Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/475

 FOETIF1CATION 451 from the fort by a ditch. There is sufficient bomb-proof cover for the garrison and munitions of war, and the faces are well traversed, while special arrangements are made for the service of the ammunition. The general arrangements may be readily perceived by a reference to the accompany ing plan (fig. G4) and sections (figs. 65, GG). Between the land fronts and the sea fronts the circle of defence is com pleted by coast batteries. These batteries, which are constructed of earth, con crete, or granite, are of various types, with em brasures pro tected by iron shields when near the sea- level, but when upon heights not below 100 FlG 66. Section through CD of Fig. 64. feet above the sea level, with unbroken parapets, the gun firing over a height of 4 feet 3 inches, the cover for the gun detachment being provided by a &quot;sunken way,&quot; 3 feet 9 inches wide and 2 feet 10 inches deep, between the platform and the parapet. Over this sunken way, which is provided with rails, a &quot; loading stage&quot; travels, upon which the charge is brought immediately under the muzzle of the gun. Though at this and heights above it the &quot; sunken way &quot; affords fair protection to the gun detachment, except at the period of loading and pointing, yet, at these periods, the men employed upon these services are highly exposed, and at all times the gun itself stands high above the parapet, and offers a good mark to an enemy s ship. Some form of &quot; dis appearing carriage,&quot; upon which the gun is raised above the crest of the parapet at the moment of delivering its fire, and falls by the force of its recoil to a safe position for loading below the parapet, has long been sought for by artillerists. Such a carriage was proposed by Corneille Redeichkeit in 1775 for the defence of the covered way; but his system, which depended on cords and counterweights, was too cum brous to move from place to place, and liable to be readily put out of order, and was abandoned. Other inventors endeavoured to attain the same end by the use of eccentric trucks and axletrees so disposed that the gun was on the greater axis for firing, on the smaller for loading ; but the difference between the heights of the gun in the two posi tions was so small that this idea was also abandoned. Two guns were next yoked together by ropes, so that one falling from the firing to the loading position raised the other from the loading to the firing position. General Chasseloup, who proposed this twin-gun system, was occupied thirteen years upon its consideration ; and though a mode proposed by him, by which one gun recoiling down one inclined plane drew its twin-gun up a similar adjoining inclined plane, was tried with some success at Milan, it does not appear to have been adopted elsewhere. The matter then rested until Moncrieff produced his counterweight carriage, in which the recoil, while carrying the gun and carriage under cover to the position for loading, raises and holds up, by means of elevators, a heavy counterweight ; this counterweight, when the time for firing arrives, is set free, and by its descent raises the gun to the firing posi tion over a parapet 9 feet high, behind which the gun detachment find ample cover one man only being exposed while laying the gun. The main objection to this system the great weight of the accessories, which for the 7-ton gun amount, including the carriage, to 20 tons. This has rendered it impossible to apply this counterweight system to guns larger than 7 tons, and even to these its application is very limited. This system is costly and difficult of exe cution as compared with barbette batteries, and as com pared with casemated batteries is far less secure against plunging and vertical fire, which cannot fail to strike some one of its many parts, a slight injury to any of which must put the gun out of action. It is asserted by its partisans that it can be applied to hill sides, so that the presence of a battery of such guns shall be undiscernable by an enemy ; but this assertion is not well founded. So much skilled labour is required for the construction of Moncrieff pits that they cannot be improvised, and when made they are by no means invisible. This system has been used to a limited extent by Great Britain, but has not been adopted in other countries. Brialmont, after describing it, says, &quot; We should not be able to share the infatuation for the Moncrieff carriage which has been manufactured in England&quot;; and, he adds, it is easy to foresee that the earth and rubbish which will be thrown into the battery during the combat will render the working of it slow, difficult, and, in some cases, impossible. Certainly the carriage is complicated, and could not be repaired during action. In earthen batteries protected with iron shields the para pets between the guns are comparatively weak, and, if they be increased in thickness so as to afford sufficient protection, they trench upon the interior space, and inter fere with the service of the battery. The parapet can, however, be strengthened by the insertion either of blocks of cement concrete or of plates of iron. But as under given conditions the disposition and thick ness of armour plates remain the same whatever be the nature of battery or fort in which the armouring is placed, the mode only in which the armouring is fixed being varied to suit the circumstances of each particular case, it will pro bably best meet the purpose of the present paper to give a short summary of the rise and progress of iron armour in its application to works of defence, illustrated by drawings of the most recent construction of each type of work. 1 Attention first began to be directed to the application of iron to works of coast and harbour defence about the year I860. At that time armour was being extensively applied to ships of war, and the manufacture of rifled guns had received considerable development, but iron had not been employed for the protection of defensive works, and nothing was known as to the best principles of construc tion for iron defences or for the capability of this metal for resisting heavy blows. It was soon perceived that it was necessary to have recourse to experiment in respect to every detail of material and construction, and it was laid down as a fixed rule that no detail should be adopted until it had obtained the stamp of experience. Previous to the period of which we are treating an advance in this direction had been made in America in 1855, by the application of metal (lead) concrete to masonry embrasures (but this did not withstand the smooth-bore guns of that day), and at Portsmouth in 1859, by the construction of an embrasure shield, 14 inches thick, of rolled iron bars, which opposed a fair resistance to wrought iron shot from the 68- pounder smooth-bore gun, the most effective gun at that date. In 1860 the most important of the preliminary trials took place against an ordinary embrasure with an iron throat 8 inches thick. The guns used were the 40-pounder, 80-pounder, and 120-pounder (shunt) Armstrong rifled guns, and the 12-ton gun, with cast iron shot. The em- 1 In this part of the subject the writer, in addition to other sources of information, has availed himself of a compilation prepared by Colonel Inglis, R.E., who has designed the principal part of the iron work of the English sea defences, and who is the highest authority upon iron constructions employed for defensive purposes.