WHAT A SUBMARINE IS LIKE
The precise details of the submarines of our own navy or of any other
for that matter are wrapped in mystery. Those who might tell do not know
and those who know must not tell. True, there have been fully
descriptive articles in many books and magazines, but it may be safely
asserted that those descriptions are nothing more than what this chapter
avowedly is, reflections by the authors on what such a craft must be
like, more or less. It is just as well that this should be clearly
understood, and the following description does not claim to be any more
than that.
Just as an aeroplane follows the general design of a bird of the swallow
type, which soars without flapping its wings, so the submarine
necessarily follows much the lines of a fish. It has fins which help to
guide it, it has rudders which compare with the fish's tail, and while
it cannot use either fins or tail to push itself along as the fishes do,
it has one or more propellers which serve that purpose admirably. It is
rather remarkable that, while we often imitate nature very closely,
there is one very important mechanical feature which almost invariably
distinguishes man-made schemes from natural ones--that is, that man
uses rotary motion for many purposes whereas nature practically never
does. To be perfectly honest, the natural mechanisms are far too
difficult for us to copy or I expect we should do so. For example, watch
a goldfish and see how cleverly it uses its tail. Man could never hope
to make anything so perfect as that tail. Absolutely under its owner's
control, it serves a double purpose of propelling and steering in a
manner which is equally beautiful and impossible to imitate.
For certain definite purposes, however, a rotary propeller is quite as
good as anything which the fishes can show us. As a straightforward,
simple, forward-pushing device it is equal to anything that a fish
possesses. It has to be given that one duty, however, and no other, the
steering being the task of a separate device, the rudder. There again,
too, we see how nature does two things with one kind of mechanism while
we have to use two, for the fish steers itself to right and to left with
its tail in a vertical plane, but if it wants to steer upwards or
downwards it twists its tail over somewhat towards a horizontal plane.
The submarine, however, needs two distinct and separate rudders, one for
right and left steering and one for up and down, the latter being
generally a pair, one each side the vertical rudder for the sake of
symmetry and balance.
So we find that a submarine has a body like that of a fish except that
it is rather more rotund, perhaps, than the most portly fish usually
seen. It has certain fixed fins projecting from its sides, which
together with the rudders enable it to be guided. It has also certain
long fins called bilge keels for the purpose of keeping it from rolling
too much. Also, it has one or more propellers and the two kinds of
rudder already referred to.
A fish, never wishing to get outside itself and walk about upon its own
upper surface, needs no deck, in which the submarine differs from it,
for the crew require somewhere where they can enjoy a breath of fresh
air when opportunity offers. It is not a very commodious place, one
could not exactly take a long walk upon it, nor even play deck-quoits,
but on the back of the submarine there is an undoubted deck where the
men can get out and upon which they can stand when she is on the
surface.
A fish, moreover, takes little heed of things upon the surface: its
interests lie almost entirely below. Hence it has no conning-tower or
periscope, but without these the submarine would be useless. The former
is a little oblong tower something like a chimney, which projects upward
from the deck, while projecting to a higher level still is the tall
hollow mast with prism and lenses at the top called the Periscope,
through which the commander of the submarine, himself comparatively
inconspicuous, can sweep the horizon for enemies or victims.
The problem of constructing a ship to travel under water is quite
different from making one to travel on the surface in the ordinary way.
When deep down the pressure of the water tending to crush the vessel is
something enormous. Roughly speaking, it is a pound per square inch for
every two feet in depth, so that if a submarine dives to a depth of
fifty feet the water presses upon it with a force of about twenty-five
pounds upon every square inch of its surface. On a square foot, that
means over a ton. And there are many square feet of the surface in even
a small submarine. Consequently, the whole shell of the ship has to be
of very substantial construction. Moreover, there are curious strains
which come upon the vessel when it dives to which surface ships are not
subject. All these have to be reckoned as far as possible and allowed
for.
The size of the modern submarine is not known with any certainty, but we
may put it down roughly as two hundred feet long and at least a thousand
tons displacement, which means that that is its actual weight, including
everything and everybody on board, when it is just about to submerge.
