The submarine is first, last, and all the time an engine of death and destruction. Even in the earliest underwater experiments, you will remember, it was fitted with a bomb the sole purpose of which was to blow the enemy ship to atoms.
The old bomb idea proved next to worthless, for it was a very hard job to fix it to the ship to be sunk, and even if the submarine operator did succeed in so doing it was at best a dangerous piece of business, and so the odds for its failure were about as 100 is to 1.
As soon, therefore, as the submarine had been developed to a point where it was clear that it was the coming weapon of modern naval warfare, inventors began to rack their brains for some scheme which would do away with the danger and uncertainty of the old-fashioned bomb, and to make the submarine safer for its crew and deadlier for the enemy.
Many attempts were made, but its improvement was very slow, for the old idea of the simple bomb was firmly fixed in the minds of the inventors and it was hard for them to break away from it.
After a long time, though—that is to say in 1860—Captain Lupius, an Austrian inventor, hit upon a new and novel plan for a torpedo which would travel under water, by means of a little motor in it and a pair of wires which connected it with the submarine so that it could be directed at will.
The First Submarine Torpedoes.—Lupius took his idea to Whitehead, an English engineer of genius and ability, and he built the first controlled torpedo which traveled under its own power in 1864. Then Whitehead did a little thinking on his own account and he built the automobile torpedo in 1868, the cleverest and most diabolical destroyer that man has ever yet been guilty of.
The automobile torpedo is one that not only runs under its own power but that steers itself as well after it has left the torpedo tube of the submarine. To Whitehead, then, must be given the credit not only of having invented the submarine torpedo that is used with such telling effect in the present war, but of making a success of it. The Germans, though, with their great dislike for everything of British name and make call their torpedo of this type blackheads.
How to Make a Model Submarine Torpedo.—Before I explain how a real automobile torpedo is made and works, I will tell you how to make a model torpedo which, while it will not explode at the end of its trip through the water, will show you how a real torpedo does its work.
The Body of the Torpedo.—Get a piece of nice soft pine 1½ inches in diameter and 10 inches long, and whittle it out to the shape shown in Fig. 36. Cut a groove down the middle of it ¾ inch deep and ¾ inch wide, to within an inch of each end. This done, screw a small screw-eye in the warhead of the torpedo, as the blunt nosed end of it is called, inside the groove.
Bore a ⅛-inch hole through the propeller end, and slip a piece of brass tube 2 inches long which has a bore of inch in it to form a bearing for the propeller shaft. Get a brass rod 1/16 inch in diameter and 2¼ inches long; make an eye on one end and then push the rod through the brass tube in the tail or propeller end of the torpedo, as shown in Fig. 36, and this is all there is to the propeller shaft. Now cut a propeller out of tin, as shown at E, in Fig. 37, and solder it to the end of the propeller shaft.
The Steering and Diving Rudders.—The torpedo, like the submarine itself, has two rudders, one for diving and one for steering.
To make the steering rudder, which is the vertical one, cut out a piece of heavy tin 1½ inches wide and 1¾ inches long, as shown at A in Fig. 37; cut out one edge ⅜ inch deep as shown by the shaded part, which will leave a tongue sticking out from each corner, and bend these to form little tubes.
Cut off two pieces of wire ⅛ inch thick, have each one 2½ inches long, and bend them as shown at C. Next drill two holes through the tail or propeller end of the torpedo, force the sharp ends of the wires into them and then put the other ends into the tubes of the rudder.
The diving rudder, which is the horizontal one, is made like the steering rudder except that the tongues for the hinge tubes are dropped down a little and a slot ½ inch wide and 1¾ inches long is cut out, as shown by the shaded part at B.
This rudder is 1½ inches wide and 2⅛ inches long; it is fastened by a pair of ⅛ inch wires to the tail end of the torpedo in the same way as the steering rudder. This arrangement leaves enough room for the propeller to turn inside of the wires, as shown at C.
The Rubber Strand Motor.—The next thing to do is to fix one end of the rubber strands to the screw-eye in the warhead and the other end to the eye of the propeller-shaft. This gives you a cheap and simple motor that is at once light, powerful, and easy to manage.
