Wrought iron is made by working the molten pig iron instead of casting it. The work is done in a different type of furnace altogether from the blast furnace and the cupola. It is more like an oven, in the floor of which is a depression wherein the molten metal lies. The fire-place is so arranged that the flames pass over the metal, being deflected downwards upon it by the roof as they pass.

It should be understood that in casting pig iron one does little more than form it into some desired shape, the nature of the metal undergoing little or no change. In working it, however, into wrought iron, we change its nature.

The pig iron contains from 2 to 5 per cent of carbon, which it obtains from the coal in the blast-furnace, and it is this particular proportion of carbon which gives it its own peculiar properties. To convert it into wrought iron a workman puts a long iron rod into the furnace and stirs the metal about, thereby exposing it to the air and permitting the carbon to be burnt out. As it loses carbon the iron becomes less and less fluid until it reaches a sticky stage. Thus the workman, who is known by the name of puddler, as the process is called puddling, works up a ball of decarbonized and therefore sticky iron upon the end of his rod. Having thus produced a rough ball or lump he draws it out of the furnace and leaves it to cool.

Thus the result of the puddling process is to produce a number of rough lumps or balls of iron with only about one-tenth per cent of carbon. They are next reheated, in another furnace, and a number of them are hammered together under a mechanical hammer into larger lumps called blooms or billets. The hammering process has the effect of driving out impurities and also of improving the texture of the metal.

Iron sheets, bars, rods and so on are formed by heating the billets and rolling them out in powerful rolling mills, machines which in principle are precisely similar to the domestic mangle, wherein two iron rollers with properly shaped grooves in them squeeze out the billet into the desired form.

Wrought iron, owing to the method by which it is produced, is not homogeneous, that is to say, it is nor quite the same all through, with the result that when it is rolled it develops a grain somewhat similar to the grain in wood, so that if bent across the grain it is somewhat liable to crack. On the other hand, it has the advantage over steel that it rusts much less readily. Hence, for outdoor purposes it is still sometimes preferred to the otherwise more popular steel.

Now the problem which Bessemer set before himself was to find out how to make a metal which could be cast like cast iron yet should be as strong and tough as wrought iron. After a little experimenting, by a happy inspiration, he hit upon the idea of blowing air through a mass of molten pig iron, thereby burning out the carbon, just as is done in the puddling process, only much quicker and with less labour. By this means he produced a metal with less carbon than cast iron and more than wrought iron, a sort of intermediate state between the two, and to his joy he found that this "Bessemer steel" could be cast like cast iron yet had strength and toughness equal to if not superior to that of wrought iron. Moreover, it was homogeneous and when rolled did not possess the troublesome grain characteristic of wrought iron.

Having thus found the way to make this new and desirable metal, Bessemer encountered a great disappointment, so great that it would have entirely beaten many men. He made samples of steel and submitted them to experts in iron manufacture. Everyone thought them admirable and many large iron works were induced by them to make arrangements with Bessemer for the right to use his process. His name was already famous and it seemed as if a new fortune was made, when, to his alarm, he learned that wherever it was tried except in his own works, the process was a miserable failure. Instead of being at the end of his labours he was just at the beginning.

It turned out that the particular iron which he happened to buy and use at his own works was particularly free from an impurity which is, generally speaking, a great nuisance in iron, namely, phosphorus. It was pure accident which had led him to use this iron: it happened to be the kind he could purchase most easily in the small quantities needed for his experiments but it led him into a great difficulty, for other people, after paying him for the right to use his process and after spending large sums on the requisite plant, found themselves unable to make the steel because of the phosphorus in their iron and finding themselves unable to make a success were inclined to write him down a fraud. As it turned out, after much labour on Bessemer's part, it was due to the presence of tiny percentages of phosphorus in most of the iron that is produced.

After much trouble he was able to induce certain owners of blast-furnaces to make, by special methods, a kind of pig iron practically free from phosphorus and therefore suitable for his process. This special pig iron was known as Bessemer Pig Iron.

A little later a new inventor, a Welshman, Thomas by name, overcame the difficulty in another way, but to explain that I must first describe the Bessemer Converter, the special apparatus designed by Bessemer for making his steel.