Of course, a submarine, alone among boats, has two "tonnages." When it
is on the surface it is comparatively light. Indeed, "running light" is
the technical term describing it when it is riding upon the surface of
the water like an ordinary ship. Then, by increasing its weight, it can
cause itself to sink until the little promenade or deck called the
superstructure is just submerged and little can be seen above water
except the conning-tower. That is termed the "awash" position, and it is
clear that it is then displacing more water than when running light, and
hence its displacement tonnage must be more.
When it is desired to sink, the vessel is set in motion in the awash
position, from which it is gradually steered downwards by the diving
rudders, until only the periscope, or it may be not even that, is left
showing above. Then the maximum of water is being displaced. It is then
actually displacing more than its own weight of water, for if left to
itself it will rise rapidly and it is only the speed and the action of
the rudders which keep it under. We see, then, that the action of a
submarine in submerging itself is a real genuine dive. It sinks upon an
even keel until it is awash, after which it goes under "head-first,"
just as a swimmer does. It also rises bow first.
This tendency to rise when the combined action of movement and rudder
ceases constitutes a very considerable safeguard, for should anything
happen to the propelling machinery the vessel simply rises. At one time
weights were attached to the under side of the hull which could be
detached from the inside so that in the event of the vessel descending
against the wish of her commander, she could be simply forced to the
surface by the great excess of buoyancy resulting from shedding these
"safety weights." Of course, in the event of a serious perforation of
the hull neither of these forms of surplus buoyancy would bring the boat
up.
Let us now trace the operations of diving right through, supposing that
our submarine is first running light. In that condition she is being
driven by the oil engines which constitute her primary propelling power.
The hatch or door at the top of the conning-tower is open, as also, it
may be, is the one lower down, just at the foot of the tower. Men are
standing upon the little platform formed by the tower, and one of them
is steering by means of a wheel, keeping his eye, moreover, upon a
compass also provided there, that being in fact, to the submarine when
light, what the bridge is to the ordinary steamer. Other members of the
crew may be upon the superstructure or deck just below, while others
again are down inside, attending to their duties there.
Under these conditions the inside is by no means an unpleasant place.
Plenty of fresh air comes down through the open hatches and through the
ventilators, it being drawn down through the latter by means of a fan.
Preparations are then made for submerging. The hand-rail along the
little deck is removed. The upper steering wheel and compass are covered
up or shut away into the coverings provided for them, the wireless
apparatus, if provided, is removed and the mast shut down. Hatches are
securely closed and valves in the ventilating pipes are closed. In fact
every opening is shut and made water-tight so that no risk shall be run
of diving prematurely and taking in water accidentally.
The quarter-master transfers himself to the steering wheel inside, where
he has another compass to guide him, not of the magnetic variety this
time but a cunning application of the gyroscope. The commander, too,
having descended before the last hatch was closed down, takes his stand
at the eyepiece of the periscope, since that is now his only means of
seeing what is going on above.
Another man takes his place at the wheel which controls the diving
rudder, conveniently near to which is a pressure gauge so connected to
the outer water that as the ship dives its depth is recorded upon its
dial: that in effect is to him what the compass is to his comrade at the
other wheel.
With every movement of men there needs to be adjustment made to keep the
ship on an even keel. Otherwise she would go down by the bow or down by
the stern according as the men's weight shifted towards either end. This
is arranged for by two small tanks formed in the structure of the
vessel, one at either end. Connected together by pipes and controlled by
compressed air, water can be transferred from one to the other at will
and so the balance be always kept. Quite simple manipulations of a valve
serve to accomplish this delicate balancing performance. It is perhaps
not of such importance at this stage, but in a moment, when the whole
vessel will be under water, a very little movement indeed will suffice
to upset the equilibrium.
Next water ballast is admitted into certain other spaces in the ship's
structure, these spaces being called, because of the use to which they
are put, ballast tanks. Gradually, as the incoming water increases the
weight of the vessel, she sinks until she is awash. Then the diving
rudders are set at the right angle (a pendulum serves to show the angle
at which the boat points) and down she goes. As the pressure-gauge
indicates the approach to the required depth the rudder is flattened out
a little until just that position is found which keeps the boat under at
the desired depth.
