An athwartship line of armor runs from the water line to the barbettes, resting upon the protective deck. In fact, the space between the protective and upper deck is so closed in with armor, with a barbette at each end, that it is like a citadel or fort or some redoubt well-guarded from the enemy. Resting upon the water-belt and the athwartship or diagonal armor, and following the same direction is a layer of armor usually somewhat thinner which is called the lower case-mate armor; it extends up to the lower edge of the broadside gun ports, and resting upon it in turn is the upper case-mate armor, following the same direction, and forming the protection for the broadside battery. The explosive effect of the modern shell is so tremendous that were one to get through the upper case-mate and explode immediately after entering, it would undoubtedly disable several guns and kill their entire crews; it is, therefore, usual to isolate each broadside gun from its neighbors by light nickel steel bulkheads a couple of inches or so thick, and to prevent the same disastrous result among the guns on the opposite side, a fore-and-aft bulkhead of about the same thickness is placed on the centre line of the ship. Each gun of the broadside battery is thus mounted in a space by itself somewhat similar to a stall. Abaft the forward turret there is a vertical armored tube resting on the protective deck and at its upper end is the conning tower, from which the ship is worked when in action and which is well safe-guarded.
The tube protects all the mechanical signalling gear running into the conning tower from which communication can be had instantly with any part of the vessel.
To build a battleship that will be practically unsinkable by the gun fire of an enemy it is only necessary to make the water belt armor thick enough to resist the shells, missiles and projectiles aimed at it. There is another essential that is equally important, and that is the protection of the batteries. The experience of modern battles has made it manifest, that it is impossible for the crew to do their work when exposed to a hail of shot and shell from a modern battery of rapid fire and automatic guns. And so in all more recently built battleships and armored cruisers and gunboats, the protection of broadside batteries and exposed positions has been increased even at the expense of the water-line belt.
Armor plate has been much improved in recent years. During the Civil War the armor on our monitors was only an inch thick. Through such an armor the projectiles of our time would penetrate as easily as a bullet through a pine board. It was the development of gun power and projectiles that called forth the thick armor, but it was soon found that it was impossible for the armor to keep pace with the deadliness of the guns as it was utterly impossible to carry the weight necessary to resist the force of impact. Then came the use of special plates, the compound armor where a hard face to break up the projectile was welded to a softer back to give the necessary strength. This was followed by the steel armor treated by the Harvey process; it was like the compound armor in having a hard face and a soft back, but the plates were made from a single ingot without any welding.
The Harvey process enabled an enormously greater resistance to be obtained with a given weight of armor, but even it has been surpassed by the Krupp process which enables twelve inches of thickness to give the same resistance as fifteen of Harveyized plates.
The armament or battery of warships is divided into two classes, viz., the main and the second batteries. The main battery comprises the heaviest guns on the ship, those firing large shell and armor-piercing projectiles, while the second battery consists of small rapid fire and machine guns for use against torpedo boats or to attack the unprotected or lightly protected gun positions of an enemy. The main battery of our modern battleships consists usually of ten twelve-inch guns, mounted in pairs on turrets in the centre of the ship. In addition to these heavy guns it is usual to mount a number of smaller ones of from five to eight inches diameter of bore on each broadside, although sometimes they are mounted on turrets like the larger guns.
A twelve-inch breech-loading gun, fifty calibers long and weighing eighty-three tons, will propel a shell weighing eight hundred and eighty pounds, by a powder charge of six hundred and twenty-four pounds, at a velocity of over two thousand six hundred and twenty feet per second, giving an energy at the muzzle of over forty thousand foot-tons and is capable of penetrating at the muzzle, forty-five inches of iron.
During the last few years, very large increases have been made in the dimensions, displacements and costs of battleships and armored cruisers as compared with vessels of similar classes previously constructed. Both England and the United States have constructed enormous war vessels within the past decade. The British Dreadnought built in nineteen hundred and five has a draft of thirty-one feet six inches and a displacement of twenty-two thousand and two hundred tons. Later, vessels of the Dreadnought type have a normal draft of twenty-seven feet and a naval displacement of eighteen thousand and six hundred tons. Armored cruisers of the British Invincible class have a draft of twenty-six feet and a displacement of seventeen thousand two hundred and fifty tons with a thousand tons of coal on board. These cruisers have engines developing forty-one thousand horse-power.
Within the past two years the United States has turned out a few formidable battleships, which it is claimed surpass the best of those of any other navy in the world. The Delaware and North Dakota each have a draft of twenty-six feet, eleven inches and a displacement of twenty thousand tons. Great interest attached to the trials of these vessels because they were sister ships fitted with different machinery and it was a matter of much speculation which would develop the greater speed. In addition to the consideration of the battleship as a fighting machine at close quarters, Uncle Sam is trying to have her as fleet as an ocean greyhound should an enemy heave in sight so that the latter would not have much opportunity to show his heels to a broadside. The Delaware, which has reciprocating engines, exceeded her contract speed of twenty-one knots on her runs over a measured mile course in Penobscot Bay on October 22 and 23, 1909. Three runs were made at the rate of nineteen knots, three at 20.50 knots, and five at 21.98 knots.
The North Dakota is furnished with Curtis turbine engines. Here is a comparison of the two ships: