The building of a navy, which has been actively going on for the past few years, has drawn public attention to naval subjects, and recent important experiments with armor plates have attracted large attention, hence it may not be amiss to give a description of the manufacture and testing of armor. It would be interesting to wade through the history of armor, studying each little step in its development, but we shall simply take a hasty glance at the past, and then devote our attention to modern armor and its immediate future.

Modern armor has arrived at its present state of development through a long series of experiments. These experiments have been conducted with great care and skill, and have been varied from time to time as the improvements in the manufacture of materials have developed, and as the physical laws connected with the subject have been better understood. There has been very little war experience to draw from, and hence about all that is now known has been acquired in peaceful experiments.

The fundamental object to be obtained by the use of armor is to keep out the enemy's shot, and thus protect from destruction the vulnerable things that may be behind it. The first serious effort to do this dates with the introduction of iron armor. With this form of armor we have had a small amount of war experience. The combat of the Monitor and Merrimac, in Hampton Roads, in May, 1862, not only marked an epoch in the development of models of fighting ships, but also marked one in the use of armor. The Monitor's turret was composed of nine one-inch plates of wrought iron, bolted together. Plates built in this manner form what is known as laminated armor. (See Fig. 1.) Fig. 1. Laminated The side armor of the hull was composed of four one-inch plates. The Merrimac's casemate was composed of four one-inch plates or two two-inch plates backed by oak. The later monitors had laminated armor composed of one-inch plates. The foregoing, with the Albemarle and Tennessee rams under the Confederate flag, are about the sum of our practical experience in the use of armor.

European nations took up the subject of armor and energetically conducted experiments which have cost large sums of money, but have given much valuable data. For a long time wrought iron was the only material used for armor, and the resisting power depending on the thickness; and the caliber and penetration of guns rapidly increasing, it was not long before a point was reached where the requisite thickness made the load of armor so great that it was impracticable for a ship to carry it. The question then arose as to what were the most important parts of a ship to protect. The attempted solutions of this question brought out various systems of distributions.

Armored ships were formerly of two classes; in one the guns were mounted in broadside, in the other in turrets. Every part of the ship was protected with iron to a greater or less thickness. In more modern ships the guns are mounted in an armored citadel, in armored barbettes or turrets, the engines, boilers and waterline being the only other parts protected. There may be said to be three systems of armor distribution. The belt system consists in protecting the whole waterline by an armored belt, the armor being thickest abreast of the engines and boilers. The guns are protected by breastworks, turrets or barbettes, the other parts of the ship being unprotected. The French use the belt system, and our own monitors may be classed under it. The central citadel system consists in armoring that part of the waterline which is abreast of the engines and boilers. Forward and aft the waterline is unprotected, but a protective deck extends from the citadel in each direction, preventing the projectiles from entering the compartments below. The hull is divided into numerous compartments by water-tight bulkheads, and, having a reserve of flotation, the stability of the ship is not lost, even though the parts above the protective deck, forward and aft, be destroyed or filled with water.

The guns are protected by turrets or barbettes. The deflective system consists in inclining the armor, or in so placing it that it will be difficult or impossible to make a projectile strike normal to the face of the plate. A plate that is inclined to the path of a projectile will, of course, offer greater resistance to penetration than one which is perpendicular; hence, when there is no other condition to outweigh this one, the armor is placed in such a manner as to be at the smallest possible angle with the probable path of the projectile. This system is designed to cause the projectile to glance or deflect on impact. Deflective armor should be at such an angle that the projectiles fired at it cannot bite, and hence the angle will vary according to the projectile most likely to be used. In the usual form of deflective deck the armor is at such a small inclination with the horizon that it becomes very effective. Turret and barbette armor may be considered as deflective armor. The term inclined armor denotes deflective armor that is inclined to the vertical. The kinds of armor that are in use may be designated as rolled iron, chilled cast iron, compound, forged and tempered steel, and nickel steel.

Iron armor consists of wrought iron plates, rolled or forged, and of cast iron or chilled cast iron, as in the Gruson armor. Compound armor consists of a forged combination of a steel plate and an iron plate. Steel armor consists of wrought steel plates. Nickel-steel armor consists of plates made from an alloy of nickel and steel.

I have spoken above of laminated armor. To secure the full benefit of this kind, the plates must be neatly fitted to each other; the surfaces must make close contact. This requires accurate machining, and hence is expensive. To overcome this point sandwiched armor was suggested. This consists in placing a layer of wood between the laminations, as shown in Fig. 2.