Gun-makers had meanwhile improved the strength of the weapon by a recognition of the fact that wrought iron was twice as strong in the direction of the fibre as across it; and thus in the 'sixties they began to coil the central tube, surrounding it by hoops, welded or shrunk on. The full advantages of fibre were thus secured for resisting circumferential strain. The bore was rifled to give the shot that rotatory motion which prevents irregularity in flight and conduces to accuracy of fire at long range. The smooth-bore gun was effective up to only 1000 yards range, as compared with the 6000 yards and 7000 yards for the modern weapon. Breechloading was first introduced into the Navy in the 'sixties, but discarded because the details for closing the breech end proved unsatisfactory. Finally, it was reintroduced in 1878, a satisfactory mechanism having been devised.
These various improvements gradually increased the power of the gun. The length and weight had enormously grown, as is shown by the particulars of successive large Naval guns, shown in Table IV. on the next page; but the increase in energy up till the 'eighties was not commensurate with the augmentation of the weights of the projectile and charge.
The advance from the 38-ton gun of 1870 to the 110-1/2-ton gun in 1887 involved the multiplying by five of the charge of powder, which quadrupled the energy of the gun, but the carrying power of the shot was still deficient. The velocity had increased in twenty years from 1600 to 2000 ft. per second, slower-burning powder having been introduced.
Particulars of the Successive Large Naval Guns, 1800 to 1905.
| Year. | Type. | Weight. | Length. | Calibre. | Weight of Projectile. | Weight of Charge. | Muzzle Energy. | Penetration of Wrought Iron at 1000 Yards Range. | |
| tons | cwt. | in. | in. | lb. | lb. | ft.-tns. | in. | ||
| 1800 | Cast-iron smooth-bore | 2 | 12 | 114 | 6.4 | 32 | 10 | 400 | |
| 1842 | Ditto | 4 | 15 | ... | 8.12 | 68 | 16 | 700 | |
| 1865 | Woolwich wrought-iron | 4 | 10 | ... | 7 | 115 | 22 | 1400 | 7 |
| 1870 | Built-up muzzle-loader | 38 | 0 | 200 | 12.50 | 810 | 200 | 13,900 | 17 |
| 1880 | Ditto | 80 | 0 | 321 | 16 | 1700 | 450 | 27,960 | 22-1/2 |
| 1887 | Built-up breech-loader | 110 | 10 | 524 | 16.25 | 1800 | 960 | 54,390 | 32 |
| 1895 | Wire-wound breech-loader | 46 | 0 | 445.5 | 12 | 850 | ... | 33,940 | 34.6 |
| 1900 | Ditto | 51 | 0 | 496.5 | 12 | 850 | 210 | 36,290 | 35.4 |
| 1905 | Ditto | 58 | 0 | 540 | 12 | 850 | ... | 49,560 | 42 |
Attention was further directed to the improvement of explosives; and ultimately, instead of gunpowder having a potential energy of 480 foot-tons per pound, modified gun-cotton was introduced, with an energy of 716 foot-tons per pound, and still later there were evolved explosive compounds of which the potential energy per unit of weight was fourfold greater than in the case of gunpowder, namely, 1139 foot-tons per pound. Finally, the explosive has taken the form of cordite, which ensures slow burning, great expansion, and, consequently, augmented propelling power behind the projectile, without material addition to the maximum strain upon the weapon. But in any case the constructional strength of the modern gun is enormously superior to the earlier built-up weapons, as around the inner tubes there is coiled something like 120 miles of wire, which itself has a breaking-strain of between 90 and 110 tons per square inch, and is put on under a tension of from 54 tons per square inch on the inner wires to 32 tons per square inch on the outer wires,[63] so that the ultimate resistance to strain consequent upon the firing of the gun is enormously increased. Velocities of 2600 ft. per second are thus realised, and even more is quite feasible, so that penetration of wrought iron at 1000 yards range has now been increased to 42 in.
If we compare the 12-in. gun to-day with the weapon of the same calibre of twenty years ago, when there was no widened chamber for the explosive, when prismatic powder of low expansive power was used, it is found, as shown in the Table opposite, that the penetration at 1000 yards has been doubled, and the possible effective range multiplied fivefold. There has also been an enormous gain in quicker fire by improved breech mechanism and efficient hydraulic and electric mountings, whereby the gun and all its loading, elevating, and training machinery is rotated.
The metallurgist has also been successfully occupied, and it is probable that the armour plate of to-day is still invulnerable. The earlier wrought-iron plates were increased from 4-1/2 in. in thickness on the Warrior of 1861, to the 24 in. on the Inflexible of 1881; the area protected being almost proportionately reduced. The artillerist with improved projectiles ultimately defeated this heavy cleading on the ships; but compound armour, first made in 1879, enabled the maximum thickness on the broadside to be reduced to 18 in., permitting a greater area to be covered for the same weight. At first the 80-ton gun failed in its attack, but heavier weapons, with improved projectiles, prevailed. The next step was the introduction of all-steel armour in 1890. Two years later there was introduced the super-carburising and subsequent chilling of the face of plates made of an alloy of nickel steel. In 1897 the process of hardening was still further developed, and now the 9-in. plate on the modern battleship is equal in resistance to a 26-in. wrought-iron plate of the 'sixties, or a 20-in. compound-plate of the 'eighties, or a 13-in. plate of the early-hardened type. For the present, therefore, the armour seems to have secured the victory, as at 5000 yards range 9-in. armour can scarcely be defeated by even the 12-in. gun.