It can best be likened to a huge iron kettle with a big spout at the top and with two projecting pins, one on each side. These pins rest in supports, so that it is easy to tilt the whole thing over on to its side. This is lined with fire-clay or some suitable heat-resisting material.

Through one of the "pins" (trunnions is their proper name) there runs a hole, communicating to what we might call a grating in the bottom of the converter. To this hollow trunnion there is connected the pipe from a powerful blowing engine, so that air can be driven in at will.

To load or charge the converter it is tilted over somewhat to one side so that molten pig iron can be poured into it. The blast is then turned on after which it is raised to an upright position with the air bubbling up from below through the iron. Thus by being brought into close contact with air, the carbon is burnt out of the metal until none is left. That, however, is not desired, so, as soon as the carbon is known to have all gone, a fresh quantity of molten iron is added of a special kind, the amount of carbon in which is known very exactly. Thus all the carbon is first removed and then exactly the right amount is added, and so the desired result is attained with certainty.

Now Thomas's improvement was this. He discovered that the converter could be lined with certain substances which have a great attraction for phosphorus and under those conditions any phosphorus which may be in the ore goes readily from the iron into the lining, or forms, with material from the lining, a slag which floats upon the surface of the metal.

When the process is completed the converter is tipped over once more and the metal, now steel, is poured into rectangular moulds from which the steel can be lifted after cooling in the form of ingots.

Steel produced by Bessemer's process as improved by Thomas is called Basic Bessemer Steel.

Incidentally Thomas, by this invention, laid the foundation of much of the steel industry of Germany and Belgium, for there are enormous deposits of ore in the neighbourhood of Luxemburg which because of the presence of phosphorus were useless until Thomas showed how it could be dealt with.

And there is another interesting feature of this "basic" process. Phosphorus is a valuable fertilizer, so that the "slag" makes a very fine chemical manure. It is ground up into a fine powder and is sold to farmers under the name of Thomas's Phosphate Powder. It owes its fertilizing virtues to the presence of the phosphorus which it has stolen from the molten iron.

Bessemer derived a huge fortune from his process after he had fought and overcome his difficulties, in addition to which he received the honour of knighthood and became Sir Henry Bessemer.

It will be noticed that one of the virtues of the process is its economy in fuel. During the whole time that the metal is in the converter, from twenty to thirty minutes, no fuel is used to keep it hot. The reason for that is that the carbon which is being got rid of is acting as fuel. It is burning with the air which is driven through, thereby generating heat.

In Bessemer's early days, it was arranged that he should attend a meeting of ironmasters at Birmingham to explain his new process. On the morning of his lecture two eminent ironmasters were breakfasting together in a Birmingham hotel when one exclaimed to the other, "What do you think, there is a fellow coming here to-day to tell us how to make steel without fuel." To this eminent South Wales ironmaster the proposal seemed preposterous but it was true all the same.

Although vast quantities of steel are made by the Bessemer process there is another one of equal importance known as the Siemens-Martin Open-hearth process. In this the molten metal is kept in a huge bath practically boiling until the carbon has been reduced to the required amount. Perhaps the most interesting feature about it is the way in which fuel is saved by what is called the "regenerative" method due to that versatile genius Sir William Siemens.

The open-hearth, as it is termed, is a huge rectangular chamber of firebrick with a firebrick roof, and doors along one side just under the roof through which the process can be watched and new materials be added from time to time.

The fire is some way away and not underneath as one might perhaps expect. Now if a deep coke fire is fed with insufficient air it does not give off carbonic acid such as usually arises from a fire, and which as everyone knows will not burn, but a gas called carbon monoxide which will burn very well. So the fire-place for these furnaces is constructed in such a manner as to produce carbon monoxide, which then passes through a huge flue to one end of the open-hearth. Here it meets air coming through another flue and the two combining burst into flame over the metal.

The hot gases resulting from this burning pass out through a flue at the other end of the hearth to a tall chimney which causes the necessary draught, but on their way they pass through a chamber loosely filled with bricks. Consequently the hot gases only reach the open air after having given up much of their heat to these bricks.

