Chapter X: 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.

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.