The Life of Sir William Fairbairn, Bart
Chapter XX - Iron Armour

From 18G1 to 18C5 Mr. Fairbairn was engaged in aiding the Government on an official investigation respecting the application of iron to defensive purposes in warfare. The present construction of the iron armoured vessels of our navy has all arisen out of this enquiry; and on account of the great public interest and importance of the question, it demands a notice at some length.

It is necessary to give a short preliminary account of the circumstances which led to the investigation.

Some twenty years ago it began to be perceived that a great change must be made in the construction of ships of war, in consequence of the introduction into heavy artillery of rifled shell. The 'Wooden Walls of Old England,' which had done such good service from the time of the Spanish Armada to that of Trafalgar, were powerless against the long range, the accurate aim, the penetrating power, and the destructive effect, of these deadly missiles; and it was seen that unless something could be done to meet the difficulty, the efficiency of our navy must be seriously endangered.

The use of iron was one of the most obvious modes of resisting the penetration of shells ; but hitherto the application of this material had not found favour with the naval authorities of the country.

It has been mentioned in earlier parts of this work how actively Mr. Fairbairn had exerted himself in introducing iron ship-building. The first application of this material had been for mercantile purposes, but in 1835-6 he had arrived at the conclusion that wrought iron was the safest and most durable material for naval constructions also, and he was anxious to impress on the Government the advisability of its being employed for vessels of war. lie was, at an early stage of the manufacture, in communication with the Admiralty, and he urged that iron ships, if applied to war purposes, would be not only superior in power, but safe under all the circumstances of attack and defence.

There was at that time a great deal of ignorance and prejudice in regard to the use of the new material. Many people (among them persons of influence in naval matters) conceived that the flotation of a timber ship was due to the fact of wood being lighter than water, and seriously argued that if a heavy material, like iron, were substituted, the ship must inevitably go to the bottom This argument was of course met in a simple way by the direct logic, of facts, inasmuch as iron ships, which did really float, were m existence; but there were other objections less easily disposed of, and one of the most formidable was the great damage likely to be done to the iron plates by heavy projectiles. In a ship with wooden sides, a shot hole was not a very serious matter; ir seldom made a great leak, and the hole could easily be plugged up. Hut a shot blow on iron plates rent them open with a fearful gash incapable of stoppage. It was suggested that this evil might be diminished by backing the plates with soft or elastic substances, and some experiments were tried, in 1840, by the- Admiralty at Portsmouth with this view; but the results were so unfavourable that they were deemed conclusive against the adoption of iron vessels for war purposes, and the Government stood aloof from the general movement, deciding to limit the construction of iron vessels to the. mail and packet services.

Still, however, in regard to wooden ships, the awkward difficulty remained of their destractibility by the new rifled shell. With solid shot the improved artillery woidd have been much less formidable. The entrance of a solid shot into a ship, was an event always expected in action ; and though it often did much damage, it did not destroy the ship, which was capable, in brave hands, of holding out for a long defence, even though 'riddled,' as the expression was, by the fire of the enemy. But large shells, bursting out like fierce volcanoes among the timbers of the structure, or scattering between the decks showers of fragments of jagged iron, every piece dealing destruction in its path, made such havoc as no bravery or skill could hold out against; and a wooden ship efficiently attacked in this way must, in a very short time, either blow up, or sink, or surrender.

Shells, in themselves, were no novelties; they had, long before the introduction of rifled guns, been used for bombardment with mortars, and had even been introduced as projectiles from ordinary cannon ; but from the. uncertainty of aim and want of force when fired from a distance, and from the imperfect construction of the missiles themselves, they were not much more effective against ships than ordinary cannon balls. It was only when rifling enabled them to be fired at long range, with great accuracy and powerful impact, and when the improvements of their construction gave full scope to their destructive capabilities, that they became so formidable.

The use of timber ships being retained, there remained the alternative of casing them with an armour of iron plate, of a thickness which shells could not penetrate. There were many difficulties in the way of this, and the first person who made any successful efforts to overcome them, was the late Emperor of the French. At the time of the Russian War, when rifled guns were first beginning to assume importance, Napoleon III. saw the necessity of an impenetrable armour, and quietly pursued experiments and investigations on the subject till he had succeeded in building three floating batteries, which were protected by thick plates of iron. They we're sent out to the Black Sea, where they arrived shortly before the conclusion of the war, and they were employed by the French in the allied attack upon Kinburn, on October 17, 1855. .