After that operation has been going on for a time certain valves are operated and the gas and air then come in at the other end of the hearth, travelling through it in the opposite direction. And the air comes through the chamber which has the hot bricks in it, bringing back into the furnace a large quantity of that heat which otherwise would have gone up the chimney but which the bricks intercepted. Thus all day long does this reversal take place at intervals, the fresh air all the time picking up and bringing back some of the heat which just previously had escaped towards but not into the chimney. This arrangement enables the process to compete, so far as economy is concerned, with the Bessemer process.

At intervals the steel is tapped off from the furnace and run into ingot-moulds, the same as with the other process. On the whole it is regarded as producing a slightly better steel, the operation being under slightly better control.

However the steel is made the ingots are reheated and either hammered under a powerful steam hammer or pressed in an enormous hydraulic press. This greatly improves the quality.

The steel can then be rolled into plates, bars or whatever form may be required.

The finer qualities of steel such as are used for making sharp tools are made in quite another way. Instead of being made from crude iron by taking out the carbon, the materials are the finest qualities of wrought iron and charcoal which are mixed together in the correct quantities and melted in a crucible. This cast steel is very hard, so that it will carry a very fine, sharp edge. It is also capable of being tempered by heating and cooling, so that the exact degrees of hardness and toughness can be attained.

Of recent years a special quality of steel for tools called "high-speed" steel has been produced, mainly by the addition to ordinary cast steel of a small percentage of tungsten. The advantage of this is that, within certain limits, this does not soften with heat, and it is, I can assure you, a great invention in war-time, when a nation is straining every nerve to turn out guns and shells as fast as possible.

For all these things need to be turned in lathes and if you have ever watched a metal-turning lathe at work you will have noticed that the tool which actually takes a shaving off the article being turned tends to get hot. For this reason lathes are usually fitted with pumps which pump cold soap-suds on to the tool as it works. What you see there is the energy employed in shaving the metal being turned into heat in the tool. If left uncooled by the water it would soon be red-hot. And the faster the machine works the hotter will the tool get.

Now with the old steel a very little heat will suffice to make it soft, when its cutting power is lost. So with the old steel, no matter how much cooling water you might use, there was a distinct limit to the speed of the lathe and the speed at which the work was finished, for if that speed were once exceeded a stop became necessary to regrind the tool or to put in a fresh one.

But with high-speed steel that limit is much higher, for it can get almost red-hot before it loses its hardness and consequently machines can be run and jobs finished at a speed which would have been out of the question only a few years ago. If one belligerent knew how to make high-speed steel while the other did not the former would have an enormous advantage in war-time.

Speaking generally, steel such as is used for tools is called hard steel, while that made by the Bessemer and Siemens-Martin processes is called mild steel. Leaving out of account for the moment fancy steels such as that just described, where other metals are added to the mixture, the essential difference between all the varieties of steel is simply a slight difference in the percentage of carbon. This is so remarkable that it is worth while to tabulate these percentages again.

Cast iron has from 2 to 5 per cent.

Steel from one-fifth to one per cent.

Wrought iron less than one-fifth per cent.

Mild steel, which has least carbon of all the varieties of steel and in this respect is therefore nearest to wrought iron, is used for the same purposes as wrought iron, such as shipbuilding, bridges and roofs, tanks, gas-holders, etc. When the Admiralty want a specially fast ship such as a torpedo-boat destroyer with a hull as light as possible consistent with strength they have it made of steel with a slightly larger percentage of carbon so that the steel is stronger and the vessel's frame can be made lighter. The steel for shells, too, needs to be of a certain strength to give the best results, so the percentage of carbon is adjusted accordingly.

For guns themselves, again, special properties are needed, and so not only is the carbon regulated to a nicety but other things such as nickel and chromium are added. Altogether, steel is one of the most marvellous substances known, certainly the most marvellous metal. Copper is just copper and no more, zinc is just zinc, and the same with lead, but iron (which really includes steel) can be adapted to so many purposes, can be endowed at will with so many different properties, that without doubt iron, common, plentiful iron, is the king of all the metals.

CHAPTER VIII
MORE ABOUT GUNS

The famous French "seventy-fives" (meaning 75 millimetres calibre) which played such a great part in the war, are field guns intended to move rapidly and to operate with infantry.

