Part 25

On the outbreak of the Crimean War (1854) the minds of many inventors were occupied by the problem of ordnance construction, and this also engaged the attention among others of two of the most eminent British mechanical engineers of the day. These were Sir W. Armstrong and Sir J. Whitworth, who, with others, were invited by our War Department to submit the best models of field and heavy guns their skill was severally able to produce. Two years afterward, Sir W. Armstrong had, after many experiments, completed a gun of 1·88 in. calibre. This had a forged steel barrel 6 feet in length; but it was only after eight such forgings had been bored and rejected on account of flaws revealed only by the boring that a sound barrel was at length obtained. This barrel was strengthened on the outside by _jackets_ made from coils of wrought iron bars welded into a piece and shrunk on while hot (of which process we shall have something more to say presently); the barrel was rifled with many shallow grooves, and the pointed projectile, 3 calibres long, was made of lead, for which afterwards iron coated with lead was substituted. This gun was a breech-loader, the breech being closed by a block let into a slot after loading, and then pressed against the barrel by some turns of a screw which advanced parallel to the axis of the piece, and was made hollow for loading through, before the closing block was put in. In a trial of the various pieces ready in 1857, it was found that the Armstrong gun made as just described had an accuracy and range immensely greater than any weapon that had ever been tested, and the Government authorities approved of the system of construction, except that they preferred muzzle-loading pieces to breech-loading, as being simpler in action, more easily kept in repair, and cheaper in original cost and ammunition.

When Sir Joseph Whitworth’s gun was, in 1863, submitted to a competitive trial against the Armstrong, as to their endurance and mode of ultimate failure when fired with ever-increasing charges of powder and shot, at the forty-second round the Armstrong breech-loader split, and at the sixtieth the Armstrong muzzle-loader had one of its coils cracked; while it was not until the ninety-second round that the Whitworth gun burst violently into eleven pieces. These competing guns were 12–pounder field-guns weighing 8 cwts., and from each 2,800 regulation rounds had been fired before they were subjected to the bursting proofs. The result of these trials being that the authorities considered that steel was not then sufficiently reliable, and they decided to adopt the system of building up rifled guns with iron jackets over an inner tube of steel. Sir Joseph Whitworth made his guns entirely of steel, and they were striking examples of beautiful and accurate workmanship. His system of rifling consisted in forming the bore of the gun so that its section is a regular hexagon, and the projectile is an elongated bolt with sides exactly fitting the barrel of the gun: the projectile is, in fact, a twisted hexagonal prism. Fig. 91 shows at the left-hand side the section of the barrel, and on the right we see the form of the projectile on a smaller scale, this last representing, in fact, the exact size and shape of the bullet of the Whitworth _rifle_ mentioned on another page. Sir Joseph’s guns were muzzle-loaders, and they were remarkable for their long range and accuracy of fire. One of these guns, with a charge of 50 lbs. of gunpowder, threw a 250–lb. shot a distance of nearly six miles, and on another occasion a 310–lb. shell was hurled through the air, and first touched the ground at a distance of more than six and a quarter miles from the gun. These distances are greater than any to which shot or shell had previously been thrown.

As the material of these Whitworth guns was very costly, and very perfect workmanship was required in the formation of the barrel and the shots, the expense attending their manufacture and use was much greater than that incurred in the case of the Armstrong guns. Sir W. Armstrong’s estimate for a 35–ton gun was £3,500, and Sir J. Whitworth’s, £6,000. The gun, as constructed at Woolwich on Mr. Fraser’s plan, was estimated to cost £2,500. The first cost of a gun is a matter for consideration, since each piece, even the strongest, is able only to fire a limited number of rounds before it becomes unsafe or useless. It appears that no cannon has yet been constructed capable of withstanding without alteration the tremendous shocks given by the explosion of the gunpowder, and these alterations, however small at any one discharge, are summed up and ultimately bring to an end what may be termed the “life of the piece.”

