SHELLS AND HOW THEY ARE MADE
Modern warfare seems to resolve itself very largely into a question of
which side can procure the most shells. During the great war there was a
time when the British and their allies were hard pressed because they
had not sufficient shells. The enemy had in that matter stolen a march
upon them and had during the winter, when military activity is at its
minimum, rapidly produced large supplies of high-explosive shells.
Discovering their lack the British set about remedying it in true
British fashion. It is quite characteristic of this strange people to
let the enemy get ahead at the commencement, after which they pull
themselves together and put on a spurt, so to speak, and after that the
enemy had better prepare for the worst, for defeat is only a question of
time. So, finding themselves short of shells, they set to and dotted the
whole country in an incredibly short time with huge factories entirely
devoted to making shells. Older factories also were adapted to the same
purpose. Places intended and normally used for the manufacture of the
most peaceable things--ploughs, gramophones and piano parts for
example--were soon turning out shells or parts thereof by the thousand.
Electric-light works, waterworks, cotton mills, technical schools, all
sorts of places where, for doing their own repairs or for some similar
reason, there happened to be a lathe or two, all these were organized
and in a few weeks they too were working night and day "something to do
with shells."
Meanwhile other factories were springing up for the purpose of making
explosives while others again were erected for producing the acids and
other chemicals necessary for the explosive works; and yet another kind
of works, the filling factories, came into being as if by magic and
thousands of girls flocked from far and near to these places, there to
fill the shells with the explosives.
Even the soldiers did not realize a few years ago how important the
supply of shells was going to be. The rifle has fallen from its old
place of importance while the gun and the shell have risen to the first
place.
What, then, is a shell? It is what its name implies, a case covering
something else, just as the shell of a fish covers its owner. It is a
hollow cylinder of steel with certain things inside it. Its chief
function is to hold these other things and to be shot out of a gun
carrying them with it to their destination. You want to cause an
explosion in an enemy's ship. You cannot get near enough to put the
explosives there by hand, for he will not let you, so you put them into
a steel shell and then hurl the whole thing at him out of a gun.
[Illustration: BOMB THROWING.
One of the most striking things about the war was the re-invention of
the bomb thrown by hand. This officer hurled bombs at the enemy for
twenty-four hours continuously.]
In the attempt to prevent your doing him any harm by thus throwing boxes
of explosives at him, the enemy clothes the sides of his most valuable
and important ships with thick steel plates, wherefore you have to make
your shell strong and tough so that it shall not splinter against the
armour but shall on the contrary bore its way through, finally exploding
in the interior of the ship.
If it is not a ship that you are attacking but, say, an earthwork or an
arrangement of trenches, then you do not need to penetrate steel armour
and your shell can be thinner and of lighter construction. It still
needs to be strong, however, for it has another function besides simply
carrying the explosive. It must hold the force of the explosion in for a
moment while it gathers force so that when the hour comes the pent-up
energy may strike all round with the utmost violence. Even the most
powerful explosives are comparatively feeble if they go off in the open.
By holding them in check for a moment and then letting their force loose
suddenly you get a much more forceful blow.
Shells which contain only an explosive are called common shells or
high-explosive shells. Shrapnel shells constitute another type in which
the force of the explosion is simply employed to release a number of
round bullets, which strike mainly because of the velocity which they
derive from the original motion of the shell. These are above all things
man-killing shells, for their result is akin to a volley of bullets at
close range.
We can thus sum up the chief types of shell as follows: the naval shell
which has to be capable of penetrating armour: the high-explosive shell
which must be able to break up earthworks and blow down the walls of
trenches: and the shrapnel shell which scatters a shower of bullets and
is most useful in attacks upon bodies of men rather than upon material
structures.
Some shells have their propellent explosive combined with them just as
the familiar rifle cartridge contains the propellant combined with the
bullet. In the larger sizes, however, it is much more convenient to have
the propellant in a separate cartridge, which can be handled separately
and loaded into the gun separately.