Both these types of gun were used by the British in South Africa, as also were some field howitzers, a type of gun to which further reference will be made later. But the Boers taught the world something new as to the possibilities of moving heavy guns quickly. Perhaps the reason for this was that they, being something of the nature of amateurs in the art of warfare, were less under the influence of tradition. Anyway, they surprised the British by the quick way in which they moved heavy guns, sometimes into quite difficult positions, over rough ground and up steep hills. These heavy guns of theirs were called by the British soldiers "Long Toms."

But the British were quick to respond, particularly the ever-resourceful navy. When the war broke out there were, in the neighbourhood of Durban, a number of warships which had as part of their own armament some of those guns which afterwards became famous as "4·7's," that being the diameter of the bore in inches. They were of the long shape usual in naval guns, and it is easy to see that they were much heavier than the field guns of 3 inches or so in diameter.

Captain Scott (now Admiral Sir Percy Scott) saw that these would be useful, so he quickly designed some carriages for them, got these made in the railway workshops at Durban, and in a few hours was rushing them up to Ladysmith. It was these guns very largely which enabled that town to hold out for so long, until, in fact, it was triumphantly relieved.

Thus the effect of the Boer war was to show that much heavier weapons could be manipulated in the field than had been considered possible before. The Great War which followed but a few years later carried on this same lesson, for one of the great surprises with which the Allies were confronted in the early days of the conflict was the inexplicable fall of fortresses which till then had been deemed almost impregnable.

Liége, Namur, Maubeuge and, finally, Antwerp, all fell to a wonderful gun of enormous dimensions which the Austrians had produced from up their sleeve, so to speak. Like conjurers they had kept them secret until the last moment.

These weapons which made history so fast were of the kind called howitzers, a name mentioned just now. It should be explained here that gunners talk of guns and howitzers as if the latter were not guns; but that is only a convenient habit which has grown up, for the latter are unquestionably guns. The distinction is, however, so convenient that we may well adopt it ourselves for the rest of this chapter.

Repeated references have been made already to the question of the length of guns, and it has been pointed out that to get high velocity, great range and vigorous hitting power a gun needs to be as long as possible. On ships this is only limited by the strength of the steel of which the gun is made, for beyond a certain length the gun bends of its own weight. Ashore, however, the difficulties of transport impose a further limitation in most cases, although the famous 4·7, like many other naval guns, has a length of 50 calibres, and the guns of small calibre do approximate somewhat to the proportions of the naval guns, since even then their length comes within manageable limits.

Modern warfare, however, requires the use of larger shells containing larger charges of explosives, and to fire these requires guns of greater calibre. We hear of shells of as great a diameter as 16 inches being thrown into the Belgian fortresses and of course nothing smaller than a 16-inch gun could do that. Now a 16-inch gun, if made to the naval proportions of 50 calibres or even 45 calibres, would mean a length of at least 60 to 70 feet. It would also mean a weight exceeding 100 tons, for the 12-inch naval gun of 50 calibres weighs about 70 tons. And it is easy to see that such a gun would be very difficult to move on the field of battle. Indeed, it would be almost useless because of the time it would take to get it into position and to construct the foundations which it would need. If the Austrians had only had such as those the Belgians would have had plenty of time to prepare for them at Antwerp, whereas it was the quickness with which they brought up their heavy guns that astonished everyone and took their opponents by surprise.

The secret of this astonishing performance lies in the fact that they were not guns at all but howitzers, which instead of being long, slender tubes are short, fat ones, and that involves a different idea in gunnery altogether. The "gun" fires at an object. The howitzer fires its shell upwards with the purpose of dropping it upon the object.

The difference between the two is well illustrated by the methods of practising with them. In learning to work a gun the gunners fire at a vertical target just as those of you who practise shooting at a miniature range fire at a target of paper placed vertically against a wall. The target for howitzer practice, on the other hand, is a square marked out on the level ground, and the object of the gunners is to see how great a proportion of a given number of shots they can drop inside that square.

Of course, being so much shorter the howitzers cannot throw a shell so far or at such a high velocity as the naval guns, but that can to a certain extent be compensated for by using a higher explosive for the propellant. That, however, involves greater stresses in the tube when firing takes place and also calls for stronger foundations in order that the aim may be steady.

A great part, too, of the velocity of a naval shell is required for the penetration of the armour, whereas against forts or earthworks it is sufficient if the shell "gets there."