About the year 1858 Sir William Armstrong (afterwards Lord Armstrong) established at Elswick, Newcastle-on-Tyne, a manufactory of ordnance, which has since developed into the great arsenal now so well known all over the world. Here all the resources of science have been applied to the problems of artillery, and experiments carried on with a prodigality of cost and promptness of execution impossible at a government establishment trammelled with official regulations. Here, and also at Woolwich, our national ordnance factory, guns have since always been constructed on the building-up plan advocated by Sir W. Armstrong, whose principle consists in disposing of the fibre of the iron so as best to resist the strains in the several parts of the gun. Wrought iron being fibrous in its texture has, like wood, much more strength in the direction of the grain than across it. The direction of the fibre in a bar of wrought iron is parallel to its length, and in that direction the iron is nearly twice as strong as it is transversely. A gun may give way either by the bursting of the barrel or by the blowing out of the breech. The force which tends to produce the first effect acts transversely to the axis of the gun; hence the best way to resist it is to wrap the iron round the barrel, so that the fibres of the metal encircle it like the hoops of a cask. The force which tends to blow out the breech is best resisted by disposing the fibres of the iron so as to be parallel to the axis of the gun; hence Sir W. Armstrong makes the breech-piece from a solid forging with the fibre in the required direction. But the Elswick building-up principle involves much more than the direction of the fibres of the iron, for each coil or jacket, after having its spires welded together, was bored out on a lathe, and the exterior of the part of the gun on which it was to be placed was also turned with the utmost exactness, so that when the enveloping piece was heated to a certain temperature and in this state brought into position, it would in cooling compress the parts it encircled just to that degree which careful calculations showed would best strengthen the gun without unduly straining the metal at any part. The Elswick guns being built up of several superimposed jackets of calculated lengths and thicknesses, the means was afforded of distributing the tensions throughout the whole mass of metal to the best advantage. In the simpler form, arranged by Mr. Fraser, and for the sake of economy adopted by the authorities at Woolwich in 1867, the greater part of the benefit derivable from adjustment of tension was no doubt sacrificed to cheapness of manufacture. These, and also the forms of Armstrong guns that have not yet been described, ceased to be made after 1880, by which time steel had replaced iron in every part of the construction and fittings of guns, and muzzle-loading had been definitely abandoned in favour of breech-loading.

Now, in 1874, when the first edition of the present work was in preparation, the Fraser-Woolwich guns were in full vogue, being spoken of by the public press as the _ne plus ultra_ of artillery construction in size, efficiency, and economy. When, accordingly, the author had been privileged to visit the arsenal and witness the production of these guns in every stage of their manufacture, he wrote a description of it which is here retained as printed at the time, seeing that it may not be without historical interest, particularly since great numbers of these guns must still be extant, mounted on our forts in various parts of the world, and seeing also that the description of the simpler formations may render more easily to be understood future references to similar operations in gun-making as have been retained in the later developments. Of course, the following description was written in the _present tense_, and therefore in perusing it the reader must constantly bear in mind that the guns with which our ships of war have since been equipped are in _every respect entirely different_ from

_The Fraser-Woolwich Guns, 1867–1880._

Until the year 1867 the guns made at Woolwich were constructed according to the original plan proposed by Sir W. Armstrong, and on this system one of the large guns consisted of as many as thirteen separate pieces. These guns, though unexceptionable as to strength and efficiency, were necessarily so very costly that it became a question whether anything could be done to lessen the expense by a simpler mode of construction or by greater economy in the material. The problem was solved in the most satisfactory manner by Mr. Fraser, of the Royal Gun Factory, who proposed an important modification of the original plan, and the adoption of a kind of iron cheaper than had been previously employed, yet perfectly suited for the purpose. Mr. Fraser’s modification consisted in building up the guns from only a few coils, instead of several, the coils being longer than Sir W. Armstrong’s, and the iron coiled upon itself two or even three times: a plan which enabled him to supersede the breech-piece, formerly made in one large forging, by a piece formed of coils. In order to perceive the increased simplicity of construction introduced by Mr. Fraser, we need but glance at the section of a 9 in. gun constructed according to his system, Fig. 94, and remember that a piece of the same size made after the original plan had ten distinct parts, whereas the Fraser is seen to have but four. Compare also Figs. 92 and 93. We shall now describe the process of making the Fraser 9 in. gun. The parts of the gun as shown in the section, Fig. 94, are: 1, the steel barrel; 2, the B tube; 3, the breech-coil; 4, the cascable screw. The inner steel barrel is made from a solid cylinder of steel, which is supplied by Messrs. Firth, of Sheffield. This steel is forged from a cast block, the casting being necessary in order to obtain a uniform mass, while the subsequent forging imparts to it greater solidity and elasticity. After the cylinder has been examined, and the suitable character of the steel tested by trials with portions cut from it, the block is roughly turned and bored, and is then ready for the toughening process. This consists in heating the tube several hours to a certain temperature in an upright furnace, and then suddenly plunging it into oil, in which it is allowed to remain for a day. By this treatment the tenacity of the metal is marvellously increased. A bar of the steel 1 in. square previous to this process, if subjected to a pull equal to the weight of 13 tons, begins to stretch and will not again recover its original form when the tension is removed, and when a force of 31 tons is applied it breaks. But the forces required to affect the toughened steel in a similar manner are 31 tons and 50 tons respectively. The process, unfortunately, is not without some disadvantages, for the barrel is liable to become slightly distorted and even superficially cracked. Such cracks are removed by again turning and boring; the hardness the steel acquires by the toughening process being shown by the fact that in the first boring 8¼ in. diameter of _solid_ steel is cut out in 56 hours, yet for this slight boring, in which merely a thin layer is peeled off, 25 hours are required; and lest there should be any fissures in the metal, which, though not visible to the eye, might make the barrel unsound, it is filled with water, which is subjected to a pressure of 8,000 lbs. per square inch. If under this enormous pressure no water is forced outwards, the barrel is considered safe. It is now ready to have the B tube shrunk on it.