These batteries were exposed to a heavy fire, at a distance of 700 yards, for about three hours, unsupported by the fleet; and though some casualties occurred from shell and shot entering the large old-fashioned port-holes, yet the vessels themselves were comparatively uninjured. This success, so creditable to the skill and perseverance of our ally, settled the question of the practicability of defending ships of war by iron armour; and in France the further development of the principle was soon rapidly pushed forward.

In England, however, the authorities were loth to distrust their time-hallowed wooden walls; and although the subject was looked into, very little was seriously done. In 1858, two floating batteries were experimentally cased in iron plates, in imitation of the French batteries at Kinburn, and were fired at for trial. Iron plates were also, about the same time, placed experimentally on the sides of some of Her Majesty's ships, and Mr. Whitworth's new rifled ordnance, with steel projectiles, were used against them. The result demonstrated the value of the protection, though it showed much imperfection through want of experimental knowledge.

In the mean time the French, profiting by their experience at Kinburn, pushed on vigorously, and, a year or two after the Crimean War, had completed a frigate plated with iron armour, which was named 'La Gloire,' and was launched about 1859. She was timber-built, resembling one of our line-of-battle ships cut down, and was cased from end to end with iron plates inches thick; she was 250 feet long, and was propelled by a screw, with engines of 900 horse-power.

When the news of the construction of 'La Gloire' reached this country, our Government became alarmed, and naturally so; for she was a formidable challenge to our navy. Accordingly, early in 1859, the Admiralty determined, in great haste, to build a ship to approch her, and they laid down the celebrated iron-plated frigate the 'Warrior,' which was built with great celerity, and was launched in December 1860. This ship was much larger than her opponent, being 380 feet long, 6,000 tons burthen, and having engines of 1,250 horse-power. Her armament was much heavier than that of 'La Gloire,' and her speed much faster. She differed also materially from the French ship, in that she was built of iron instead of timber. The Government had, as already stated, arrived, twenty years before, at the conclusion, that iron was an unfit material for ships of war; but the subject had since been much discussed, and the opinions of scientific naval constructors in its favour had been urged so strongly, in opposition to the prejudices of the Admiralty, that they were induced, almost against their own will, to fall in with Mr. Fairbairn's original recommendation. This has since become universally adopted, and wooden ships of war are now things of the past.

Although, however, there was no timber hull to set on fire, yet the thin plates were easily penetrable both by shot and shell, and hence it was as necessary to protect an iron as a wooden ship. But nothing was known experimentally as to how the iron armour could be applied, our authorities having wasted, in indecision, the time that the French Government had employed in investigation and experiment.

In this state of ignorance our designers considered they could not do better than repeat the plan they had followed with the floating batteries, namely, copy from the French as nearly as they could. They, therefore, first made the hull of the ' Warrior' represent that of 'La Gloire,' by fastening, on the outside of the iron skin, a thick cushion of timber, on which they proceeded to iix the plates by bolting. They introduced certain novelties into the details, which, however, were afterwards found to be no improvement, but rather inferior to the French designs.

On the finishing of the ' Warrior,' the Government bethought themselves that it would be desirable to do what they ought to have done five years before, namely, to ascertain something about the principles which should guide the design of iron armour. In other words, having already built the ship, they began to enquire how they ought to have built her (a curious line of policy which, it will be seen, was repeated in an analogous case a few years later). It was apparent that the use of iron for such a novel purpose was so complicated by considerations of a mechanical and metallurgical character as to demand a more searching technical investigation than it could receive at the hands of purely military or naval authorities; and at the end of 1860 the Government wisely determined to submit the whole matter to a mixed special committee. The Secretary-at-War, Mr. Herbert (afterwards Lord Herbert) therefore selected six gentlemen, and, having obtained their consent to act, the Committee, called the 'Special Committee on Iron,' was formally appointed on January 12, 1861. The members were:—

Captain (afterwards Sir John) Dalryrnple Hay, chairman, to represent the Navy.
Major Jervois, R.E., to represent the Royal Engineers.
Col. W. Henderson, R.A., to represent the Royal Artillery.
Dr. John Percy, F.R.S., the eminent metallurgist

Mr. William Fairbairn, F.R.S.
Mr. William Pole, F.R.S., experienced in the uses and properties of iron.