Moreover, generally speaking, it is possible to get much nearer to a fortress or entrenched position for the purpose of attacking it than it is to an enemy ship on the sea. Except for the occasional help of a mist there is no "cover" to be obtained at sea, while on land the ground must be very flat indeed if there is no low hill or undulation behind which a gun can be set up unnoticed.

The Austrians cherish a piece of steelwork from one of the forts of Antwerp which they smashed with a shell from one of their big howitzers at a range of seven miles. They evidently were able to get their big howitzers within that comparatively short distance of the Antwerp fortifications without being molested.

In this connection one often hears the word mortar used, and just a reference to that will be appropriate here. Many years ago short guns which threw their balls very high were in use, and because of their resemblance to the mortar which is used for pounding up things with the aid of a pestle these were termed mortars. Later a man named Howitzer introduced a type of gun which was something of a compromise between the long thin gun and the short stubby mortar. As time has gone on, however, the mortars have grown in length while the howitzers have shortened, until to-day the two names are used almost indiscriminately to denote the same thing. Hence the giant howitzers of the Austrians are often spoken of as the "Skoda" mortars, Skoda being the name of the factory where they were made.

At one time many people wondered why the Germans did not put some of these huge mortars on their battleships: many thought that they would do so, and that by that means they would demolish our navy as they had already smashed the Belgian forts. The reason they did not is, no doubt, the very simple one, that our naval guns would have probably sunk their ships before the howitzers could have reached ours, because if they had attempted to make up for the shortness of the weapons by using higher explosives, these mortars would, there is little doubt, have knocked to pieces the ships on which they were mounted.

The old-fashioned fortress, suddenly made "out-of-date" by the Skoda mortars, was usually armed with guns of the naval type. Sea-coast forts are always so armed. Nowadays, however, the inland fortress takes the form of a labyrinth of trenches and underground passages, combined with deeply excavated chambers known as dug-outs, and these do not fitly accommodate large guns at all. The guns are placed well back behind the trenches sheltered behind hills or woods, over which they hurl their shells. The chief defenders of the actual trench are the machine gun, which is little more than an automatic rifle on a stand, and the trench mortar.

We are now in a position to sum up broadly the features of modern artillery. There is first the naval gun, the ideal gun, long and of great range, able to send forth its shells with great velocity. This gun appears again in the sea-coast forts, where the conditions are very much those which obtain on a ship and where the attacking party is of necessity a ship.

In the field we have the field and horse artillery, which we may regard as the naval gun modified somewhat in order to make it easy to move about, so that it can accompany troops and support the operations of both infantry and cavalry. These light guns are supported by the field howitzers, which are also light and easily handled, and the guns of the 4·7 type, originally naval guns but now mounted on wheels and possessing a certain amount of mobility, not equalling the field guns it is true, but still very serviceable in a campaign.

Then we have the howitzers of various sizes which have rendered the old-fashioned steel and concrete forts useless, and which are the chief weapons used in the modern trench warfare. It is these which blow in the walls of the trenches and dug-outs, shatter the barbed-wire entanglements and render it possible for the infantry to attack an entrenched position.

Finally, we have the machine guns, each of which is equivalent to a considerable number of riflemen and which, with the trench mortars, form the chief defences of the actual trench itself. Of course these are only useful against attacks by infantry: they cannot in any way cope with the heavy artillery. That has to be dealt with by the opposing artillery posted away back behind the trenches.

And now let us take a rather more close look at some of these weapons. Essentially each one is a steel tube. It may be a single tube or it may be several one outside another. It may even have a layer of wire between two tubes as many naval guns have. It is invariably (one small exception will be mentioned later) loaded at the breech or rear end and not through the muzzle as used to be the custom. For this purpose it needs a breech-block or door, which can be opened to put in the shell and explosive, and which can then be closed tightly so that it will not be driven out or burst open when the explosion takes place and also shall be gas tight so as not to let any of the force of the explosion escape.