Cut out a cover of wood to fit over the groove containing the motor, as shown in D, Fig. 37, and screw it to the body of the torpedo. Melt some paraffin wax and run it around the cracks to make the motor chamber watertight.
Bore half a dozen or more holes ½ inch in diameter and about an inch deep along the exact middle of the bottom of the torpedo; fill each hole with shot and seal them in with sealing-wax. There must be enough shot in the bottom to weight the little torpedo so that it will just sink on an even keel when you put it in the water. Finally, paint the torpedo all over with black enamel (you can buy it in drug stores for 10 cents a can), and your model torpedo is ready for its deadly work.
Your Torpedo in Action.—To set your model torpedo scooting under the water and, perchance, aimed at an enemy ship, fix the steering rudder in a line with the long axis of the hull and tilt the diving rudder at a very slight angle, say about 2 degrees, down from the top of the torpedo.
Hold the hull with your left hand and wind up the rubber strand motor good and tight by turning the propeller clockwise—that is, in the direction the hands of a clock move—with your right hand. When you have done this, push the torpedo down under the water, let go of the propeller and she will shoot forward as though shot by compressed air from a torpedo tube.
After it has made a run of from 25 to 100 feet—the distance depends on the skill you have shown in building it—it will sink to the bottom.
Of course if you are playing a naval war game and you are shooting at some enemy ship, it will give her a good hard bump, and this counts ten points in your favor.
How a Real Torpedo Is Made.—A torpedo, as you can plainly see, is nothing more nor less than a miniature submarine boat that moves under its own power and that is self-controlled. And now that you have built and experimented with a little model it will be easy for you to understand how a real one is made and works.
The Warhead of a Torpedo.—A real torpedo such as is shot by a submarine to sink real ships is made of three chief parts, as far as the outside of it is concerned. These are: (1) the warhead, (2) the body, and (3) the tail.
The warhead is the blunt-nosed hollow part that forms the business end of the torpedo; it contains two things: (a) the charge of high powered explosive which plays such terrific havoc when it is touched off; and (b) the detonating mechanism which fires it.
The High Powered Explosive.—The explosive used is either guncotton, or nitrocellulose, to call it by its chemical name, or tri-nitrotoluene (pronounced ni-tro-tol´-u-en) and which is called TNT for short.
Guncotton is simply ordinary cotton which has been treated with nitric and sulphuric acids; when this is done it becomes highly explosive.
TNT is toluene, a chemical formed of hydrogen and carbon, which has been treated with nitric acid. It is used by the Germans in the warheads of their submarine torpedoes because it is a more powerful explosive than guncotton. Besides it can be melted as easily as lard and poured into the warhead, which makes it an easy, quick, and safe job to fill them. Further, it does not explode easily by shocks when it is transported but it instantly explodes with a detonator.
The reason these explosives cannot be ignited by fire but explode when struck a sharp tap is because they are very unstable compounds; that is, they are very easily decomposed into their original chemical parts.
Curiously enough, but by the very discovery of this advanced scientific principle men are now able to make the mightiest, which means the deadliest, explosives that the world has ever known and this makes war a thousand times as terrible now as it was in the olden days when men fought their battles at close range with their ancient lances and cross-bows.
The Detonating, or Firing Mechanism.—A modern submarine torpedo has a diameter of from 18 to 21 inches through the warhead, and this is loaded with from 200 to 330 pounds of guncotton or TNT, as the case may be.
This charge is exploded by a firing pin, or pistol, as it is called. This firing pin goes clear through the charge and into a percussion cap, which sets just back of the charge; the other and front end of the firing pin goes clear through the warhead and has a threaded end on which is screwed what is known as a butterfly-nut.
The percussion cap is simply a little copper cup and in it is placed a small charge of an explosive which is easily detonated by the percussion of the pin, that is by the pin striking it. The explosive mostly used in percussion caps is mercuric fulminate, which is a compound formed of mercury, carbon, nitrogen, and oxygen.