The Committee were actively at work four years, during which time they presented to the Government four Annual Reports, each accompanied with a large volume of minutes of experiments and proceedings. The information contained in these volumes was of the greatest value, but unfortunately they were never published. The Government, although no particular secrecy had been observed in the proceedings (foreigners having been often admitted freely to them), were reluctant to make the mass of knowledge gained public property, and accordingly only-extracts and abstracts were made known from time to time.

It is, however, no breach of confidence, after this lapse of time, to give a summary of the principal matters that occupied the Committee's attention.

Their first duty was to collect and classify all the meagre information that existed, and the results of all the experiments that had been made on the use of iron for resisting shot.

They then called before them various persons whom they considered likely to have knowledge of the subject, military and naval officers, engineers, ship-builders, and iron manufacturers; and their evidence, given very fully, was recorded find considered. But the great diversity of the opinions thus gathered showed the obscurity in which this novel application of the material was involved.

The Committee then commenced an elaborate series of investigations and experiments systematically carried out; first on a small scale on single plates of various sizes and thicknesses; and then on targets of large size, made to represent actual ships' sides, of a great variety of constructions. These enquiries extended over several years, and led to the establishment of many important principles as to the nature of the material best adapted to the purpose; the arrangement and dimensions of the armour; the mode of fastening to the ship; the effect of the iron and material of the shot; and so on. It may be interesting to give an account of some of the trials made and the results arrived at on these points.

One of the most important considerations was as to the nature of the material best fitted to be used for armour; for as this was capable of being given many varieties of character, according to the mode of its preparation, it was desirable to ascertain which was best for the purpose in view. On this point the opinions of the witnesses had varied a good deal, but there had been a general impression that one of the most important qualities to give was hardness. It was urged that the harder the armour was made the better would it resist the shot, and that in fact the best material, if it could be made and applied conveniently, would be hard steel, or at least a combination of steel and iron.

This was a plausible idea, but it was not borne out by investigation and experiment. It was found that hard plates were brittle, and were broken up by the blows, when the detaching of the fragments exposed the vessel to penetration; soft plates, on the contrary, gave way, and became dented, bruised, and distorted, but still held together and formed an efficient protection.

Both theoretical considerations and practical experiments showed that the best principle of defence was not to attempt to resist the blow, but to receive it in such a way as would do the least mischief. The obvious mode of accomplishing this with iron armour was to make it of soft, tough plates, which would allow the energy of the shot to be expended in indenting and battering them without producing fracture.

The Committee, therefore, came to the conclusion that the best material for armour was wrought-iron, free from hardness and brittleness, but as soft and tough as could be procured. This opinion, though it was arrived at in opposition to the ideas generally prevalent, has been fully confirmed by subsequent experience.

The mode of making the plates also engaged the attention of the Committee. It was a new thing in the iron trade to fabricate plates of this enormous size; and the first attempts were imperfect, the iron being of inferior quality. The Committee requested the principal houses to produce plates for trial, invited them to witness the experiments, and gave them every aid in their endeavour to perfect the manufacture; and the result was a marked improvement and a much better approach to the quality required.

Two processes were used for making the plates— hammering and rolling. In the former, large lumps of iron, previously prepared from 'scrap' or from 'puddled bars,' were brought to a welding heat, and being laid together, were placed under heavy steam hammers, the repeated blows of which welded the masses together, and shaped them to the required form and dimensions. This process was the first adopted for the manufacture of armour plates; it was used by the Thames Iron Company, who built the 'Warrior,' and the plates of that ship were made in that way.

Shortly afterwards a firm in Yorkshire adopted another plan, namely, by rolling—a process in tact the same as that used for ordinary boiler-plates, but on a much larger scale. The masses of iron, first prepared, were fiat iu shape, and several of these, being laid one on the other, were heated to the welding point in a furnace, and then passed between large rollers, which rolled them out into one solid plate of the required size. The process was a difficult one, from all the apparatus requiring to be of such great size, and the machinery of such immense power.