Then the gun must be mounted upon a carriage so that it can be quickly moved about. The lighter forms of artillery are fired when upon the same carriage upon which they travel. In years gone by the whole thing, carriage as well as gun, used to run back when the gun was fired, which was a great nuisance since it had to be got back into position again after each shot. To obviate this the gun is now mounted upon a slide, and it is the slide which is fitted to the carriage. Thus the gun can slide back without the carriage moving at all. The latter is made very strong, and shoes are provided at the end of chains which go under the wheels just like the "drag" which coaches and heavy carts have for use going down hills. There is also a part like a spade which can be driven down into the ground so that, what with the shoes and the spade, the carriage is fixed very firmly.

The gun is kept at the front part of the slide by means of a powerful spring, which is compressed when the gun is fired but which, as the force of the recoil is spent, pushes the gun back to its original position once more. The spring is often reinforced by a cylinder and a piston with compressed air or water behind it, acting after the manner of those door checks with which we are all familiar, its function being to steady the motion of the gun and to let it go gently back to its place without slamming, just as the door check prevents a door from slamming.

By this means the gun is returned automatically after each shot to practically the same position which it occupied before, so that it does not need re-aiming each time, but only a slight readjustment if even that. The result of this is that such a gun can be fired very rapidly. In fact, it can be fired just as fast as the gunners can keep on reloading it.

The big Skoda mortars owed their mobility to the clever way in which they were constructed. The gun tube itself, the support for it or mounting, and the steel foundation were each fitted to a special motor-driven trolley. The steel foundation was dumped down on the ground, which of course was prepared for it in advance, then the mounting was run right on to it so that it simply needed bolting down and finally the tube was hoisted by specially prepared appliances into its place. It is said that the whole operation occupied less than an hour.

For firing, these mortars of course are pointed at a very high angle, almost like an astronomical telescope. No doubt the gunners have many jokes about "shooting the moon" and so on, for that is just what they seem to be attempting. For loading, however, they are lowered into a horizontal position: the shell comes up on a small hand-truck, is raised by a specially designed jack until it is level with the breech, and is then pushed into its place. The breech is then closed, the tube re-elevated, and all is ready for firing.

Between these two forms of gun, the field gun on its light carriage, which not only bears it from place to place but forms its support while in action, and the great mortar carried in parts on specially made trolleys, there are now an enormous variety of guns and mortars adapted for the various purposes which experience in the Great War revealed. Artillery suffered many changes in the light of the South African campaign and of the Russo-Japanese war, but of far more importance have been the lessons learnt in Northern France and on the plains of Poland. To some extent these lessons have been learnt and profited by during the actual war, but there is no doubt that as men have time to think over them in the years of peace which are ahead many more developments will take place. Unless, that is, we are on the threshold of that happy time when guns and fighting material of all sorts will be looked upon as the relics of a bad and ruinous time now happily past.

In conclusion, a passing reference must be made to the trench mortars and similar contrivances which have arisen as the result of the prolonged spell of trench warfare which no one had ever contemplated. These are in effect very short range mortars or howitzers, specially intended for throwing bombs from trench to trench. Some are simply the larger mortars on a small scale, but one has decidedly original features.

This consists of a short light mortar into which the bombs are slipped through the muzzle, thus reverting to the old method of loading. The propellant is combined with the bomb and there is a percussion cap which fires it as soon as it strikes the bottom of the tube. Thus the operation is just about as simple as it can be: the man merely places the bomb in the upturned muzzle and lets it slide down. An instant later, up it comes again, to go sailing through the air into the trench of the enemy a hundred yards away.

One must not conclude this chapter, however, without a reference to those useful weapons which are known among the soldiers as "Archibalds" and officially as anti-aircraft guns. These are perhaps the most familiar guns of all to the general public, since they were installed in many places in Britain for the purpose of dealing with the Zeppelins. No doubt not a few of my readers have had the experience of being awakened from their beauty sleep by the cracking of the anti-aircraft guns and have seen their shells bursting like squibs in the air.

They are fairly long guns, not unlike field guns, but they are mounted upon special supports which enable them to be pointed at any angle so that they can fire right up into the sky. The sights, also, are somewhat different, being fitted with prisms, or reflectors, so that the gunners can look along the sights and align the gun upon an object overhead without lying on their backs.

Much more could be said on this subject, but national interests forbid, so with this general review of modern artillery we must pass to another subject.

CHAPTER IX
THE GUNS THEY USE IN THE NAVY

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.

CHAPTER X
SHELLS AND HOW THEY ARE MADE

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.