Part 27

An extremely effective plan for the defence of coasts and harbours was originated by Colonel Moncrieff, when about 1863 he contrived a method of mounting large guns on the disappearing system, by which almost complete protection against hostile fire is given to both gun and gunners. He utilizes the recoil as a means of bringing the gun down into a protected position the moment it has been fired, and retains this energy by a simple arrangement until the piece has been reloaded, when it is allowed to expend itself by again raising the gun above the parapet into the original firing position. The configuration and action of Colonel Moncrieff’s gun-carriage will be understood by an inspection of the annexed illustrations, where in Fig. 100 is shown the gun raised above the parapet and ready for firing. When the discharge takes place, the gun, if free, would move backwards with a certain speed, but the disposition of the mounting is such that this initial velocity receives no _sudden_ check, the force being expended in raising a heavy counterpoise, and at the same time the gun is permitted to descend, while maintaining a direction parallel to its firing position. At the end of the descent, which, it must be understood, is caused by the force of the recoil, and not by the counterpoise, for this more than balances the weight of the gun, the latter is retained as shown in Fig. 101 until it has been reloaded; and when it has again to be fired, it is released so as to allow the descent of the counterpoise to raise it once more into position. The great advantage of this invention is the protection afforded to the artillerymen and gun while loading; and even the aiming can be accomplished by mirrors, so that the men are exposed to no danger, except from “vertical fire,” which involves but little risk.

Colonel Moncrieff took out a patent for his invention in 1864, but committed the practical working out of his idea to the firm of Sir W. G. Armstrong & Co., in whose hands the design was ultimately transformed from the original somewhat cumbersome arrangement of the mounting into the compact and manageable form shown in Fig. 102, which represents a 13·9 inch 68–ton breech-loading disappearing gun on the Elswick hydro-pneumatic mounting. The principle of hydraulic power is fully explained in our article on that subject, and an example of its application to cranes as devised by Sir W. Armstrong is there described. When guns began to be made very large, and projectiles weighing several cwts. had to be dealt with, the application of power in some form became essential for loading, running out, elevating, training, etc.; and though steam-power naturally was first used, hydraulic power was adopted at Elswick, and has been there applied to the mountings of large guns with the greatest success by Mr. G. W. Rendel. To mention the various arrangements in which this power is applied, or to attempt any description of the elaborate machinery by which it is regulated, would carry us far beyond our limits. But the powerful weapon depicted in Fig. 102 is designed to be worked only by the manual effort of a few men. In this mounting the pressure of condensed air sustains the gun in the firing position; that pressure, acting upon the water in the recoil presses, having previously forced up their rams so as to turn into a nearly vertical position the strong brackets or beams on which the trunnions are supported. The recoil is checked in the usual way by the forcing of the water through small ports or valves as the ram descends, but these valves are so arranged that the water is in part forced back into the air chamber, and there recompresses the air, to restore the power for again raising the gun. The pressure in the air chamber when the gun is down may be about 1,400 lbs. per square inch; when it is up this will be reduced to perhaps one half by the expansion of the air in doing work. We have here the reaction of compressed air taking the place of the gravity of the counterpoise originally designed. There are in this hydro-pneumatic mounting a number of adjusting appliances, such as forcing pumps, brakes, etc., for regulating the pressures, or quantity of liquid, as, for instance, when lowering the gun without any recoil action in operation. Then again, with any change in the weight of projectile or in the powder charge, there would be a corresponding change in the power of the recoil, and therefore the necessity for compensatory adjustments, which are made with great readiness. The nicety with which the parts are adapted to each other in this mounting must be obvious, when we observe the magnitude of the mass to be moved with the least delay, and brought to rest, quite gently and exactly, in a new position. Details cannot here be given even of the method by which the valves in the recoil cylinders are automatically controlled for this purpose. Means are also supplied for setting the gun, while still in its protected position, to the required angle of elevation or depression. The adjustment is made by the long rods attached near the breech and set at their lower ends to the position giving the intended angle to the raised gun. The varied and powerful strains to which the parts of this mechanism are subject, and which have had to be calculated and provided for, may be inferred from the enormous recoil energy of the gun, which under ordinary conditions amounts to no less than 730 foot-tons. The gun is provided with ordinary, and also with reflecting, sights, so that no one need be exposed to the enemy’s fire. Protective armour above the gun is not required, as the pit itself being usually on some elevation is imperceptible to the enemy, and the gun is visible but for a few seconds, forming a quite inconspicuous object. The pit in which the gun is mounted is commonly lined with concrete. Italy, England, Norway, Japan and other countries have appreciated the advantages of the disappearing system in providing the most powerful coast defences yet devised, and a great many guns have been mounted on this principle.