As has been already explained, the propellant is a "powder" which gives
a steady push rather than a destructive blow: moreover, it is
practically smokeless, so as not to "give away" the position of the gun
to the enemy. The "high explosive," however, shatters and usually makes
a dense smoke, so that the observers can see where it fell and report to
the gunners whether or not they have got the range. Soldiers' letters
have told us of the "black Marias" and "coal boxes" used by the Germans,
those terms being simply soldiers' nick-names arising no doubt from the
fact that certain particular shells are filled with "tri-nitro-toluene"
which gives a black smoke. Clearly, smoke, which is most objectionable
in the propellant, is a positive advantage in the bursting charge.
And now let us take a glimpse at the manufacture of one of these
terrible missiles. An ingot of shell-steel is first cast as described in
an earlier chapter. Since impurities are apt to rise, while the metal
is liquid, the top of the ingot is always cut off and discarded. This
waste material is used for many other purposes, in which a chance flaw
would not be a serious matter, under the title of "shell-discard" steel.
The lower part is then heated and passed through a rolling mill, a
machine very similar in principle to the domestic mangle, the rollers
being of iron with suitable grooves cut in them. A few passages through
this machine transforms the ingot into a thick round bar. This is then
sawn into short pieces called billets, each of which is the right size
to form a shell. Again heated, a powerful press drives a pointed bar
through the softened steel, thereby converting the short billet into a
rough tube. Another press then slightly closes in one end, making it
resemble a bottle without a bottom and with the neck broken off.
The rough forging is then ready to be machined, an operation which is
performed in a lathe. The outside is made perfectly round and smooth and
of precisely the right size. The inside is also bored out to the correct
diameter and finished off to an exceeding smoothness so as to avoid the
possibility of any rough places irritating the explosive which in due
time will be filled into it. For the same reason, the inside, when
finished, is varnished in a certain way and with a certain varnish. The
formation of this varnish is one of those little thought of but highly
important services which alcohol renders to us, as mentioned elsewhere.
The smaller end (that which has already been partially squeezed in) is
bored out and screwed for the reception of the nose-bush, while the
other end is recessed for the reception of the plate which forms the
bottom.
Most of these operations have to be very accurately carried out and, to
ensure that that is so, gauges are continually employed to check the
work. These gauges are based upon a very simple principle, known as the
"limit" principle. This is both interesting and important, sufficiently
so to merit a more detailed reference.
It must first be realized that no two things are alike and no
measurement is perfectly correct. When we lightly speak of two things
being "alike" we really mean that for the purpose contemplated they are
nearly enough alike. Two things might be "alike" for one purpose and yet
be so unlike as to be useless for another.
What the authorities do in the case of shells, therefore, and what is
done nowadays in many branches of engineering, is to recognize this fact
and at the same time overcome the difficulty by stating what difference
is permissible. In other words, instead of saying that a thing must be a
certain size, it is required to fall between two limits: it must not be
more than one or less than the other.
For example, suppose a hole is required to be nominally an inch in
diameter it may be specified that it shall not exceed an inch plus
one-thousandth or fall short of an inch minus one-thousandth. In such a
case a variation of a thousandth of an inch either way is permitted.
The permitted variation may be more than that, or it may be less and be
measured in ten-thousandths, it all depends upon circumstances. Clearly
in every case it is desirable to permit as large a variation as is
consistent with a good result.
Now to make measures with the degree of accuracy just mentioned is not
easy. One can just about see through a crack a thousandth of an inch
wide if held up to a bright light. How then can dimensions such as these
be dealt with easily and quickly in the rough conditions of a large
workshop?
Let us again think of that one-inch hole and we shall see how simply and
easily it is done. The gauge in such a case would be shaped somewhat
like a dumb-bell, one end being the "go" end and the other the "not-go"
end. The former is made to agree as nearly as possible with the lower
limit, the other with the higher limit, and all the inspector has to do
is to try first one end in the hole and then the other. One must "go" in
and the other must "not-go." So long as that happens he knows that the
hole is correct within the prescribed limits. If, on the other hand,
both go in, then he knows the hole is too large, or if neither goes in
he knows it is too small. It may be urged by some acute reader that the
gauges themselves cannot be correct, and that is quite true, but it is
possible, by great care and laborious methods, to produce gauges which
are correct to within far narrower limits than those mentioned.
