The heaviest of our up-to-date ordnance is of moderate calibre, the largest breech-loaders being 12-inch, 10-inch, and 9.2-inch guns. But the elaborateness of its manufacture is such that one big gun takes nearly as long to "build up" as the ship for which it is destined.

Each weapon has to pa.s.s through about sixteen different processes:--

(1) The solid (or hollow) ingot is _forged_.

(2) _Annealed_, to get rid of strains.

(3) It is placed horizontally on a lathe and _rough-turned_.

(4) _Rough-bored_ in a lathe.

(5) _Hardened._ Heated to a high temperature and plunged, while hot, into a bath of rape oil kept cold by a water-bath. It cools slowly for seven to eight hours, being moved about at intervals by a crane. This makes the steel more elastic and tenacious.

(6) _Annealed_, _i.e._ reheated to 900 Fahr. and slowly cooled. Siemens' pyrometer is used in these operations.

(7) _Tested_ by pieces cut off.

(8) _Turned_ and _bored_ for the second time.

(9) Carefully turned again for _shrinkage_. Outer coil expanded till large enough to fit easily over inner. Inside, set up vertically in a pit, has outside lowered on to it, water and gas being applied to make all shrink evenly. Other projections, hoops, rings, &c., also shrunk on.

(10) Finish--_bored_ and _chambered_.

(11) _Broached_, or very fine bored, perhaps _lapped_ with lead and emery.

(12) _Rifled_ horizontally in a machine.

(13) Prepared for breech fittings.

(14) Taken to the Proof b.u.t.ts for trial.

(15) Drilled for sockets, sights, &c. Lined and engraved.

Breech fittings, locks, electric firing gear, &c., added. Small adjustments made by filing.

(16) _Browned_ or _painted_.

When worn the bore can be lined with a new steel tube.

These lengthy operations completed, our gun has still to be _mounted_ upon its field-carriage, naval cone, or disappearing mounting, any of which are complicated and delicately-adjusted pieces of mechanism, the product of much time and labour, which we have no s.p.a.ce here to describe.

Some account of the princ.i.p.al parts of these guns has already been given, but the method by which the breech is closed remains to be dealt with.

It will be noticed that though guns now barely reach half the weight of the monster muzzle-loaders, they are even more effective. Thus the 46-ton (12-inch) gun hurls an 850-lb. projectile with a velocity of 2750 foot-seconds, and uses a comparatively small charge. The famous "81-ton" needed a very big charge for its 1700-lb. sh.e.l.l, and had little more than half the velocity and no such power of penetration.

This change has been brought about by using a slower-burning explosive very powerful in its effects; enlarging the chamber to give it sufficient air s.p.a.ce, and lengthening the chase of the gun so that every particle of the powder-gas may be brought into action before the shot leaves the muzzle. This system and the subst.i.tution of steel for the many layers of welded iron, makes our modern guns long and slim in comparison with the older ones.

To resist the pressure of the explosion against the breech end, a tightly-fitting breech-plug must be employed. The most modern and ingenious is the Welin plug, invented by a Swedish engineer. The ordinary interrupted screw breech-plug has three parts of its circ.u.mference plane and the other three parts "threaded," or grooved, to screw into corresponding grooves in the breech; thus only half of the circ.u.mference is engaged by the screw. Mr. Welin has cut steps on the plug, three of which would be threaded to one plane segment, each locking with its counterpart in the breech. In this case there are three segments engaged to each one left plane, and the strength of the screw is almost irresistible. The plug, which is hinged at the side, has therefore been shortened by one-third, and is light enough to swing clear with one touch of the handwheel that first rotates and unlocks it.

The method of firing is this: The projectile lifted (by hydraulic power on a ship) into the loading tray is swung to the mouth of the breech and pushed into the bore. A driving-band attached near its base is so notched at the edges that it jams the sh.e.l.l closely and prevents it slipping back if loaded at a high angle of elevation. The powder charge being placed in the chamber the breech-plug is now swung-to and turned till it locks close. The vent-axial or inner part of this breech-plug (next to the charge), which is called from its shape the "mushroom-head," encloses between its head and the screw-plug the de Bange obturator, a flat canvas pad of many layers soaked with mutton fat tightly packed between discs of tin. When the charge explodes, the mushroom-head--forced back upon the pad--compresses it till its edges bulge against the tube and prevent any escape of gas breechwards.

The electric spark which fires the charge is pa.s.sed in from outside by means of a minute and ingenious apparatus fitted into a little vent or tube in the mushroom-head. As the electric circuit cannot be completed till the breech-plug is screwed quite home there is now no more fear of a premature explosion than of double loading. If the electric gear is disordered the gun can be fired equally well and safely by a percussion tube.

This description is of a typical large gun, and may be applied to all calibres and also to the larger quick-firers. The mechanism as the breech is swung open again withdraws the empty cartridge. So valuable has de Bange's obturator proved, however, that guns up to the 6-inch calibre now have the powder charge thrown into the chamber in bags, thus saving the weight of the metal tubes. .h.i.therto necessary.

Of course several types of breech-loading guns are used in the Service, but the above are the most modern.

The favourite mode of construction at the present time is the wire-wound barrel, the building up of which is completed by covering the many layers of wire with an outer tube or jacket expanded by heat before it is slipped on in order that it may fit closely when cold. A previous make, without wire, is strengthened by rings or hoops also shrunk on hot.

The quick-firers proper are of many sizes, 8-inch, 7.5-inch, 6-inch, 4.7-inch, 4-inch, and 3-inch (12-pounders). The naval type is as a rule longer and lighter than those made for the rough usage of field campaigning and have a much greater range. There are also smaller quick-firers, 3-pounders and 6-pounders with bore something over 1-inch and 2-inch (Nordenfelt, Hotchkiss, Vickers-Maxim). Some of the high velocity 12-pounders being employed as garrison guns along with 6-inch and 4.7-inch, and the large calibre howitzers.

