THE GUNS THEY USE IN THE NAVY
Both the great English-speaking nations are immensely proud of their
navies. They can, on occasion, produce soldiers by the million of the
very highest and most efficient type, but they never feel quite that
pride and patriotic fervour over their soldiers that they do over their
ships of war and their sailors.
The guns, therefore, with which the ships are armed, always form a
subject of great interest, especially those large ones which constitute
the armament of the Dreadnought battleships and battle-cruisers.
Let us first consider what is required in a naval gun, for it must be
remembered that the naval and military weapons are different in some
respects. Experience at the Dardanelles showed that even the guns of the
_Queen Elizabeth_, the largest and most powerful then known, fresh from
the finest factories, were not particularly successful against the
Turkish forts. The Germans, too, set up what was probably a naval gun
and occasionally dropped shells into Dunkirk with it at a range of
twenty miles or so, but without causing much harm, and the fact that
they only did it occasionally and then abandoned it altogether seems to
indicate that in their opinion they were not doing much good with it.
It must not be assumed from this that naval guns are bad guns or poor
guns, however, but simply that they are made for a special purpose for
which they are highly efficient, from which it follows almost as a
natural consequence that they are somewhat less efficient when used for
some other purpose. Their purpose is to pierce the hard steel armour
with which warships are protected and then to explode in the enemy's
interior, whereas in modern warfare the greatest military guns are
chiefly required to blow a big hole in the ground or to shatter a block
of concrete. In both cases the ultimate object is to carry a quantity of
explosive into the enemy's territory and there explode it, but whereas
the land gun has simply to do that and no more, the naval gun has to
pierce thick armour-plate as well.
And just think what that means. Many large ships have their vital parts
protected by armour-plates twelve inches thick. Moreover, the
armour-plates are made of very special steel, the finest that can be
invented for the purpose. Vast sums of money have been expended in
experimenting to find out just the best sort of steel for resisting
penetration by shells. Some time ago I saw several pieces of
armour-plate which had been used in one of these tests. They had been
set up under conditions as nearly as possible the same as those
obtaining on the side of a ship and then they had been fired at from
varying distances, the effects of the various shots being carefully
recorded. And that is only one experiment out of tens of thousands
which have been tried again and again, while the steel manufacturers are
always trying to improve and again improve the shell-resisting
properties of their steel. Thus, we see, the presence of the steel
armour which has to be perforated before the shell can do its work makes
the task set before the naval gun somewhat different from that which
confronts its military brother.
These considerations result in the naval gun needing to have as flat a
trajectory as possible and its projectiles the highest possible speed.
Now trajectory, it may be useful to explain, is the technical term
employed to denote the course of a projectile, which is always more or
less curved.
Let us imagine that we see a gun, pointed in a perfectly horizontal
direction, and let us also imagine that by some miracle we have got rid
of the force of gravity and also that there is no air. Under those
conditions the shot from the gun would go perfectly straight and with
undiminished velocity for ever and ever. Then let us imagine that the
air comes into being. The effect of that is to act as a brake which
gradually slows the shell down until finally it stops it. Theoretically,
perhaps, it would never quite stop it, but for all practical purposes it
would.
Again, let us suppose that while the air is absent the force of gravity
comes into play, what effect will that have? It will gradually pull the
shell downwards out of its horizontal course, making it describe a
beautiful curve.
But, someone may think, does not a rapidly-moving body remain to some
extent unaffected by gravity? Not at all: it falls just the same and
just as quickly as if it were falling straight down.
If our imaginary horizontal gun were set at a height of sixteen feet and
a shell were just pushed out of it so that it fell straight down the
shell would touch the ground in one second. If the ground were perfectly
flat and the shell were fired so that it reached a point half a mile
away _in one second_ it would strike the ground exactly half a mile
away. You see, the horizontal motion due to the explosion in the gun and
the downward motion due to gravity go on simultaneously and the two
combined produce the curve.
To make this quite clear, let us imagine two guns precisely alike side
by side and both pointed perfectly horizontally. From one the shell is
just pushed out: from the other it is fired at the highest velocity
attainable: both those shells will fall sixteen feet or a shade more in
one second, and if the ground were perfectly level both would strike the
ground at the same moment although a great distance apart.
Clearly, then, the faster the shell is travelling the more nearly
horizontally will it move, for it will have less time in which to fall,
and the slower the more curved will be its path, from which we see that
the air by reducing the velocity causes the curve to become steeper and
steeper as the shell proceeds.
