ABOUT THE DEADLY TORPEDO
 IF I were to ask you what a torpedo is, some of you might reply that it is a small ship that goes under the water
and attacks a large ship. Others might say that this is rather the description of a submarine, and that a
torpedo is a projectile shot from a submarine. But a torpedo is not a projectile; it does act like a big shell
in exploding when it strikes the enemy ship, but it is not thrown at the ship as a shell is.
You remember that when we were talking about bullets flying through the air we found that the ocean of air
offered a great resistance to the passage of the quickly flying bullet. And yet you can move your hand to and
fro in the air quite freely. You have no difficulty in realising that water is much thicker or what we call
denser than air. When you are bathing, you find that you cannot move your hand to and fro under the water,
without some effort.
 If the water did not offer considerable resistance to the movements of your hands and feet, you could not push
your way along as you do in the act of swimming.
When you are throwing a stone through the air the resistance of the air does not worry you very much, but if
you try to throw a stone under water, you will find that the great resistance of the water prevents your
throwing the stone to any distance. And so it is apparent that if a submarine had to shoot a torpedo at the
enemy ship, the submarine would require to be close up to the ship. It would also mean that the enemy ship
would require to be at rest, whereas a ship may be torpedoed while it is steaming along. It would also mean
that the submarine being so close would be blown up along with the enemy ship.
The boys or girls who suggested that a torpedo is a small ship that goes under the water and attacks an enemy
ship were quite correct. A torpedo is just a small submarine; it has propellers and engines to drive it along;
it has a steering rudder and also diving rudders to keep it at the required depth. But there is no one on
board this small ship to control it.
 Therefore it must be self-acting, or what we call automatic.
Of course the engines could be started before the torpedo left the submarine, and the torpedo could travel
along as your mechanical toys do. Those boys who have had clockwork boats will agree that a clockwork engine
would not be good enough for a torpedo which has to travel a long distance and which must go very quickly if
it is to hit the moving enemy ship. A steam-engine cannot be used, as the torpedo is a submarine. However, we
may use compressed air to drive an air-engine instead of a steam-engine. This is the most convenient kind of
engine to put on board a torpedo, so we have one part of the torpedo filled with compressed air.
We all had one complaint against our mechanical toys: they set off very well, but they fell off in speed very
quickly, getting slower and slower, until they came to a standstill. The reason was that as the clockwork
spring unwound, the pressure became less and less. Now there is the same difficulty about compressed air; as
the air is withdrawn to drive the engines the pressure of the remaining air
 becomes less and less. This would not matter if the torpedo could reach the enemy ship before the falling off
of the air pressure began to tell. But the submarine may be required to strike the enemy ship from a distance
of, say, a quarter of a mile, and before the torpedo had travelled that distance its speed would have begun to
fall off considerably. As for discharging torpedoes from battleships, it is not likely that the ships would
ever get within such close range, unless in fog or darkness, for their great guns would enable them to destroy
one another from a greater distance. You can understand how necessary it is that the speed of a torpedo must
not fall off. In the great naval battle off Jutland (June, 1916) some of our warships discharged torpedoes at
enemy ships which were about three miles distant. The invention which enables the torpedo to continue at full
speed is very ingenious, but unfortunately it is not permissible to describe it.
You must not picture the torpedo travelling along at a speed similar to that of a mechanical toy. If the
torpedo cannot travel quickly it is of no use; it must make haste if it is to strike the moving steamer. I ask
the boys to guess
 at what speed the torpedo travels. Knowing that the great shells from some of our giant guns set off with a
speed of 2000 miles per hour, one boy guesses that a torpedo travels about 1000 miles per hour. But this boy
forgets the great resistance offered by the water, and he also forgets, what is of more importance, that the
torpedo is not shot off like a shell. Remembering that a submarine does not travel any more than ten miles an
hour while under water, another boy suggests that a torpedo travels at a similar speed, but a torpedo can
travel four times as fast as a submarine. The speed of a modern torpedo may reach 36 knots, which means 36
nautical miles per hour, and as a knot is equal to about 14 land miles, 36 knots is equal to about 41 miles
A TORPEDO ON BOARD A MAN-OF-WAR
YOU CAN SEE THAT THE TORPEDO
IS SOMETHING LIKE A GREAT FISH, AND HAS A PROPELLER AT ITS TAIL. HOW THESE DEADLY WEAPONS CAME TO BE
INVENTED IS EXPLAINED IN CHAPTER 11.
