The life of Isambard Kingdom Brunel, Civil Engineer Part 50

If you suppose a bar, say an axle of uniform section and uniform quality in every respect, it will bear bending into extraordinary forms even by a blow; and if you a.s.sume that portions of it become more tenacious and stronger, but remain equally elastic, the ultimate strength of this bar will not, I think, be materially increased or diminished; but if you suppose the elasticity of these portions either increased or diminished, I believe the ultimate strength of the bar under a blow is diminished. In like manner, I imagine that in the section of a gun barrel, if portions are more or less elastic than others, or at all different in their character, not only many points of fracture may be determined on, but that the whole may be rendered much less able to resist the violent explosion. The strain produced by the explosion and the plane of fracture is almost certain to be in a plane pa.s.sing through the longitudinal axis, and therefore I had a.s.sumed that one would avoid as much as possible having any variation of quality which f.a.gotting must produce to some extent in planes in this direction. To attain this end, I had endeavoured to scheme some way of welding up 'cheeses' or discs, which might be hammered up splendidly h.o.m.ogeneous of the full diameter and of a considerable thickness, and I wish that you would scheme the best way of welding them together. I should suppose that the centre surface might be welded, and wedges welded in all round, or some other mode devised, bearing in mind that the strain in any plane transverse to the axis is small, only that arising from the recoil of the breech and the friction of the shot.

I have also an impression that something harder than ordinary wrought iron is wanted for the inner surface to resist the explosion. This you might give probably in f.a.gotting up. I am trying the effect--as much for the amus.e.m.e.nt of the thing as with any great expectation--of a cylinder of hardish material wrapped round with iron wire, laid on with a certain amount of tension proportioned to the diameter. Such a barrel ought to be strong--whether practically successful is another thing.

The scheme of making a gun with the barrel wrapped round with wire, which is referred to in this letter, was one which Mr. Brunel and Mr.

Armstrong were very desirous of making the subject of actual experiment.

Whether or not it would under their hands have become practically successful, could not be ascertained, as they were obliged to abandon the project, in consequence of the wire covering being patented, in May 1855, by Mr. Longridge.

The following letter to Mr. Armstrong relates to the same subject, and is interesting not only as showing Mr. Brunel's correct appreciation of a principle which is the essence of the coil system of constructing guns, but as further ill.u.s.trating his objections to the patent laws:--

June 8, 1855.

Have you ever done anything towards my experiment of the wire gun?

I have been anxious for some time past to learn about it, but have waited to see you; to-day I learn that Longridge is taking out a patent for it. I daresay it is his own idea, and I only regret it, as I suppose it will now prevent my pursuing it; and I think it likely that with your a.s.sistance we should have succeeded in making at least as good a gun as he will. The principle I am disposed to think good; the success would depend upon the practical application, and but for these patents, the more compet.i.tors the better for the public. As it is, compet.i.tion is destroyed. Let me know if you had done anything. Pray let me know also what you are doing about your own, in which I feel equally interested.

Mr. Brunel had also considered the advantages of making the bore of the gun polygonal, with a projectile shaped to fit it. He had a portion of cannon tube and a projectile made by Mr. Armstrong in the beginning of 1855, but he did not himself pursue the question further.

Indeed, after the middle of the year 1856, when the works of the 'Great Eastern' steam-ship began to occupy a large portion of his time, Mr.

Brunel was unable any longer to take part in gunnery investigations; but he watched with unabated interest the proceedings of those friends who have continued their experiments, with the great practical success of which he lived to see only the beginning.

_Floating Gun-Carriage._

The plan of a gun-boat, or, as it would be more correctly called, a floating gun-carriage, which Mr. Brunel designed for an attack on Cronstadt and other Baltic forts during the Russian war, is clearly described in the following memorandum, which he drew up for the information of the Admiralty:--

December 20, 1855.

The principle is simply the fixing a very heavy gun in a floating shot-proof chamber or casemate, exposing the smallest possible surface; that surface to be of such a form as to be struck by shot only at a very oblique angle; and the gun being a fixture, with the means only of elevating and depressing to an extent of 10 or 12 degrees, but with no lateral motion, the port or embrasure need be only of the size of the muzzle of the gun, so that the gun, the men working the gun, and everything on board will be perfectly protected.

The gun will be directed by elevating the breech, and by slewing the vessel slightly and slowly backwards and forwards across the line of aim, by means afterwards explained.

The men loading the gun will simply load as quickly as they can, and when the gun is loaded push out a trigger.