In the case of outside dimensions the gauges take the form of a thumb
and finger capable of spanning the object to be measured, and in that
case also two are used, one of which must "go" and the other "not-go."
By methods such as these the shells are measured and examined.
One of the most important features of a shell is its driving band. In
the old days of round cannon balls it is said that the gunners used to
wrap greasy rag round each so as to make it fit the cannon and to
prevent the force of the explosion to some extent wasting itself by
blowing past the ball. That is one of the functions of the driving band.
It is made of copper which is comparatively soft, and it forms a fairly
tight fit in the bore of the gun, so that while the shell is free enough
to slide out of the gun it is tight enough to prevent the loss of any of
the driving force of the explosive.
Its second purpose is to give the necessary spinning action to the
shell. The old cannon ball suffered from the fact that it offered a
considerable surface to the air in proportion to its weight. The idea
arose, therefore, of making projectiles cylindrical and with a pointed
nose, so that while the weight might be increased the resistance to the
air might be even reduced. But it was clearly no use doing this unless
the thing could be made to travel point foremost. Now for some rather
mysterious reason, if you shoot a cylindrical object out of a gun, it
will turn head over heels in the air, unless you give it a spinning
motion. This motion, however, because of a gyroscopic effect, keeps the
shell point first all the time.
It has another effect, too, known as "air-boring." A spinning shell
seems actually to bore its way through the air. Probably this is due to
a centrifugal action, the spinning shell throwing the air outwards from
itself and so to some extent sucking the air away out of its own path.
Whether that be the true explanation or not, the fact remains that the
spinning shell makes its way through the air better than a non-spinning
one would do.
The gun, therefore, has formed in its bore a very slow screw-thread
called "rifling," from a French word meaning a screw. And it is the
second function of the copper band to catch this rifling and by it be
turned as the shell proceeds along the barrel. The soft copper conforms
to the shape of the rifling and so itself becomes in a sense a screw
engaging with the rifling.
This band is situated near the base of the shell, lying in a groove
turned in the shell for its reception. To prevent the band turning round
without turning the shell there is a wavy groove turned in the bottom of
the larger groove, and the band, being put on hot, is squeezed into the
latter by a powerful press.
The nose-bush is a little fitting of brass which screws into the smaller
end of the shell and it has a hole in its centre into which another
brass fitting, the nose itself, is screwed.
The base of the shell is closed with a little disc of steel plate.
People sometimes wonder why the original forging is not made solid at
the bottom so as to save the necessity for this disc, but the reason is
that if that were done defects might very possibly arise in the steel
in the centre which, since it is the very spot whereon the propellant
acts, might let some of the heat or force of the propellant through,
causing a premature explosion of the charge inside the gun itself
instead of among the ranks of the enemy.
In the case of naval shells, the nose is not of brass but of a soft kind
of steel. One might expect it to be of the very hardest steel, since it
has to pierce the hard armour, but experience has shown that the soft
nose is better than a hard one. The reason probably is that a hard nose
splinters, whereas a soft one spreads out on striking the armour and
then acts as a protection to the body of the shell behind it. In these
shells, too, the fuse which explodes the charge is placed in the base.
In the others it is in the nose, but clearly it could not be so placed
in the armour-piercing shell.
It is interesting to mention that the propellent "powder" has combined
in it some vaseline or other greasy matter which acts as a lubricant
between the gun and the shell when firing takes place.
Shrapnel is so different from the other types of shell that it merits a
short paragraph or two to itself. Instead of being filled, as the others
are, solely with explosive, the front part of it accommodates a
considerable number of small round bullets, behind which comes a charge
of gunpowder. The front half of the shell is separate from the back
part, the two being connected by rivets of soft iron wire, so that a
sudden shock can rend them apart. The shell is fired from the gun and
comes flying along: suddenly, owing to the action of the fuse, the
gunpowder explodes: the case then flies in two, the bullets are
liberated and fall in a shower. In the South African War, where
fortifications were few, these shells were very effective, but against
fortifications, and particularly against trenches and barbed wire, big
explosive shells are of much greater value.