An extraordinary piece of ordnance is represented in Fig. 103. It is one of two huge mortars, the idea of which presented itself to Mr. Mallet during the Crimean War, the intention being to throw into the Russian lines spherical shells a yard in diameter, which would, in fact, have constituted powerful mines, rendering it impossible for the fortifications to continue tenable. Mallet’s original design was to project these shells from mortars of no less than 40 tons weight. When it was pointed out that the transport of so heavy a mass would be impracticable, the design was changed to admit of the mortar being made in pieces not exceeding eleven tons in weight, and built up where required. During the most active period in the siege of Sebastopol this plan was submitted to Lord Palmerston, who at once ordered two of these apparently formidable pieces to be constructed, without waiting for official examinations of the scheme, and the usual reports of experts,—promptness in this case being considered of the utmost importance. A contract was made with a private firm, who undertook to deliver them in ten weeks. But the difficulties attending such constructions not being understood at the time, delays arose, the contractors failed, and two years elapsed before the mortars were completed. In the meantime peace had been concluded, and the mortars were never fired against any hostile works; but experiments were made with one of them at Woolwich. The heaviest of the shells it was intended to project weighed 2,940 lbs., and for this it was proposed to use a charge of 80 lbs. of gunpowder. In the experiments the charges first used were low, but gradually increased: when it was found that after every few rounds repairs became necessary in consequence of the weak points in the construction, and after the nineteenth round the mortar was so much damaged that the trials were definitely discontinued. The other mortar, though mounted, was never fired, but remains at Woolwich, an object of some interest to artillerists, especially since there has been some talk of reverting to this very old-fashioned form of ordnance as a means of attacking ironclads in their most vulnerable direction by the so-called vertical fire. In one of the rounds of the Mallet mortar tried at Woolwich, a shell weighing 2,400 lbs. was thrown by a charge of 70 lbs. of gunpowder a distance of more than a mile and a half, and it buried itself in the soil to a very great depth.

For high-elevation firing, howitzers will more probably be the form of ordnance most in use. The range of the howitzer is determined by the angle at which it is elevated, whereas with the mortar it is chiefly by variation of the powder charge that the aim is adjusted. Many of the old short 9 in. muzzle-loaders have already been converted into 11 in. rifled howitzers, and these are likely to prove of great service in defending our harbours and channels against war vessels.

Some account has been given in a preceding article of the great steel works of Krupp & Co. at Essen, and the place has been noted as one of the greatest gun factories in the world during the second half of our century. The process there practised of casting crucible steel ingots, and already described, is precisely that used in the first stage of gun-making. The steel for guns put into the crucibles is a carefully adjusted mixture of one quality of iron puddled into steel and subjected to certain treatment; the other portion is made from a different quality of iron from which all the carbon has been puddled out. The cast ingot is forged under a great steam hammer, bored, turned, and steel hoops shrunk upon it, in several layers, and other operations are performed upon it like those which have already been mentioned. A 14 in. gun is said to require sixteen months for its manufacture, and its cost to be about £20,000.

Artillerists had long carried on a warm controversy as to the relative merits of wrought iron and steel in gun construction, the latter material being regarded with shyness on account of its want of uniformity as formerly produced. Krupp however began as early as 1847 to make guns of his excellent crucible steel, and through bad report and good report confined himself to this material until, it is asserted, by 1878 he had supplied over 17,000 steel guns of all calibres. He began by making a 3–pounder gun, but soon produced pieces of larger size, all of which were bored and turned out of solid masses of metal. At a later period the plan of shrinking on strengthening hoops of steel was adopted. The Krupp guns have found extensive favour, and many very heavy ones have been made, some indeed of greater weight than the 110–ton Armstrong; but the excess of weight is due to the mass of metal which the Krupp construction of the breech mechanism requires. Thus Krupp’s 120–ton gun has a muzzle energy of but 45,796 foot-tons, while that of the Elswick piece is 55,105 foot-tons.

