THE IRON FORT EXPERIMENTS.
THE recent Gunnery experiments at Shoeburyness present a satisfactory contrast to the famous experiments of last winter with the " Gibraltar Shield." The contrast is satisfactory in more senses than one. In the first place, there was no attempt at secrecy, but an honest and worthy endeavour, carried perhaps almost to an excess, to admit who- ever might be interested in the result to witness them. In 'the next place, instead of forming isolated experiments, stand- ing out in a great Sahara of ignorance and official reserve,
they furnish so many links in the chain of careful practiat reasoning, by which at last we are endeavouring to work out the important problem of the defensive application of iron to land defences. Finally, we have no failure, as in the case of the Gibraltar Shield, to record; but, on the contrary, a very sub- stantial and satisfactorysuccess. We must, however, guard against exaggerating the success in this instance, as it is necessary to guard against exaggerating the failure in the former instance. The world is liable to err in the direction of extremes. The Gibraltar Shield, although a failure in many senses, a failure which reflected considerable discredit upon its designers, and still more upon those who were responsible for the execu- tion of the contracts before a single trial had been made, a failure, too, which has been rather deepened than relieved by the report of the Special Committee upon the subject, was nevertheless very far from being as black as it has been painted by some of our contemporaries. So, on the other hand, there is danger lest, carried away by the high resisting powers exhibited by the section of the Plymouth fort, we should hastily infer that this particular application of iron is all that can be desired. That it is very good when allied with the excellent bolts designed by Major Palliser, and with all sorts of contrivances for diminishing concussive effect and reducing the liability of the bolts to break, cannot be denied. But we are impressed with the conviction that a more favourable disposition of the iron might be adopted for future defences ; and this is precisely the point which the late experiments, and those which will ere long follow, are designed to establish.
We may, of course, suppose, in considering the problem to be solved, that the necessity for erecting forts, their nature, and position have been already decided upon. These are matters involving separate and independent study. They are matters which must first be decided, if the present question is to be worth the working out. We are thus concerned for the moment with purely structural considerations ; how best to secure a detachment of gunners and other defenders from possible attack ; or, if we chose so to put it, how to make a position so strong that an enemy will scarcely care to attack it at all. We may assume also that it has been decided to employ iron for this purpose. Granite, masonry, and other materials of this nature are not permissible in certain positions, having in view the range, power, and accuracy of modern ord- nance ; and earthworks cannot profitably be employed on such positions as those for which these forts have been designed. Thus we are driven to the use of iron. Then, the questions arise, 1st, what thickness of iron is necessary ? 2nd, how can the iron be best disposed ? With regard to the first point, many circumstances have to be taken into account, among which the probable powers of the enemy's guns, and their possible posi- tion of attack, stand prominent. With our knowledge of foreign ordnance we may fairly assume, that if the forts are strong enough to resist the most powerful guns which we could bring against them, they will be adequate to resist the guns likely to be brought against them by any of our neigh- bours. This is the first condition. The second depends upon the nature of the approach and other circumstances. Obviously, if a fort is not liable to approach within 1,000 or 2,000 yards, it need not be as strong as one against which ships may be ranged at 200 yards' distance. In the case of the Plymouth fort, the minimum distance of possible attack was assumed to be 500 yards. It is not, therefore, without reason that the designers of the fort complained that the Shoeburyness structure should by an arbitrary and, we may perhaps add, ignorant exercise of the Secretary of State for War's prerogative, have been experi- mented upon at 200 hundred yards. As it happened, how- ever, the structure proved so good that even at this range it triumphantly resisted the battering of the 12-inch, 10-inch, 9-inch, and 7-inch English rifled guns, and the American 15-inch smooth-bore, the latter firing a charge largely in excess of that for which it was designed,—a charge which, looking to the uncertain nature of the material of the gun, can never be fired without more or less of risk. We may say at once with regard to this last gun that it produced upon the target literally no appreciable effects. Its supporters have always claimed for it the merit of being capable of inflicting a large amount of concussive or general damage, as distin- guished from mere penetrative or local effect. On this occasion it was brought to bear under exceptionally favour- able circumstances for the gun, and unduly unfavourable circumstances for the target. That is to say, the range was short, the charge was large, and the target had hand been condemned by its opponents as one peculiarly rore
liable to be destroyed by general damage—to be smashed and "racked " to pieces. But as a matter of fact the great Rod- man failed to " rack " in any perceptible degree. In one instance, even when striking within a few inches of a bolt, it nevertheless failed to injure it in the least. And as it failed to rack, so even more signally did it fail to penetrate. An in- dent of a few inches, like the mark of a football upon a soft cheese, was all that the gun was able to accomplish on plates which our own 10-inch gun, weighing 11 tons less, firing 60 lb. of powder against 831 lb., and shell of 400 lb. in lieu of solid shot of 451 lb., succeeded in actually getting through in at least one instance. Never was more strikingly exhibited the great superiority of our own system of ordnance over that upon which the Americans to this day largely depend for the defence of their coasts and fleets. We say our " system " of ordnance, for our projectiles as much as, or perhaps even more than our guns, deserve the credit of the achievement. It is to the introduction of the formidable Palliser projectiles that the success of our guns is mainly due. These re- markable shot have become so established by their re- peated performances, that people are apt to overlook the extraordinary results which they accomplished on the late occasions. But to be able to penetrate with shell fifteen inches of iron, however disposed and under whatever circum- stances, is an extraordinary achievement, and one not dreamt of in an artilleryman's philosophy a few years ago. It may be worth while to notice, in passing, that these projectiles could not be fired from the Rodman, since one of the elements of their success is the pointed head, which is of course inadmis- sible in a smooth-bore gun. Passing from the attack to the defence, we have in the Plymouth fort a structure capable of very nearly setting at defiance the concentrated powers of our heaviest guns at the shortest range. The fort is composed of three 5-inch plates of iron, bolted through, and strutted at the back into rigidity. Anti-concussive agents have been intro- duced wherever practicable. The bolts are sheathed in wood, and provided with elastic washers ; leather is interposed between the layers of plates ; and wooden buffers have been applied at intervals. It would be wrong to say that the guns made no impression upon this defence. They made, indeed, a very considerable impression, and in two instances shells actually penetrated. But the damage done by the shot and shell which did not penetrate was not such as would cause alarm to the defenders, and the protection afforded internally by the concrete piers and a stout rope mantlet reduced the effects of the shell to a minimum. And as for the shell which did penetrate, they struck upon exceptionally weak places—places naturally weak by the construction of the target, but further weakened by the injury inflicted by pre- ceding rounds. And this effect was wrought, as we have explained, at ranges within that at which, on all reasonable suppositions, it would be possible for ships to engage the forts. It is a question whether even under these circumstances a single defender of the casemate would have been killed by the whole of the firing directed against it during three days' prac- tice. Therefore, we say, the fort stood well ; and reflects credit upon those who are responsible for the erection.
But after this comes the question whether, in forts of this sort, fifteen inches of iron, or its equivalent, may not be more profitably disposed. The result of some other trials made during these experiments was certainly unfavourable to solid blocks of iron, as opposed to a stratified construction. Two fine specimens of solid iron of this thickness — the one hammered, the other rolled, and both of at least as good quality as it would be possible to secure in ordinary manufac- ture—fell to pieces under comparatively little battering. The hammered plate broke in halves at the second shot ; the rolled plate scarcely stood much better. Moreover, solid plates have other disadvantages, structural and economical, and it is pro- bable, all things considered, that we have now heard the last of them for some time to come. But this does not prove that in using plates of moderate thickness they may not be more profitably applied than by placing them in close contact with one another, and without any elastic backing. Our impression, derived from former experiments, and confirmed to some extent by the recent trials, is that Palliser projectiles, which it must henceforth be the main object of forts to keep out, may be better resisted by interposing other substances between the plates, by the application of cellular structures with the iron end on, and by paying more attention to the backing and supports. Perhaps, too, the intermediate plates might be hardened with advantage, so as to break up these brittle pro-
jectiles, which pass so readily and with such terrible effect through iron of a softer brand. These, however, are points to be speculated upon only, not solved, except by a series of careful experiments. But we can see no reason why these experiments should not be conducted upon a less costly scale than at present. Inductive experiments would probably indicate the superiority of one application of iron over another, and it would then rest with the Committee to select the more promising structures for more complete trial. This is a course which we hope to see pursued,—meanwhile, we need be under no uneasiness with regard to the strength of our present or proposed forts. If the experiments which we have suggested come to nothing, they will, at least, not have entailed much expense, nor so much waste of time, for the matter of that, as ex- periments on the present scale, while they will satisfy us that our forts are as good and as cheap as they can be made with advantage. On the other hand, if the experiments show no better way of using our iron, they will probably enable a very great saving to be accomplished in our coast defences, with a material augmentation of strength.
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