Since it is the violent explosion of the percussion charge which strikes the main charge of the high explosive in the warhead, and the fire made by the explosion of the percussion charge has nothing to do with it, the main charge of guncotton, where this explosive is used, is often wet down with water before it is packed in, for by so doing a great deal more of it can be put in the same-sized space.
A safety pin (see Fig. 38) is set into the firing pin, so that by no possible chance can the latter pin work loose and explode the charge until it strikes the ship it is intended to destroy. Also the butterfly-nut, which I spoke of above, is used as a further safety factor.
The safety pin is simply a pin which is threaded on one end and which extends down through the steel casing of the warhead and screws into the firing pin, or pistol, and holds it securely so that it cannot strike back against the charge until it is unscrewed and taken out or broken off, when it strikes the ship.
The butterfly-nut is simply a thumb nut with a couple of wings on it. When the torpedo is shot out of the torpedo tube the butterfly-nut, which is screwed up close to the warhead on the firing pin, begins to unscrew itself by the action of the water on the wings, which now form little propeller blades; by the time the nut reaches the end of the firing pin and drops off, the torpedo is quite a distance from the submarine which shot it. In this way, all danger of the torpedo’s exploding when it is in, or leaving, the submarine, is done away with. Fig. 38 shows a cross-section of the warhead and just how the detonating mechanism is made and works.
The warheads of the latest torpedoes, especially those used by the Germans, are fitted with steel cutters, so that they can cut their way through nets which ships may spread out to protect themselves.
The Body of the Torpedo.—The next part of the torpedo is the body, and there are five separate and distinct parts to it. These we have named in the order of their position, and they are,
(1) The air pressure chamber; (2) the balance chamber; (3) the power chamber; (4) the buoyancy chamber, and (5) the tail-piece which supports the propellers and the rudders.
The Compressed Air Tanks.—The air pressure chamber is simply a large steel tank and air is pumped into it until it is under a pressure of about 2,000 pounds to the square inch; this means that for every square inch of the surface of the tank there is a force pressing against it of about one ton.
The air is let out of the tank through what is known as a reducing valve, which is in turn connected to the engines, and more about it will be said a little later. A reducing valve is simply a valve that regulates the amount of air which flows from the tank into the engine and keeps it at the same pressure all the time.
If the valve were not used, the air in the tank, which is at first under 2,000 pounds pressure, would drive the torpedo forward at a tremendous rate of speed at first, but as the air from the tank was used up by the engine it would lose pressure and the torpedo would soon stop altogether. But when a reducing valve is used the torpedo keeps up its same high speed until it has run its course and has either hit the ship or missed it.
What Is in the Balance Chamber.—In the balance chamber is the mechanism that controls the steering and the diving rudders, and it is these that keep the torpedo on a straight course and at the right depth under the water.
The controlling mechanism is formed of four chief devices, which are (1) a gyroscope (pronounced ji´-ro-skop); (2) a compressed air motor, which drives the gyroscope; (3) a water pressure control; and (4) a pendulum control.
The Automatic Gyro Control.—The gyroscope, or just gyro, as it is called for short, is a kind of spinning top and you can buy a toy one for a quarter.[22] It is simply a heavy wheel fixed to a shaft, or spindle, and this is pivoted in a ring, as shown at A in Fig. 39.
Now hold the gyro as shown at B and give the wheel a good spin. This done, walk straight ahead, and as long as you do so you will hardly know that you are carrying the gyro, but the moment you try to change your direction you will feel the gyro twisting in your hand to counteract the movement.
This is the purpose of the gyro in a torpedo, but in this case the wheel is very heavy and it is revolved at a high speed by a compressed air motor. The gyro is set with its shaft at right angles with the long axis of the torpedo, as shown at C.
Now, just as long as the torpedo moves straight ahead in its course, the gyro has no effect on it, but the moment the torpedo tries to swerve from one side to the other, or shift out of its course, the gyro pulls it back by acting on the steering rudder; it does this by regulating the air supply of a compressed air motor, called the servo-motor, and this in turn works the rudder by means of a series of levers. In this way the torpedo is automatically kept to its course.
The Hydrostatic, or Water Pressure, Control.—The water pressure control is one of the devices which keeps the torpedo at the right depth in the water.