If, then, our gun is placed low down, as it must be on a ship, to get
the longest range we must point it more or less upwards because
otherwise the shell will fall into the water before it has reached its
target. When we do that we complicate matters somewhat, for gravity
tends to reduce the velocity while the shell is rising and to add to it
again while it is falling. We need not go too deeply into that, however,
so long as we realize that, whatever the conditions may be, the shell in
actual use has to follow a curved course, first rising and then falling.
The really important part about a shell's journey is the end. So long as
it hits it really does not matter what it does on the way, and if it
misses it is equally immaterial. The reason why we need to bother about
the first part of the trip is because upon it depends the final result.
Whatever the trajectory may be we see that the shell must necessarily
arrive in a slanting direction. And the more steeply slanting that
direction is _the less likely is the target to be hit_.
If the shell went straight it would only be necessary to point the gun
in the right direction and the object would be hit no matter how far
away it might be. The more curved the course is, the more likely the
shell is to fall either too near or too far, in the one case dropping
into the water, in the other passing clear over the opposing ship.
Let us look at it another way. Suppose the vital parts of a ship rise 20
feet out of the water and the shell arrives at such an angle that it
falls 20 feet in 100 yards: then, if the ship be within a certain zone
100 yards wide it will be hit in a vital spot. If it be nearer the shell
will pass over, if it be further the shell will fall into the water.
That 100 yards is what is called the "danger zone." If the shell is
falling less steeply, say, 20 feet in 200 yards, then the danger zone
is increased to 200 yards and so on, which gives us the rule that the
flatter the trajectory, or the more nearly straight the course of the
shell the greater is the danger zone and the more likely is the enemy
ship to be hit.
We have established two facts, therefore, first, that the trajectory
must be as flat as possible and, second, that to make it flat the
velocity must be high. We can also see another reason for high velocity,
namely, to give penetrating power.
To obtain a high velocity the gun must be long, and consequently naval
guns are always long, a fact which is very noticeable in the photographs
of warships. The reason for this is quite obvious after a little
thought. You could not throw a cricket ball very far if you could only
move your hand through a distance of one foot. To get the best result
you instinctively reach as far back as ever you can and then reach
forward as far as you are able, so that the ball shall have as long a
journey as possible in your hand. Perhaps you do not know it but all the
time you are moving your hand with the ball in it you are putting energy
into that ball, which energy carries it along after you have let go of
it. And it is just the same with the shell in the gun. So long as it is
in the gun energy is being added to it but as soon as it leaves the
muzzle that ceases. After that it has to pursue its own way under the
influence of the energy which has been imparted to it.
The powder which is employed as the propellant or driving power is of
such a nature and so adjusted as to quantity that as far as possible it
shall give a comparatively slow steady push rather than a sudden shock,
so as to make full use of the gun's length, the expanding gases
following up the shell as it goes forward and keeping a constant push
upon it.
On the other hand, a gun can be too long, for no steel is infinitely
strong and stiff, so that beyond a certain limit the muzzle of the gun
would be likely to droop slightly of its own weight and so make the
shooting inaccurate. The limit seems to be about 50 calibres or, in
other words, fifty times the diameter of the bore.
For a considerable time the standard big gun of the British Navy was the
12-inch, that being the calibre or diameter of the bore. The famous
_Dreadnought_ had guns of that calibre and so had her immediate
successors.
The 12-inch gun of fifty calibres weighs 69 tons and fires a projectile
weighing 850 lbs. which it hurls from its muzzle at a velocity of about
3000 feet per second.
More recently the size has grown to 13½, 14 and even as great as 15
inches calibre, but we may for the moment take the 12-inch gun as
typical of all these large guns and have a look at its construction.
It is made of a special kind of steel known as nickel-chrome gun steel,
formed by adding certain proportions of the two rare metals nickel and
chromium to the mixture of iron and carbon which we ordinarily call
steel. The metal is made after the manner described in another chapter
and is cast into the form of suitably-sized ingots which are afterwards
squeezed in enormous hydraulic presses into the rough shape required.
