In protecting warships against shell fire it is recognized that there are certain parts of the ship which are of paramount importance, inasmuch as their disablement would leave it at the mercy of the enemy. These are the "vitals" of the ship, and they comprise the magazines, the boilers, the engines and the steering gear. If a shell penetrated the magazines, it would be liable to result in the blowing up of the whole ship, and if it entered the boiler, engine or steering rooms, it would probably render the ship unmanageable, in which event she would run the risk of being rammed and sunk by the enemy.

In all warships the vitals are covered by a complete protective deck of steel, which varies in thickness from 1 1-2 to 3 inches. The highest part of the deck is generally at a slightly higher level than the water line amidships, and it curves down at each end to meet the bow and the stern. In the battleship this deck is generally flat from side to side amidships for about two-thirds of the ship's length. At the sides it rests upon a wall of vertical armor from 15 to 18 inches in thickness, which extends in the wake of the magazines, engines and boilers. This side armor is usually about 7 1-2 feet in height, 3 feet of it being above and 4 1-2 feet below the water line. At each end of the side armor a transverse wall of armor extends clear across the ship. This rectangular wall with its roof of 3-in. steel thus forms a kind of inverted box, snugly sheltered below which are the before mentioned "vitals" of the ship. At each end of this inverted box two huge barbettes, with walls 15 to 17 inches thick, are built up to a few feet above the main deck, and just within and above them revolve a pair of turrets with walls of 15 to 17 inch steel. (See perspective view.) The turrets give shelter to the big guns, of which there are a pair in each, and the barbettes protect the turning gear by which the turrets are rotated. There is thus a continuous wall of 15 to 17 inch steel extending from 4 feet below the water line to the roofs of the turrets.

With this description in mind the reader will see, on looking at diagram No. III., that before heavy shells can injure the engines, boilers or guns, they must pass through from 15 to 18 inches of solid and, in the case of American battleships, face-hardened Harvey steel. The 6-inch and 8-inch guns are protected by 6 and 8 inches of steel.

Now it can readily be understood that all this amount of heavy armor and guns adds greatly to the weight of the ship, and for this reason, in spite of her smaller engine power, a firstclass battleship rarely displaces less than 10,000 tons, and in some foreign navies the displacement runs up to nearly 16,000 tons. This will be understood by reference to the perspective view, where the armored portions of the ship are indicated by full lines and shading. It will be seen that all that part of the ship lying below the water line is shut in by a continuous roof of steel which is 3 inches in thickness forward and aft of the bulkheads. Over the central armored citadel it is 2 3-4 inches thick. All the plating indicated by dotted lines might be shot away without the "vitals" suffering injury or the ship being sunk. The reader will see that it is the battleship's sides and the extra deck and freeboard which they provide which constitute practically the difference between a battleship and a monitor.

The Invulnerable, Floating Fort, Within The Outer Walls Of A Modern Battleship.

(All parts above the water lines shown by dotted lines and light shading, might be shot away without destroying the fighting power of the ship.)

The Invulnerable, Floating Fort, Within The Outer Walls Of A Modern Battleship.

This brings us to the consideration of the monitor type. Take away from a battleship all that portion which is shown in our drawing in shaded lines above the water line; lower the barbettes until they rise only a few feet above the steel deck, and we have a ship of the general monitor type. The monitor is distinguished by very low freeboard - only a few inches in the extreme type - the absence of a heavy secondary battery and the possession of a main armament of heavy guns. Such a ship labors heavily in bad weather and is not intended for service at any distance from the coasts. To make a seagoing vessel out of her it would be necessary to add one, or even two decks, placing the guns well up above the water, after which changes she would be no longer a monitor, but a seagoing battleship.

In the cruiser type the protective deck does not extend across the ship at one level, but curves down to meet the hull at a point several feet below the water line. This sloping portion is made thicker than the flat portion, as in diagram No. II., where the deck is 3 inches thick on the flat and 6 inches on the slopes. In the case of the armored cruisers, a belt of vertical armor is carried at the water line and in all cruisers the V-shaped space between belt and sloping deck is filled in with coal or with some form of water-excluding material, such as corn-pith cellulose. In diagram II., which represents the fine armored cruiser "Brooklyn," it will be seen that before it could reach the engine room a shell would have to pass through 3 inches of vertical steel, about 6 feet of coal and 6 inches of inclined armor - a total resistance equal to 14 or 15 inches of solid steel. The guns and turning gear are protected by 5 1-2-inch steel turrets and 8-inch barbettes. The barbettes, it will be seen, do not extend continuously down to the armored deck, as in the battleship, for this would require a greater weight of armor than can be allowed. Consequently, the architect is only able to furnish the guns with a small armor-plated tube for protecting the ammunition in its passage from the magazines to the barbettes.

In the protected cruiser the side armor at the water line disappears altogether, and dependence is placed entirely upon the sloping sides of the protective deck, the water-excluding cellulose and the 6 or 8 feet of coal which is stowed in the bunkers in the wake of the engines and boilers. The barbettes, turrets and armored ammunition tubes of the armored cruiser disappear, and their place is taken by comparatively light shields and casements of 4-inch steel which serve to protect the gun crews.

It will be seen from the above description that each class of vessel is only fitted to engage ships of its own type. The protected cruiser "Columbia" (No. I.) might, with her light 6 and 4 inch guns, hammer away all day at the "Indiana" (No. III.) without being able to do much more than knock the paint off the latter's 18-inch armor, whereas one well-directed shot from the 13-inch guns of the "Indiana" would be sufficient to sink or disable the "Columbia." The "Brooklyn" would fare better, and at close range her 8-inch guns might happen to penetrate the belt or turret armor of the "Indiana," but the issue of the duel would never be in doubt for an instant. A "Columbia" or a "Brooklyn" would show its heels to an "Indiana" or "Massachusetts," and their great speed would give them the option of refusing or accepting battle with almost any craft that is afloat upon the seas to-day.

It should be mentioned, in conclusion, that the dividing lines in the classification of warships are somewhat flexible.