It consists of a steel cylinder with a piston working in it. A cylinder which is open at both ends is set in the hull of the torpedo so that one end opens into the water outside. A spring presses against the piston on the inside of the hull and the water presses on the piston on the outside.
The spring can be adjusted by a screw to just balance the pressure of the water at any depth. A small valve rod is fixed to the piston, and this opens a valve which lets compressed air into a motor when the pressure of the water is greater or lesser than the pressure of the spring and this in turn works the diving rudder as shown in Fig. 40.
Suppose, for example, that the captain wants the torpedo to travel at a depth of exactly 15 feet during its whole course. The spring is adjusted to offset the pressure of the water at this depth, and the torpedo is launched. Should it for any reason try to go deeper than 15 feet or to rise above 15 feet, the spring or the water presses on the piston and closes or opens the air valve of the motor, when it moves the diving rudder up or down until the torpedo is brought back to its right depth.
The Automatic Pendulum Control.—The water pressure control, however, is not enough to make the torpedo stick to an absolutely constant depth, and so to help it a pendulum control is also used.
This control consists of a pendulum which swings to and fro from fore to aft as the torpedo dives and rises, and it also starts the compressed air motor which operates the diving rudder, and this brings the torpedo back to its proper depth. It is shown in Fig. 41.
The Engine That Drives the Torpedo.—Next comes the engine that drives the torpedo, and it, too, is run by compressed air.
As I mentioned before, the air which runs it is regulated by a reducing valve, but there is another important part of the power plant, and this is the heater for heating the compressed air before it is admitted to the engine.
Compressed air is as good to run an engine with as steam, for both of them have tremendous powers of expansion. As soon as the air is released from the supply tank—which keeps it compressed in a space that is many times smaller than it would take up when it is free—and has passed into the cylinders of the engine, it begins to expand, or to spread out in every direction, exactly as steam does.
Now when air is pumped into the tank it gets very hot and this heat is stored up in the air as energy; this makes the air when it is released expand with much force and gives it the power to do useful work.
But as the air is let out of the tank through the reducing valve it expands and loses its energy—or latent heat, as it is called—and this makes it lose its power to keep on expanding to its greatest extent and so it gets weaker and weaker.
To overcome this bad feature of compressed air, a heater is fixed on the engine, and just as the compressed air reaches the cylinders of the engine it is suddenly heated and this gives it all the expansive force it needs. The heater consists of a small oil-burner which is so fixed that the instant the torpedo is shot from the tube an electric spark ignites the oil, and there is, in consequence, neither the loss of time nor power.
The engine is often of the cylinder and piston type and is built quite like an automobile engine, except that the inlet valve—which lets the air into the cylinders—is disk-shaped so that it can operate all the cylinders one after another. The exhaust ports open outside of the torpedo, and it sets up a tell-tale white streak of bubbles on the surface of the water.
Some torpedoes as, for instance, the Bliss-Leavitt, use a rotary engine. But whichever kind is used, the power plant develops from 30 to 50 horsepower, and thus each torpedo weighs about as much and is as costly as a high-priced motor car.
The Propeller-Shaft and Propellers.—The Propeller-Shaft.—The engine drives the propeller-shaft, or, as it is called in England, the cardan-shaft. To the end of this shaft outside of the torpedo is fixed one of the propellers.
Another hollow shaft is slipped over the first shaft and one end is connected to the engine and to the other and outside end of the shaft another propeller is keyed on. This shaft is driven in the opposite direction to the solid shaft inside of it by gears that is, a set of cog-wheels.
The Propellers.—The propellers have four blades; and the reason two propellers are used is to counteract the force of each other. That is to say, if only one propeller is used, the force of the blades striking the water tends to tilt the craft to one side, and hence by using two propellers this effect is very largely offset.
The Steering and Diving Rudders.—The vertical or steering rudder and the diving or horizontal rudders are hinged to a frame around the propellers as shown in Fig. 42.
As it takes a lot of power to move these rudders against the varying water currents, an air engine must be used to work them instead of levers that are connected directly with the gyro, pendulum, or water pressure controls.