Of course, when all hatches and openings were closed the supply of fresh
air was cut off and after that the crew had to depend upon the air
contained in the submarine. Also, they had to stop the engine, for
without air it cannot work: nor can it work without giving off fumes,
which, if admitted to the ship, would soon suffocate the crew. Just
before closing up, therefore, the engine is stopped and electric motors
take up the task of driving the ship.
Now suppose that, while running submerged, the commander espies, through
his periscope, an unsuspecting enemy. He tries forthwith to get as close
as he can. Having noted the direction of the vessel and which way she is
going and as far as possible her speed, he submerges more deeply, in all
probability, lest the white streak which represents the wake caused by
his periscope should reveal his presence. For possibly she is one of
those terrible destroyers in fair fight with which he has but a poor
chance. His only safety lying in complete invisibility, he therefore
submerges entirely, trusting to his calculations to lead him in the
desired direction. Thus he attempts and, if he have good luck, he
succeeds in getting reasonably near to his foe.
Then he must try so to man[oe]uvre that his bow shall at the right
moment be pointing towards the quarry, for his torpedo tubes are in the
bow and they are fixed, or nearly so at all events, so that he can only
fire them in a direction nearly, if not precisely, in the direction of
the centre line of his ship.
Nay, he must do even more than that. It will not do to fire the torpedo
directly at the ship, for a torpedo is comparatively slow. Suppose it is
capable of forty miles an hour, and the other ship is a mile away: the
torpedo will take ninety seconds to reach it. And in that time it may
have travelled a mile or so itself. So the submarine man has to allow
for that.
Occasionally, therefore, he comes up a little for a moment in the hope
of getting a sight of the enemy while not revealing his own presence.
Or perhaps he may decide to risk being seen and caught, trusting
to the chance of getting his own blow in first. He needs to be a
most resourceful man, with clear and keen judgment and supreme
self-confidence, or he can never grapple with such a task.
Supposing, then, that he succeeds in getting undetected into a
favourable position, as he thinks; at the critical moment the other ship
may change its course, and the whole scheme goes awry. Perhaps he then
tries to follow, but that is bad, for the end of a ship is not nearly so
good a target as the side and the part hit is not so vulnerable. The
first torpedo may, however, so disable the vessel as to give him chance
to get into position for a second and better shot.
Anyway, when he thinks he has got his best chance he lets off a torpedo,
immediately diving to be safe out of harm's way for a while. Then he
rises to see the result of his work. If successful he would be sure to
hear the sound, for water is an excellent sound-conductor and a
submarine is like a gigantic telephone ear-piece.
It must be a nerve-racking job at the best of times, for the submarine
is a very vulnerable craft. A member of the crew of a German submarine
captured during the war is reported to have said that out of ten
submarines attacked, nine were sunk. That may or may not be true, but it
is certain that a very little damage, which would hardly affect an
ordinary craft, is enough to sink a submarine. That is because, in order
to be able to sink at will, the reserve of buoyancy has to be very low.
An ordinary surface ship has at least as much of its bulk above water as
below: hence it can take on board a weight of water almost equal to, if
not exceeding its own weight before it sinks. At the best a submarine
has not more than 30 per cent of excess and so it sinks if water
amounting to only 30 per cent of its weight gets into it. In other
words, the reserve in one case is at least 100 per cent: in the other at
most 30 per cent.
During the war a submarine saw and tried to track down, somewhat after
the manner described, a slow, steady-going collier which plies between
London and the north carrying coal for a London gas-works. Having, as it
thought, got into position for discharging its torpedo it rose for a
final look when (it must have been to the amazement of the crew) the
collier was seen making straight for them. What they really thought no
one will ever know, for the collier had the best of the encounter, the
submarine was crushed beneath her blunt bows and sank, no doubt, for
ever. The mere fact that a slow, clumsy, heavily-laden collier could
ever thus vanquish an up-to-date submarine is eloquent testimony to
their vulnerability.