The Iron Committee tried extensive experiments on plates made by both these systems. They found the hammered plates had a tendency to be hard and unequal. The repeated blows of the hammer hardened the material, and this effect was not always the same in different parts, some receiving more action than others. Moreover, from the irregular form of the primitive masses, the parts were not always perfectly welded together. The rolled plates, on the other hand, from the more uniform and less sudden action of the compressing force, were softer and more uniform in quality, but they still had the defect of what was called 'lamination,' i.e. a want of perfect welding between the different layers. The Committee, on the whole, preferred the rolled plates, and this mode of manufacture has now superseded the other almost entirely

Another point investigated by the Committee was the effect of the form and material of the shot. They considered, however, that too much importance had" been attached to these particulars. The shot was merely a means of transferring to the plate a certain amount of mechanical energy generated at a distance by the powder; and the orly way in which form and material influenced the result was by causing a greater or less proportion of this energy to be absorbed by the shot itself, and so wasted, or diverted from its intended purpose.

It was attempted by a very ingenious process to ascertain the amount of work absorbed by the shot. It was found that, after striking the plates, the shot, or the fragments of them, became highly heated, and, according to the recently established thermo-dynamic law, by measuring the rise of temperature, an approximate estimate could be given of the work absorbed. It was thus found that with a hard-tempered steel shot, the energy expended upon the projectile was about one-tenth of that stored up in it at the moment of striking; while with softer steel it was two-tenths; with soft wrought-iron it amounted to above one-half of the whole ; and with cast-iron to probably still more.

These results, which were fully corroborated by the effects produced on the plates, pointed to hard steel as the best kind of shot to be used against iron armour ; but this expensive material was afterwards superseded, in consequence of a discovery made by Capt. Palliser, that cast-iron shot would answer, if made of a particular quality, and in a particular form. In the ordinary shapes, shot of cast-iron, whatever the quality of metal, broke up with great facility; but Capt. Palliser showed that if the head were made pointed and the metal were very hard, the shot would penetrate the plate before breaking, and the minimum amount of work would be lost on the projectile. The shot so designed was accordingly adopted in the service.

The Committee further investigated the laws of resistance offered by plates of different thicknesses to projectiles of different natures and weights, and with different velocities. Reverting to the principle that the damage to the iron plate was proportional to the work in the shot, or to the charge of powder, it was assumed that some definite estimate might be made of the thickness of plate necessary to resist certain artillery. As far as could be made out, there appeared reason to believe that, within certain limits, the resisting power of a plate bore a tolerably near ratio to the square of its thickness; but there was so much difficulty in estimating the amount of damage done, and the quality of the plates tried was so variable, that no trustworthy relation could be fixed. In heavy plates, moreover, practical effects came in which disturbed the application of any general law.

Another question that occupied the attention of the Committee was what form it was most advantageous to give to the defensive material. Several forms were proposed, such as bars, superposed thin plates, corrugations, ribs, bosses, and many other ingenious contrivances. More than four hundred of such plans were submitted to the Committee ; and a great many were fully considered and tried; but, through all these complications, they arrived at the. simple result that the best application of the material was a single plate of uniform thickness, with the surface perfectly plane.

Great interest and importance were attached to the mode of applying the iron armour-plates upon the h ill of the vessel In the ' Warrior,' as already explained, a cushion or bed of timber about eighteen inches thick had been interposed between the armour plates and the iron skin of the vessel, a plan followed, probably, more for the purpose of imitating the construction of 'La Gloire,' than with any very definite idea of what object the wood was to serve.

Many objections were raised to this by persons of considerable authority in ship-building and mechanical science. It was said that the plates had better be fastened at once upon the iron skin, and that the wood backing was not only unnecessary, but was absolutely prejudicial, as liable to decay, and to destruction by fire and shells. It was necessary to test this, and no less than three expensive targets were constructed for the purpose.

The result of these trials was to convince the Committee that the wood backing performed several important functions, which, though they had not been foreseen, were of much advantage.

