The coming of the Armstrong gun at once revolutionized artillery practice and material in this country. The sum of all the improvements embodied in it was so great that existing material scarcely bore comparison with it. Its accuracy as compared with that of the smooth-bore field piece which it displaced was stated in parliament to be in the ratio of fifty-seven to one. And the effect of its inventor’s achievement was, “that from being the rudest of weapons, artillery has been advanced to be nearly on a par mechanically with the steam engine or the power-loom; and it differs as essentially from the old cast-iron tube dignified with the name of a gun, as the railway train of the present day differs from the stagecoach of our forefathers.”[127] A revolutionary invention it certainly was. Yet, like most revolutionary inventions, it relied for its grand effect more on the aggregate effect of the small improvements in its various elements than on the materialization of some new-born idea. The building up of guns in coils was not a new discovery, polygroove rifling was already in use abroad, breech-loading, lead-coated projectiles, elevating screws—all had been known for years. Nor does this fact detract in the least from the fame of Mr. Armstrong in this connection. His greatness lay, surely, in the insight and initiative with which he made use of known forms and combinations, summoning to his aid the new powers placed at his disposal by Whitworth, Nasmyth, Bessemer and their contemporaries in order to evolve a system incomparably superior to anything hitherto achieved.
In England, too, an independent development was at the same time taking place in yet another direction. Mr. Whitworth, having satisfactorily established the principles governing the design of rifles, felt confident of extending them to field and heavy ordnance. Adhering to the muzzle-loading principle and to his hexagonal form of rifling he manufactured, between the years 1854 and 1857, several guns which fired projectiles of from six to twenty-four pounds’ weight with great accuracy and to ranges greater than any yet attained. Events occurred which caused him to be given every encouragement by the government. The attitude of the French in these years was suspicious and unfriendly. Schemes of invasion were openly discussed in their press, and war vessels of various types equipped with armour plate were designed and actually built. Reports of their plans, following closely on the exposures of the Crimean War and the Indian Mutiny, rendered the country increasingly restless and apprehensive as to the value of our offensive and defensive armaments. And then, although the new Armstrong gun was acclaimed as eminently suited for service in the field, doubts had been cast as to whether the principles of its design could be applied satisfactorily to the heaviest ordnance. Other rifled artillery had certainly failed to give the results expected from it. The Lancaster rifled gun, a muzzle-loading gun with a twisted bore of a slightly oval section, had failed lamentably at the Crimea owing to the tendency, according to one account, of the oval projectile to wedge itself against the slightly larger oval of the bore; according to another account, owing to the flames from the powder gases penetrating the interior of the welded shells which had been supplied for it. The breech-loading ordnance of Cavalli had failed the Italians. In Sweden several accidents had occurred with Wahrendorf’s breech-loading pieces. The French system, which had been copied by the majority of the powers, was that which appeared to be giving the least unsatisfactory results.
In these circumstances every encouragement was given Mr. Whitworth to develop ordnance on his own lines. In ’58 a committee on rifled guns was appointed by parliament to examine and report on the relative merits of the various systems in use. The committee quickly set to work. No difficulty was found in eliminating all but two, on which attention was soon concentrated: the Armstrong and the Whitworth. The result of the final investigation was a report in favour of the Armstrong gun, which, as we have already seen, was adopted in the same year for field service. Mr. Armstrong, who had handed over his rights in the gun for the benefit of the nation, was knighted and his services were subsidized for the improvement of rifled ordnance generally. The title of “Engineer to the War Department” was conferred on him, and later he received the further appointment of “Superintendent of the Royal Gun Factory” at Woolwich.
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The revolution in field guns was closely followed by a corresponding revolution in heavy ordnance. The experience of the Crimean War proved two things: that the development of the shell gun necessitated the provision of armour to protect the flanks of warships; and that the development of armour necessitated a heavy ordnance of a greater power than existing smooth-bore cannon. The shell gun, in fact, induced a rifled ordnance.
The French, who had already found a cheap and sufficiently effective rifled field artillery in the conversion of their smooth-bores on the de Beaulieu principle, merely had to extend this conversion to their heavier pieces. By 1860 they had converted their 30- and 50-pounder cannon in this way, thus enabling them to be used for the discharge of either spherical or elongated projectiles.