Many a submarine, too, has fallen to the shells of an armed fishing
trawler simply because the shells of the latter were so much quicker in
action than a torpedo, coupled with the fact that one well-placed shot,
by preventing a submarine from diving, renders it almost helpless.
Some submarines, however, have a gun on the deck, so that when light
they can fight like a destroyer or other lightly-armed vessel. The gun
shuts down into a cavity when the vessel goes below.
The periscope, which forms such an important part of the submarine's
equipment, is really very little more than a telescope. On the top there
is a little mirror, or more probably a prism or three-cornered piece of
glass which serves precisely the same purpose in that it reflects
exactly as a mirror does. This is so placed that it throws the light
from distant objects down the tube into the interior of the ship. In the
tube are lenses very like those of an ordinary telescope and the light
may be made to throw a picture upon a little table or screen or else can
be viewed through another prism directly by the eye. In either case the
periscope is just like an ordinary telescope set up vertically with a
prism at the top so that it can "see" at right angles, and possibly
another at the bottom so that the picture can be viewed at right angles
to the direction of the tube. The latter is necessary only for the
convenience of the observer, since otherwise he would have to be upon
his back to look up the tube. The whole apparatus can be rotated
mechanically and a scale forms a means of measuring the precise
direction in which the prism or mirror is at any moment pointed. This is
useful for measuring roughly the position of the "prey," and it may
even be used as a rough means of getting the range.
Another feature is the gyroscope compass, to which a passing reference
has already been made. It is fairly well known that an object when
spinning exhibits properties quite different from those which it
possesses when still. A boy's top is a familiar illustration, for while
spinning it will stand perfectly steady, supported only upon a tall peg
with a sharp point, a pose which it will absolutely refuse to maintain
when not spinning. Now fortunately for the present purpose it so happens
that one of the peculiarities of the gyroscope or spinning-wheel is
this: that if mounted in a certain way it persists in placing its axis
in the same plane as that in which the axis of the earth lies. If you
imagine for a moment a plane or flat surface of which the earth's axis
forms a part you will see that wherever that plane cuts the surface of
the earth will be a line in a north and south direction. Consequently,
if any horizontal object has its axis in that same plane it, too, will
always point north and south. A wheel, small but heavy, is therefore
mounted with its axis supported horizontally upon a little metal raft
floating in a trough of mercury and driven round at a very fast speed by
a small electric motor fixed in it.
Whatever its position may be to start with, this revolving wheel will in
a short time slew itself round upon the supporting mercury until its own
axis is in the same plane as the axis of the earth: until, in fact, its
axis points due north and south. Arrived in that position, it will
remain there no matter how the ship upon which it stands may turn. Since
it floats freely upon mercury the motion of the ship has little effect
upon it, so little indeed, that it has no difficulty in following its
own peculiar bent, even if the ship be describing circles.
The advantages of this are various: two of them may be stated. First,
the apparatus points to the actual geographical north and not to the
magnetic north, which is a slightly different direction and one,
moreover, subject to frequent variation. Second, it is absolutely
unaffected by the presence of iron or other magnets, a very fruitful
source of error in the magnetic compass when used upon an iron ship
close to steel guns and electrical machinery. Surrounded with iron as is
the compass in the interior of a submarine, the magnetic needle
practically refuses to work at all, so that, although employed on other
ships, it is on the submarine that the gyro-compass finds its most
important field of usefulness.
The pressure-gauge or manometer, which indicates the depth, is probably
not different in any respect, except in its dial, which is marked in
feet-depth instead of in pounds-pressure, from the pressure-gauge used
on steam boilers. It has either a little cylinder with a piston in it
which the water presses upwards more or less against the force of a
spring, a diaphragm which is bent more or less, or a bent tube which
tries to straighten itself out as the pressure inside it increases.
The older submarines derived their power from petrol engines similar to
those which drive high-power motor-cars, but nowadays these have given
place to engines of the type invented by the unfortunate Diesel who,
after making one of the most brilliant and successful inventions of
modern times, committed suicide, apparently in the height of his
success.
These engines burn cheap heavy oil in place of the costly refined
petrol: they are exceedingly reliable and well-behaved, and are free
from many of the troubles which affect the petrol motor. They are
referred to in more detail in another chapter.