In the first place, by its softness, it deadened the jar and vibration caused by the blow of the shot. In the iron targets this was severely felt, breaking the bolts and rivets, and shaking and damaging the structure generally ; but with the interposition of the soft cushion these evils were much reduced, and the structure was greatly preserved.

Secondly, it had the advantage of distributing the effect of the blow over a much larger area of the skin plate. When the armour was fastened directly upon the skin the shot acted upon a small area, which gave it a better chance of penetrating; but with the large thickness of wood between, the area of operation enlarged backwards, like a cone, thereby increasing materially the power of the thin skin to resist the damaging effect.

Thirdly, if. under heavy fire, the armour-plate became broken, the pieces did not fall off, but became imbedded m the wood, and were thereby hold in their places, retaining their utility of defence in a considerable degree.

Fourthly, the wood was useful in catching what is called 'langrage,' or pieces of shot and shell, and preventing their entering the ship.

For these reasons the Committee recommended the retention of the wood backing to the armour, and it has ever since formed an essential feature of naval defence.

The best sizes of armour plates, the process of bending them and adapting them to the form of the ship, and the modes of fastening them to the hull, and securing them in their places, also received the consideration of the Committee* and were fully reported on.

The Committee wished to carry their experimental investigations so far as to put the ' Warrior' herself under the fire of heavy guns. This was thought too expensive and troublesome a proceeding, but the case was met by the construction of a target, about 20 feet long and 10 feet high, which was made exactly a counterpart of a portion of the ship's side. This target was erected at Shoeburyuess in 1801, and was fired at with the old 68-pounder gun, and with the Armstrong rifled ] 10 and 120-pouuders, the maximum charge of powder being 20 lbs. It received altogether, from these guns, twenty-nine rounds, the combined weight of the shot being 3,229 lbs.

It was, of course, a good deal damaged at the front, but it was not penetrated, and would still have afforded efficient protection. This result, considering how small an area the fire was concentrated upon, was very favourable, and showed that the ship's armour was strong enough to resist guns of the size then used.

The Committee also experimented cm many other targets of different kinds, made to represent ships' sides defended by different iron constructions. One of these was designed specially by Mr. Fairbairn, for the purpose •of testing certain views held by him.

The experiments were carried on for the most part at Shoeburvness, where it was possible to get a large area of free ground, and where the artillery depots enabled the Committee to obtain the most powerful guns and the most skilled gunners. The trials involved a great deal of risk, but by admirable precautionary arrangements no accident ever occurred.

Mr. Fairbairn, in addition to a frequent attendance at the meetings and experiments of the Committee, undertook, at their request, some special investigations for them, reports of which were published in their proceedings. These were:—

In 1861:—

On the Mechanical Properties of Specimens of the Iron and Steel Plates subjected to Experiments with ordinance, their Strength, Ductility, Resistance to Punching Force, &c.

In 1862 :—

On the Resistance of different kinds of Shot to a Force tending to crush them, and the forms they assume under Pressure.

Experiments on Punching.

In 1863 :—

On the Mechanical Properties of Iron Plates.
On the Manufacture of Armour Plates.
Experiments to test the value of annealing Armour Plates.
On the Tenacity of Cast-Iron Shot.

In 1861:—

On the Mechanical Properties of Iron Plates.
On the Manufacture of Armour Plates.
General Summary of Results.

In these investigations he was ably assisted by Mr. Unwin, whose services in the matter were specially acknowledged by the Committee.

Mr. Fairbairn communicated information on this subject in two papers read before the British Association in 1861 and 1862 ; at a lecture at the Royal Institution in 1862; and in a memoir to the Institution of Naval Architects in 1869.

In December 1867, the War Office called the Iron Armour Committee together again, with the addition of some other members, for the purpose of investigating the construction and properties of certain large iron shields for land defences which had been sent out to the forts at Gibraltar and Malta.

As iu the case of the 'Warrior,' previously mentioned, the Government had first made the shields, and afterwards begun to consider how they ought to be constructed. To enlighten themselves on this point, they had one of the shields fired at, and it proved so weak that, in alarm, they appealed to the Committee, who, after due examination, reported unfavourably of the strength and construction of the shield.

Mr. Fairbairn attended some of the meetings, but his great age and infirm health prevented his taking a very active part in their proceedings.

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