The B tube, like certain other portions of these guns, is constructed from coiled iron bars, and this constitutes one great peculiarity of Sir W. Armstrong’s system. It has the immense advantage of disposing the metal so that its fibres encircle the piece, thus applying the strength of the iron in the most effective way. The bars from which the coils are prepared are made from “scrap” iron, such as old nails, horse-shoes, &c. A pile of such fragments, built up on a wooden framework, is placed in a furnace and intensely heated. When withdrawn the scraps have by semi-fusion become coherent, and under the steam hammer are soon welded into a compact mass of wrought iron, roughly shaped as a square prism. The glowing mass is now introduced into the rolling-mill, and in a few minutes it is rolled out, as if it were so much dough, into a long bar of iron. In order to form this into a coil it is placed in a very long furnace, where it can be heated its entire length. When sufficiently heated, one end of the bar is seized and attached to an iron core of the required diameter, and the core being made to revolve by a steam engine, the bar is drawn out of the furnace, winding round the core in a close spiral, so that the turns are in contact. The coil is again intensely heated, and in this condition a few strokes of the steam hammer in the direction of its axis suffice to combine the spires of the coil into one mass, thus forming a hollow cylinder.

The B tube for the 9 in. gun is formed of two double coils. When the two portions have been completely welded together under the steam hammer, the tube, after cooling, is roughly turned and bored. It is again fine bored to the required diameter, and a register of the diameter every few inches down the bore is made. These measurements are taken for the purpose of adapting most accurately the dimensions of the steel barrel to the bore of the B tube, as it is found that perfect exactness is more easily obtained in turning than in boring. The steel barrel is therefore again turned to a size slightly _larger_ than the bore of the B tube, and is then placed muzzle end upwards, and so arranged that a stream of water, to keep it cool, shall pass into it and out again at the muzzle, by means of a syphon, while the B tube, which has been heated until it is sufficiently expanded, is passed over it and gradually cooled.

If now the B tube were allowed to cool spontaneously, its ends would, by cooling more rapidly than the central part, contract upon the steel barrel and grip it firmly at points which the subsequent cooling would tend to draw nearer together longitudinally, and thus the barrel would be subjected to injurious strains. In order to prevent this, the B tube is made to cool progressively from the breech end, by means of jets of water made to fall upon it, and gradually raised towards the muzzle end, which has in the meanwhile been prevented from shrinking by having circles of gas-flames playing upon it.

The breech-coil, or jacket, is formed of three pieces welded together. First, there is a triple coil made of bars 4 in. square, the middle one being coiled in the reverse direction to the other two. After having been intensely heated in a furnace for ten hours, a few blows on its end from a powerful steam hammer welds its coils perpendicularly, and when a solid core has been introduced, and the mass has been well hammered on the sides, it becomes a compact cylinder of wrought iron, with the fibres all running round it. When cold it is placed in the lathe, and the muzzle end is turned down, leaving a shoulder to receive the trunnion-ring. The C coil is double, welded in a similar manner to the B coil, and it has a portion turned off, so that it may be enclosed by the trunnion-ring.