In twin-screw boats there are two distinct engines, one for each
propeller. Each engine, too, is coupled to a dynamo by which it can
generate electric current, which is stored in large accumulator
batteries until required and then withdrawn to drive the dynamos as
motors while the boat is submerged, for if you feed a dynamo with
current it becomes a motor.
A great deal of work is done, on the submarine, by compressed air, of
which large stores are carried in strong steel cylinders. For example,
the ballast is ejected from the ballast tanks, when the boat is required
to rise, not by pumps but by the action of compressed air from a
cylinder. The simple movement of a tap thus suffices to blow out the
water in a very short time. The torpedoes, too, are given their initial
push which sends them out of their tube into the water by compressed
air. In other ways, too, compressed air is employed and to facilitate
its use there are many tubes and valves whereby the cylinders and other
apparatus are connected. Like all things human, these tubes and valves
have their defects, which in this case means that they leak somewhat,
but this defect is of value since the leaking air helps to keep pure and
sweet the air inside the boat which, when submerged, the men have to
breathe.
To what extent it is used I do not know, but it is a fact that certain
chemicals, caustic soda for instance, have the power to absorb the
objectionable carbonic acid which makes tightly-shut rooms seem "close"
and uncomfortable, and if something of that sort be employed, it,
together with the fresh air which thus leaks in by accident, is
undoubtedly enough to enable men to live under water for many hours at a
stretch.
On the other hand, several instances are on record in which strong
healthy young officers have, after a course of service on a submarine,
been found to be suffering seriously from chest and lung trouble,
brought on, no doubt, by long spells of duty in this unhealthy
atmosphere.
It used to be the custom to keep some white mice on board a submarine to
give warning of the impurities in the air. Being very susceptible to the
smell of petrol vapour, which used to be a source of considerable
danger, and also to carbonic acid, these little creatures squeaked with
anxiety some time before the conditions became really dangerous, thus
giving timely warning. There is an instrument, however, which will give
an indication of this sort and probably it has been brought in to
reinforce the mice if not actually to supplant them. This interesting
little instrument, which the gasworks people use for detecting leakage,
consists of a metal drum with a porous diaphragm. Normally the pressure
of the atmosphere upon the diaphragm is equalled and balanced by the
pressure of the air inside the drum, but if there be gas in the air this
balance is upset, the diaphragm is bulged in or out and a finger is
thereby moved, which movement forms a measure of the amount of gas
present.
In conclusion, we may fittingly take a glance at what happens when a
submarine founders. Only a few years ago this occurred with lamentable
frequency, though now it is quite rare except under the actual stress of
warfare. Several interesting schemes were therefore invented to give the
men at least a sporting chance of getting to safety. One was to make the
conning-tower detachable and water-tight, so that the men could get into
it, fasten themselves in and float up to the surface. The practical
difficulties in the way prevented this being a success. For example, if
sufficiently detachable in an emergency it was difficult to make it
sufficiently water-tight in ordinary use.
Another and better device provided the men with small helmets and
jackets, like the dress of a diver very much simplified. One of these
for each man was stored in an accessible place in the boat and
partitions were devised inside the hull itself in order that whatever
happened there should be air entrapped somewhere wherein the men could
live for a time and put on their helmets in safety. Then, thus provided,
they could crawl out through the hatchway and float up to the surface.
Arrived there they could inflate their jackets by blowing into them,
open the window of the helmet and float upon the surface in comparative
safety until rescued.
This apparatus was largely installed in British submarines and a tank
was built at Portsmouth where the men could actually practise with it
under water.
A third device may also be mentioned. This takes the form of a buoy
fitted into a recess in the boat's upper surface. Sufficient line is
coiled up inside it and when the occasion arises it can be released from
inside. This does not in itself save the crew but it may go a long way
towards ensuring their safety by letting those above know just where the
sunken craft is and guiding them in their efforts to raise it.
The torpedo, the weapon without which the submarine would be practically
useless, is dealt with in another chapter. Enough has been said here to
give a good general idea of these interesting craft, their fittings,
their uses and the sort of life which befalls those who man them.