We still use howitzer batteries of 5-inch bore in the field and in the siege-train, all being short, rifled, breech-loading weapons, as they throw a heavy sh.e.l.l with smallish charges at a high angle of elevation, but cover a relatively short distance. A new pattern of 8-inch calibre is now under consideration.

It is interesting to contrast the potencies of some of these guns, all of which use cordite charges.

+----------+---------------+-----------+----------------+-----------+ |Calibre. | Charge. |Weight of |Muzzle Velocity |Number of | | | | Shot. | in |Rounds per | | | | | Foot Seconds. | Minute. | +----------+---------------+-----------+----------------+-----------+ | 12 inch |207 lbs. | 850 lbs. | 2750 | 1 | | 8 " | 52 " | 210 " | 2750 | 5 | | 6 " | 25 " | 100 " | 2775 | 8 | |4.7 " | 9 " | 45 " | 2600 | 12 | | 3 " | 2 lbs. 9 oz. |12.5 " | 2600 | 20 | +----------+---------------+-----------+----------------+-----------+

[Ill.u.s.tration: _The Simms armour-clad motor-car for coast defence.

Maxim guns and Pom-pom in action._]

In the armament of our fine Navy guns are roughly distributed as follows:--81-ton, 13-1/2-inch, and superseded patterns of machine-guns such as Gatling's, Gardner's, and Nordenfelt's, besides a few surviving muzzle-loaders, &c., are carried only by the oldest battleships.

The first-cla.s.s battleships are chiefly supplied with four 12-inch guns in barbettes, twelve 6-inch as secondary batteries, and a number of smaller quick-firers on the upper decks and in the fighting tops, also for use in the boats, to which are added several Maxims.

The first-cla.s.s cruisers have 9.2 as their largest calibre, with a lessened proportion of 6-inch, &c. Some of the newest bear only 7-1/2 or 6-inch guns as their heaviest ordnance; like the second-cla.s.s cruisers which, however, add several 4.7's between these and their small quick-firers.

Vessels of inferior size usually carry nothing more powerful than the 4.7.

All are now armed with torpedo tubes.

These same useful little quick-firers and machine-guns have been the lethal weapons which made the armoured trains so formidable. Indeed, there seems no limit to their value both for offence and defence, for the battle chariot of the ancient Briton has its modern successor in the Simms' motor war car lately exhibited at the Crystal Palace. This armour-plated movable fort is intended primarily for coast defence, but can work off beaten tracks over almost any sort of country. It is propelled at the rate of nine miles an hour by a 16-horse-power motor, carrying all its own fuel, two pom-poms, two small Maxims, and 10,000 rounds of ammunition, besides the necessary complement of men and searchlights for night use, &c., &c.

The searchlight, by the way, has taken the place of all former inventions thrown from guns, such as ground-light b.a.l.l.s, or parachute lights with a time-fuse which burst in the air and remained suspended, betraying the enemy's proceedings.

In like manner the linked chain and "double-headed" shot, the "canister"--iron b.a.l.l.s packed in thin iron or tin cylinders which would travel about 350 yards--the "carca.s.ses" filled with inflammable composition for firing ships and villages, are as much out of date as the solid round shot or cannon-ball. Young Shrapnell's invention a century ago of the form of sh.e.l.l that bears his name, a number of b.a.l.l.s arranged in a case containing also a small bursting-charge fired either by percussion or by a time-fuse, has practically replaced them all. Thrown with great precision of aim its effective range is now up to 5000 yards. A 15-pounder shrapnell sh.e.l.l, for instance, contains 192 bullets, and covers several hundred yards with the scattered missiles flying with extreme velocity.

Common sh.e.l.l, from 2-1/2 to 3 calibres long, contains an explosive only. Another variety is segment sh.e.l.l, made of pieces built up in a ring with a bursting charge in the centre which presently shatters it.

The Palliser sh.e.l.l has a marvellous penetrating power when used against iron plates. But, _mirabile dictu!_ experiments tried within the past few months prove that a soft cap added externally enables a projectile to pierce with ease armour which had previously defied every attack.

EXPLOSIVES.

Half a century ago gunpowder was still the one driving power which started the projectile on its flight. It is composed of some 75 parts of saltpetre or nitrate of potash, 15 parts of carefully prepared charcoal, and 10 parts of sulphur. This composition imprisons a large amount of oxygen for combustion and is found to act most successfully when formed into rather large prismatic grains.

On the abolition of the old flint-lock its place was taken by a detonating substance enclosed in a copper cap, and some time later inventors came forward with new and more powerful explosives to supersede the use of gunpowder.

By treating cotton with nitric and sulphuric acid reaction _gun-cotton_ was produced; and a year later glycerine treated in the same manner became known to commerce as _nitro-glycerine_. This liquid form being inconvenient to handle, some inert granular substance such as infusorial earth was used to absorb the nitro-glycerine, and _dynamite_ was the result.

The explosion of gun-cotton was found to be too sudden and rapid for rifles or cannon; it was liable to burst the piece instead of blowing out the charge. In order to lessen the rapidity of its ignition ordinary cotton was mixed with it, or its threads were twisted round some inert substance.

When repeating-rifles and machine-guns came into general use a smokeless powder became necessary. Such powders as a rule contain nitro-cellulose (gun-cotton) or nitro-glycerine, or both. These are combined into a plastic, gluey composition, which is then made up into sticks or pellets of various shapes, and usually of large size to lessen the extreme rapidity of their combustion. Substances such as tan, paraffin, starch, bran, peat, &c., &c., and many mineral salts, are used in forming low explosives from high ones.