The governor or person directing the gun will stand behind the hood or chamber, looking direct at the object through a telescope of low power, fixed horizontally in the axis of the vessel, and made to move vertically parallel with the axis of the gun, and mounted with reflectors; so that both telescope and man are completely under cover, and he, keeping the vessel truly in range and the elevation correct, will only touch the trigger whenever his line of sight crosses the object.

The vessel will carry a small engine, of power sufficient to drive it for a short time at a good speed, say eight or nine knots, and at other times to keep up a small forward motion to counteract the recoil, and to keep the vessel's head moving a few degrees right and left across the line of range.

A sufficient portion of the vessel to contain and to float the gun, ammunition, and engine, will be shot-proof.

A fore-body and after-body, the top of which will be _a fleur-d'eau_, or a few inches under water, will be added, to give such a form of entrance and run as will admit of the vessel attaining the speed mentioned; but these parts will be mere sh.e.l.ls, and may be full of water, and if damaged by shot will not affect the buoyancy of the float, besides which, not being above the surface of the water, they cannot be much exposed to injury.

The mode of propelling may be by a screw, but I prefer the 'jet,'

which, whether an economical mode of propelling or not, is a sufficiently good one for this purpose, and exposes _nothing_ whatever to be injured by shot.[185]

Whether propelled by jet or not, I should have two small lateral jets for directing the vessel, such jets being governed by two c.o.c.ks handled by the gunner.

Such a mode of directing the aim by a man under cover looking through a telescope, with one hand directing the gun and the other on the trigger, will admit of an almost unlimited degree of accuracy.

The gun being in a perfectly shot-proof casemate, machinery may be adapted to expedite the loading of the gun; and it is not difficult to make a mechanical arrangement by which the shot and cartridge shall be lifted up to the gun, inserted, and rammed home, at a rate far exceeding anything that can now be done by hand; and as the weight and clumsiness of the gun, the carriage, and machinery are of no object, I think I can make a breech-loading gun capable of carrying 12-inch solid shot with a full charge, which may be loaded and discharged at the rate of two or three per minute; but the principle of mounting a gun in such a float is equally applicable to a common gun, which might still be loaded mechanically.

A few loopholes may be provided through which a fire could be kept up from a couple of heavy swivel rifles, carrying, say 6-oz. shot, which would pierce any mantelets or other cover likely next year to be provided against ordinary rifles.

A battery, say of twelve such guns, should probably have also two, or perhaps three, shot-proof vessels of about the same size without guns, but pierced with a longitudinal fin or ridge, like a wall, standing, say 10 feet above the water, and 50 or 60 feet long, strong enough to stand the direct blow of heavy shot at long range, or the oblique blow of the same shot at short range, and which could be placed as screens or traverses to cover the flanks of the battery against distant shot. Against vertical fire I cannot suggest any defence: the point of attack must be selected to avoid it.

The covering vessels may be provided also with loop-holes for heavy swivels.

There should also be two or three small and comparatively light, but shot-proof vessels, to run in and bring out a disabled gun-boat.

These last-named auxiliary unarmed boats form an essential part of the system.

In all probability the enemy have by this time thrown stones and other obstacles, and placed infernal machines round the detached fort, to impede a close approach. They cannot, however, have covered a very large surface, so that, with some previous sounding, an approach may be found and a position taken up.

The auxiliary boats should therefore have strong bottoms under the engine-room, and the rest of the body be so subdivided into compartments that they would be proof against serious damage from rocks and infernal machines, and be able to run in under fire and ascertain if obstructions exist, and find the channel if they do.

A battery of such guns could be placed at various points out of range, say at 3,000 yards, at which distance they would hardly attract attention by daylight, and would not be visible in the twilight of night, and could then be concentrated in a few minutes at the point selected for attack within safe breeching distance, say 250 yards; and, if twenty-four shot per minute, of 200 lbs. to 250 lbs. each, thrown with a full charge at 250 yards, can be directed against a small surface of any stone wall yet built (which is pierced with embrasures), the effect ought to be great and rapid. I believe, moreover, that the means of directing the aim will be so effective that if the embrasures can be seen a sh.e.l.l or shot may always be sent in with certainty at 250 yards, and the enemy's guns dismounted.

Such vessels can rapidly change their position, retreat or advance, be replaced by fresh ones, or withdrawn altogether.

The means of transport of such vessels to the seat of war, although a secondary consideration, has been considered.