We see how this little automatic ship, called the torpedo, can fly along through the water from the submarine
to the enemy ship. But suppose a current of water should turn the nose of the torpedo to one side, off it
would go in a wrong direction. That would render it useless, as it would not strike an enemy ship. But one boy
says that the torpedo has a steering rudder to keep it travelling straight; if he
 thinks for a moment, he will remember that when out in a boat we do not use the rudder only when we wish to
alter our course. We have to keep using it to counteract the effect of the water currents which would turn us
out of our way. But the torpedo would appear to be in a hopeless state, as it has no one on board to control
the steering rudder. It looks as though we must just set the rudder as we think best, and chance that being
able to keep the torpedo on a straight course, but that is not what we do.
There is a very clever invention which controls the steering rudder of a torpedo. This is called a
"gyroscope." The gyroscope was not invented for this purpose. It is far older than torpedoes, but it has been
applied to the torpedo. Most of you will know what a gyroscope is. Some of you have played with a small
gyroscope sold as a toy. It is like the fly-wheel of an engine mounted within a ring. Here is a drawing of a
FIG. 9.—THE GYROSCOPE
YOU MAY HAVE SEEN ONE OF THESE
GYROSCOPES USED AS A SPINNING TOP. IN THE STORY YOU WILL READ HOW THESE GYROSCOPES ARE USED IN SUBMARINES.
You know how it resists any attempt to turn it into another position; it wants to stand steady in one
position. Suppose you mount a small gyroscope on a toy boat. You could
 turn the boat to the right or the left, and the gyroscope would keep on pointing in one direction. In a
torpedo the gyroscope will keep acting in the same manner, but this action
does not prevent the torpedo turning one way or the other. The gyroscope is made to control the steering
rudder. If the torpedo tends to turn to the left, the gyroscope, refusing to turn, pulls the steering rudder
so that the torpedo cannot go to the left. If the torpedo tends to turn to the right, then the gyroscope
 pulls the rudder the other way and keeps the nose of the torpedo straight.
One boy suggests that a very strong water current, by keeping pressing the nose of the torpedo round, might
cause such a strain on the rudder that it would in the end succeed in turning the gyroscope. He is quite
right; the gyroscope could be forced to alter its position in this way, but the difficulty is overcome just in
the same way as the difficulty in steering a great steamer is overcome. If a sailor had to turn the rudder of
a very large steamer, he might find a current of water pushing his ship round so hard that he could not pull
the rudder against it, and so the rudder might force his steering wheel round in the opposite direction to
that in which he tried to move it. You know how this difficulty is overcome by making small engines do the
actual work of turning the rudder. The man at the wheel only controls those little engines which turn the
rudder. When he turns his steering wheel in one direction, one of the two engines pulls the rudder to the
right, and when he turns the wheel in the other direction, the other engine pulls the rudder to the left. No
matter what water
 current opposes the movement of the rudder, these do not worry the man at the wheel, as the engines take up
all the strain. The gyroscope is just in the same position as the man at the wheel. All the gyroscope does is
to control two small air engines which turn the steering rudder. Any opposition to the movements of the rudder
does not reach the gyroscope. And so we see how the torpedo can be kept steering straight at the enemy ship.
But it is most important that the torpedo does not duck down any lower in the water or rise to the surface.
We saw how the Commander of the submarine had to operate his diving rudders constantly, to keep the submarine
at the required depth; how the Commander had to watch a pendulum arrangement to see that his boat was
travelling in a level course; and how the water-pressure gauge told him at what depth he was. How is the
torpedo to do all this on its own account?