The breech arrangement in the Krupp guns consists of a lateral slot into which slides a closing block after the charge has been inserted from the rear. An obsolete form of this breech piece is seen in Fig. 104, which represents a 32–pounder gun such as was used in sieges by the Prussians in the Franco-German War. It will be observed here that the slot and breech piece are of rectangular form; but this shape, causing the piece to be weak where most strength was required, was afterwards altered into a D-shaped section, the curved side being of course to the rear. That difficulty which baffled the earliest attempts at breech-loading is the same that has given much trouble to modern gunmakers. It consists in so closing the breech that no escape of the powder gases can take place there at the moment of discharge. When we remember that the momentary pressure of the gases in the powder chamber may amount to more than 40 tons on the square inch, we can well understand the enormous velocity with which they will rush forth from even the smallest interspace between the base of the gun and the breech block, but we can hardly realise without actual inspection the mechanical action they produce in their passage: when once the escape occurs, a channel is cut in the metal as if part had been removed by an instrument, and the piece in that condition is disabled for further use. Several devices are in use obtaining perfect closure of the breech, which is technically called _obturation_ (Latin, _obturare_, to close up). One of these consists in fitting closely into the circumference of the bore a ring of very elastic steel, turned up at the edges towards the powder chamber. The gas pressure forces the edge of this ring still more closely against the interior of the powder chamber, much in the same way as the Bramah collar acts in the hydraulic press (see Fig. 165). The shaded circle shown on the breech piece in Fig. 104 is an additional device for obtaining obturation. The Broadwell ring, as the above-mentioned contrivance is called, is not used in English guns, but another plan of obtaining a gas-joint has been much adopted, in which a squeezable pad is by compression forced outwards to close up the bore.

A very long range was claimed for Krupp’s guns at the time of the Franco-German War, for at the siege of Paris (1870) it was said they could hurl projectiles to the distance of five miles, though probably there was some exaggeration in this statement. There is no doubt however that the Prussians had very effective and powerful artillery, as may be gathered from Fig. 105, which is taken from a photograph of part of the fortifications of Strasburg after the bombardment of that fortress. The explosive shells used by the Prussians against masses of troops were not precisely segment shells of the form already described, but the principle and effect were the same, for the interior was built up of circular rings, which broke into many pieces when the shell exploded.

Out of the very numerous forms in which modern ordnance is constructed, we have been able to select but a few examples for illustration and description. These will suffice, it is hoped, to give an idea of the progress that the century has witnessed. It would be beyond our scope to give details of the ingenious mechanical devices that have come to be applied to guns: such as the breech-closing arrangements, the various ways in which recoil is controlled and utilized, etc. A good illustration, had space permitted, of the scientific skill applied to ordnance would be found in the contrivances fitted to certain projectiles in order to determine their explosion at the proper moment. These are very different from the cap or time fuse that did duty in the first half of the century. We have indeed said little of the projectiles themselves beyond mention of the Palliser chilled shot and the obsolete studded projectiles. We have not explained how bands of copper, or other soft metal, are put round a certain part of the shot or shell, in order that, being forced into the grooves, the axial rotation may be imparted, or how windage is prevented by “gas checks” attached to the base of the projectiles. We must now be contented to conclude this section by showing the structure of two kinds of explosive shells which have been much used.

Shrapnel shell takes its name from Lieutenant Shrapnel, who was its inventor about the end of last century, but the projectile began to be used only in 1808. Fig. 105_a_ is a section showing the shell as a case containing a number of spherical bullets, of which in the larger shells there are very many, the interspaces being filled with rosin, poured in when melted; the bullets are thus prevented from moving about. The figure shows the shell without the fuse or percussion apparatus, which screws into the hollow at the front. The bursting charge of gunpowder is behind the bullets, and when it explodes they travel forward with a greater velocity than the shell, but with trajectories more or less radiating, carrying with them wide-spreading destruction and death.

A shrapnel shell may be said to be a short cannon containing its charge of powder in a thick chamber at the breech end; the sides of the fore part of the shell are thinner than those of the chamber, and may be said to form the barrel of the cannon. This cannon is loaded up to the muzzle with round balls, which vary with the shell in size. An iron disc between the powder and the bullets represents the wad used in ordinary fowling-pieces. A false conical head is attached to the shell, so that its outward appearance is very similar to that of an ordinary cylindro-conoidal shell: that is to say, it looks like a very large long Enfield bullet. The spinning motion which had been communicated to the shell by the rifling of the gun from which it had been fired causes the barrel filled with bullets to point in the direction of the object at which the gun has been aimed. Consequently, when the shrapnel shell is burst, or rather fired off, the bullets which it contained are streamed forward with actually greater velocity than that at which the shell had been moving; and the effect produced is similar to firing grape and canister from a smooth-bore cannon at a short range.