How a Torpedo Is Shot at a Ship.—And now comes the most exciting moment of all, and that is when a torpedo is shot from a submarine at an enemy ship.
The latest type of submarine usually has eight torpedo tubes, four of them fore, and four aft. These tubes are shaped as shown in Fig. 43, and are built right into the hull of the craft.
Now, when we say that a torpedo is shot from a submarine we do not mean that it is fired from it, for it does not explode until it hits the ship it is aimed at, but we simply mean that it is forced out of, or driven from, the tube of the boat.
The force that drives the torpedo from the tube is our old friend compressed air, and this is taken from the torpedo air tanks of the submarine; they are placed just above the torpedo tube and are connected with the rear part of it.
Shooting the Torpedo.—Now let’s see just what happens from the moment an enemy ship is sighted up to the time the torpedo hits it and explodes.
An up-to-date torpedo makes about 40 knots, and it will travel about six miles before its compressed air is used up. But it cannot be aimed and shot with certainty at a distance of over half a mile. So when an enemy ship is sighted, the submarine creeps up upon her, with nothing but her periscope out of the water, until she is within accurate shooting range.
In the meantime the speed of the enemy ship has been calculated, the depth at which the torpedo must travel to strike the ship below the water-line has been determined, and the angle, or course, the torpedo must take to hit the ship is figured out.
Due allowance must be made for the speed of the ship and the speed of the torpedo to the end that the distance both will travel in a given time may be known. Of course, if the ship is speeding along and the torpedo is shot point-blank at her it will pass a good many yards astern of her.
This operation is very much like that of rabbit hunting, in which you do not fire directly at the running rabbit, but aim several feet ahead of him, and he simply runs into the bullet or shot. So it’s all his fault if he gets killed. Just so with the ship and the torpedo; for instead of the torpedo running into the ship, the ship runs into the torpedo, and so if the ship sinks it isn’t the fault of the torpedo—or at least that is the way the German captain of a U-boat looks at it.
Before the torpedo is loaded into the torpedo tube the safety pin is taken out of the firing pin and the butterfly-nut is loosened so that it will unscrew easily. The torpedo is then slipped into the tube and the breach-block of the tube is closed. The compressed air is now turned on at the torpedo air tank; when the air rushes into the torpedo tube behind the torpedo, but the latter is kept from being forced out by a lock.
The Course of the Torpedo.—Next the captain sights his ship and finds its speed and its distance from his own craft. To direct the torpedo so that it will hit her target fairly, an instrument called a torpedo director is used. It is shown in Fig. 44, and this picture also shows how the torpedo and the ship come together.
Now as the torpedo tube is fixed in the hull of the submarine the whole craft must be turned and aimed at the enemy ship. To do this the torpedo arm of the director is set parallel with the torpedo tube; then the torpedo speed scale is adjusted at the speed that the torpedo makes and which is known.
The speed of the distant ship having been calculated, the ship speed scale is set at that speed and parallel to the ship’s course, and this brings the sight arm in line with the observer’s eye and the line that the ship is sailing.
When the ship crosses the line of sight the catch of the lock is released, the compressed air blows the torpedo out of its tube, and away she goes. The instant the torpedo has left the tube the engine and other contrivances start to work and it then moves swiftly and surely over a straight course.
Long before the torpedo reaches its goal the butterfly-nut drops off, and so when it strikes the ship the firing pin which projects out of the warhead is pushed back with a deal of force and explodes the charge which either sinks the ship or cripples it.
A Torpedo with a Cannon in It.—Lieutenant Davis, of the U. S. N., has invented a new kind of warhead for torpedoes, one that is even more deadly than the style I have described.
It is made by placing a cannon in the warhead. When the torpedo strikes the ship the cannon shoots a projectile clear through the hull and into the inside of the ship, where it explodes. As the projectile is fitted with a time fuse, it does not explode until it gets well into the ship, and then it does far more damage than the old-style of warhead, which explodes just as it strikes the hull. The projectile is loaded with 250 pounds of guncotton or TNT but the warhead is not loaded at all.
On the submarines that are now being built cradles which hold several extra torpedoes are fitted to the decks, and in this way the number of torpedoes which can be shot is increased.