Instead of an ordinary water-pressure gauge, which merely indicates the amount of pressure, and leaves the
observer to take action, the torpedo has a special water gauge. The pressure of the water pushes against a
 plate; what we call a diaphragm. You have such a diaphragm in a telephone receiver; it is made of a thin sheet
of iron, and is fairly flexible. In the water gauge the diaphragm is caused to bulge inwards when the pressure
increases, and you know that the pressure will increase if the torpedo should sink into deeper water.
Therefore if the torpedo should tend to duck downwards this diaphragm will bulge inwards, and in so doing it
will move the diving rudders, so that they cause the torpedo to steer upwards. On the other hand, if the
torpedo should dive too far upwards, the diaphragm will not bulge in, and the diving rudders still steer the
torpedo downwards. Of course the diaphragm and the diving rudders have to be arranged to balance each other at
the depth at which the torpedo is to keep.
While this ingenious arrangement would ensure that the torpedo did not rise too high or fall too low, the
torpedo's course might be something like that of a switchback; in any case, it is not likely that its course
would be level, and so there is added a pendulum arrangement, which also controls the diving rudders and helps
to keep the torpedo level.
 By the very clever invention just described, we can depend upon the torpedo travelling straight to the enemy,
provided it is well aimed to start with.
Although the torpedo is not to be shot at the enemy ship, it is necessary to give it a good send-off. We saw
in the previous chapter that it is dispatched from a torpedo tube. As the submarine is not at rest, and as the
enemy ship is almost sure to be in motion also, it is necessary to lose no time in setting off the torpedo.
The necessary push-off may be given by compressed air.
When it reaches the enemy ship, the torpedo must explode, and how this takes place will be explained in the
following chapter. But we have been talking about the torpedo as though it belonged entirely to the submarine,
and if you knew nothing of the subject you might imagine that the idea of the torpedo had been got from the
invention of the submarine. The torpedo is practically an automatic submarine, having propellers, steering
rudders, and diving rudders, which might pass as copies of those of the submarine. But that is not how the
torpedo came to be invented, for this ingenious
 torpedo was invented before we had any submarines.
Our great battleships carry torpedoes, but ships which have guns capable of hitting the enemy ten miles away
cannot often have opportunities of using torpedoes. A torpedo may be fired from a tube on the deck as well as
from a tube under water, as, once in the water, the torpedo will keep the required depth. Seeing that the
great battleships were not likely to get close enough to the enemy to use their torpedoes, it was suggested
that we should have special torpedo boats. Although it is possible to send a torpedo nearly three miles, it
would not be easy to hit a moving ship at such a distance.
You have heard people speak of torpedo boats and torpedo boat destroyers, and I have been asked more than once
what is the difference between these two kinds of boats. The torpedo boat was built specially to get close
enough to the enemy ship to fire torpedoes at her. In the dark one of these torpedo boats might succeed in
getting close enough to send a torpedo, but in daylight the only hope would be for a group of these boats to
 enemy, and trust to one of them striking the enemy ship before the torpedo boats were all sunk.
The invention of these torpedo boats gave rise to the torpedo boat destroyers. These destroyers were made to
travel so fast that they could overtake the enemy torpedo boats, and with quick-firing guns destroy the
torpedo boat, thus ridding the great battleship from the danger of torpedo attacks. These destroyers were
fitted with torpedo tubes, so that they became torpedo boats and destroyers combined, and therefore we have no
need of the original boat nowadays. It requires very little imagination to realise that the submarine has a
far better chance of using torpedoes, as the under-water boat can get within half-a-mile or even a quarter of
a mile of the enemy ship without being seen.
In the illustration facing page 160 we see that a modern battleship still carries torpedoes in case she should
happen to get close enough to an enemy ship. But for the invention of a submarine the torpedo would never have
come to be the deadly weapon which it now is.