Besides giving the metal the desired form this action has the effect of
improving its quality. Since a gun is necessarily a tube it may be
wondered why the steel is not cast straight away into that shape instead
of into a solid block and the reason why that is not done is very
interesting. It is found that any impurities in the metal--and it is
impossible to make it without some impurities--collect in that part
which cools last and obviously that part of a block which cools last is
the centre. Thus the impurities gather together in the centre of the
mass whence they are removed when that centre is cut away, whereas if
the first casting were a tube they would collect in a part which would
remain in the finished gun.
The ingot, then, is cast and pressed roughly to shape. Then it is put
into a lathe where it is turned on the outside and a hole bored right
through the centre.
But that is by no means all of the troubles through which this piece of
steel has to pass. It undergoes a very stringent heat treatment, being
alternately heated in a furnace to some precise temperature and then
plunged into oil, whereby the exact degree of hardness required is
attained.
Moreover, this is only one of the tubes which go to make up the gun,
which is a composite structure of four tubes placed one over another
with a layer of tightly wound wire as well.
First, there is the innermost tube, the whole length of the gun, then a
second one outside that, usually made in two halves. Both are carefully
made to fit, and then the outer is expanded by heat to enable it to be
slidden over the inner one, after which on cooling it contracts and fits
tightly. Outside this second tube is wound the wire, or more strictly
speaking tape, for it is a quarter of an inch wide and a sixteenth
thick. It is so strong that a single strand of it could sustain a ton
and a half. It is carefully wound on; first several layers running the
whole length of the gun and then extra layers where the greatest
stresses come, that is to say, near the breech, for that has to
withstand the initial shock of the explosion. Altogether about 130 miles
of wire go on a single gun.
The advantages of this form of construction are many. For one thing, a
wire or strip can be examined throughout its whole length and any defect
is sure to be found, whereas in a solid piece of steel, no matter how
carefully it may be made, there may lurk hidden defects. Moreover, if a
solid tube develops a crack anywhere it is liable to spread, whereas a
few strands of wire may be broken without in any way affecting the rest.
It has been found that even if a shell burst while inside one of these
guns no harm is done to the men in the turret where it stands, a thing
which cannot be said for guns composed entirely of tubes, so that the
merit rests with the wire. A third advantage is that the wire can be
wound on to the tube beneath it at precisely that tension which is
calculated to give the best result, whereas in shrinking one tube on to
another this cannot always be attained.
Over the wire there come two more tubes not running the whole length
but meeting and overlapping somewhat near the middle, so that at one
point there are actually four concentric tubes besides the wire.
At the rear end a kind of cap called the breech-piece covers over the
ends of all the tubes, itself having a central hole into which fits the
breech-block, one of the triumphs of modern engineering, of which more
in a moment.
While we have in mind the wire-wound form of construction it is
interesting to note that something similar but in a crude form was
practised sixty years or more ago. The guns of that era were some of
them even of cast iron while the more refined consisted of a steel tube
strengthened with coils of wrought iron. This iron was first rolled into
flat bars, then it was made hot, and wound on spirally round an iron bar
the same size as the tube. A little hammering converted this spiral into
a tube which was then fitted round the steel tube. Thus, although very
different there is still a distinct resemblance between this old method
and the up-to-date wire-wound weapon.
The manufacture of guns, it may be remarked, owes more to one man than
to any other, namely, Mons. Gustave Canet, a French engineer who, having
fought in the Franco-German War, decided to devote his engineering
talents to developing the artillery of his native land. He spent many
years in England but later established works at Havre for the
manufacture of guns upon improved methods, finally merging his interests
into those of the great French armament firm of Schneider of Creusot.
By French and English artillerists at all events the name of Canet is
regarded with reverence.
But to get back to our naval gun. It will be clear that operations such
as have been described, involving the handling of great tubes fifty feet
or more in length, heating them as required, dipping them in oil while
hot and so on, can only be carried out at works specially designed for
the purpose.
The furnaces where the tubes are heated are well-like formations in the
ground, deep enough to take the tube vertically. To lift them in and out
there have to be tall travelling cranes capable of catching the tube by
its upper end and lifting it right out of the furnace so that its lower
end clears the ground. To accomplish this with a little to spare the
cranes need to be seventy feet or so high.
Then there are deep pits full of oil so that a tube can be heated in a
furnace, drawn out by a crane and quickly dropped into the adjacent oil
bath. Likewise there have to be pits of a third kind wherein a cold tube
can be set up while a hot one is dropped over it for the purpose of
shrinking the latter on.