Britain, on the other hand, found herself committed to an entirely new and experimental system which could not be applied to existing ordnance; a large outlay of money was thereby involved for new plant and guns; our vast establishment of smooth-bore cast-iron cannon was in danger of being reduced to scrap material. At the same time doubts were expressed whether this new system, whose success as applied to medium pieces was generally admitted, would be found satisfactory when applied to the largest size of ordnance. It was natural, then, that great interest should be centred in what was regarded as a less experimental alternative to the Armstrong system, in case the latter failed. The results obtained by Mr. Whitworth in the manufacture of solid cannon, rifled hexagonally, muzzle-loading and capable of firing hexagonal bolts or, in emergency, spherical balls, were such as to give promise of competing successfully with those obtained from the ordnance officially patronized. To the public the simplicity of his system strongly appealed. Mr. Whitworth himself, far from being deterred by the decision given in favour of his rival, was now an enthusiastic exponent of the constructive principles which he had made his own. Trial succeeded trial, piece after piece was made and tested to destruction. By 1860 a very successful ordnance was evolved at Manchester by him: guns made of homogeneous iron, forged in large masses, and formed of cylindrical tubes forced one over another by means of a known hydraulic pressure—not, as in the Armstrong system, by heating and shrinking. And on the sands at Southport a series of public trials were carried out with these guns, the results of which proved a great advertisement for the Whitworth system. The accuracy of flight of the projectiles was unprecedented, and all records in ranging power were broken by one of the pieces, a 3-pounder, which threw a shot to a distance of 9,688 yards![128]
Even if the new Whitworth system were adopted, the utilization of the old smooth-bore cannon which formed the existing national armament of ships and fortresses was not secured. Neither the Armstrong nor the Whitworth system provided an expedient for converting to rifled ordnance the thousands of cast-iron guns in which the defence of the country was invested. Efforts were therefore made to reinforce the old pieces so that, when rifled, they would be sufficiently strong to withstand the greater stresses entailed. Greater stresses in the metal, due to higher chamber pressures of the powder gases, were almost a necessary concomitant of rifling. For, apart from the increase in the size and mass of the projectile and its greater initial resistance to motion, pressures tended to increase in a greater ratio than the size of the pieces themselves; the mass of the projectile increased as the cube, the propulsive force of the gases as the square, of the diameter of the bore; hence to attain a given velocity, the larger the bore the higher the pressure required to propel it with a given type of powder,—other things being equal. No limit, therefore, could be assigned to the strength and power required of heavy ordnance. Moreover a struggle had begun in ’59, with the building of the Gloire and Warrior, which was already foreshadowing tremendous developments both of guns and of armour.
The experiences of America in this connection were not encouraging. The civil war served as an incentive to the Americans to rifle all their large calibre guns as quickly as possible. In ’62 large numbers of cast-iron cannon were rifled and reinforced by external hoops of iron. The results were deplorable. A great number of pieces burst; and experience made it clear that “a gun made up of a single homogeneous casting soon reaches a limit of resistance to internal pressure beyond which the addition of extra metal has little or no effect.” Two improvements must be mentioned as having more than a passing effect on the progress of ordnance in America: first, the adoption of compressed and perforated powder which, by prolonging the combustion period, caused a more even distribution of stresses over all sections of the barrel; second, the casting of guns hollow and the chilling of their interiors, so as to form on the inside of the piece a hardened stratum on which the outer parts of the casting contracted as they slowly cooled, thus giving it support. But in spite of these inventions it became apparent that cast iron was in its nature unsuited as a material for rifled ordnance.
In England a safer method of conversion was followed. Guns were bored out, on a scheme proposed in ’63 by Major Palliser, and accurately turned tubes of coiled wrought iron were fitted in them, which were afterwards rifled. The resulting pieces consisted, then, of a wrought-iron inner tube, supported by a surrounding cast-iron jacket against which, on firing, the inner tube expanded. Thus converted, the old smooth-bores were enabled to develop an energy far in excess of their original limit, and so to prolong for some years their period of usefulness.