They might easily be placed in an outer sh.e.l.l of iron of a good form, which could be rigged complete, and so constructed as to give up its burden when arrived in the seas where it is to act--in fact, a ship of the cla.s.s of small screw colliers, made to open at the bows and its contents floated out ready for action; but the gun-boat itself, when lightened of ammunition, and the gun lowered to the bottom as ballast, and fitted up with bulwarks, and a light movable iron chamber, forming a water-tight forecastle-deck reaching back, say 30 feet, and schooner-rigged, will, I undertake to say, make a very fair sea boat. Probably no compa.s.ses could be 'corrected' to be trusted to in such a ma.s.s of iron, but a compa.s.s fixed to the mizenmast, say at 30 feet from the deck, would be all that could be required.

Immediately abaft the hood or gun-chamber there would be a s.p.a.ce under cover from shot where a companion and skylight could be fitted up when at sea, and through which light and air could be obtained at all times when fitted for service.

The funnel, if ever used when the vessel is not in action, would be removed for fighting, and the steam and smoke ejected through an oblique aperture right aft.

The only point to be determined by experiment is whether a moderate thickness of iron of the best quality will stand heavy shot at short range striking very obliquely, say at the worst at an angle of 30 degrees.

By the form of the proposed vessel, however, when placed in position at 250 yards of any of the Cronstadt forts, it could not be struck at 30 degrees, and probably 99 out of 100 shots that hit would graze at an angle of 10 to 20 degrees.

A small part only round the port, or what may be more correctly termed the muzzle-hole, could be struck with a direct blow.

There is every reason to believe that slabs of iron of good quality of 4 inches thick would stand against such grazing, provided they are put together without being weakened by holes and with some other precautions, and that sound forgings of 10 or 12 inches thick, if of sufficient weight in a single piece, would stand the direct blow. I do not believe that less than this would be safe against 68-lb., or, as we must expect to meet with, 120-lb. shot at short range, even when struck obliquely, and this thickness can be applied without requiring, with the gun ammunition, &c., more than 6 feet 9 inches, say 7 feet draught of water.

Another inch of thickness would require another foot of draught; but if it has been ascertained that the charts are correct, there would appear to be 10 to 15 feet of water close up to the princ.i.p.al detached forts, and it would be an immense advantage to take 9 feet draught of water, and have an unquestionably invulnerable skin.

If it were considered desirable to construct such a battery, it is now barely possible to do it in time for the coming season; but if possible, it could only be rendered so by ascertaining exactly the dimension and form of iron that each of the large makers could turn out with their present tools, and according to their present experience and habits, and to design the details to suit their existing means, sacrificing probably much that would render the result more perfect for the sake of rendering it possible to obtain anything in time. No doubt promises and even contracts could easily be obtained for making anything in any given time, and zealous and honest efforts afterwards made to effect what had been undertaken; but if the slightest attempt is made that involves new tools or new practices, promises and contracts will not effect impossibilities, and the probability is that the short time still available will be lost.

While all the preparations shall be made on the a.s.sumption that the result is attainable and will be successful, trials must be made, without loss of time, on the several points to be determined--as to the resistance of the iron, &c. If they fail, the expense incurred up to that time in preparing for the whole work will not have been great. If they succeed, it is just possible that by great exertions but, above all, by judicious and methodical plans of proceeding, a complete battery might be launched ready for service in five months.

Lastly, I should observe that although the main feature of the plan is the resisting the effects of the enemy's shot by always exposing an oblique surface, yet the chances of fatal damage would be small if such vessels were to run the gauntlet, at night, through the deep channel, and get into the waters east of Cronstadt. Or if this is very desirable, as I should think it must be, nothing is easier than to lift the whole flotilla over the shoal water and launch them into the deep water beyond.

Mr. Brunel had matured these plans in September 1854, and they were then brought under the notice of the Admiralty; but no steps were taken to test the practicability of the scheme.

He was, however, induced to make a further representation to the Admiralty in the following July. He wrote,--

Having endeavoured ineffectually several times at the commencement of the war to impress upon members of the Government the great advantages that might be derived from the use of iron floating batteries or gun-boats, if properly constructed, I made another effort at the close of the last year's campaign, but early enough to have allowed of the construction of what I proposed before the opening of the Baltic in the present year, and caused my plans to be submitted to the Admiralty through a friend. They were not approved, and I should judge from the answer I received that they were not understood, and I was never applied to for an explanation.

I had no object in view but the public good, and I therefore kept the idea, such as it was, unpublished, believing the principle to be sound and good, and that the day would come when it might be usefully applied, and the more usefully to this country if not previously publicly discussed.