Then, of course, there have to be lathes of gigantic dimensions capable
of taking a length of nearly sixty feet and of swinging an object
weighing anything up to fifty tons. But of those machines we can only
pause to make mention, for we must pass on to the breech-block, in some
ways the most interesting part of the gun.
When it was first suggested to leave the back end of the gun open so
that the powder and projectiles could be put in that way instead of
through the muzzle, people at once foresaw how much would depend upon
the arrangements for stopping up the hole while the gun was fired. For,
of course, the force of the explosion is exerted equally in all
directions, backward just as much as forward, so that unless very
securely fixed the stopper closing the breech would be liable to become
a projectile travelling in the wrong direction. To fix such a thing
securely enough to avoid accidents would surely take up too much time
and so largely neutralize any advantage arising from its use. These
fears were, indeed, to some extent justified by accidents which actually
occurred with the early examples of breech-loading guns, and for that
reason our own authorities for a time looked askance at breech-loaders.
Now let us take a look at the breech-block of the 12-inch naval gun of
to-day, which never blows out, not even when 350 lbs. of cordite go off
just the other side of it. The explosion hurls an 850-pound shell at the
rate of 3000 feet per second but it never stirs the breech-block. Yet it
can be opened and closed so quickly, including the necessary
fastening-up after closing, that shots can be fired from the gun at the
rate of one every fifteen seconds.
The breech-block partakes of the nature of a plug and also of a door. It
swings upon hinges like the latter but its shape more resembles the
former. If we want to make such a thing very secure we usually make it
in the form of a screw with many threads, but that entails turning it
round many times and that takes time. Given plenty of time to screw the
breech-block into its place and there would never have been any anxiety
as to the possibility of its blowing out, but there is not time. The
problem, therefore, was to get the strength of a screw combined with
quickness of action.
This dilemma is avoided in the following simple manner. The breech-block
is given a screw thread on its exterior surface, and the hole in the
breech-piece is given a similar screw-thread on its inner surface, just
as if the one were to be laboriously screwed into the other after the
manner of an ordinary screw in machinery. Then four grooves are cut
right across the threads on the block and similarly on the breech-piece,
so that at four different places there is no thread left. In other
words, instead of the thread running round and round continuously, each
turn is divided up into four sections with sections of plain unthreaded
metal in between. Thus in a certain position the block can be pushed
into the hole without any threads engaging at all, for each strip of
threaded block passes over an unthreaded strip in the hole and vice
versa, in other words, the threads on the one part miss those on the
other part. Yet an eighth of a turn serves to make all the threads
engage and the thing is held almost as securely as if it were just an
ordinary screw with threads its whole length.
The block is carried upon a hinged arm so that although it can be turned
in this manner it can also be swung back freely when necessary.
Combined with the breech-block is a pneumatic contrivance which blows a
powerful jet of air through the gun every time the breech is opened,
thereby cleaning away the effects of the last explosion.
Each of these great guns is mounted upon a slide so that when it is
fired it can slide back, thereby exhausting the effect of the recoil,
yet can be returned instantly to its original position. Indeed, this
return is brought about quite automatically by the agency of springs,
compressed air and hydraulic power. Thus the gun fires, slides back,
returns and is at once ready for the next shot.
It is trained, or pointed in a horizontal plane, by turning the turret
in which it stands but the correct elevation is gained by the use of
telescopic sights.
The principle of these sights is very simple. Imagine a graduated circle
fixed to the side of the gun. Pivoted at the centre of the circle is a
small telescope. The telescope can be turned round to any angle upon the
circle and it can then be clamped at that particular angle.
The range having been given to the officer in command of the gun from
the range-finding station on another part of the ship, the telescope is
set to the correct angle. Then the gun is elevated or depressed until
the ship being aimed at is precisely in the centre of the field of view
of the telescope, in other words, until the telescope is pointing
exactly at the ship. Then the gun is fired.
The effect, therefore, is this. The telescope always points (while the
gun is being fired) at the object aimed at, but the gun is pointed
upwards at a certain angle, which angle depends upon how the telescope
is set upon the divided circle. Thus the setting of the telescope for a
given range produces the correct upward tilt of the gun for that range.
The breech-block carries a trigger and hammer arrangement whereby the
firing can be done and also an electrical arrangement so that an
electric spark can be employed. Both these firing contrivances are so
made that they cannot be operated until the breech-block has been
inserted and _made secure_. Thus a premature explosion is guarded
against.