To comprehend fundamentally the subsequent development, we must recur to the rudimentary idea that a ship of war possesses two chief factors, motive force and fighting force, the latter being composed of guns mainly and of men. Corresponding to these two chief powers there were of old, and there are still, two vulnerable elements, two targets, upon one or the other of which hostile effort logically and practically must be directed. A century ago the French, aiming at sails and spars, sought the destruction of the motive force; the British directed their fire upon the guns and men. In strict analogy now, the heavy guns seek the motive power, over which the heaviest armor is concentrated; the rapid-fire guns, searching the other portions of the ship, aim at the guns and men there stationed. BATTLE-SHIPS OF THIS DAY The logical outcome of these leading ideas is realized in the present battle-ships as follows: There are two turrets, protected by armor, the thickest that can be given them, considering the other weights the ship has to carry, and of the highest resisting quality that processes of manufacture can develop. Armor of similar character and weight protects the sides about the engines. In each turret are guns whose power corresponds to the armor which protects them. Their proper aim—not, of course, always reached—is the heavy armored part of the enemy, chiefly the engines, the motive power. When they strike outside of this target, as often must happen, there is excess of blow, and consequent waste. The turrets are separated, fore and aft, by a distance as great as possible, to minimize the danger of a single shot or any other local incident disabling both. The fact that the ends of ships, being comparatively sharp, are less waterborne and cannot support extreme weights, chiefly limits this severance of the turrets. Between the two, and occasionally before or abaft them, is distributed the broadside rapid fire of the ship, which in its development is in contradistinction to the compressed fire of the monitor. This fire is rapid because the guns are many and because individually they can fire fast. Thus, the turret gun, twelve or thirteen inch in bore, fires once in five minutes; the five-inch rapid-fire gun thrice in one minute. The rapid-fire battery aims outside of the heaviest armor. When it strikes that, unless it chance to enter a gun port, its effect is lost; but as much the greater part of the ship is penetrable by it, the chance of wasting power is less than in the case of the heavier guns. As most of a ship’s company are outside the protection of the heaviest armor, the rapid-fire gun aims, as did the British in the old line-of-battle ship, at the personnel of the enemy.