very great deal more than a high explosive shell. The torpedo has so much delicate machinery, and has to be so very carefully made, that the latest American torpedoes have cost as much as $7000, which is equal to about £1400. This is a lot of money, but a single torpedo may sink a great battleship costing £1,000,000.
During the great European War we heard a great deal about floating mines. Many of these drifted about and were struck by warships. The mines thereupon exploded and the great ships were sunk. These deadly mines are ingenious inventions, but they are descended from the early mines, which were very simple affairs. The first idea was that a soldier might bury barrels of gunpowder in the ground, so that when the enemy tramped over them the explosives would go bang, and blow them up. You can see from this how these weapons of war came to be called mines. Our armies still make mines in the ground, and to get near the enemy they have to dig tunnels, just as the coal miner does.
When the Navy came to place explosives, say, at the entrance to a harbour, there was really no connection with mining, but because the object was similar to that of the Army, the same word, "mines," was used to describe this means of blowing up an enemy. Fixed mines in the water might be blown up by means of an electric spark, wires leading out an electric current from the shore station.
You see that such mines were intended merely to defend our harbours and rivers against an enemy seeking to invade us, but if our ships were in harbour, and were to sink a large enemy battleship in the entrance to the harbour, we might lock our own ships in and render them useless until we could clear the entrance, and so when the submarine boat was invented, we counted these boats as much more able to deal with an invading enemy.
What are floating mines like? They might be described as steel shells or buoys filled with explosives, and having projecting horns, which, if knocked by any passing ship will cause the floating mine to explode, but that is not all. As the mine is floating freely the blow from the passing steamer might not be sufficient to cause an explosion, as is done in the case of a fast-travelling torpedo. To overcome this difficulty the horns may be made of glass protected by a lead cover, so that the passing ship bends the lead, and thus breaks the glass tube within. This frees some chemicals which act on a battery and cause the explosives to go off. There are some very ingenious floating or drifting mines which are called torpedo mines. These have a tank for compressed air, and they are provided with a propeller underneath them. The propeller is driven by clockwork, but the idea is not to make the mine travel along, but merely to keep it under water, and yet not too deep, so that it will remain in the way of a passing steamer. When it sinks below this depth the water pressure switches on the clock-work, and the propeller causes the mine to rise until, the water pressure being relieved, the propeller stops. In this way the mine, which would gradually sink, is prevented going below the depth at which it can trap a steamer. These torpedo mines have horns which when struck bring a battery into play and cause the mine to explode.
These mines, which are the invention of a Swedish engineer, were used by the Turks against some of our battleships in the Great European War, and the loss of several of our ships, and also one of the French battleships, was said to be brought about by these floating torpedo mines. However, by far the greatest number of mines are anchored, as will be explained in the following chapter.
It is apparent that drifting mines may be a great danger, as they may drift away beyond the war area, and be struck by a merchant or passenger ship not engaged in war, and belonging to nations that are not at war with anyone, therefore ships are not at liberty to scatter these mines wherever they like. Hence the wider use of mines that are anchored.