Segment shells were first brought into use by Lord Armstrong in 1858 in connection with his breech-loading guns. The segment shell consists of a thin casing like a huge conical-headed thimble, with a false bottom attached to it. It is filled with small pieces of iron called “segments,” cast into shapes which enable them to be built up inside the outer casing into two or more concentric circular walls. The internal surface of the inmost wall forms the cavity of the compound or segment shell, and contains the bursting charge. The segment shell is fitted with a percussion fuse, which causes it to explode when it strikes. In the shrapnel shell, the powder charge is situated in rear of the bullets, and consequently produces the chief effect in a forward direction. In the segment shell, the powder is contained inside the segments, and therefore produces the chief effect in a lateral direction. When the shrapnel shell is burst at the right moment, its effect is greatly superior to that of the segment shell; on the other hand, the segment shell, when employed at unknown or varying distances, is far more unlikely to explode at the proper time.

Shrapnel and segment shells can be used with field artillery, _i.e._, 9–pounders, 12–pounders, 16–pounders; and also with heavy rifled guns in fortresses, viz., 40–pounders, 64–pounders, 7–in. and 9–in. guns. But the conditions of their service are very different in each case. With regard to field artillery, the distance of the enemy is rarely known, and is constantly changing, and hence the men who have to adjust the fuses would probably be exposed to the fire of the enemy’s artillery, and, consequently, could not be expected to prepare the fuses with the great care and nicety which are absolutely necessary to give due effect to the shells. There are, however, some occasions when the above objections would not hold good—as, for instance, when field artillery occupy a position in which they wait the attack of an enemy advancing over ground in which the distances are known.

Segment shells require no adjustment of their percussion fuse. They enable the artillerymen to hit off the proper range very quickly, since the smoke of the shell which bursts on striking tells them at once whether they are aiming too high or too low.

With regard, however, to the service of heavy rifled guns in fortresses, the conditions are quite different. In the first place, the distance of all objects in sight would be well known beforehand; and in the second place, the fuses of the shells would be carefully cut to the required length in the bomb-proofs, where the men would be completely sheltered. The 7–in. shrapnel contains 227 bullets, and a 9–in. shrapnel would contain 500 bullets of the same size, and these shells could be burst with extraordinary accuracy upon objects 5,000, 6,000, or 7,000 yards off.

_MACHINE GUNS._

The name of machine guns has been applied to arms which may be regarded as in some respects intermediate between cannons and rifles, since in certain particulars they partake of the nature of both. Like the former, they are fired from a stand or carriage, and in some of their forms require more than one man for their working: in the calibre of their barrels and the weight of their projectiles, they are assimilated to the rifle, but they are capable of pouring forth their missiles in a very rapid succession—so rapid indeed as practically to constitute volley firing. The firing mechanism of the machine gun has always an automatic character, but the rifle has acquired this feature, so that it cannot be made a distinguishing mark: on the other hand, since machine guns have been made to discharge projectiles of such weights as 1 lb. or 3 lb. there is nothing to separate them from quick-firing ordnance unless it be the automatic firing.

The idea of combining a number of musket-barrels into one weapon, so that these barrels may be discharged simultaneously or in rapid succession, is not new. Attempts were made two hundred years ago to construct such weapons; but they failed, from the want of good mechanical adjustments of their parts. Nor would the machine gun have become the effective weapon it is, but for the timely invention of the rigid metallic-cased cartridge. Several forms of machine guns have in turn attracted much attention. There is the Mitrailleur (or Mitrailleuse), of which so much was heard at the commencement of the Franco-German War, and of whose deadly powers the French managed to circulate terrible and mysterious reports, while the weapon itself was kept concealed. Whether this arose from the great expectations really entertained of the destructive effects of the mitrailleur, or whether the reports were circulated merely to inspire the French troops with confidence, would be difficult to determine. Our own policy in regard to new implements of war is not to attempt to conceal their construction. Experience has shown that no secret of the least value can long be preserved within the walls of an arsenal, although the French certainly apparently succeeded in surrounding their invention with mystery for a while. The machine gun, or “battery,” invented by Mr. Gatling, an American, is said by English artillerists to be free from many defects of the French mitrailleur. In 1870 a committee of English military men was appointed to examine the powers of several forms of mitrailleur, with a view to reporting upon the advisability or otherwise of introducing this arm into the British service. They recommended for certain purposes the Gatling battery gun.