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
substituted 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 associated 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 shore 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 title 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 passes 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 shore 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 classes 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 anchored 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 passing 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 passing 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 pass from the link to the shore, 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 shore. 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 anchored 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, surreptitiously 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 assume 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 anchored 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 glass
vessels containing chemicals. The ship, striking a horn, bends it,
breaks the glass, 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 passing ship,
but the arm simply trails or scrapes along. Thus the mine turns in
relation to the arm, and a trigger is thereby released, which fires the
mine.
In this, be it noted, the ship only pulls the trigger, so to speak, and
releases a hammer which does the work, just as the trigger of a gun
releases the hammer. The motive force which makes the hammer do its work
when the trigger is "pulled" is the pull on the anchor rope. That
arrangement has a virtue which is not apparent at first sight.
Since it is the pull on the anchor rope which actually fires the mine,
it follows that if such a mine break away from its moorings it instantly
becomes harmless.
Safety for the men who lay the mines is secured in several ways. One is
by the use of a hydrostatic valve. The firing mechanism is locked until
the pressure of water releases it, and that pressure does not exist
until the mine is several feet under water. Another way is to seal up
the firing mechanism with a soluble seal made of some substance such as
sal-ammoniac. The mine cannot then explode until it has been under water
long enough for the seal to be melted.
It now remains to relate how these mines are swept up and removed, yet
there is very little really to tell, for the process is so exceedingly
simple. So far as is generally known, no method has been found that is
superior to the primitive plan of dragging a rope along between two
ships so as to catch the anchor ropes. The vessels employed are usually
of very light draft, so that they stand a good chance of passing over
the mines themselves, and the rope used is as long as possible, so that
a mine, if exploded by being caught in the loop of the rope, explodes so
far away as to do no harm.
When dragged to the surface the mines are exploded from a distance by
shots from a small gun, or even from a rifle. In the case of those mines
which have horns, a blow from a bullet is enough to break the glass and
cause explosion, and in all cases mines seem sooner or later to succumb
to a sharp blow. Thus they are destroyed, by their own action, at a safe
distance from the sweepers. Accidents happen, however, and mine-sweeping
is no job for anyone but the bravest.
It has been somewhat difficult to crowd a description of torpedoes and
mines into the small space of one chapter, and so many details have had
to be omitted, but the above descriptions give the broad, general
principles underlying practically all forms of these terrible weapons.