The trunnion-ring is made by punching a hole in a slab of heated iron first by a small conical mandrel, and then enlarging by repeating the process with larger and larger mandrels. The iron is heated for each operation, and the trunnions are at the same time hammered on and roughly shaped—or, rather, only one has to be hammered on—for a portion of the bar which serves to hold the mass forms the other. The trunnion-ring is then bored out, and after having been heated to redness, is dropped on to the triple breech-coil which is placed muzzle end up, and the turned end of the C coil (of course, not heated) is then immediately placed within the upper part of the trunnion-ring. The latter in cooling contracts so forcibly as to bind the ends of the coils together, and the whole can thus be placed in a furnace and heated to a high temperature, so that when removed and put under the steam hammer, its parts are readily wielded into one mass. The breech-coil in this state weighs about 16 tons; but so much metal is removed by the subsequent turnings and borings, that it is reduced to nearly half that weight in the gun. It is then turned in a lathe of the most massive construction, which weighs more than 100 tons. Fig. 34, page 95, is from a drawing taken at Woolwich, and shows one of the large guns in the lathe. No one who witnesses this operation can fail to be struck with the apparent ease with which this powerful tool removes thick flakes of metal as if it were so much cheese. The projections of the trunnions prevent the part in which they are situated from being finished in this lathe, and the gun has to be placed in another machine, where the superfluous metal of the trunnion-ring is pared off by a tool moving parallel to the axis of the piece. Another machine accomplishes the turning of the trunnions, the “jacket” being made to revolve about their axis. The jacket is then accurately bored out with an enlargement or socket to receive the end of the B tube, and a hollow screw is cut at the breech end for the cascable.

The portion of the gun, consisting of the steel barrel with the B tube shrunk on it, having been placed upright with the muzzle downwards, the breech-piece, strongly heated, is brought over it by a travelling crane, and slips over the steel barrel, while the recess in it receives the end of the B tube. Cold water is forced up into the inside of the barrel in order to keep it cool. As the breech cools, which it is allowed to do spontaneously, it contracts and grips the barrel and B tube with great force. The cascable requires to be very carefully fitted. It is this piece which plays so important a part in resisting the force tending to blow out the end of the barrel. The cascable is a solid screw formed of the very best iron, and its inner end is wrought by scraping and filing, so that when screwed in there may be perfect contact between its face and the end of the steel barrel. A small annular space is left at the circumference of the inner end, communicating through a small opening with the outside. The object of this is, that in case of rupture of the steel barrel, the gases escaping through it may give timely warning of the state of the piece.

Besides minor operations, there remain the important processes of finishing the boring, and of rifling. The boring is effected in two operations, and after that the interior is gauged in every part, and “lapping” is resorted to where required, in order to obtain the perfect form. Lapping consists in wearing down the steel by friction against fine emery powder and oil, spread on a leaden surface. The piece is then ready for rifling. The machinery by which the rifling is performed cannot be surpassed for its admirable ingenuity and simplicity.

In this operation the gun is fixed horizontally, its axis coinciding with that of the bar, which carries the grooving tools. This bar is capable of two independent movements, one backwards and forwards in a straight line in the direction of the length of the bar, and the other a rotation round its axis. The former is communicated by a screw parallel to the bar, and working in a nut attached to the end of it. For the rotatory movement the bar carries a pinion, which is engaged by a rack placed horizontally and perpendicularly to the bar, and partaking of its backward and forward movement, but arranged so that its end must move along another bar placed at an angle with the former. It is this angle which determines the pitch of the rifling, and by substituting a curved guide-bar for the straight one, an increasing twist may be obtained in the grooves.

The projectile used with these guns is of a cylindrical form, but pointed at the head, and the moulds in which these shots are cast are so arranged that the head of the shot is moulded in iron, while the body is surrounded with sand. The rapid cooling induced by the contact of the cold metal causes the head of the shot to solidify very quickly, so that the carbon in the iron is not separated as in ordinary casting. In consequence of this treatment, the head of the shot possesses the hardness of steel, and is therefore well adapted for penetrating iron plates or other structures. The projectiles are turned in a lathe to the exact size, and then shallow circular cavities are bored in them, and into these cavities brass studs, which are simply short cylinders of a diameter slightly larger than the cavities, are forced by pressure. The projecting studs are then turned so as accurately to fit the spiral grooves of the guns. Thus the projectile in traversing the bore of the piece is forced to make a revolution, or part of a revolution, about its axis, and the rapid rotation thus imparted has the effect of keeping the axis of the missile always parallel to its original direction. Thus vastly increased accuracy of firing is obtained.